Power Supply Arrangements at Sub-Stations

25 kV, AC, 50 Hz single-phase power derived from State Electricity Boards' grid, through traction substations.

Typically 35-50 km apart, but can be less depending on train traffic and load.

Four different arrangements exist for providing power to traction substations: 1. EHV supply, 2. 3-phase supply, 3. Shared EHV/25kV equipment, 4. Shared EHV/remote 25kV breakers.

Essential for continuous power supply to traction substations, often from two power sources or two transmission lines.

Traction substations typically have two single-phase transformers; one operating and one backup, with a standard capacity of 21.6 MVA (ONAN) or 30.2 MVA (ONAF).

Installed at substations to quickly isolate faults in transmission lines and equipment, ensuring continuous power supply.

Various scenarios exist regarding the ownership and upkeep of EHV and 25kV equipment at the traction substations.

Transformers used for stepping down grid voltage to 25 kV for the traction system typically have a capacity of 13.5 MVA (ONAN) or 10.8 MVA (ONAN).

Feeding posts are located near the tracks and are responsible for distributing the 25 kV power from the substation to the overhead lines.

A 25 kV feeder is a conductor that carries power from the substation to the feeding posts near the tracks and is protected by a circuit breaker.

The voltage at the substation busbars is regulated within a range of +10% and -5% of the nominal 25 kV, meaning it can fluctuate between 27.5 kV and 23.75 kV.

The tapping on the transformers is used to adjust the output voltage to maintain the highest possible value within the permissible range, ensuring efficient power delivery.

Traction substations are designed for remote operation and include provisions for flexible operation, including switching between feeders and isolating sections.

One end of the transformer's secondary winding is solidly grounded at the substation and connected to the track return feeder through buried rails, providing a path for current return.

The single-phase traction load draws uneven current from the three phases, causing voltage unbalance. This can negatively impact other consumers and generators.

To minimize negative effects, the voltage unbalance at the point of common coupling is limited to 5% instantaneously, 3% for 2 hours, and 2% continuously.

An electrically isolated gap between two substations on the overhead equipment (OHE) to prevent power from one phase from being bridged to another by passing trains.

The shortest length of OHE that can be isolated by opening only the interruptors. This segment might be 10-15 km long.

A smaller division within a sub-sector, isolated by manually operated isolator switches.

A location on the OHE where power is supplied to individual lines using interruptors. For a two-track line, there will be four interruptors at each feeding post.

A post marking the boundary between two zones powered by different phases from adjacent substations. Usually located midway between two feeding posts.

OHE is sectioned to isolate faults quickly, facilitate maintenance work, and ensure safety during repairs. It also allows for power supply flexibility.

These arrangements provide alternative power sources for feeding stations and yards, ensuring continuous power supply even during outages.

These isolators isolate the OHE when power is removed and also earth it, creating a safe working environment for maintenance.

These devices allow switching off the OHE power locally and earthing it, making it safe for working on rolling stock roofs.

To maintain electrical balance on the 3-phase grid, trains tap power from different phases in a cyclical order at adjacent substations.

A central location that monitors and controls the switching operations in the electrical system for railway lines. It runs 24/7.

The person responsible for maintaining a continuous power supply to the railway lines. They monitor and control switching operations from the Remote Control Centre.

To avoid interference caused by the high-voltage electric lines used for railways.

A communication circuit used to control the movement of trains and coordinate with various railway offices.

A communication circuit used for overall traffic management, connecting to important railway offices.

Voltage regulators are used to limit fluctuations in the 240V supply, ensuring stable operation of signalling equipment.

Auxiliary transformers provide a reliable 240V AC supply to various signalling locations, like level crossings and wayside stations.

Voltage fluctuations are typically limited to +/- 5% by voltage regulators installed in signalling systems.

Portable generating sets provide emergency power supply in case of power outages on both overhead line sub-sectors, ensuring continued signalling operation.

Voltage regulators are typically installed in separate kiosks, remote control cubicles, ASM's rooms, or cabins, depending on the location of load centers.

Potential transformers monitor the supply voltage to each sub-sector, ensuring consistent power distribution.

A wayside station refers to a signal station located in a remote area, typically along the railway line, used to control train movements.

Remote control cubicles accommodate essential equipment like remote control panels, batteries, and chargers for interruptors and other signalling components.

Power outages on both sub-sectors lead to a complete suspension of electric traffic, including colour light signalling.

Power blocks on signalling systems are typically short-lived, usually not exceeding one hour, and rarely occurring.

Electric trains use 25 kV, AC, 50 Hz single-phase power, supplied from the grid through traction substations.

Located along electrified lines, typically 35-50 km apart, they transform high voltage power to 25 kV for trains.

A post located between feeding posts (FPs) with interruptors for sectioning and paralleling the OHE, allowing for isolating and connecting sub-sectors of the OHE.

A post similar to SSPs, but only provides for sectioning the OHE, without paralleling capabilities.

Devices installed at substations to protect against voltage surges caused by lightning strikes.

Transformers used at posts and intermediate points to provide a 240V, 50Hz AC supply for signaling and operational lighting.

Devices that allow one feeding post to feed beyond a sectioning post to the next FP if its supply is interrupted.

Neutral sections are essential to prevent power from one phase from being bridged to another when trains pass between substations, ensuring the safety of the electrical system and preventing voltage fluctuations.

SSPs and SSs allow for the sectioning and paralleling of the OHE, enabling isolation of faults, maintenance, and flexible power supply arrangements.

Lightning arresters protect the system from voltage surges, while auxiliary transformers provide a reliable power supply for signaling and lighting, ensuring safety and operational functionality.

Bridging interrupters provide a backup power source by allowing one feeding post to feed beyond a sectioning post to the next FP if its supply is interrupted, ensuring uninterrupted power supply to the trains.

A reliable 240V AC supply is provided through 25kV/240V auxiliary transformers, tapped from the 25kV OHE, to power signaling equipment.

This 240V supply is provided at wayside stations for CLS, level crossings far from stations, IBH (Inter Block Housing), and all power supply installations.

If both OHE sub-sectors powering the signal supply are blocked, electric traffic must be halted. Colour light signaling also becomes inoperable.

Voltage regulators are located in kiosks, remote control cubicles, ASM's room, or cabins, depending on the location of load centers.

Potential transformers are used at switching stations to monitor the supply voltage to each sub-sector, ensuring consistent power distribution.

Small masonry cubicles house remote control equipment, control panels, telephone, batteries, and chargers for interruptors and other signaling components.

A wayside station is a signal station located along the railway line, typically in remote areas, controlling train movements.