Power Supply Installation PDF

1. GENERAL DESCRIPTION OF FIXED INSTALLATIONS 1.0 POWER SUPPLY ARRANGEMENTS AT SUB-STATIONS 1.0.1. Power Supply 25 kV, AC, 50 Hz single phase power supply for electric traction is derived from the grid of State Electricity Boards through traction sub-stations located along the route of...

1. GENERAL DESCRIPTION OF FIXED INSTALLATIONS 1.0 POWER SUPPLY ARRANGEMENTS AT SUB-STATIONS 1.0.1. Power Supply 25 kV, AC, 50 Hz single phase power supply for electric traction is derived from the grid of State Electricity Boards through traction sub-stations located along the route of the electrified sections at distance of 35 to 50 km apart. The distance between adjacent substations may however be even less depending on intensity of traffic and load of trains. At present there are broadly four different arrangement in existence as under 1. The Supply Authorities supply power at 220/132/110/66 kV Extra High Voltage (EHV) at each traction substation which is owned, installed, operated and maintained by the Railways. 2. The Railway receives 3-phase power supply from the supply Authority at a single point near the grid substation from where the Railway runs its own transmission lines providing its own traction sub-stations. 3. All EHV and 25 kV equipment is owned, installed, operated and maintained by the Supply Authority except 25 kV feeder circuit breakers which are owned, installed, operated and maintained by the Railway. 4. All EHV and 25 kV equipment is owned, installed, operated and maintained by the Supply Authority but 25 kV feeder circuit breakers alone are operated on remote control by the Traction Power Controller (TPC). 1.0.2 Duplicate Supply 1. Fig 2.01 shows schematically the arrangement at a typical traction sub- station. 2. To ensure continuity of supply under all conditions, the high voltage feed to the traction substations is invariably arranged wither from two sources of power or by a double transmission line, so that if one source fails the other remains in service. Suitable protective equipment is installed at the substations to ensure rapid isolation of any fault in transmission lines and substation equipment, so that the power supply for electric traction is maintained under all conditions. 3. At each traction substation, normally two single phase transformers are installed, one which is in service and the other is 100% stand by. The present standard capacity is 21.6 MVA (ONAN)/30.2 MVA (ONAF). 1  However transformers of capacity 13.5 MVA (ONAN)/10.8 MVA (ONAN) have also been used at many of the substations. These transformers step down the grid voltage to 25 kV for feeding the traction overhead equipment (OHE). 25 kV feeders carry the power from the substations to feeding posts located near the tracks. Each feeder is controlled by a single pole circuit breaker equipped with protective devices. 1.0.3 Voltage Regulation The permissible variation of the bus bar voltage on the busbars at the grid substations is +10% and -5% i.e. between 27,500 V and 23750 V. The tappings on the transformers are on the secondary winding and set to ensure the voltage is maintained as high as possible but not exceeding 27.5 kV at the feeding post at any time. 1.0.4 25 kV Supply at Traction Substations 1. On the secondary side one transformer circuit breaker and one feeder circuit breaker are installed with associated double pole isolator the busbar connections being such that full flexibility of operation is assured. 2. The traction substation is designed for remote operation. 3. The facilities exist to change over from one feeder to the other by means of isolator/bus coupler. 4. One end of the secondary winding of the transformer is solidly earthed at the substation and is connected to track/return feeder through buried rail. 1.0.5 Feeding and Sectioning Arrangements 1. The generation and transmission systems of Supply Authorities are 3 phase systems. The single phase traction load causes unbalance in the supply system. The unbalance has undesirable effects on the generators of the supply Authorities and equipment of other consumers. If its value becomes excessive. 2. The permissible voltage unbalance at the point of common coupling on the grid supply system should not exceed the following llimits:- Voltage unbalance (%) Instantaneous 5 2 hours 3 Continuous 2 2 TYPICAL SCHEMATIC OF TRACTION POWER SUPPLY FEEDING ARRANGEMENT FIG 1.01 3  3. To keep the unbalance on the 3 phase grid system within the above limits, power for ac single phase traction is tapped off the grid system across the different phases at adjacent substations in cyclic order. 4. Thus it becomes necessary to separate electrically the overhead equipment systems fed by adjacent substations. This is done by providing a ‘Neutral Section’ between two substations on the overhead equipment to ensure that the two phases are not bridged by the pantographs of passing electric locomotives/EMUs. 5. To ensure rapid isolation of faults on the OHE and to facilitate maintenance work, the OHE is sectioned at intervals of 10 to 15 km along the route. At each such point a ‘switching station interruptors, usually rated at 600 A are provided. The shortest section of the OHE which can be isolated by opening interruptors alone is called a ‘sub- sectors’. Each sub-sector is further sub-divided into smaller ‘elementary sections’ by provision of off-load type manually operated isolator switches. 6. At some stations with large yards, alternate feeding arrangements are provided so that the power for feeding and yards may be drawn from alternate routes. Normally the switch is locked in one position, being changed to the other when required after taking necessary precautions. 