Power Supply Arrangements at Sub-Stations

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Questions and Answers

What is the primary voltage for the feeders that are used to support the overhead equipment for traction?

25 kV (correct)

27.5 kV

23.75 kV

30 kV

What is the permissible voltage variation range for the bus bars at the grid sub-station?

$27,500 V$ to $23,750 V$ (correct)

$23,000 V$ to $29,000 V$

$20,000 V$ to $27,500 V$

$25,000 V$ to $30,000 V$

How is the single-phase traction load managed to prevent unbalance in the 3-phase grid system?

By cyclic tapping across different phases (correct)

By reducing the voltage to lower levels

By using transformers

By using only one phase for traction

Which component ensures that the voltage does not exceed 27.5 kV at the feeding post?

Transformer settings Signup and view all the answers

What is the maximum allowable instantaneous voltage unbalance at the point of common coupling in the grid supply system?

5% Signup and view all the answers

What type of operation is the traction sub-station designed for?

Remote operation Signup and view all the answers

What connects one end of the secondary winding of the transformer at the sub-station?

Buried rail Signup and view all the answers

What is the maximum speed allowed when the runners of the section insulator assembly are not installed in the first one-third of the span?

80 km/h Signup and view all the answers

What kind of structures are used to ensure mechanical independence of the overhead equipment (OHE) for each track?

Independent structures Signup and view all the answers

What is the maximum speed potential for an OHE designed with a span of 72 m and a tension of 1000 kgf in both contact and catenary wires?

160 km/h Signup and view all the answers

What precaution is necessary when approaching an unwired track with an electric locomotive?

A diesel engine must be used to pull the locomotive Signup and view all the answers

What should a driver be ready to do when approaching a neutral section indicated by warning boards?

Open the DJ (Disconnector Junction) Signup and view all the answers

What is indicated about electric traffic during a power block on both OHE sub-sectors?

Electric traffic must be suspended until power is restored. Signup and view all the answers

What is the purpose of static type voltage regulators in the railways?

To maintain voltage fluctuations within + 5%. Signup and view all the answers

Where are static type voltage regulators typically installed?

Inside dedicated kiosks or rooms based on load positions. Signup and view all the answers

What is the duty of the Traction Power Controller (TPC) during his shift?

To monitor and maintain continuity of power supply. Signup and view all the answers

What kind of emergency provision can be found at large stations?

Standby diesel generator sets installed by S&T. Signup and view all the answers

How often is the Remote Control Centre (RCC) manned?

24 hours a day. Signup and view all the answers

What is the maximum duration a power block is likely to last?

One hour at a time. Signup and view all the answers

Which of the following personnel is in charge of switching operations on the railway system?

The Traction Power Controller (TPC). Signup and view all the answers

What arrangement is suggested for authority communication during a power block?

Close liaison with Section Controllers. Signup and view all the answers

What is the purpose of staggering the contact wire in OHE systems?

To allow the pantograph to sweep across the current collecting strips. Signup and view all the answers

What defines a regulated OHE system?

It incorporates automatic tensioning mechanisms. Signup and view all the answers

How far apart are uninsulated overlap spans in OHE systems?

200 mm. Signup and view all the answers

What is the role of section insulators in OHE systems?

To isolate adjacent elementary sections from each other. Signup and view all the answers

Why are insulated overlaps provided in OHE systems?

To prevent arcing and ensure safety. Signup and view all the answers

What is the maximum distance OOHE conductors can be terminated with an overlap?

1.5 Km. Signup and view all the answers

What factor typically dictates the spans adopted for catenary support intervals?

Degree of curvature. Signup and view all the answers

What happens when pantographs transition between OHE systems?

They can cause sparks if not designed correctly. Signup and view all the answers

What is the length of overlap in insulated overlaps in OHE systems?

500 mm. Signup and view all the answers

At what speed are section insulator assemblies designed to be effective?

120 km/h. Signup and view all the answers

What is the primary purpose of the Emergency Control Circuit?

To facilitate quick communication between traction maintenance gangs and TPC. Signup and view all the answers

Where are emergency telephone socket boxes installed?

Along the track at specific intervals and near important posts. Signup and view all the answers

Which of the following is NOT a purpose of walkie-talkie sets in maintenance depots?

To interact with passengers. Signup and view all the answers

Who primarily operates the Emergency Control Circuit?

TPC (Traction Power Control). Signup and view all the answers

What is the role of Hot Line Communication?

To establish a connection between headquarters and electric loco sheds. Signup and view all the answers

What interval is recommended for placing emergency telephone socket boxes along the track?

Every 0.75 to 1 km. Signup and view all the answers

Which of the following is a function of the independent inter-communication circuit?

To facilitate local communication among Section Controllers and Chief Controller. Signup and view all the answers

Which personnel are equipped with portable emergency telephones?

Train crew, maintenance gangs, and Station Masters. Signup and view all the answers

What is a key benefit of providing walkie-talkie sets in maintenance depots?

