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TOJO THOMAS -
Posted 35 days Ago

Signalling Installation Design - Part 1

Signalling

In general, least importance are given to Installation Design compared to System Design ! This is mainly due to lack of awareness and knowledge  among  the key personals within an organisation. An error in a system application software or any design engineering document can be rectified by spending few hours and the cost impact is minimal compared to an error in an Installation Design. As a person who worked in both aspect of these two designs, I felt that we should emphasize more on Installation Design. A minor error in a mechanical cable frame, cable junction box, fixing brackets or a signal mast design will have a huge impact on material wastage, impact of schedule and budget in a larger way. There are various things to be considered to produce an error free design, which I describe based on design and site experience I received in the projects I have executed. I have tried to explain in this article the flow of work that happens in Installation design engineering from the Tender to the execution of installation activities at site. I have divided the work done by installation engineer into the following section. It is defined as per the schedule/flow of activities. TENDER: Firstly, before starting any Installation engineering activities we do have a tender phase. In this phase we analyse basically 2 main information which is important for the project management team to decide the cost. Ultimately everything comes down to the cost, each system has forecasted!!! The 2 main information required during the tender phase is the number of hours we will spend and the number of items we will be procuring. This information is collected in the format of BOQ (Bill of quantity and workload file. So, in this section I will explain what should not be missed (inputs and outputs) during the tender phase: Inputs/Reference documents Requirement matrix: This document has the information from the customer required for each system. Installation engineering team has to extract the installation requirements with respect to each other engineering sub system. This drawing also will have the standards(EN, IS, ASTM, IEC, etc) that should be followed in the respective country. Civil Architecture drawings/CSD(Combined Services drawing): These are a set of drawing which will give an outline of the building and the location of the equipment room in the station or control centre. This will also have the general information on the cable routing inside the building. This drawing will help us to calculate the cable length that has to be considered for each run of the cable. Cross Section drawing of the track: This will give a general information on the type of accessories and mounting support we need to consider for each equipment defined in the scheme plan. This will also provide the information on the cable ducts that can be used for SIG and COM. With this drawing, we also get to know what strategy that can be applied to cross the cables between the tracks. Track Alignment drawing: This drawing will give us the gradient of the tracks and the vertical/horizontal alignment of both the up & down track. This drawing along with scheme plan will help us to calculate the cable length along the track along. Also, this drawing will help us to analyse if the track is elevated, on ground and underground which will in turn help the team to analyse the mounting arrangement for trackside equipment. Scheme plan: This is the deliverable from engineering team that defines the kilometric point of each equipment and the number of trackside equipment. It is used to calculate the cable length and quantify the number of mounting arrangements that needs to be considered against each signalling and telecom equipment along the track. System BOQ: This document will have the information on the quantity of the equipment that will be installed along the trackside and in the stations. We can decide on quantity of the support required for each different equipment. Cable layout: This drawing gives a general information on the cabling schematics between the cubicle in the equipment room and trackside equipment. We use this deliverable to define the type of cables and the length required for each type of equipment. Interface management: This is plan created along with the customer on who will give what information. This also states what are the supports other subsystem require from installation team. Planning schedule: This will provide a general information on the schedule of each activity during the execution of project. This will in turn help the team to forecast the installation engineering activities. Output/ Installation Deliverables Installation BOQ: After analysing the inputs from the customer and other engineering team within the project team (inputs are listed above), Installation team will prepare the installation BOQ. This document contains all the items related to installation such as cable trays and it accessories, mounting support and its accessories, cables, material needed for cable crossing the track, cable tags, tags, racks, base frames, conduits, trackside junction box and its accessories, clamps, cable glands, grounding mechanism, etc. Installation workload file: This document consists of the number of deliverables that needs to be considered along with the hours dedicated to each deliverable. This document will also include the information on the scope of work for installation design team with respect to the site activities (Whether shared or full-time resources is dedicated for each activity). We also include the information on the assumptions taken during the workload calculation. According to the planning of the schedule for each activity we forecast the hours.   For Preliminary installation Design to Detailed Installation Design do follow the page for more....

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Kathy Shen -
Posted 41 days Ago

Pantograph CCTV Intelligent Analysis System for rolling stock

Communication Systems

  1. Overview By the arrangement of the Ministry of Machinery and Vehicles of the National Railway Group on the intelligent analysis of the pantograph video monitoring system, the existing pantograph video monitoring system intelligently analyses the installation requirements, identifies pantograph mechanical structure abnormalities, electrical faults, and other problems, and assists mechanics in judging pantograph faults. Through the analysis of the failure mode of the existing vehicle and the vehicle protection logic, mainly for pantograph failures that cannot be detected by the car itself, such as pantograph tilt, pantograph structure deformation, etc. Such failures are not easily identified during operation and lead to more severe consequences. The intelligent analysis function of the pantograph video monitoring system can analyze the pantograph video monitoring images, identify pantograph faults and make alarm prompts to assist the mechanic in judging and taking effective measures to avoid more significant hazards. 2. Pantograph CCTV System composition The pantograph CCTV system is used to monitor the operational status of the pantographs and contact network on the roof of the train in real-time during operation. The intelligent analysis function adds intelligent identification technology to the original video monitoring system to achieve automatic real-time identification of abnormal pantograph conditions. Save videos of the working state of the pantographs during train operation and pictures of structural abnormalities in the pantographs to provide supplementary surveillance videos and analysis images for the accompanying mechanics to deal with abnormal bow network faults. The intelligent analysis function of the pantograph CCTV system for rolling stock consists of the following main components: pantograph video monitoring server, intelligent analysis host, pantograph camera, and monitoring screen. 3. Application conditions of the intelligent analysis function of the pantograph CCTV system   The intelligent analysis function of the pantograph video monitoring system mainly identifies pantograph faults during vehicle operation. For significant pantograph faults, such as ruptured ducts and dislodged carbon skids, the pantograph will be automatically lowered without further judgment and operation by the mechanic. This intelligent analysis function alerts for bow abnormalities that are not easily detected directly, such as pantograph tilting and pantograph structural deformation, with priority given to identifying bow structural abnormalities as they have the most severe impact. Combined with the technical item analysis of pantograph faults in the high voltage system of the rolling stock, the application items for which the intelligent analysis function of the pantograph video monitoring system assists the mechanic in making judgments were identified as follows. 1. The pantograph is tilted during operation. At this time, the pantograph duct does not break and will not automatically lower the bow. If no alarm is provided, the tilted pantograph may be pulled by the contact network or knocked out by other foreign objects, causing severe secondary damage, so fault identification and alarm are required under this working condition. 2. Structural deformation occurs during the pantograph operation; the types of structural deformation include missing bow angles and bending deformation of the bow structure, etc., when the duct is not broken. Alarm failure may result in problems such as drilling bows, so fault identification and alarming are required for this condition. 3. Foreign objects caught in the pantograph during operation. Identification and alarm for foreign objects hanging on the bow structure and identification and notice for foreign objects on the support frame. 4. When large sparks are generated during pantograph operation, and the sparks occur in the working area, intelligent analysis functions are required to effectively identify the large sparks and provide alarms to avoid secondary accidents. Tiny sparks generated during operation are not identified, and alarm for the time being because they are not a significant hazard. 5. There is a small amount of dirt in the pantograph CCTV system camera, with a small portion at the bow structure captured by the camera when the intelligent analysis is required to allow for chunking and identification without interference from foreign objects. 4. Pantograph structure anomaly identification 4.1 Pantograph structure deformation alarm There is a small amount of dirt in the pantograph CCTV system camera, with a small portion at the bow structure captured by the camera when the intelligent analysis is required to allow for chunking and identification without interference from foreign objects.                                                           Picture of pantograph in normal condition After running for some time, the vehicle pantograph is subjected to structural deformation by foreign object impact; it is necessary to effectively identify this type of fault and alarm through the pantograph video monitoring system; the identification picture is shown below.                                                         Pantograph structure failure picture 4.2 Pantograph tilt alarm Pantograph tilt faults can occur during operation and need to be brought to the mechanic's attention in time for judgment and action. However, the structure of the pantograph and the position of the pantograph camera installed on different models are different, so the decision of the tilt angle of the pantograph is different. Combined with the relevant video of the pantograph tilt, the tilt angle of the alarm needs to be given.                                                 Intelligent identification of pantograph tilt angle pictures 4.3 Pantograph angle break alarm There are two scenarios for pantograph angle breakage, one in which the angle is broken and suspended but not dislodged, and one in which the angle is broken and dislodged. Both scenarios require testing the bow integrity and sending an alarm signal to the monitoring screen when the pantograph form is incomplete. The difference lies in the trade-off threshold settings needed in both cases to reduce the rate of missed alarms. It also needs to be combined with video testing to define that an image above 40 frames in 3 seconds is a fault that will send an alarm condition.                                                            Pictures of the pantograph lowering process   (1)Bow horn fracture not detached The situation is as shown in the diagram below when the pantograph angle is broken and not dislodged from the fault.                                             Picture of pantograph with broken bow angle not dislodged Intelligent analysis of such situations requires correct identification of faults and alarms and actual testing of breakage without dislodging video detection. (2)Bow angle completely broken This type of pantograph fault needs to be identified when a complete break in the pantograph arch angle occurs, as follows.                                             Intelligent identification of complete pantograph angle breakage Intelligent analysis of such situations requires correct identification of faults and alarms and actual testing of breakage without dislodging video detection.   4.4 Pantograph foreign object intrusion alarm False alarms caused by various factors are considered when the pantograph intelligent analysis mainframe identifies foreign object intrusion faults in the pantograph. Analysis from the intrusion results currently only identifies foreign object intrusion faults hanging from the bow for a long time. (1)Pantograph body For the intrusion of foreign objects into the bow of the pantograph, it is necessary to identify whether there is a foreign object intrusion, as shown in the diagram below, which requires the apparent detection of a foreign object in a plastic bag hanging from the pantograph of the “Fuxing” D1702.                        Intelligent identification of foreign objects hanging from the pantograph body 4.5 Pantograph spark alarm Currently, tiny pantograph sparks are not analyzed for identification due to their minor impact on vehicle safety. Pantograph intelligent analysis of pantograph sparks identifies only significant spark faults (Spark area > half of the pantograph head area; this indicator can be modified for configuration). The spark is judged to be in the working area of the carbon skid (x1 to x2, as shown in the picture below) to avoid false alarms. The large pantograph sparks intelligent identification alarm result is shown in the following picture of the large spark intelligent identification alarm.                                Image of the coordinates of the area where the spark occurred                                  Pantograph large spark intelligent identification alarm result picture 5.Intelligent pantograph fault recognition and alarm for particular operating conditions In opening the intelligent analysis function of the pantograph video monitoring system, special working conditions can have a significant impact on the intelligent analysis function, resulting in missed and false alarms. The following special conditions are required. 5.1 Tunnel mode alarm During the process of entering and exiting the tunnel and running in the tunnel, the camera's exposure and the influence of the environment in the tunnel will affect the intelligent analysis function, as follows. When entering and leaving the tunnel, algorithms need to be designed to recognize the tunnel entry and exit patterns and filter out false exposure alarms for the entry and exit tunnel entrance process. The diagram below shows that the exposure images need to be filtered out, and no warnings are made.                                                 Instant exposure picture of entering the tunnel In the tunnel, it is necessary to identify whether the current environment is suitable for detection, i.e., whether the pantograph video monitoring screen is blurred or not. If the screen is blurred due to insufficient fill light intensity or fill light failure, then the intelligent identification detection function is switched off. If it is not confusing, then detection is activated, as shown in the picture of the system generally operating in the tunnel. In addition, false alarm scenarios caused by reflections from fill lights are recommended to be included in the category of unsuitable detection, with the alarm function turned off, as shown in the picture of the bow blur caused by reflections from fill lights in the tunnel.                                                 Pictures of the system in operation in the tunnel                                          Image of bow blur caused by reflections from fill light in the tunnel 5.2 Background mode alarm (1)Background factors such as bridges, power supply equipment Interference caused by background factors such as bridges, power supply equipment, etc., are a few frames that will occasionally be detected as anomalies during intelligent analysis. The alarm will be triggered when there is an anomaly greater than a certain number of frames so that false images can be effectively filtered out. The specific algorithm needs to be set up in conjunction with the vehicle's speed, the time consumed by the car to pass background objects at different rates (i.e., the number of frames) is counted, and the thresholds are optimized to exclude such interference ultimately. For example, by analyzing the background railings shown below, it was found that the train took up a total of about 4 frames as it passed through the above background facilities. The pantograph detection result is normal after 4 frames, so set that for this type of railing background. It is possible to set more than 20 frames in 1 second for normal recognition without alarm.                                                          Background pattern interference picture (2)Background factors for train stops For train stops, the speed threshold needs to be set to 0, i.e., the intelligent identification function is switched off when the speed is 0. The pantograph video monitoring picture of the train stop is shown below. The image on the left shows background interference, which will give rise to false alarms. In the picture on the right, if the pantograph stops on the railing behind the image after the train has ceased to produce an overlap, false alarms will occur, so setting the speed to 0 when the intelligent analysis function is switched off will filter out such interference.                                             Video surveillance images of pantographs at train stops (3)Train entry contextual factors During the train's progress, the intelligent analysis function can be affected by false alarms due to changes in the background of the station. Due to the low-speed state, pantograph abnormalities have less impact on vehicle operation safety, and the low-speed state is less likely to cause abnormal pantograph structure problems. A certain speed threshold must be set to shield the station from false interference alarms. The pantograph video monitoring intelligent analysis function is switched off below a specific operating speed. According to the vehicle in and out of the station speed limit, tentatively set lower than 40 km / h, the speed threshold can be adjusted according to the application of the analysis to minimize the occurrence of false alarm problems. 5.3 Dirty mode alarm The dirty mode affects the clarity of the pantograph CCTV system camera and thus the alarm of the intelligent identification function. Intelligent analysis can be switched off directly to reduce false alarms for dirty stains with a significant impact, such as sand, dust, heavy rain, or snow. For less impactful dirt, such as small smear spots, false alarms need to be reduced. The judgment of the influence of dirt can be realized by identifying whether the video picture is blurred.                                                     Pantograph video image clarity comparison image The amount of dirty intrusion needs to be identified for judgment. For example, as shown in the diagram below, if you set the intelligent analysis to turn off when the rainwater intrusion exceeds 30%. The graph below does not identify the pantograph as a whole, i.e., rainwater soiling encroaches on the pantograph area by more than 30%. The rain is judged to be too heavy, and the intelligent analysis is switched off. If the rainwater dirt encroaching on the pantograph area is less than a certain threshold, the intelligent identification function is not switched off.                                      Pantograph video surveillance images under heavy rain conditions For cases where the soiling is minor, the video image is identified as edge soiled, and the overall structure of the bow is not affected; therefore, no alarm is made, as shown below.                                        Pictures of pantograph video surveillance affected by dirty edges For more minor dirty cases, the dirty area of the lens is primarily fixed.   6.Client   when the intelligent analysis function detects an abnormality in the pantograph, an alarm box pops up directly on the interface of the pantograph video monitoring screen, which contains the type of pantograph fault and the fault picture. At the same time, you can click on the "Associated Video" button in the alarm box to call and play the 2-minute video where the fault picture is located (1min before and 1min after the fault alarm picture), as shown in the figure below.                                            Pantograph monitoring screen fault video alarm picture    

