Traction Power System
Posted by Anup Mohan on Wednesday, November 16, 2011 Under: Traction
In an Overhead electrification systems, the electricity is supplied by means of electrified wires (live conductors) that run parallel and above the track. These wires are termed as Contact wire. Contact wires can be found attached ( or perhaps supported by ) another length of wire which is termed as Catenary wire.
The electric locomotive uses a Panto-graph, a metal structure which can be raised or lowered so as to make contact with the catenary-contact system and draw current. The return path for the electricity i.e. the return current is through the body of the locomotive and wheels to the rails (tracks) that are electrically grounded. Ground connections are provided from the rails at periodic intervals. The return current, after flowing from the wheels to the rails, flow through the rails and also partly through the earth beneath it. Earth bonding are provided periodically to keep the rails firmly connected to the earth so as to prevent form formation of a step voltage ( For information on Step Voltage, refer the post "Earthing Design")
The Power Flow to the OHE
The overhead catenary-contact system which feeds the electric locomotive is in turn electrified by the "Feeding Posts" that are frequently places along the track. The Feeding Posts (FP) are themselves are a part of the Traction Power Substation (TSS). The FP is fed by the TSS, which is placed at an interval of 50 to 70 km. The interval between two TSS shall be reduced (or suitably adjusted) considering the load and the traffic on the route.
A Remote Control Center, usually close to the Divisional Traffic Control office has the facilities of controlling the power fed to the catenay system through different TSS at a particular section.
The TSS gets the input power from the regional grid (of the state electricity board). The supply authorities supply power at 220kV, 132kV, 110kV, 66kV Extra High Voltage (EHV) at each TSS which is owned and maintained by the railways. To ensure the continuity of the supply, the high voltage feed to the TSS is arranged form a double transmission line, so that even in the event of failure of one, the other service remains. Suitable protective equipments and other required switch-gears are installed at the TSS.
Each TSS, normally has two single phase traction power transformer ( one taking 100% load and other as Standby - for more information on selection of transformer, refer to the post "Transformer Selection" posted earlier). This voltage level is then stepped down to 25kV which is the suitable voltage for railways. One lead form the secondary terminal of the transformer is solidly earthed and is connected to the rails.
The power from the TSS reaches the OHE system through the FP. The TSS has two leads (voltage bus) running into the FP with a coupling unit ( in the form of an Interrupter ) between them. Each of the two leads feeds into two different electrical sections formed by an insulated overlap (IOL) in the catenary-contact system. The coupling interrupter is installed so that the power supply can be extended from one section to the other in case of a failure in any one of the sections. An insulated overlap is to create different sections in OHE. In an IOL, the two catenary-contact wires forming different sections are kept apart 500mm away from each other and the electrical discontinuity is bridged by an interrupter or isolator.
Traction Substation
The power received form the supply authorities are from the three phase power system. The single phase traction load will cause an unbalance in the three phase power system. This unbalance will have undesirable effects on the suppliers generator. Hence, to keep the unbalance within a permissible limit, the power for traction load is tapped off form the grid system across different phases, in a cyclic manner. One of the phase is electrically grounded and connected to the rails. The other phase is supplied to the FP through the required switch-gear equipment. Apart form the single phase traction power transformers, Capacitor banks are installed in the TSS for power factor correction. For instance, consider a TSS - 1 feeding R phase supply to the OHE. In this case the TSS -2 or TSS-3 that is placed 50 to 70 km away or before (respectively) will not be feeding R phase supply to the OHE. Hence, consecutive TSS are not connected in parallel.
Thus, it becomes necessary to separate electrically the OHE systems fed by adjacent substations. This is done by the provision of a Neutral Section in the OHE, to ensure that the two different phases are not bridged. In the neutral zones, the catenary-contact system is not energized. These neutral zones are the limits till where a TSS feeds. In this zone, the two energized portion of OHE is separated by a PTFE.
Section and Paralleling Post
In order to avoid wrong phase coupling, between every two TSS, a Sectioning and Paralleling Post (SP) is placed. The SP is placed at a point where there is a neutral zone in the OHE. The portion of OHE between the feeding point and the nearest neutral is called as a section. Normally, a TSS feeds two sections.
The location on an SP is also decided such that it is far away from the signals or level crossing gates. This is done so that the locomotive could pass the neutral section with sufficiently high speed to avoid the possibility of getting stuck in the neutral section. The SP, provided at the neutral zone has paralleling interrupters to keep the two portion of OHE ( one in each direction) to be supplied in parallel. It also has a bridging interrupter that is normally open with under voltage relays, used to bridge the two different sections, extending power supply in case of emergency. This is in case of an SP operating for more than one line. In case of only one line, the SP has only a bridging interrupter, which is normally kept open.
Subsectioning and Paralleling Posts
The sections may be further sub-divided into sub-sections for the purpose of maintenance in OHE. Each section is split into sub-sections every 10 to 15km by placing a Sub-sectioning and paralleling post (SSP) at required intervals. The SSP has paralleling interrupters to parallel the Up and down tracks ( in case of more than one line ) and bridging interrupters to bridge different sub-sections when required.