7. To meet requirements at electric loco running sheds, isolators with an earthing device in the ’off’ position is provided. At watering stations manually operated interruptors and isolators with earthing heels are provided to enable switching off of the power supply locally and earthing the OHE to enable working on roofs of rolling stock. There are several types of switching stations as detailed in the following paras. 1.0.5 Feeding Post (FP) Each feeder supplies the OHE on one side of the feeding post through interruptors controlling supply to the individual lines. Thus, for a two track line, there will be four interruptors at each feeding post. 1.0.6 Sectioning and Paralleling Post (SP) These posts are situated approximately midway between feeding posts marking the demarcating point of two zones fed from different phases from adjacent substations. At these posts, a neutral section is provided to make it impossible for the pantograph of an electric locomotive of EMU train to bridge the different phases of 25 kV supply while passing from the zone fed from one substation to the next one. Since the neutral section remains ‘dead’ warning boards are provided in advance to warn and remind the Driver of an approaching electric locomotive /EMU to open locomotive circuit breaker (DJ) before approaching ‘neutral section’. to coast through it and then switch ‘on’ on the other side. Special care is taken in fixing the location of 4 neutral sections on level tangent tracks far away from signals level crossing gates etc to ensure that the train coasts through the neutral section at a sufficiently high speed to obviate the possibility of its stopping and getting stuck within the neutral section. A paralleling interrupter is provided at each ‘SP’ to parallel the OHE of the up and down tracks of a double track section ‘bridging interruptors’ are also provided to permit one feeding post to feed beyond the sectioning post upto the next FP if its 25 kV supply is interrupted for some reasons These bridging interruptors are normally kept open and should only be closed after taking special precautions as detailed in these rules. 1.0.7 Sub-Sectioning and Paralleling Post (SSP) One or more SSPs are provided between each FP and adjacent SP depending upon the distance between them. In a double track section. Normally three interruptors are provided at each SSP i.e. two connecting the adjacent sub- sectors of up and down tracks and one for paralling the up and down tracks. 1.0.8 Sub-Sectioning Post (SS) These are provided only occasionally. These are similar to SSPs with provision for sectioning of the OHE but not paralleling. 1.0.9 Certain Equipment at Switching Stations Certain equipments are installed at various points to protect the lines, to monitor the availability of power supply and provide other facilities. These are generally as under- 1. Lightning arresters are provided to protect every sub-station against voltage surges. 2. Auxiliary transformers are provided at all the posts and also at certain intermediate points to supply ac at 240 V, 50Hz required for signaling and operationally essential lighting installations. To ensure a fairly steady voltage. Automatic voltage regulators are also provided where required. 3. Potential transformers are provided at the various switching stations for monitoring supply to each sub-sector. 4. A small masonry cubicle is provided to accommodate remote control equipment, control panel, telephone and batteries and battery chargers required for the control of interruptors and other similar equipments. 5 1.2 POWER SUPPLY FOR SIGNALLING 1.2.1 Supply Arrangements 1. To ensure reliability of ac 240V, supply through 25 kV/240V auxiliary transformer by tapping 25 kV OHE is made available at following places: (a) At each way side station for CLS. (b) Level crossings located more than 2 km away from Railway Station. (c) At IBH. (d) At all the power supply installations. 2. In the event of power block being given on both the OHE sub sectors from which the signal supply is derived electric traffic would necessarily have to be suspended on the line. During such periods colour light signally will not also be in operation. Such cases are likely to arise very rarely at any station and the duration of the block is not likely to exceed one hour at a time. Therefore, no additional power supply arrangement need be made by the Electrical Department at wayside stations. However, to cater for this condition portable generating sets should be kept by the S&T Department to be operated until 25 kV supply is restored. At large stations with considerable shunting movements a stand by diesel generator set may be installed by the S&T Department to meet emergencies, if considered essential. 1.2.2 Voltage Regulators. The fluctuating nature of the traction load causes perceptible fluctuation on the 240 V supply affecting operation of signalling equipment. To overcome this, static type voltage regulators are provided by S&T Department to limit voltage fluctuations to + 5%. These voltage regulators are installed either in separate kiosks inside the remote control cubicles, inside the ASM’s room, or inside the cabins depending upon the position of various load centers. 