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Sharon Yin -
Posted 85 days Ago

Development and evolution of trackgauge measurement tools

Rail Tracks

Development and evolution of trackgauge measurement tools. From tap-analogue track gauge-digital track gauge-digital rolling gauge and track geometry trolley. Each upgrade will bring unexpected convenience to railway maintenance work . Which of the following tools are you using?  

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Suman Pathak -
Posted 93 days Ago

POWER QUALITY ISSUES IN RAILWAY ELECTRIFICATION

Rail Electrification

  POWER QUALITY ISSUES IN RAILWAY ELECTRIFICATION The power quality issues through electric railway development are overviewed as follows :    Voltage Unbalance Voltage imbalance (also called voltage unbalance) is defined as the maximum deviation from the average of the three-phase voltages or currents, divided by the average of the three-phase voltages or currents, expressed in percent. The most frequent problems of voltages are associated with their magnitudes. The major problem is unbalanced currents produce unbalanced voltages. Traction motors and other related loads in trains are designed to function properly with reduced voltage amplitude by 24% or increased amplitudes by 10% than the nominal voltage of electric railroad drives. System imbalance System imbalance is the most serious problem in electric railway power quality because most trains are single phase, and a single-phase load produces a current NSC (Negative Sequence Current) as much as a PSC (Positive Sequence Current). A new traction power supply system adopting a single-phase traction transformer and active power flow controller (PFC) is proposed. In the new system, the power quality problems caused by single-phase traction load are solved on the grid side and the continuous power can be Arcing The interaction between the pantograph/catenary of overhead systems or between brushes and the third or fourth rail causes arcs because of dynamic latitudinal tolerance between the wheels and rail. Arcs will occur, which can distort voltages and currents and produce a transient dc component in the ac systems causing a breakdown of dielectrics. Flicker As the train passes between two adjacent substations voltage sag may happen and affect other customers electrical light performance so-called flicker. EMI/EMC The movement of rolling stock along an electrified track produces Electromagnetic interference in the system. EMC covers a wide range of phenomena, including inductive noise in parallel communication lines, impulse noise from lightning and traction transients, the production of hazardous voltage under step and touch conditions, and the appearance of stray currents. EMI and EMC are very complicated for high-speed railway systems. Nowadays, the investigation in EMI/EMC high-speed railway is highly relying on simulation and measurement. Waveform Distortion Waveform distortion is defined as a steady-state deviation from an ideal sine wave of power frequency. There are five primary types of waveform distortion :  1. DC offset     The presence of a dc voltage or current in an ac power system is termed dc offset  2. Notching    Notching is a periodic voltage disturbance caused by the normal operation of power electronic   devices when current is commutated from one phase to another.    3. Noise    Noise is the unwanted electrical signal with broadband spectral content lower than 200 kHz  superimposed upon the power system voltage or current in phase conductors, or found on neutral  conductors or signal lines.   4. Interharmonics  Voltages or currents having frequency components that are not integer multiples of the frequency  at which the supply system is designed to operate (e.g., 50 or 60 Hz) are called inter harmonics.   5. Harmonics Harmonics can be best described as the shape or characteristics of a voltage or current waveform relative to its fundamental frequency. The ideal power source for all power systems is smooth sinusoidal waves. These perfect sinewaves do not contain harmonics. When waveforms deviate from a sinewave shape, they contain harmonics. These current harmonics distort the voltage waveform and create distortion in the power system which can cause many problems. In short (Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the frequency at which the supply system is designed to operate.) Types of Harmonics: Odd and Even Order Harmonics: As their names suggest, odd harmonics have odd numbers (e.g., 3, 5, 7, 9, 11) , and even harmonics have even numbers (e.g., 2, 4, 6, 8, 10) . Harmonic number 1 is assigned to the fundamental frequency component of the periodic wave. Harmonic number 0 represents the constant or DC component of the waveform. The DC component is the net difference between the positive and negative halves of one complete waveform cycle. Total Harmonic Distortion (THD) is defined as the measurement of the harmonic distortion present in a waveform. The power quality of a power system is inversely proportional to THD. More harmonic distortion in the system, lower will be the power quality and vice versa. THD is equal to the ratio of the RMS harmonic content to the fundamental:   Where Vn-rms is the RMS voltage of nth harmonic in the signal and Vfund-rms is the RMS voltage of the fundamental frequency. The Destructive Effects of Harmonic Distortion A power system’s ability to perform at optimal levels is compromised when harmonic distortion enters the system. It creates inefficiencies in equipment operations due to the increased need for power consumption. The increase of overall current required creates higher installation and utility costs, heating, and decreasing profitability. Harmonics in Electrified Railways It is well known that the rapid spread of power electronics brought along not only great advantages but also some drawbacks as they are the main sources of harmonics and voltage waveform distortion. Harmonic has emerged as a matter of great interest for electrical power system engineering. The electrified railway is one of the main harmonic sources in utility. Because electrified railway is supplied by High Voltage (HV) power system directly, lots of harmonic (mainly including 3rd, 5th, and 7th) produced by electric locomotive penetrate in the whole utility from HV. Compared with normal load, the most characteristics of traction are random time-varying and non-symmetry. So, the harmonic of traction load is very different from the normal load of utility. In an electrified railroad, the traction power is delivered to the catenary by substations, which in turn receive their supply from the utility network. For the electric utility transmission systems, the alternating current catenary is an unfavorable consumer.  Two major reasons for this are: i)    the catenary is a single-phase load, which power consumption unbalances the main supply three-phase system, ii)   the use of power electronics converters to drive traction motors, generates harmonic currents that perturb interconnection busbar voltage. Basically, the power quality issues in railway electrification systems include the studies of the influence of traction loads on three-phase utility systems. Most of the high-speed trains are single-phase loads. Due to a large amount of power electronics application to the motor driving circuits of trains, they contribute to the high harmonic currents flowing to the railway catenary system.  Traction load is varying dynamically, and arcs may occur because of pantograph/catenary and switching actions. Modern drive trains rely on power electronic converters combined with transformers, which inject low amounts of current harmonics into the supply system. Therefore, power quality must be considered in all aspects of the design for every system dealing with electric power systems. Some especially connected transformers are widely used, such as V-V, Scott, Le Blanc, and Modified Woodbridge connection schemes have been utilized in traction substations to compensate for negative sequence current (NSC) of the grid-side. Due to the nature of time-varying traction loads, it is almost impossible to compensate the whole NSC in all loading conditions.  Passive filters have been adapted to suppress harmonics in electrical railway systems. Among derivations of filters, a C-type filter (CTF) introduces no power loss at the fundamental. frequency and performs as a first-order high-pass filter at tuned resonance frequency. Accordingly, the CTF is generally used to mitigate high-order harmonics caused by the PWM converters of the traction trains and prevent harmonic resonance. Although passive devices are affordable with a simple configuration, their performance is not satisfactory when operational conditions are varying. Therefore, active devices in AC electric railways have been proposed to resolve this issue. Static VAR compensators (SVC ) and static synchronous compensators (STATCOM) were proposed to compensate the load reactive power of trains dynamically. Since electric locomotives introduce harmonic contents, there is no chance to compensate harmonics by these devices, concurrently.  Many other strategies have been also proposed for power quality improvement in electric railways, investigated in a comprehensive historical perspective. Nowadays, power quality improvement strategies have developed to a mature degree for new electric railway systems, among which Railway static Power Conditioners (RPC) and its alternatives (e. g. APQC, HBRPC, HPQC) have the main place.  These compensation schemes are connected to the TSS secondary, as shown in Fig. , and theoretically operate based on instantaneous active/reactive power theory, in which the three-phase currents at the TSS primary side are supposed to be:  (i)    three-phase symmetrical, (ii)    fully sinusoidal with no relevant harmonic content (iii)    aligned with the three-phase voltage featuring negligible reactive power.  Thereafter, the difference between the load currents and the ideal currents must be generated by the compensator, called compensation currents. The compensator operates as an independent three-phase current source, generating the desired compensation currents. The RPC consists of two single-phase back-to-back converters sharing the same DC-link capacitor through which active and reactive power are applied compensates voltage, NSC, total harmonic distortions (THD), and PF simultaneously and each AC side of inverters are connected to the two phases of the secondary side of feeding transformer, main phase, and teaser, respectively. These inverters work as effective power balancers and reactive power compensators. For example, if a load of the main phase is larger than that of the teaser, the RPC transfers effective power from the teaser bus to the main phase bus. This system works to balance the effective power of different phases and compensate for reactive power to reduce voltage unbalance and fluctuation. The various structures of the RPC such as active power quality conditioner (APQC), half-bridge RPC (HBRPC) and Hybrid power quality conditioner (HPQC) were presented. These devices can perform at a full compensating method which results in grid-side power factor unity, zero current unbalance, and harmonics.   DIFFERENT COMPENSATORS USED IN SCOTT CO-PHASE SYSTEM  Hazards of Poor Power Quality Problems in Railways Impacts on Signaling and Communications: Track circuits are designed to work with a special frequency that must not have any interference with the power frequency. But in presence of harmonics, communication signals may be affected by harmonic frequencies, resulting in erroneous signals and faulty train positioning, which lead to a disaster. Also, high-order harmonics may cause an interference problem between communication and power systems. Malfunction of the protective system: Protection relays may operate incorrectly in the presence of harmonics and NSCs of currents and voltages. Traction load injects many harmonics and NSCs resulting in the malfunction of the protective system. Decreased Utilization Factor: Since the traction load is a large single-phase load, it results in high current NSCs, which will flow in only two phases, and it decreases the utilization factor of the transmission line. Incorrect Operation of Transmission Line Control Systems: Voltages and currents sampling is based on fundamental components of either voltage or current. Every control system in the transmission line would work not appropriately because traction loads inject large amounts of harmonics and NSC current into the transmission lines.     References: " IEEE Paper 10.1109/TIE.2014.2386794”, IEEE Paper 10.1109/TVT.2017.2661820, IEEE Std 519-1992    