Improving efficiency and productivity during maintenance and breakdowns. Signup and view all the answers

Which of the following roles is NOT involved in the Hot Line Communication circuit?

Traffic Control Officers. Signup and view all the answers

What is the standard capacity of the transformers typically installed at traction sub-stations?

21.6 MVA (ONAN)/30.2 MVA (ONAF) Signup and view all the answers

Which arrangement describes when the Railway owns certain circuit breakers at sub-stations while the Supply Authority manages all other equipment?

Railway owns feeder circuit breakers but not transformers Signup and view all the answers

How is continuity of power supply ensured at traction sub-stations?

Through dual power sources or double circuit transmission line Signup and view all the answers

What is a typical distance between traction sub-stations along electrified sections?

35 to 50 km Signup and view all the answers

Which of the following explosion prevention measures is commonly installed at traction sub-stations?

Rapid fault isolation equipment Signup and view all the answers

How does the Railway receive its power supply if it runs its own transmission lines?

From a single 3-phase power supply point near the grid sub-station Signup and view all the answers

What is the role of the Traction Power Controller regarding the 25 kV feeder circuit breakers?

To operate feeder circuit breakers remotely Signup and view all the answers

What is the main function of the Emergency Control Circuit in the railway system?

To facilitate the communication between traction maintenance gangs and TPC during emergencies Signup and view all the answers

Which personnel are typically provided with portable emergency telephones?

Train crew, maintenance gangs, and Station Masters Signup and view all the answers

What interval is recommended for the placement of emergency telephone socket boxes along the railway track?

Every 0.75 to 1 km Signup and view all the answers

What purpose do walkie-talkie sets serve in maintenance depots?

To enhance communication during power blocks and maintenance activities Signup and view all the answers

What does the Hot Line Communication circuit primarily connect?

Divisional HQ traction loco controller to electric loco sheds and senior officials Signup and view all the answers

What is the purpose of a 'Neutral Section' in the overhead equipment system?

To ensure that pantographs do not bridge different phases Signup and view all the answers

What is referred to as a 'sub-sector' in the overhead equipment management?

A section that can be isolated by opening interruptors alone Signup and view all the answers

Why are warning boards placed in advance of the neutral section?

To alert drivers to open the locomotive circuit breaker Signup and view all the answers

What are 'interruptors' used for at feeding posts?

To control supply to individual lines Signup and view all the answers

What feature does a sectioning and paralleling post (SP) provide?

It marks the boundary of two zones with different power phases Signup and view all the answers

What type of isolators are provided for electric loco running sheds?

Isolators with earthing device in the 'off' position Signup and view all the answers

How are 'elementary sections' created in the overhead equipment system?

Using off-load type manually operated isolator switches Signup and view all the answers

What does the term 'earthing heels' refer to in the context of overhead equipment?

Devices used to ground the overhead equipment safely Signup and view all the answers

What is the expected functionality of manually operated interrupters at watering stations?

To enable local power disconnection and earthing Signup and view all the answers

What is the role of the bridging interruptors in the overhead equipment system?

To allow one feeding post to supply power beyond its sectioning post. Signup and view all the answers

What type of equipment is typically installed to protect each sub-sector from voltage surges?

Lightning arresters Signup and view all the answers

How many interruptors are normally provided at each Sub-Sectioning Post (SSP) in a double track section?

Three Signup and view all the answers

Where is the 25 kV AC supply tapped to ensure a reliable supply of 240V?

At each wayside station for CLS and level crossings more than 2 km from a station Signup and view all the answers

What is the primary purpose of auxiliary transformers installed at posts?

To supply AC at 240 V, 50 Hz for lighting and signaling Signup and view all the answers

What occurs with the bridging interruptors under normal operation conditions?

They are normally kept open. Signup and view all the answers

What type of posts are occasionally used for sectioning but do not support paralleling of tracks?

Sub-Sectioning Post (SS) Signup and view all the answers

What provides accommodation for remote control equipment and other essential devices?

Masonry cubicle Signup and view all the answers

What is typically monitored at switching stations using potential transformers?

Power supply to each sub-sector Signup and view all the answers

What is the role of lightning arresters in the sub-sector equipment?

To protect against voltage surges Signup and view all the answers

What is the primary purpose of the Traction Loco Control circuit?

To manage the movements of electric locomotives and EMU stock Signup and view all the answers

Which circuit is primarily responsible for train movements within a section?

Train Control/Section Control Signup and view all the answers

What type of communication does the Traction Power Control circuit focus on?

Power supply and switching operations Signup and view all the answers

Which personnel primarily operates the Dy.Control Telephone circuit?

Deputy Controller Signup and view all the answers

What is a key benefit of having multiple independent telephone circuits in electrified railway sections?

To enable quick communication and coordination Signup and view all the answers

Which circuit is specifically used for continuous monitoring of wagon movements?

Stock Control Telephone Signup and view all the answers

Which of the following offices is NOT connected to the Train Control/Section Control circuit?