1.3. REMOTE CONTROL AND COMMUNICATION ARRANGEMENTS 1.3.1. Remote Control The interrupters at the various switching stations as well as the feeder circuit breakers (and other switchgear owned and operated by the Railway) at the sub- stations are controlled from a Remote Control Centre (RCC) manned throughout the 24 hours of the day. During each shift there is one more number of Traction Power 6 Controller (TPC), depending upon the work load. All switching operations on the system are thus under the control of one single person, namely TPC, who is responsible for maintaining continuity of power supply on all section of the OHE. He also maintains continuous and close liaison with the Section Controllers in regard to train operations on electrified sections. Further details regarding Remote Control are given in Vol II of this manual 1.3.2 Communication Facilities All aerial telecommunication lines running by the side of the tracks are replaced with under-ground cables/microwave to overcome the interference caused by 25 kV single phase ac traction. The cables contain adequate number of pairs of conductors for the various types of Railway telecommunication circuits on ac traction. For technical details reference may be made to Indian Railways Telecommunication Manual. In an electrified section it is essential, in the interest of efficiency to provide several independent telephone circuits to facilitate quick communication and to achieve co-ordination between different branches of the Railway. In an emergency several alternate telephone channels will be available for communication should one fail. The various telephone circuits provided in electrified sections are described below briefly :- 1. Train Control/Section Control: This circuit is operated by the Section Controller and is used mainly for controlling train movements within his jurisdiction. It has connections with Signal Cabins, ASMs’ Offices, Loco Sheds and Yard Masters’ Offices. 2. Dy. Control Telephone: This circuit is operated by the Deputy Controller and is used for directing traffic operations in general. It has connections with the important Station Masters’ offices. Yard Masters’ Offices, Loco Sheds and Signal Cabins. 3. Stock Control Telephone This circuit is operated by the Stock Controller and is mainly used for keeping a continuous watch and to maintain control over the movements of wagons. It has connections with Yard Masters and important Station Masters office. 4. Traction Loco Control This is a circuit provided for ac traction and is operated by the Traction Loco Controller who is responsible for movements of electric 7  locomotives and Electric Multiple Unit (EMU) stock. It has connections with Electric Loco Sheds, EMU Sheds, Important Station Masters, Yard, Divisional Officers such as Sr. DEE/DEE, AEE(RS), Sr. DEE/DEE/AEE(OP), Traffic Control Offices, Traction Foreman and important crew booking points. 5. Traction Power Control This is a special circuit on ac traction and is used by TPC for all communications in connection with power supply switching operations and ‘permit-to-work’. It has connections with Station masters’ offices, cabin. Traction sub-stations, feeding posts, sectioning and sub- sectioning posts, traction maintenance depots, important Signal Cabins, Divisional Officers such as Sr. DEE(TrD), Sr. DEE/OP and Traffic Control Offices. 6. Emergency Control Circuit This circuit is provided to facilitate the traction maintenance gangs and electric train crew to get in touch with TPC with the least possible delay in emergencies. It is also used by train crew in times of accidents for communication with the Control office. This circuit is operated by TPC and is located in the RCC. Emergency telephones socket boxes are provided along the track at an interval of 0.75 to 1 km and also and near the signal cabins, sub- sectioning and sectioning posts, insulated overlaps and feeding posts etc. Portable emergency telephones are given to maintenance gangs, train crew and station Masters. By plugging the portable telephone into an emergency socket it is possible to communicate with the TPC. 7. Hot Line Communication Hot line communication circuit should be provided between the HQ, divisional HQ traction loco controller and electric loco sheds. These would be provided in the HQ with CEE, CEE/Loco, Dy.CEE/RS, Sr.DEE/RS in the sheds and Sr.DEE/OP in the divisions. 8. Walkie Talkie sets : Every maintenance depots of OHE should have adequate numbers of walkie-talkie sets to be available with them during their normal maintenance work as well as break-downs so that not only effective communication is available at site but also to increase the efficiency and productivity of the work during power blocks. These walkie-talkie sets are to be used primarily for the following purposes: a) To communicate to the maintenance/breakdown gangs/parties that power block has been sanctioned. 8  b) To direct and supervise work during the period power block is in force; c) Confirmation regarding cancellation of power block by each individual party and cancellation of power block. 9. Other Communication facilities: An independent inter-communication circuit is also provided between the various Section Controllers and the Chief Controller for local communication between themselves. Facilities are also provided for the Chief Controller to talk to any station on train control, deputy control, stock control and traction loco control circuits. Similarly, facilities are provided to TPC to talk to any station on the train control and traction loco control in an emergency. However, it will not be possible for Chief Controller or TPC to ring independently any station on station on any control circuit as this ringing facility is only provided to the respective Controllers. View of Traction Substation -------------------- 9