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Suman Pathak -
Posted 96 days Ago

Various Systems of Railway Electrification

Rail Electrification

Various Systems of Railway Electrification Several different types of Railway Traction Electric Power System configurations have been used all over the World. The choice of the system depends on the train service requirements such as  I.    Commuter rail  -Commuter rail typically includes one to two stops per city/town/suburb along a greater rail corridor II.    Freight rail -Rail freight transport is the usage of railroads and trains to transport cargo on land. It can be used for transporting various kinds of goods III.    Light rail -The LRT vehicles usually consist of 2–3 cars operating at an average speed of 55–60 km/h on the lines with more dense stops/stations and 65–70 km/h along the lines with less dense stations IV.    Train load s V.    Electric utility power supply. Railway electrification loads and systems required for light rails, commuter trains, fast high-speed trains, and of course the freight trains are all different. The power demands for these different rail systems are very different. The selection of an appropriate electrification system is therefore very dependent on the Railway system objectives Presently, the following four types of track electrification systems are available: 1. Direct current system—600 V, 750 V, 1500 V, 3000 V  2. Single-phase ac system—15-25 kV, 16 23, 25 and 50 Hz  3. Three-phase ac system—3000-3500 V at 16 2 3 Hz  4. Composite system—involving conversion of single-phase ac into 3-phase ac or dc.   Direct Current Traction System In this traction system, electrical motors are operating on DC supply to produce the necessary movement of the vehicle. Mostly DC series motors are used in this system. For tramways, DC compound motors are used where regenerative braking is required. Regenerative braking   In this type of braking the motor is not disconnected from the supply but remains connected to it and feeds back the braking energy or its kinetic energy to the supply system. The essential condition for this is that the induced emf should be slightly more than the supply voltage.  The various operating voltages of the DC traction system include 600V, 750 V, 1500V, and 3000V. •    DC supply at 600-750V is universally employed for tramways and light metros in urban areas and for many suburban areas. This supply is obtained from a third rail or conductor rail, which involves very large currents. •    DC supply at 1500- 3000 is used for mainline services such as light and heavy metros. This supply is drawn mostly from an overhead line system that involves small currents. Since in the majority of cases, track (or running) rails are used as the return conductor, only one conductor rail is required. Both these supply voltages are fed from substations which are located 3-5 KM for suburban services and 40 to 50KMs for mainline services. These substations receive power (typically, 110/132 KV, 3 phase) from electric power grids. This three-phase high voltage is stepped-down and converted into single-phase low voltage using Scott-connected three phase transformers. This single-phase low voltage is then converted into DC voltage using suitable converters or rectifiers. The DC supply is then applied to the DC motor via a suitable contact system and additional circuitry.   Advantages 1. In the case of heavy trains that require frequent and rapid accelerations, DC traction motors are the better choice as compared to AC motors. 2. DC train consumes less energy compared to AC unit for operating same service conditions. 3. The equipment in the DC traction system is less costly, lighter, and more efficient than the AC traction system. 4. It causes no electrical interference with nearby communication lines. Disadvantages 1. Expensive substations are required at frequent intervals. 2. The overhead wire or third rail must be relatively large and heavy. 3. Voltage goes on decreasing with an increase in length.                 Single-phase ac system In this type of traction system, AC series motors are used to produce the necessary movement of the vehicle. This supply is taken from a single overhead conductor with the running rails. A pantograph collector is used for this purpose. The supply is transferred to the primary of the transformer through an oil circuit breaker. The secondary of the transformer is connected to the motor through switchgear connected to suitable tapping on the secondary winding of the transformer. The switching equipment may be mechanically operated tapping switch or remote-controlled contractor of group switches. The switching connections are arranged in two groups usually connected to the ends of a double choke coil which lies between the collections to adjacent tapping points on the transformer. Thus, the coil acts as a preventive coil to enable tapping change to be made without short-circuiting sections of the transformer winding and without the necessity of opening the main circuit.  Out of various AC systems like 15-25 kV, 16 23, 25, and 50 Hz. Mostly the 25KV voltage is used in railways. The main reason for the 25kV voltage used in the railway is, that 25 kV AC is more economical than a 1.5kV DC voltage system. Since the 25kV voltage system has a higher voltage, the higher voltage reduces the current flow through the conductor; this reflects reducing the conductor size. The cost of the conductor gets less.  However, there are other major advantages for using 25kV voltage system in railway are quick availability and generation of AC that can be easily stepped up or down, easy controlling of AC motors, a smaller number of substations requirement, and the presence of light overhead catenaries that transfer low currents at high voltages, and so on.   Disadvantages 1.  Significant cost of electrification. 2.  Increased maintenance cost of lines. 3.  Upgrading needs additional cost especially in case there are bridges and tunnels. Composite System As the name suggests this system is classified into two types  I single phase to dc system II single phases to 3 phase system Single Phase to DC system The first one single phase to dc system is used where the voltage level is high for transmission and the dc machine is used in the locomotive. This system combines the advantages of high-voltage ac distribution at the industrial frequency with the dc series motors traction. It employs an overhead 25-kV, 50-Hz supply which is stepped down by the transformer installed in the locomotive itself. The low-voltage ac supply is then converted into dc supply by the rectifier which is also carried on the locomotive. This dc supply is finally fed to dc series traction motor fitted between the wheels.                                                                                     Single-phase to 3 phase system Single-phase to 3 phase system is used where 3 phase machine is used in the locomotive and Single-phase track available. In this system, the single-phase 16KV, 50 Hz supply from the sub-station is picked up by the locomotive through the single overhead contact wire. It is then converted into a 3-phase AC supply at the same frequency by means of phase converter equipment carried on the locomotives. This 3-phase supply is then fed to the 3-phase induction motor. References: various EMC Europe IEEE papers, slideshare.net presentations, rail systems, etc.

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Somnath Pal -
Posted 104 days Ago