Stock Control Offices Signup and view all the answers

For managing all power supply communications, which circuit is utilized?

Traction Power Control Signup and view all the answers

Which of the following statements accurately describes the role of the Section Controller?

Directing train movements within their jurisdiction Signup and view all the answers

The connections for the Traction Loco Control circuit include which of the following?

Electric Loco Sheds and Important Station Masters Signup and view all the answers

Study Notes

Power Supply Arrangements at Sub-Stations

25 kV, 50 Hz single-phase power supply for electric traction is derived from the grid system of State Electricity Boards.
Sub-stations are located approximately 35-50 km apart (or less depending on traffic and load) along electrified sections.
Four primary arrangements exist for power supply:
- Supply Authorities provide 220/132/110/66 kV EHV at the sub-station.
- Railways receive 3-phase power from the Supply Authority, maintain their own transmission lines, and operate sub-stations.
- Supply Authority owns all EHV and 25 kV equipment, except 25 kV feeder circuit breakers owned by the Railways.
- Supply Authority owns all EHV and 25 kV equipment, except 25 kV feeder circuit breakers operated remotely by the Traction Power Controller (TPC).

Duplicate Power Supply

Double circuit transmission lines or dual power sources ensure uninterrupted power supply in sub-stations.
Protective equipment isolates any fault in transmission lines or sub-station equipment quickly.
Normally, two single-phase transformers (21.6/30.2 MVA capacity) are used to step down the grid voltage to 25 kV and feed traction equipment.
25 kV feeders carry power from sub-stations to feeding posts, controlled by circuit breakers with protective devices.

Voltage Regulation

Permissible busbar voltage variation at the grid sub-station is +10% and -5% (27,500 V to 23,750 V).
Transformer tappings regulate voltage at the feeding posts (maximum 27.5 kV).
Multiple transformer circuits on the secondary side include a transformer circuit breaker and feeder circuit breaker with associated double pole isolators.

Feeding and Sectioning Arrangements

3-phase supply systems from power authorities create supply imbalances affecting generators and other equipment.
Voltage unbalance at the point of common grid coupling should not exceed 5% (instantaneous) or 3% (continuous).
Tapping off single-phase traction power from grid phases at substations (in a cyclic order) helps reduce imbalance.
Overhead equipment systems in adjacent sub-stations are electrically separated by "neutral sections."
Switching stations and other equipment segment 10-15 km sections of overhead equipment (OHE), facilitating rapid isolation for maintenance.
Alternative feeding arrangements are provided for yards and electric loco-running sheds.
Automatic switching mechanisms on some sections allow flexible power supply (e.g., for watering stations or for maintenance on OHE).

Feeding Posts (FP)

Each feeder supplies OHE on one side of the feeding post through interruptors.
Two-track lines require four interruptors at each post.

Sectioning and Paralleling Posts (SP)

Located midway between feeding posts (marking neutral sections).
Connect adjacent substations for better load distribution.

Sub-Sectioning and Paralleling Posts (SSP)

Provided between FP and adjacent SPs, typically with three interruptors.
Help to divide sections of OHE into smaller segments.
May include interruptors or other switch gear to help divide up the section into sub-sectors.

Other Equipment at Switching Stations

Essential equipment: Lightning arrestors, auxiliary transformers (240 V AC), potential transformers, controls, and communication equipment.
All of this equipment safeguards transmission lines and monitors the power grid, protecting against potential damage.

Power Supply for Signaling

240V AC supply is made available at railway stations and other locations through auxiliary transformers.
Locations include the side of tracks, level crossings, and installations.

Remote Control and Communication

Remote Control Centre (RCC) manages circuit breakers and related switch gear in sub-stations.
One or more Traction Power Controllers (TPCs) operate switching functions during each shift.
Continuous communication between TPCs and Section Controllers maintains power supply and train operations.
Telecommunication lines (now largely underground cable/microwave) are necessary to accommodate the electrification.

Overhead Equipment (OHE)

Catenary and contact wire system (cadmium copper/aluminum alloy).
Grooved contact wire with a specific cross-section (equivalent copper section of 157 mm²) and is supported by droppers.
Looping lines, sidings, yards use a simpler OHE design with lower contact wire specifications than main lines.
Contact wire height varies based on temperature and gauge.
Spans for structures supporting OHE vary based on track straightness; larger spans used in straight sections/smaller spans in curved sections.
The contact wire is properly staggered to ensure consistent pantograph contact/uniform wear.
Two types of overlap spans.

Special Warning Signals

Visual cues indicating neutral sections (and when they're being used), helping drivers to operate safely and smoothly.
Warnings are used for unwired tracks, or when the OHE ends.

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Description

This quiz explores the various power supply arrangements at sub-stations, specifically focusing on electric traction systems. It covers the distances between sub-stations, the roles of supply authorities, and the strategies for ensuring a reliable power supply. Gain insights into the technical aspects that keep the electric railways running smoothly.