The electric locomotive uses a Panto-graph, a metal structure which can be raised or lowered so as to make contact with the catenary-contact system and draw current. The return path for the electricity i.e. the return current is through the body of the locomotive and wheels to the rails (tracks) that are electrically grounded. Ground connections are provided from the rails at periodic intervals. The return current, after flowing from the wheels to the rails, flow through the rails and also partly through the earth beneath it. Earth bonding are provided periodically to keep the rails firmly connected to the earth so as to prevent form formation of a step voltage ( For information on Step Voltage, refer the post "Earthing Design")
The Power Flow to the OHE
The overhead catenary-contact system which feeds the electric locomotive is in turn electrified by the "Feeding Posts" that are frequently places along the track. The Feeding Posts (FP) are themselves are a part of the Traction Power Substation (TSS). The FP is fed by the TSS, which is placed at an interval of 50 to 70 km. The interval between two TSS shall be reduced (or suitably adjusted) considering the load and the traffic on the route.
A Remote Control Center, usually close to the Divisional Traffic Control office has the facilities of controlling the power fed to the catenay system through different TSS at a particular section.
The TSS gets the input power from the regional grid (of the state electricity board). The supply authorities supply power at 220kV, 132kV, 110kV, 66kV Extra High Voltage (EHV) at each TSS which is owned and maintained by the railways. To ensure the continuity of the supply, the high voltage feed to the TSS is arranged form a double transmission line, so that even in the event of failure of one, the other service remains. Suitable protective equipments and other required switch-gears are installed at the TSS.
Each TSS, normally has two single phase traction power transformer ( one taking 100% load and other as Standby - for more information on selection of transformer, refer to the post "Transformer Selection" posted earlier). This voltage level is then stepped down to 25kV which is the suitable voltage for railways. One lead form the secondary terminal of the transformer is solidly earthed and is connected to the rails.
The power from the TSS reaches the OHE system through the FP. The TSS has two leads (voltage bus) running into the FP with a coupling unit ( in the form of an Interrupter ) between them. Each of the two leads feeds into two different electrical sections formed by an insulated overlap (IOL) in the catenary-contact system. The coupling interrupter is installed so that the power supply can be extended from one section to the other in case of a failure in any one of the sections. An insulated overlap is to create different sections in OHE. In an IOL, the two catenary-contact wires forming different sections are kept apart 500mm away from each other and the electrical discontinuity is bridged by an interrupter or isolator.
Traction Substation
The power received form the supply authorities are from the three phase power system. The single phase traction load will cause an unbalance in the three phase power system. This unbalance will have undesirable effects on the suppliers generator. Hence, to keep the unbalance within a permissible limit, the power for traction load is tapped off form the grid system across different phases, in a cyclic manner. One of the phase is electrically grounded and connected to the rails. The other phase is supplied to the FP through the required switch-gear equipment. Apart form the single phase traction power transformers, Capacitor banks are installed in the TSS for power factor correction. For instance, consider a TSS - 1 feeding R phase supply to the OHE. In this case the TSS -2 or TSS-3 that is placed 50 to 70 km away or before (respectively) will not be feeding R phase supply to the OHE. Hence, consecutive TSS are not connected in parallel.
Thus, it becomes necessary to separate electrically the OHE systems fed by adjacent substations. This is done by the provision of a Neutral Section in the OHE, to ensure that the two different phases are not bridged. In the neutral zones, the catenary-contact system is not energized. These neutral zones are the limits till where a TSS feeds. In this zone, the two energized portion of OHE is separated by a PTFE.
Section and Paralleling Post
In order to avoid wrong phase coupling, between every two TSS, a Sectioning and Paralleling Post (SP) is placed. The SP is placed at a point where there is a neutral zone in the OHE. The portion of OHE between the feeding point and the nearest neutral is called as a section. Normally, a TSS feeds two sections.
The location on an SP is also decided such that it is far away from the signals or level crossing gates. This is done so that the locomotive could pass the neutral section with sufficiently high speed to avoid the possibility of getting stuck in the neutral section. The SP, provided at the neutral zone has paralleling interrupters to keep the two portion of OHE ( one in each direction) to be supplied in parallel. It also has a bridging interrupter that is normally open with under voltage relays, used to bridge the two different sections, extending power supply in case of emergency. This is in case of an SP operating for more than one line. In case of only one line, the SP has only a bridging interrupter, which is normally kept open.
Subsectioning and Paralleling Posts
The sections may be further sub-divided into sub-sections for the purpose of maintenance in OHE. Each section is split into sub-sections every 10 to 15km by placing a Sub-sectioning and paralleling post (SSP) at required intervals. The SSP has paralleling interrupters to parallel the Up and down tracks ( in case of more than one line ) and bridging interrupters to bridge different sub-sections when required.
The below given is a schematic sketch of a 132kV/25kV Taction Substation.
In : Traction
Tags: "traction"
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