Fault Tree Analysis of Route Initiation Circuit

Safety and RAMS

CHAPTER -3  I would describe the Route Initiation Circuit for the given Yard. Before proceeding with development of the Circuit, we consider that Route Initiation is possible only if SM’s Key is Inserted ( SMCR Relay Pick up) , Signal knob is operated ( GNR Relay Pick up ), Route Button is operated ( UNR Relay Pick up) and No Conflicting Route is already Initiated ( LR Relays Drop for conflicting Routes ). We will start from the operation of SMCR Relay.Refer Figure 1 for State Transition Diagram. Figure 1 State Transition Diagram  This Relay is energized when the SM’s Panel Key is ` IN ’ and turned to Normal.  The Energisation of SMCR / SMR Relay provides authorized operation of all the functions on the Panel . When SM’s Key is turned to Reverse and taken out from panel by SM , it prevents un-authorized operation and locks the Panel in the last operated position. The Circuit is very simple as the SMCR Relay operation depends on only one condition – Insertion of SM’s KEY. The SMCR Circuit is given below. If needed, a Repeater Relay SMCPR can be used. One Pick-up Contact of SMCR can be used for operating a Repeater Relay SMCPR , if needed. The Vital Event is showed in a box. Boolean Equation for SMCR is:                                                     SMCR = SM’s KEY Refer Figure 2 for Operating Circuit for SMCR and SMCPR  Relay  Figure 2 The Operating Circuit for SMCR and SMCPR Relay The energised contacts of SMCR are used in Knob circuits, Button circuits, Point operation circuits, Route Initiation circuits, Route Cancellation circuits, Emergency circuits, Crank Handle circuits, Timer circuits etc. Repeaters of SMCR Relay ( SMCPR ) may be used as required. Now, we will prepare a Fault Tree to find out how the Circuit can fail in a Safe mode (Relay does not Pick-up when SM’s KEY is Inserted).Refer Figure 3 & 4 Figure 3 Fault Tree  Unsafe failure (Relay picks up without SM’s KEY) can be due to two causes only. Figure 4 Fault Tree  showing two causes  Failure Mode Effect and Criticality Analysis for SMCR Relay is shown in Table 1  Table 1  Failure Mode Effect and Criticality Analysis for SMCR Relay  All the above failures are detected . Safe failures will not allow ALR to operate and Route cannot be initiated. Signal will not go to OFF. But, Unsafe Failures are not detected until SM tries Route Setting, without insertion of the Key or when the Panel is tested.   The Rate of Safe Failure is   λ safe       = λ SMCR  + λ FUSE  + λ POWER  + λ WIRING  + λ CONTACT. FLT          As per MIL Std. 217F, for less than 1 operation / Hr. (SM’s KEY is not Inserted for every Signal clearance), λ CONTACT. FLT        = 0.0594 X 10 –6 / Hr.,     So, λ safe = (0.7495 X 10 – 6 + 0.4307 X 10 –6 + 6.554 X 10 – 8   + 2 X 0.04 X 10 – 6                     + 2 X 0.0594 X 10 – 6 ) / Hr                                   = 1.3855 X 10 –6 / Hr . The Rate of Unsafe Failure is    λ unsafe       = λ WIRING  + λ CONTACT. FLT In this case, Wiring fault has negligible probability except Human Interference, which is difficult to calculate. Thus, it can be limited to λ CONTACT. FLT     =  ( 0.0594 X 10 –6 ) 2  / Hr.   =   0.003528 X 10 –12  / Hr.  Event Tree Analysis of the SMCR Relay Operation is shown in Figure 5  Figure 5 Event Tree Analysis of the SMCR Relay Operation  The Timing Diagram for operation of SMCR Relay is shown in Figure 6 Figure 6 The Timing Diagram for operation of SMCR Relay Route Initiation A Signal Route Selection Relay ” LR ” decides a particular Route for a Signal and all the Points required for that Route including Isolation and Overlap will be operated to the required position by the LR Relay.  Every Signal will have One LR Relay for each of the Routes that the Signal can lead to, including different Overlaps.  Some Signals e.g. Advance Starter, Starters etc will have only one LR as there is only one Route. Refer Figure 7 for Flowchart representing  the conditions needed for LR Relay Operation for Route Initiation: Figure 7 Flowchart with the  conditions needed for LR Relay Operation for Route Initiation Route Initiation / Selection is done by the Operation of Individual LR Relay for the Signaled Route. LR Relay picks up only when there is an operation to Clear a Signal. From the conditions to be satisfied for Route Initiation, and considering one extra Information that Emergency Signal Cancellation (EUGGN) is not applied, we can find the Boolean Equation as :         LR = Signal GNR. Route UNR. SMCR. Conflicting LRs*. EGGNR* If we Initiate the Signal ‘1’ for Route ‘A’ in the given Yard, the Signal Button ‘1GN’ and Route Button ‘AUN’ are to be pressed simultaneously. The Flowchart of operation of ‘1ALR’ is as follows.  Refer Figure 8 for The Flowchart of operation of ‘1ALR’  Figure 8 The Flowchart of operation of ‘1ALR’  Refer Figure 9 for Logic Diagram for operation of 1 ALR Relay  Figure 9 Logic Diagram for operation of 1 ALR Relay  Refer Figure 10 for  State Transition Diagram   made for 1ALR Relay along with Contact use. Figure 10 for  State Transition Diagram is made for 1ALR Relay along with Contact use. Refer Figure 11 for the  Basic A1LR Circuit with Signal Button 1GN and Route Button A1 UN pressed  Figure 11 The Basic A1LR Circuit with Signal Button 1GN and Route Button A1 UN Pressed  In the above circuit with SMCR Pick up, the Signal button 1 and the concerned Route Button A are pressed simultaneously to pick up concerned relay ALR through 1GNR and ‘ A’ UNR . Once Picked up, it will remain Up through its own front contact and TSR front contact even when Buttons are released (1GNR and ‘A’ UNR front contacts are broken) and even if SM’s KEY is removed . On arrival of train, when the Train passes the Signal, with TSR drop, LR also drops . In case of cancellation, EGGNR (Emergency Signal Cancellation Relay) will pick up and cause LR to drop . EGGNR Contact is bypassed by 1GNR contact , so that only the particular Signal can be Cancelled .   For Route 1A1 , the Conflicting LRs are – 1A2LR, 1BLR, 1C1LR, 1C2LR, Co1A1LR, Co1BLR, Co1C1LR, 2DLR, 4ELR, 6ELR, 8ELR, 10A1LR, 10BLR, Co10A1LR, Co10BLR, SH11A1LR, SH11BLR, SH11C1LR, SH12A1LR, SH12BLR, 13FLR and 14A1LR (22 conflicting routes!!). We could have used Drop contact of Sequential Route Release Relay, UYR2 or UYR3 in place of TSR pick up contact to drop LR after a Train crosses the Signal. But it will be a delayed drop . With TSR front contact LR will drop immediately. Refer Figure 12 for  Safe Failures of LR Relay indicated in the Fault Tree.   Figure 12  Safe Failures of LR Relay   Fault Tree. It shows that Safe failure can be caused by any of the twelve individual Causes, one Cause having variable combination depending on yard (Conflicting Routes can vary in different Yards).             Unsafe Failure can occur if 1 ALR Relay either operates when not wanted or it does not release when needed . There are three causes of Unsafe failures: The first case can occur if the operating path is available due to simultaneous failures of Contacts of Relays in the path . If ALR operates when not wanted, UCR and subsequently HR Relays will operate clearing the Signal for the Route . The second case can occur if the Stick Path does not break due to simultaneous contact failures of TSR and ALR (own) Relays . In this case also UCR and subsequently HR Relays will remain operated clearing the Signal for the Route.   Unsafe condition can also occur if the Emergency Release of Route is not possible . Refer Figure 13 for Unsafe Failures of LR Relay   in the Fault Tree. Figure 13 Unsafe Failures of LR Relay  Refer Table 2  for Failure Mode Effect and Criticality Analysis for ALR Relay  Table 2 Failure Mode Effect and Criticality Analysis for ALR Relay  All the above failures are detected . Safe failures will not allow ALR to operate and Route cannot be initiated. Signal will not go to OFF since UCR and subsequently HR Relays do not operate. Unsafe Failures are detected by the Panel Indication . The Rate of Safe Failure is   λ safe       = λ LR + λ GNR  + λ UNR + λ SMCR + λ EGGNR  + λ TSR  + λ CONFLR + λ FUSE                                                        + λ POWER   + λ WIRING + λ LR (STICK CONTACT)   Using Failure Rates and considering 22 Conflicting LR Relay Contacts,   λ safe = (28 X 0.7495 X 10 – 6 + 1.1802 X 10 –6 +   6.554 X 10 – 8   + 2 X 0.04 X 10 – 6 ) / Hr            = 22.3117 X 10 –6 / Hr .   The Rate of Unsafe Failure due to unwanted operation of ALR Relay seems to be much less because all Failures must occur simultaneously . In this case only one Conflicting LR is to be considered since only one Route can be initiated at a time. But, Short Cct of ALR Stick Contact along with short Cct. Failure of TSR Relay contact, leads to Unsafe condition as ALR will directly operate and Signal would come if no other Route is initiated. Luckily the Fault will be detected by Panel Indication . Unsafe failure can also occur due to Short Cct. Of EGGNR Relay contact during Emergency Release .  Westinghouse Q Series Relays have Mean Time Between Wrong Side failure of 6.89 X 10 – 9 .  So, the Rate of Unsafe Failure is λ unsafe = (λ ALR (OWN) . λ TSR )+(λ GNR . λ UNR . λ SMCR . λ CONFLR . )+(λ EGGNR +   λ GNR ) .          As per Railtrack IRM CCA Model, λ RELAY (short )     = 0.4307 X 10 –6 / Hr    λ unsafe       =  (0.1451 X 10 – 9 / Hr) 2 + (0.1451 X 10 – 9 / Hr) 3 . ( 0.7495 X 10 – 6 / Hr)                                                                                    + 2 X 0.1451 X 10 – 9 / Hr                                 =  0.021 X 10 – 18 / Hr + (3.0549 X 10 – 27 / Hr).( . 0.7495 X 10 – 6 / Hr )                                                           + 0.2902 X 10 – 9 / Hr                            =  0.2902 X 10 – 9 / Hr , as the other terms are negligible.         We observe that Unsafe operation has a low probability and satisfies Safety Integrity Level .  Refer Figure 14 for Event Tree Analysis of the LR Relay operation   Figure 14 Event Tree Analysis of the LR Relay Operation  The Timing Diagram for LR Relay operation is shown in Figure 15  Figure 15 The Timing Diagram for  LR Relay operation Refer Figure 16 for Timing Diagram for Emergency Release of the Relay Figure 16 Timing Diagram for Emergency Release of the Relay There is an option of connecting the Crank Handle Relay contacts in the operating Path of LR Relays, if Motor Points are used in the Yard. This increases Safety since both UCR as well as LR Relays are controlled by the Crank Handles . Route now cannot be initiated if any Crank Handle in the Route is unlocked. But the Rate of Safe Failure would increase due to additional contacts in Series. Thus, there are several ways of designing the Circuit for LR Relay when Signal Button is used. They are: Using EGGNR and GNR Drop contacts in Parallel, in the Operate Path of LR Relay and using TSR and LR Pick-up Contacts in Series in the Stick Path of LR Relay. This design is described above. Using EGGNR and GNR Drop contacts in Parallel, in the Stick Path of LR Relay.  Figure 17 LR relay Circuit  A Relay draws less Current in Stick Path with respect to the Current drawn in Operate Path. So, inclusion of EGGNR and GNR Contacts in Stick Path is a better idea . UYR Drop Contact in the Operate Path of LR Relay . Figure 18  LR Circuit  Proving UYR Relay instead of TSR is a better idea , since UYR gives a Positive proof that the Train has passed Signal . TSR, on the other hand, can Drop due to Track Bobbing or Power Supply problem Using UYR and LR Pick-up Contacts in Series in the Stick Path.   SMCR   1 GNR   ‘A1’ UNR           Figure 19 LR Circuit    Using Conflicting Signal ASR Pick-up Contacts in Operate Path of LR Relay.   Figure 20  In some Panels, Signal Initiation is done by using Signal Switch instead of Button. In this case, the GNR Relay Contact of the Circuits described above, is replaced by the ‘ R’ Band of the Signal Switch.   The Basic Circuit with Signal Switch is Figure 21  ‘R’ Band of the Signal Switch is bypassed by SMCR Drop Contact to allow Locking of the Panel by SM after the Signal is Taken OFF and to prevent any unauthorized normalization of Signal. Bypassing SMCR Front Contact and Route Button Contact by Pick-up Contact of the concerned LR Relay is to prevent   Dropping of LR Relay when Route Button is released (thereby breaking Button Contact ‘A1’UNR). Dropping of LR Relay when SM’s Key is removed after the Signal is Taken OFF. LR can Drop when Signal Switch is made Normal , if SM’s Key is In (SMCR is Up).

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Somnath Pal -
Posted 107 days Ago

FAULT TREE ANALYSIS OF ROUTE RELAY INTERLOCKING BUTTON CIRCUITS

Safety and RAMS

Chapter -2  The Buttons are Self-restoring type Push Buttons and are used for the following purposes: The Signal Buttons (GN’s) are provided near the concerned Signal on the Panel, one Button for each Signal with distinct colours. For Stop Signal --  Red For Calling `ON’ Signal -- Red with White dots For Shunt Signal --  Yellow button etc) and are numbered 1,2,3 etc.   Route Buttons (UN’s) are provided in the middle of each Berthing Track / Overlap Track / Exit Track on the Panel, one Button for each Route / Overlap / Exit Route. The Colour of Route / Overlap Button is Grey / White .  They are marked alphabetically as A, B, C etc or with the respective Route number. Point Buttons (WN) nearer or on the concerned Point and Common Point Group Button WWN (NWN) & WWR (RWN) and Emergency Point Operation Button (EWN). Concerned Point Button is pressed along with the Common Point Group Button. Crank Handle Control Button (CHN) and Common Crank Handle Buttons (CHYYN, CHYRN). These Buttons are pressed for Crank Handle or Siding Key Transmissions. Emergency Signal Cancellation Button (EGGN). Emergency Route Cancellation Button (EUYYN)     and Siding Control Key Button (KTN). SIGNAL BUTTON RELAY (GNR) CIRCUIT To operate any Signal, the concerned Signal Button is to be pressed . Whenever the Signal Button is pressed, the corresponding Signal Button Relay (GNR) will operate, provided no other Signal Button is simultaneously pressed. So, Drop Contacts of all other GNR Relays are proved in the operate path of GNR Relay. The Flowchart for the operation of GNR Relay is shown in Figure 1 and State Transition Diagram is shown in Figure 2  Figure 1 Operation of GNR Relay Figure 2 State Transition Diagram The Boolean Equation is very simple --                                                GNR = GN Button . Confl GN Buttons * Refer Figure 3 for basic Circuit Diagram  Figure 3 Basic Circuit Diagram  The circuit is self-explanatory. Relay GNCR is normally in Pick up condition , proving that all Signal Button Relays are dropped i.e. no Signal Button is pressed .  Now, we will prepare a Fault Tree (Figure 4 & Figure 5)  to find out how the GNR Circuit can fail in a Safe mode (Relay does not Pick-up when Signal Button is Pressed). Figure 4 Fault Tree  Unwanted operation of GNR (Relay picks up without GN Button) can be due to two causes only. This cannot cause any Unsafe Failure since a Button-Stuck condition beyond a specified Time limit is indicated by Button Stuck-up Relay NNCR. Figure 5 Fault Tree     Failure Mode Effect and Criticality Analysis for GNR Relay is givenin Table 1. Table 1 : Failure Mode Effect Criticality Analysis  All the above failures are detected . Safe failures will not allow GNR to operate and Signal Clearance cannot be initiated. Signal will not go to OFF. Unwanted operation of GN Button is detected by Button stuck-up Alarm . The Rate of Safe Failure         λ safe = λ GNR +λ FUSE +λ POWER +λ WIRING +λ CONTACT. FLT (Button) + λ Other GNRs (13)   As per Railtrack IRM CCA Model,            λ RELAY (open )          = 0.7495 X 10 –6 / Hr.,   λ RELAY (short )          = 0.4307 X 10 –6 / Hr          λ WIRING ( Open )         = 6.554 X 10 –8 / Hr.,    λ FUSE                          = 0.04 X 10 –6 / Hr.,             λ POWER                      = 0.04 X 10 –6 / Hr.   and     As per MIL Std. 217F               λ CONTACT. FLT         = 0.3468 X 10 –6 / Hr. ( considering 5 operations / Hr.),             (for GN Button)                                     Replacing these values in the equation                  λ safe =  (0.7495 X 10 – 6 + 0.4307 X10 –6 + 6.554 X10 – 8   + 2 X 0.04 X10 – 6                                                                                             + 0.3468 X10 – 6 + 13 X 0.7495 X 10 – 6 ) / Hr                        =  1 1. 416 X 10 –6 / Hr . The Rate of Unwanted Operation is      Λ unwanted   = λ Direct Supply    + λ CONTACT. FLT (Button) In this case, Fault due to Direct Supply has negligible probability except Human Interference, which is difficult to calculate. Thus, λ unwanted can be limited to λ CONTACT. FLT    or    0.3468 X 10 –6 / Hr.   Event Tree Analysis of the GNR Relay Operation is shown in Figure 6  Figure 6 Event Tree Analysis The Timing Diagram for operation of GNR relay is given in Figure 7  Figure 7 The Timing Diagram  Figure 8 Operation  EMERGENCY SIGNAL CANCELLATION INITIATION RELAY (EGGNR) EGGNR Relay picks up without SMCR contact to allow the Signal to be thrown back to danger in case of emergencies even without SM’s Authorization .  This Relay operates as soon as EGGN Button in the Panel is pressed. T he Boolean Equation is     EGGNR = EGGN Button The basic Circuit Diagram is shown in Figure 9  Figure 9 Basic Circuit Diagram  The Fault Tree, Failure Mode Effect and Criticality Analysis, Event Tree Analysis and Timing Diagram all are similar to the GNR Relay. The Safe and Unwanted Operation Rates are same as for GNR Relays. Refer Figure 10 for a Single Line  layout of which the circuit is made  Figure 10 Single Line Layout  The detailed Circuit Diagram for all GNR Relays and EGGNR Relay of the given Yard is shown in Figure 11 . The operating path for 1GNR Relay is marked in RED Lines. The vital condition to be proved, i. e. operation of Signal Button 1GN is highlighted by Blue Box. Figure 11 Detailed Circuit Diagram 

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Somnath Pal -
Posted 108 days Ago

RAMS of a Vital Input Card

Safety and RAMS

CHAPTER -1  Introduction For a Railway Signal Interlocking system, Field Input conditions to be monitored by the Interlocking equipment are Track Cct / Axle Counter, Point Detection, Signal Aspect Proving, Level Crossing Gate, Crank Handle and Panel Buttons. The monitoring is done by reading the Pick-up or Drop contacts of corresponding Relays. This could have been done by operating a Transistor through external Voltage fed via the pick-up Contact of the Relay. The Output of Transistor is processed by the Logic Solver ( Processor). But in that case, there would be no Isolation between external Analog Input and internal Digital Output circuits. An Opto Coupler is used for this purpose, where the Input LED and Output Phototransistor are electrically isolated . The Input through Pick-up contact of Relay operates the LED of the Opto Coupler, light from which turns the output Phototransistor. The  interfacing using a Transistor and an Opto coupler is showed in Fig 1(a)&(b) When the Relay is in Pick-up condition, the Transistor is Forward biased and Collector Output to Processor is ‘0’ . During Drop condition of the Relay, Collector Output is ‘1’ . Input Interface Card converts the Analog information of DC Voltage fed through the Relay contacts to send TTL level to Processor. The basic features of the Card are: All Inputs are fed through Opto Couplers having a minimum Isolation Voltage of 1500V.   All Inputs are protected from Transient Voltages and Surges by using Varistors. To reduce Single-point Failure, both Front and Back potential-free contacts of each external Relay are interfaced. They are read through different Ports and Bits to avoid common-mode failure. Each Card gets Hardware Address of the particular Slot of the Backplane, to which it is inserted. This Address must be matched with the Software Address sent by Logic Solver Card before the external Relay Inputs are read. Input Cards can be inserted or extracted with System Power-ON conditions. A special circuit is used to prevent transient to Stable +5V Supply to ICs, Input data are read employing Input Toggle by the logic Solver or using multiple sets of Opto Couplers ensuring Hardware redundancy. The Input Data Structure of the Interlocking System Inputs is given in Fig 2: Panel Buttons and Keys are called Non-Vital Inputs and a Non-Vital Input / Output Card is used to read 32 Inputs . All other Inputs are Vital Inputs and a Vital Input Card reads 16 Relay Inputs.   A detailed diagram is showed in Fig 3 . Since Railway Interlocking is a Safety-critical System, Inputs from both Pick-up and Drop Contacts of a Relay is analysed. Each Input is monitored by Opto Couplers by supplying Current from an Isolated 12V Supply . The Input to Processor will be ‘ 01’ in Drop Condition and ‘ 10’ in Pick up Condition . These two combinations are Valid Inputs . Other two Inputs ‘ 00’ and ‘ 11’ are Invalid and Processor will show Fault. But during transition of Relay between Drop to Pick-up or Pick- up to Drop , both the Opto Couplers will be OFF . So, Output will be ‘11’ , which is Invalid A De-bouncing circuit (U1) is used for feeding steady Input to the Logic Solver. In this case, during transition of Relay, the Input to Processor will remain unchanged from Last State. When the Relay X is not operated , current flows through the Drop Contact , Inductor, L1, Current Limiter R1, Resistor R2 and input Diode of Opto Coupler OC1. The Opto Coupler conducts and a level ‘ 0 ’ is fed to Pin1 of U1 . This makes output Pin 3 of U1  as ‘ 1 ’. At the same time, since no current passes through Input Diode of OC2, it does not  conduct. Level ‘1’ is fed to  Pin 5 of U1 and output   Pin 6 of U1 to Port becomes ‘0’. Thus we get a pattern 0101 at the Port. When the Relay X is operated , current flows through the Pick-up Contact ,  Inductor L2,  Current Limiter R5, Resistor R6 and input Diode of Opto Coupler OC2. The Opto coupler conducts and a level ‘0 ’ is fed to Pin 5 of U1 . This makes output to Pin 6 of U1   as ‘0’ . At the same time, since no current passes through Input Diode of OC1, it does not  conduct. Level ‘1’ is fed to  Pin 1 of U1 and output to Pin 3 of U1 to Port becomes ‘0’ .This time, the inputs to Port changes to 1010 . We find that Port inputs 0101 and 1010 are the valid levels . All other combinations  are invalid levels. If Hardware De-bounce Cct U1 is replaced by Software De-bounce to reduce Parts Count to enhance Reliability, the inputs to Port will change to 01 when Relay X is not operated and 10 when it is  operated. If a vital decision is taken by   Pick-up condition of Relay X, then a failure to read Pick-up condition as Drop, is a Safe failure . But if Drop condition is read as Pick-up condition, it will be Unsafe failure . Now we shall have to do an Failure Mode Effects & Criticality Analysis (FMECA)  study of the Cct showed in Fig 3 and identify the critical component to cause Unsafe Failure and mitigate the Hazard. Failure Mode Effects & Criticality Analysis (FMECA) We shall first study the failure modes of the components. For every failure mode of components , we shall their effect for Drop and Pick-up conditions. Typical faults of an Electronic component are Open Cct, Short Cct, Drift in Parameter and Functional Faults. Average relative frequencies of Failure Modes of various Components are given in the Table 1 below. Terminating Resistors and Current Limiting Resistors are of mainly Metal Film type for which Short cct Mode is incredible and hence are not considered. When Resistors are used in Nodes with Pull up Totem-pole Driver , even Drift in value is not to  be considered. For open Collector Modes like Opto coupler output, the design ensures much higher Collector current as well as Diode input current , so that even  ± 20% Drift does not affect the Circuit behaviour. So, for Resistors , only Open Cct Mode is considered. For Inductors, any Drift will not affect normal operation and only Open Mode of failure is considered. For Varistor, Open Mode does not affect normal operation and if the Clamp Voltage is chosen much higher than the required Value , Drift also does not have any effect. Only Short cct Mode is analysed . For ICs, both s-a-0 and s-a-1 Faults are considered for every Pin. Now we will consider component-wise FMECA. The effects during Relay Drop  and Pick-up conditions are analysed for each Component Failure. a) If Inductor L1 is Open Relay Drop condition: Current does not pass through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  aIso ‘1’. Output  to Port will be ’1011’. Fault is detected as Invalid Data and failure is Safe.  Since both the Inputs to Debounce Cct are at ‘1’, its Output will remain at last State, i.e. 01. Relay Pick-up condition : Current  passes through input of Opto Coupler OC2. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘0’. Output  to Port will be ’1010’. Fault is not detected  and failure is Safe.  b) If Inductor L2 is Open Relay Drop condition: Current does not pass through input of Opto Coupler OC2. U1 pin5  is at ‘1’ and U1 pin 1 is at ‘0’. Output  to Port will be ’0101’. Fault is not detected and failure is Safe.  Relay Pick-up condition : Current  passes through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  also at ‘1’. Output  to Port will be ’1011’. Fault is  detected  as invalid data. c) if Metal Oxide Varistor RV1 is Short : Relay Drop condition: Current does not pass through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  aIso ‘1’. Output  to Port will be ’1101’. Fault is detected as invalid data and failure is Safe.  Relay Pick-up condition : Current  passes through input of Opto Coupler OC2. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘0’. Output  to Port will be ’1010’. Fault is not detected  and failure is Safe.  d) if Metal Oxide Varistor RV2 is Short : Relay Drop condition: Current does not pass through input of Opto Coupler OC2. U1 pin5  is at ‘1’ and U1 pin 1 is at ‘0’. Output  to Port will be ’0101’. Fault is not detected and failure is Safe.  Relay Pick-up condition : Current does not pass through input of Opto Coupler OC2. U1 pin 5 is at ‘1’ and U1 pin 1 is  aIso ‘1’. Output  to Port will be ’1011’. Fault is detected as invalid data and failure is Safe.  e) If Current Limiting Resistance R1 is Open: Relay Drop condition: Current does not pass through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  aIso ‘1’. Output  to Port will be ’1101’. Fault is detected as invalid data and failure is Safe.  Relay Pick-up condition : Current  passes through input of Opto Coupler OC2. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘0’. Output  to Port will be ’1010’. Fault is not detected  and failure is Safe.  f) If Current Limiting Resistance R2 is Open: Relay Drop condition: Current does not pass through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  aIso ‘1’. Output  to Port will be ’1101’. Fault is not detected data and failure is Safe.  Relay Pick-up condition : Current  does not pass through input of Opto Coupler OC2. U1 pin 1 is at ‘1’ and U1 pin 5 is also at ‘1’. Output  to Port will be ’1011’. Fault is  detected  as invalid and failure is Safe.  g) If Current Limiting Resistance R5 is Open: Relay Drop condition: Current does not pass through input of Opto Coupler OC2. U1 pin 1 is at ‘0’ and U1 pin 5 is  aI ‘1’. Output  to Port will be ’0101’. Fault is not detected data and failure is Safe.  Relay Pick-up condition : Current  does not pass through input of Opto Coupler OC2. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘1’. Output  to Port will be ’1010’. Fault is not detected  and failure is Safe.  h) If Current Limiting Resistance R6 is Open: Relay Drop condition: Current does not pass through input of Opto Coupler OC2. U1 pin 1 is at ‘0’ and U1 pin 5 is  aI ‘1’. Output  to Port will be ’0101’. Fault is not detected data and failure is Safe.  Relay Pick-up condition : Current  does not pass through input of Opto Coupler OC2. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘1’. Output  to Port will be ’1010’. Fault is not detected  and failure is Safe.  i) If Protection Diode D1 is open: Normal operation of the cct is not affected. But a reverse voltage of more than 6V during Drop condition would damage the Diode of Opto coupler OC1. During Pick-up condition, there is no effect. j) If Protection Diode D2 is open: Normal operation of the cct is not affected. But a reverse voltage of more than 6V would damage the Diode of Opto Coupler OC2 during Pick-up. There is no effect during  Drop condition. k) If Protection Diode D1 is short: Relay Drop condition: Opto coupler OC1 will be OFF since current will  be bypassed via D1. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘1’. Output  to Port will be ’1101’. Fault is detected as invalid data and failure is Safe.  Relay Pick-up condition : Opto coupler OC1 will be OFF since current will  be bypassed via D1. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘1’. Output  to Port will be ’1010’. Fault is not detected failure is Safe.  l) If Protection Diode D2 is short: Relay Drop condition: Opto coupler OC2 will be OFF since current will  be bypassed via D2. U1 pin 1 is at ‘1’ and U1 pin 5 is  also at ‘1’. Output  to Port will be ’ 0101’. Fault is not detected and failure is Safe.  Relay Pick-up condition : Opto coupler OC2 will be OFF since current will  be bypassed via D2. U1 pin 1 is at ‘1’ and U1 pin 5 is  aIso ‘1’. Output  to Port will be ’1011’. Fault is detected as invalid data and failure is Safe. m) If Input Diode of Opto Coupler OC1 is open: Relay Drop condition: Current does not pass through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  aIso ‘1’. Output  to Port will be ’1101’. Fault is detected as invalid data and failure is Safe.  Relay Pick-up condition : Current does not pass through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  at ‘0’. Output  to Port will be ’1010’. Fault is not detected  and failure is Safe.  n) If Input Diode of Opto Coupler OC2 is open: Relay Drop condition: Current does not pass through input of Opto Coupler OC2. U1 pin 5  is at ‘1’ and U1 pin 1 is at ‘0’. Output  to Port will be ’0101’. Fault is not detected and failure is Safe.  Relay Pick-up condition : Current  does not pass through input of Opto Coupler OC2. U1 pin 1 is at ‘1’ and U1 pin 5 is  also at ‘1’. Output  to Port will be ’1011’. Fault is  detected  as invalid data. o) If Collector in Opto Coupler OC1 is open: Relay Drop condition: Due to the pull up Resistor 5, Current does not pass through input of Opto Coupler OC1. U1 pin 5  is at ‘1’ and U1 pin 1 is at ‘0’. Output  to Port will be ’0101’. Fault is not detected and failure is Safe.  Relay Pick-up condition : Opto Coupler OC2 starts conducting  and port input becomes 0101. Fault is not detected  and failure is Safe.  p) If Collector in Opto Coupler OC2 is open: Relay Drop condition: Current does not pass through input of Opto Coupler OC2. U1 pin5  is at ‘1’ and U1 pin 1 is at ‘0’. Output  to Port will be ’0101’. Fault is not detected and failure is Safe.  Relay Pick-up condition : Current  passes through input of Opto Coupler OC1. U1 pin 1 is at ‘1’ and U1 pin 5 is  also at ‘1’. Output  to Port will be ’1011’. Fault is  detected  as invalid data. q) If Collector and Emitter of OC1 is short: Relay Drop condition: We get  1 in Pin 1 of U1 and port gets data 0101. Fault is not detected and failure is Safe.  Relay Pick-up condition : Both pins 1 and 5 get 1 and we get 0110. Fault is  detected  as invalid data. r) If Collector and Emitter of OC 2 is short: Relay Drop condition: We get  1 in Pin 5 of U1 and port gets data 1010. Fault is not detected and failure is Safe.  Relay Pick-up condition : Both pins 1 and 5 get 1 and we get 0110. Fault is  detected  as invalid data. s) If Pull up Resistor R3 is open: Relay Drop condition: Since Opto Coupler OC1 is in operated condition, we get  0 in Pin1 of U1 and port gets data 0101. Fault is not detected and failure is Safe.  Relay Pick-up condition : If there is large leakage current from Supply and Ground, the Collector of Opto coupler OC1 will be at level ‘0’. So data to  port will be 0110. Fault is  detected  as invalid data. t) If Pull up Resistor R7 is open: Relay Drop condition: Since Opto Coupler OC2 is in operated condition, we get  0 in Pin5 of U1 and port gets data 0110. Fault is detected as invalid data and failure is Safe.  Relay Pick-up condition : If there is large leakage current from Supply and Ground, the Collector of Opto coupler OC1 will be at level ‘0’. So data to  port will be 1010. Fault is  not detected.  u) If S-a-0 fault is at Pin 1 of U1: Relay Drop condition: Pin 3 of U1 will be ‘1’ and Port Input is 0101. Fault is not detected. Relay Pick-up condition : Port Input will be 0110, which is invalid. v) If S-a-0 fault is at Pin 5 of U1: Relay Drop condition: Pin 6 of U1 will be ‘1’ and Port Input is 0110 which is invalid. Relay Pick-up condition : :Port Input will be 1010. Fault is not detected. w) If S-a-1 fault is at Pin 1 of U1: Relay Drop condition: Pin 1 and Pin 5 of U1 both will be ‘1’ and Port Input remains 0101. Fault is not detected. Relay Pick-up condition : Port Input will be 1010. Fault is not detected. x) If S-a-1 fault is at U1-5: Relay Drop condition: Pin 6 of U1 will be ‘0’ and Port Input is 0101.  Fault is not detected. Relay Pick-up condition : Pin 1 and Pin 5 of U1 both will be ‘1’ and Port Input remains 1010. Fault is not detected. y) If S-a-0 fault is at U1-3: Relay Drop condition: Pin 3 of U1 will be ‘0’ and Port Input is 0011, which is invalid. Relay Pick-up condition : Port Input is 1010. Fault is not detected. z) If S-a-0 fault is at U1-6: Relay Drop condition: Port Input is 0101. Fault is not detected. Relay Pick-up condition : Port Input is 1100, which is invalid. aa) If S-a-1 fault is at U1-3: Relay Drop condition: Port Input is 0101. Fault is not detected. Relay Pick-up condition : Port Input is 1101, which is invalid. ab) If S-a-1 fault is at U1-6: Relay Drop condition: Port Input is 0111, which is invalid. Relay Pick-up condition : Port Input is 1010. Fault is not detected. ac) If R4 is Open: Relay Drop condition: LED 1 will not glow. Since LED 2 also does not glow, fault can be usually detected. Relay Pick-up condition : Since LED 2 glows, fault cannot be detected. ad) If R8 is Open: Relay Drop condition: Since LED 1 glows, fault cannot be detected. Relay Pick-up condition : LED 2 will not glow. Since LED 1 also does not glow, fault can be usually detected . ae) If LED1 is faulty: Relay Drop condition: LED 1 will not glow. Since LED 2 also does not glow, fault can be usually detected. Relay Pick-up condition : Since LED 2 glows, fault cannot be detected. af) If LED2 is faulty: Relay Drop condition: Since LED 1 glows, fault cannot be detected. Relay Pick-up condition : LED 2 will not glow. Since LED 1 also does not glow, fault can be usually detected. In summary, Invalid Input is obtained in Relay Drop condition if OC1 Output is Short OC2 Input or Output is Open U1-3 S-a-1 U1-6 S-a-0 Similarly, Invalid Input is obtained in Relay Pick-up   condition if OC1 Input or Output is Open OC2 Output is Short U1-3 S-a-0 U1-6 S-a-1 It also shows that a single fault cannot lead to Unsafe Failure. After the completion of FMECA, we are to perform Fault Tree Analysis (FTA) of the Circuit to identify the causes of Safe and Unsafe Failures .                                                        Fault Tree Analysis (FTA) We shall now learn how the Circuit can fail to operate. So, we shall make a Fault Tree Analysis as shown below. Fault trees are individually made for both Safe as well as Unsafe Failures. Safe Failure can occur due to Two simultaneous Faults --- Open Cct Fault in Opto Coupler OC2 as well as Short Cct Fault in Opto Coupler OC1. Unsafe Failure can occur due to Two simultaneous Faults --- Open Cct Fault in Opto Coupler OC1 as well as Short Cct Fault in Opto Coupler OC2.     Unsafe Failure can happen only due to simultaneous Faults in Open cct in Relay NO path and Short cct in Relay NC path.         CCT UNSAFE FAILURE (0101 is read as 1010)               Once we prepare the Fault Tree, we are to calculate the Failure Rate of the Card .               For this, we are initially to find the Basic Failure Rate for each component as per Calculations given in MIL Std 217F . Then we are to Calculate the actual Failure Rate under environmental stress.   The environmental stress factors are : λ C =  Contact Constitution Factor λ Q = Quality Factor λ E =  Environmental Factor. We consider Ground Fixed λ T =  Temperature Factor λ s =  Electrical Stress Factor λ R =  Resistor Value factor λ CV = Capacitor Value Factor   Typical Calculations for a Components are showed in Chapter. The following Table shows the individual Component Failure Rates for the Input Interface Cct. We have seen that Unsafe Failure can be caused only by 2 simultaneous failures – Open Circuit in OC 1 and Short Circuit of OC 2 Output. So, the Failure Rate will be the Product of Individual Failure Rates of the 2 Opto Couplers. From the table above, we find that the Failure Rate of an Opto Coupler is 0.0257 X 10 -6 . So, the Unsafe Failure Rate will be ( 0.0257 X 10 -6 ) 2 = 6.6040 X 10 -16.  This is far above the requirement of SIL 4. Total Failure Rate of the Card is 3.375477 X 10 -6 giving a Mean Time Between Failure of 296254.4 Hours. Reliability after a period of One year (8760 Hrs) i s R = e – λt     = e - 0.0000033754 X 8760    = e – 0.029568    = 0.97086   Designed Life with 99% Reliability = (- ln 0.99) / 0.0000033754 = 0.01005033585 / 0.0000033754 = 2977.5 Hrs. Preventing Common- Mode Failures: To reduce Common- mode failures, we can feed U1 outputs in two different Ports and that too at different Input Pins . For example, if Pin 3 of U1 is fed to D0 of Port A, Pin 6 of U1 should be fed to D7 of Port B . Then we can match them through Software in Processor Card. See the Diagram of the connection in Fig 4 A Program for the same task is written below in 8085 Assembly language. START:          IN Port 1                     :   Read Drop Contact Data                        MOV D, A                  :    Save Data                        IN Port 2                     :    Read Pick-Up Contact Data MATCH:         PUSH D                     :    Save Drop Contact Data                        CMA                           :    Invert Pick-Up Contact Data                        MOV B, A                  :   Save Data                        MVI C, 00                  :   Initialize Register ‘C’                        LXI H, 0180                :   Initialize Registers : ‘H’ and ‘L’                        MVI E, 08                  :    Load Count (8) for the Loop Iterator LOOP  :         ANA H                        :    Mask Unconcerned Bits of the Pick-Up* Data                        JNZ ONE                    :    If Data Bit is Not 0, Go to Label ONE                         MOV A, L                   :    Transfer Data from Register ‘L’ to ‘A’.                         CMA                           :    Invert Data of Accumulator                         ANA C                        :    Mask Unconcerned Bits                         JMP ZERO                 :    Go To Label ZERO . ONE    :          MOV A, C                  :    Copy Contents of ‘C’ to Accumulator                       ORA L                        :    Make MSB ‘1’ and progress with other bits ZERO  :          MOV C, A                  :    Save the new value in Register C                      MOV A, H                  :    Load Bit Position Indicator in Accumulator                      ADD H                       :    Shift Left for Next Bit indicator                        MOV H, A                  :   Save the Bit Indicator Data.                                     MOV A, L                   :   Load Bit Position in Accumulator                            RRC                           ;    Go to Next Bit Position                        MOV L, A                :    Save Updated Bit Position Data                        MOV A, B                :    Read saved Pick-up* Contacts Data                        DCR E                    :    Check for completion of all 8 Bits           JNZ LOOP             :  Repeat Rearranging for all 8 Bits                         MOV A, C              :  Save Rearranged Pick-up* Data                         POP D                   :  Restore Saved Drop Contact Data                        RET                       :  Go back to Main Programme                        CMP D                   :   Compare Drop and Pick-up* Data                       JNZ FLT                 :   If not Matched, Go to Fault This Subroutine is Executed in 34.5 μs, considering that each State in 8085 generally takes 330 ns for execution .   Toggling of Input data to detect Opto Coupler Faults Instead of keeping the Emitter of Opto Coupler permanently Grounded, we feed ‘0’ from Processor through Port C of Programmable Peripheral Interface 8255, to the Emitters as showed in Fig 5.   After reading the input and analysing, we momentarily feed ‘1’ to the Emitters. Now, all the opto-couplers should be OFF. That means, Opto-coupler outputs should follow the Toggling input from the microprocessor. Now, we again feed ‘0’ from the Processor and analyse the Opto-coupler Outputs finally. We take inputs from Drop Contacts of 4 different relays along with the Output of U1 Pin 3 of their De-bounce circuits, via Port ‘A’ of 8255. Similarly, the pick-up Contacts of the same four Relays and Output from U1 Pin 6 are taken through Port ‘B’. For 16 relays, Interface to the Card, 4 numbers of 8255 ICs PPI 8255   1 are needed. The Programme for the Toggle Operation is given below:   MVI A, 92                 Programme Four PPIs (8255) having     OUT 03                           PORT A -- INPUT OUT 07                           PORT B -- INPUT OUT 0B                          PORT C -- OUTPUT OUT 0F                           LXI H, 1100               Starting Location to keep Drop Contacts Data SUB A                       Enable Opto Couplers in PPI 1 OUT 02 IN 00                         Read Drop contact Status from PPI 1 MOV M, A                 Save in Location 1100 IN 01                         Read Pick-up contact Status from PPI 1 CALL MATCH          Rearrange Bits and Match them. INX H                        Go to Next Location SUB A                       Enable Opto Couplers in PPI 2 OUT 06 IN 04                        Read Drop contact Status from PPI 2 MOV M, A                Save in Location 1101 IN 05                        Read Pick-up contact Status from PPI 2 CALL MATCH         Rearrange Bits and Match them. INX H                       Go to Next Location SUB A                      Enable Opto Couplers in PPI 3 OUT 0A IN 08                        Read Drop contact Status from PPI 3 MOV M, A                Save in Location 1102 IN 09                        Read Pick-up contact Status from PPI 3 CALL MATCH         Rearrange Bits and Match them. INX H                       Go to Next Location SUB A                      Enable Opto Couplers in PPI 4 OUT 0E IN 0C                        Read Drop contact Status from PPI 4 MOV M, A                Save in Location 1100 IN 0D                        Read Pick-up contact Status from PPI 4 CALL MATCH         Rearrange Bits and Match them.                            STA 1100                Bring Drop Contact Data from Location 1100 LXI H , 1200             Initialize Flag Location for First Relay of PPI 1 IN 00                       Read Drop contact Status from PPI 1        CPI 55                      Check if this Data is same as the Saved Data JZ PPI 2 CALL DELAY 1ms  Wait for 1 milli second MVI A, FF                 Disable Opto Couplers OUT 02 IN 00 CALL DELAY 1ms  Wait for 1 milli second CPI FF JNZ FLT                   If not, Go to Fault SUB A                      Again Enable Opto Couplers OUT 02 IN 00 CPI 55 CNZ PROCESS PPI 2    :             STA 1101                   Bring Drop Contact Data from Location 1101 LXI H , 1204                 Initialize Flag Location for First Relay of PPI 2 IN 04                           Read Drop contact Status from PPI 2 CPI AA JZ PPI 3 CALL DELAY 1ms     Wait for 1 milli second MVI A, FF                    Disable Opto Couplers OUT 06 IN 04                            Read Drop contact Status from PPI 2 CALL DELAY 1ms     Wait for 1 milli second CPI FF                        Check if Opto Couplers are Disabled JNZ FLT                      If not, Go to Fault SUB A                        Again Enable Opto Couplers OUT 06 IN 04                           Read Drop contact Status from PPI 2 CPI AA CNZ PROCESS PPI 3       :        STA 1102                   Bring Drop Contact Data from Location 1102 LXI H , 1208                Initialize Flag Location for First Relay of PPI 3 IN 08                          Read Drop contact Status from PPI 3 CPI 55                   JZ PPI 4 CALL DELAY 1ms   Wait for 1 milli second MVI A, FF OUT 0A IN 08                         Read Drop contact Status from PPI 3 CALL DELAY 1ms   Wait for 1 milli second CPI FF                      Check if Opto Couplers are Disabled JNZ FLT                   If not, Go to Fault SUB A                       Again Enable Opto Couplers OUT 0A IN 08                        Read Drop contact Status from PPI 2 CPI 55 CNZ PROCESS PPI 4    :             STA 1103                 Bring Drop Contact Data from Location 1104 LXI H , 120C              Initialize Flag Location for First Relay of PPI 4 IN 0C                        Read Drop contact Status from PPI 4 CPI AA   JZ NXT_CARD CALL DELAY 1ms  Wait for 1 milli second MVI A, FF                 Disable Opto Couplers OUT 0E IN 0C                         Read Drop contact Status from PPI 4 CALL DELAY 1ms  Wait for 1 milli second CPI FF                       Check if Opto Couplers are Disabled JNZ FLT                   If not, Go to Fault SUB A                       Again Enable Opto Couplers OUT 0E IN 0C                         Read Drop contact Status from PPI 4 CPI AA CNZ PROCESS   PROCESS   :    MOV B, A     MVI C, 04                MVI D, 40                              CHK             :     MOV B, A               ANA D               JNZ PICK-UP               MVI A, FF               MOV M, A PICK-UP       :  MOV A, D RLC MOV D, A ANA D JNZ FLT SUB A MOV  M, A INX H MOV A, D RLC MOV D, A DCR C JNZ CHK   dELAY 1 ms :   PUSH D BACK           :    LXI B , 0BB1                            DCX B JNZ BACK POP D RET  This Programme to check the Status of the Relays Interfaced in One Card takes about 9.64 ms . Thus to check all 16 Input Cards, a total time of 154 ms is needed. It covers up the Transition periods for QN1 Relays. Card AcCcess Whenever an Input Card is inserted into one of the I/O Slots, it gets the I/O Slot address , which is Hardwired in Back-plane . Processor Card sends Motherboard Slot addres s through the I/O Bus. When the two addresses match, the Comparator Output Pin gets low and a Decoder and Data Buffer are enabled. The arrangement is showed in Fig 6 .    The FMECA of this sub- circuit is given below. a) If Pin 19 of Comparator UA is s-a-1: The Decoder UD and Buffer UC will not be enabled. Processor cannot read ID andID* of Input Card. b) If pin 19 of Comparator UA is s-a-0: The fault will not be detected. c) If any Input Pin of P or Q Comparator of UA is s-a-0 / s-a-1 : Software data sent by Processor will not match with Hardware data from the Backplane. Failure is same as (a). d) If any Pull- up resistor for Backplane is Open: The corresponding Pin may float to either 0 or  1. Depending on that the Hardware and Software addresses may or may not match. e) If any Input Pin of Buffer UB is s-a-0 or s-a-1. Software data will be faulty and may or may not match with Hardware data. f) If Pin 19 of Bus Driver UC is s-a-1: UC will not be enabled. Card ID and ID* cannot be read. g) f) If Pin 19 of Bus Driver UC is s-a-0 : UC will be permanently enabled and the fault will remain undetected while accessing the Card. h) If Pin 1of Bus Driver UC is s-a-1 : UC will not allow reading Card ID and ID*. i) if any Data Pin of Bus Driver UC is s-a-0 or s-a-1 : Processor will get wrong ID and ID*. j) If Pins 1 and 19 of Buffers UE or UF are s-a-1 : Processor will not get ID or ID* depending on whether UE or UF has got the fault. j) If Pins 1 and 19 of Buffers UE or UF are s-a-0 : UE or UF will be permanently enabled . There will be Bus contention while reading ID and ID*.    

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Suman Pathak -
Posted 110 days Ago

Earthing works in Railway building/Metro Stations or Substation

General

MAJOR PARTS OF E&M WORKS IN RAILWAY BUILDING/METRO STATION OR SUBSTATION CONSTRUCTION 1.    Earthing 2.    Conduiting 3.    Light Point wiring, Power Point 4.    Installation, testing, commissioning of light fixtures 5.    laying of cables, jointing, termination etc. 6.    laying of Cable Tray, HDPE pipe. RCC pipe Let’s get a short brief about all one by one EARTHING The earthing protection is an integral part of any electrical system and is required to  a.    Protect personnel and equipment from electrical hazards. b.    Achieve a reduction in potential to the system neutrals. c.    Reduce or eliminate the effects of electrostatic and electromagnetic interference on the signaling and Telecom equipment arising from auxiliary electrical systems. The main purpose of earthing in the electrical network is for safety.  i)    When all metallic parts in electrical equipment are grounded then if the insulation inside the equipment fails there are no dangerous voltages present in the equipment case.  ii)    To maintain the voltage at any part of an electrical system at a known value to prevent over current or excessive voltage on the appliances or equipment.  iii)    Lightning, line surges, or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical distribution system.  The earthing is broadly divided as a)    System earthing (Connection between a part of a plant in an operating system like LV neutral of a Power Transformer winding and earth). b)    Equipment earthing (like motor body, Transformer tank, Switch gearbox, Operating rods of Air brake switches, etc.) to earth. Earthing provides an alternative path around the electrical system to minimize damages in the system.  There are several types of earthing systems such as Earth Mat, Plate Earthing & Pipe Earthing which could be used in an elevated station and Substations.  The selection of earthing depends upon several factors such as: i)    Availability of Land ii)    Type of Soil iii)    Resistivity of Soil Mainly we follow two Specifications for earthing I.    IS:3043 II.    IEEE 80 The most commonly used earthing method is Earthmat or Grid  Earth Mat or Grid The primary requirement of Earthing is to have a low earth resistance.   Substation involves many Earthlings through individual Electrodes, which will have high resistance.  But if these individual electrodes are interlinked inside the soil, it increases the area in contact with soil and creates a number of parallel paths.  Hence the value of the earth resistance in the inter-linked state which is called combined earth value which will be much lower than the individual value. The interlink is made through a flat or rod conductor which is called an Earth Mat or Grid.  It keeps the surface of substation equipment as nearly as absolute earth potential as possible.                                                                                             Picture: Earthmat  To achieve the primary requirement of Earthing system, the Earth Mat should be designed properly by considering the safe limit of Step Potential, Touch Potential, and Transfer Potential. The factors which influence the Earth Mat design are: a.    Magnitude of Fault Current b.    Duration of Fault c.    Soil Resistivity d.    The resistivity of Surface Material e.    Shock Duration f.    Material of Earth Mat Conductor g.    Earthing Mat Geometry Step Potential It is the potential difference available between the legs while standing on the ground. When a fault occurs at a tower or substation, the current will enter the earth. Based on the distribution of varying resistivity in the soil (typically, a horizontally layered soil is assumed) a corresponding voltage distribution will occur. The voltage drops in the soil surrounding the grounding system can present hazards for personnel standing in the vicinity of the grounding system. Personnel “stepping” in the direction of the voltage, gradient could be subjected to hazardous voltages Touch Potential Touch potential is the voltage between any two points on a person’s body – hand to hand, shoulder to back, elbow to hip, hand to foot, and so on. The touch potential or touch voltage could be nearly the full voltage across the grounded object if that object is grounded at a point remote from the place where the person is in contact with it .       The earth resistance shall be as low as possible and shall not exceed the following limits: EHT Substations    -    1.0 Ohms 33KV Stations        -    2.0 Ohms Metro Stations    -    < 1.0 Ohms Specification of Earthing Depending on soil resistivity, the earth conductor (flats) shall be buried at the following depths.             Soil Resistivity in ohms/metre     Economical depth of Burial in metres                                                                      1)        50 – 100                                              0.5                                                                       2)       100 – 400                                            1.0                                                                       3)        400 – 1000                                         1.5 To keep the earth resistance as low as possible to achieve safe step and touch voltages, an earth mat shall be buried at the above depths below ground and the mat shall be provided with grounding rods at suitable points. All non-current carrying parts at the Substation shall be connected to this grid to ensure that under fault conditions, none of these parts are at a higher potential than the grounding grid.      

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Suman Pathak -
Posted 114 days Ago

Basic of MEP

General

  Basic of MEP MEP, or mechanical, electrical, and plumbing engineering, are the three technical disciplines that encompass the systems that allow stations/building interiors to be suitable for human use and occupancy. MEP construction must require all types of commercial, residential, and industrial purposes where services and facilities are required. MEP consists of installing air conditioning systems, water supply & drainage systems, firefighting systems, electrical power, and lighting systems including transformer substations and emergency power generators, fire protection and alarm systems, voice & data systems, security access, and surveillance systems, UPS, public address systems, Mast antenna TV system, and building management systems. MECHANICAL WORKS IN MEP PROJECT In MEP, major works are to be handled by Mechanical people because of HVAC or air conditioning system and that has piping work for cold and hot water, fabrication works for ducts, dampers and controllers, thermal/cold insulation works, and erection of machines like chiller unit, air handling units, grills, diffusers, etc. along with works of Drinking water, Drainage, and Sewerage systems. Other important Mechanical works are Firefighting works that included piping, sprinklers, and Pumps. ELECTRIC WORKS IN MEP PROJECT Electric works mainly included Electrical Power and Lighting but others like Transformer substations, Emergency power, UPS/Central battery, Voice/Data communication, TV, Security systems like CCTV surveillance system, Access control System, Public address system, Building management system (BMS), Fire alarm system, Surge Protection system, and Lightning protection system. PLUMBING WORKS ON MEP PROJECT Plumbing is a system of pipes and fixtures installed for the distribution and use of potable (drinkable) water, and the removal of waterborne wastes. It is usually distinguished from water and sewage systems that serve a group of buildings or a city.

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Josef Winter -
Posted 114 days Ago

Solar-powered video surveillance for tracks

Safety and RAMS

The solar video surveillance system was specially developed for an application without power supply and network connection for railroad use. This system is the ideal and cost-effective solution for video surveillance, at locations without existing infrastructure. The RAILWAY CONTROLLING models can be used in all locations where sunlight and mobile phone reception are available. All models meet strict security requirements.   Ideally suited for: - Track surveillance - Tunnel portal surveillance - Storage yard surveillance - Weather monitoring   Visit: http://railway-controlling.com/index.html  

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Patrick Fitzgerald -
Posted 115 days Ago

WiFi for Train Communications

Communication Systems

  WiFi for Train Communications   WiFi can be used to communicate with moving trains in a metro system. Ordinary WiFi like in my home? Could be.  IEEE802.11g 2.4GHz band, like you use in your home.  But the 5.8-5.9GHz band using 802.11a or 802.11n has certain advantages. There is even an 802.11p available but I think that is reserved for trucking.   http://standards.ieee.org/about/get/802/802.11.html By using WiFi in the 5.8-5.9GHz band you can go to higher power EIRP.  http://en.wikipedia.org/wiki/U-NII  shows this spectrum for 802.11a in the United States.  Most countries, Canada, Europe, Saudi Arabia, etc. will more-or-less follow this spectrum;  perhaps with blocks reserved or different maximum powers. When you want your WiFi access points spread out along the guideway, power determines how close or how far apart your wayside access points can be located.  According to  http://en.wikipedia.org/wiki/U-NII  you can go up to 4Watts=36dBm in the USA. Trains move, fast.  A higher power allows you to space out your Wayside Access points.  100 or 200m being typical.  If the train had to perform a complete logon for every change of access point more time would be spent authenticating than transferring data.  A wireless access controller can reduce time wasted.    http://www.youtube.com/watch?v=0n-uIusTpU8 Finally, everybody has a device that can affect the 2.4GHz range. Laptops, smartphones.  By going to the 5.8-5.9GHz band a cyber-intruder needs to have a wifi device that can work in that "exotic" range. What is in the data? Train position, train speed, commands to stop, commands to go, status and health of train electronics and mechanical equipment, perhaps even who is logged in as driver.  Each manufacturer:  Thales, AnsaldoSTS, Siemens, Bombardier, to name just a few, will have their own proprietary messaging and their own way of doing things for CBTC communications based train control.  But they all have the same goal of moving trains, or stopping trains, without the nuisance of the trains hitting each other. Any WiFi link carrying ATC or CBTC data must be secured.  WPA encryption is only the beginning.  Authentication with passkey and MAC address control are needed, as well.  By writing the CBTC protocol to conform to IEC EN 50159 the actual data messages will be encrypted, again, authenticated and they must make sense to the CBTC servers and clients or they will be rejected.  Any lost messages must be detected and re-transmitted. Just like your home WiFi the SSID beacon can be suppressed.  The train knows what network to connect to and it's not like railway tracks move around a lot.   What else is special about WiFi for Metro Trains Rail alignments are long and skinny. By using a directional antenna you amplify the signal along the track and reduce the waste of power going to the sides. 12-15-18 dBi are common antenna gains. EIRP is the total power put into the antenna, directional gain means the receiver will receive a greater portion of that power. On board the train are many systems using open protocols. To talk to doors, HVAC, break systems you will commonly encounter CANBus, MVB or TWN standards. A voice circuit is needed for a manual operator, a SoftPhone using a VoIP client can connect through the WiFi network along with the ATC, ATS and ATO protocols.   image from researchgate.net

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