Traction Substation Spacing and Energy Consumption

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Questions and Answers

What is the breaking capacity of the interruptor specified for a recovery voltage of 27.5 kV?

8000 Amps

2000 Amps

4000 Amps (correct)

6000 Amps

Which of the following is a primary function of isolating switches in a sub-station?

To regulate current flow

To automatically clear faults

To create a visible break in the circuit (correct)

To increase voltage levels

What type of isolating switch is primarily used on the HV side of traction substations?

Two post single break type

Single pole single break type

Vertical break type

Centre post rotating double break type (correct)

What is the rated normal current of the new specifications for interruptors according to RDSO?

800 Amps Signup and view all the answers

When should isolating switches be operated regarding the current flow in the circuit?

When negligible or no current is flowing Signup and view all the answers

What is the typical spacing between successive substations in high density routes?

40 to 60 km Signup and view all the answers

What voltage is the incoming supply stepped down to for use in traction substations?

25 kV Signup and view all the answers

Which of the following is NOT a voltage level at which Indian Railways purchases electric power?

250 kV Signup and view all the answers

How did Indian Railways evolve the management of traction substations in the late sixties?

They started purchasing bulk power and maintained their own substations. Signup and view all the answers

What is the role of transformer circuit breakers in traction substations?

To act as a backup to the feeder breaker. Signup and view all the answers

Where is the secondary winding of the step down transformer connected?

To the overhead equipment and solidly earthed to the rails. Signup and view all the answers

What is the primary purpose of having substations located close to railway traction?

To enable faster inspection and maintenance by staff. Signup and view all the answers

What is the primary function of the feeder breaker in a traction substation?

To break the circuit under both normal and abnormal conditions Signup and view all the answers

Which statement accurately describes the role of the interrupter in a traction substation?

It is a non-automatic device for breaking load current Signup and view all the answers

How many circuit breakers are typically provided at each traction substation?

Six circuit breakers Signup and view all the answers

What is the purpose of the neutral section in a traction supply system?

To separate two different phases Signup and view all the answers

What do the paralleling interrupters do at each subsectioning post?

They allow for connection of two lines in a double track section Signup and view all the answers

In case of an emergency due to the failure of an adjacent substation, what does the bridging interrupter do?

Extends feed from one substation to another Signup and view all the answers

What is the role of the transformer breakers in a traction substation?

To act as primary protection for feeder circuit breakers Signup and view all the answers

What are the subsectors in the traction supply system divided by?

Interrupters at subsectioning posts Signup and view all the answers

Which devices are primarily used to control the supply for each track?

Interrupters Signup and view all the answers

What is the maximum fault current for a nominal system voltage of 110 kV?

26.24 kA Signup and view all the answers

What method is used to calculate fault current on the primary side of the substation?

Fault MVA divided by 3 times Voltage in kV Signup and view all the answers

What is the total reactance when two transformers running in parallel have reactances of 1% and 30%?

31% Signup and view all the answers

What is the primary purpose of circuit breakers in a power supply system?

To isolate faulty sections of the system Signup and view all the answers

Which ambient conditions must circuit breakers operate reliably under?

High altitudes and heavy pollution Signup and view all the answers

For a 20 MVA transformer, what is the assumed short circuit impedance for calculations?

12% Signup and view all the answers

What is the percentage reactance of the transformer at 100 MVA base if the short circuit impedance is 12%?

60% Signup and view all the answers

What types of quenching mediums do different circuit breakers use?

Oil, compressed air, and SF6 gas Signup and view all the answers

What is the estimated maintenance cost range for oil circuit breakers as stated?

Rs.3000/- to Rs.40,000/- per annum Signup and view all the answers

What is the fault level on the 25 kV bus adjacent to the substation with total reactance of 61%?

163.93 MVA Signup and view all the answers

What is the fault current just opposite the substation for a fault level of 163.93 MVA on the 25 kV bus?

6.557 kA Signup and view all the answers

Which of the following accurately describes the duties of power circuit breakers?

They are designed to carry normal currents and interrupt under various conditions. Signup and view all the answers

What is the maximum fault MVA at a nominal system voltage of 66 kV?

3500 MVA Signup and view all the answers

Which type of circuit breaker was predominantly used by Indian Railways before switching to indigenous manufacturers?

Oil circuit breakers Signup and view all the answers

If a transformer has a short circuit impedance of 12% at 20 MVA, what would its percentage impedance be at 100 MVA base?

60% Signup and view all the answers

How do circuit breakers minimize adverse effects during switching operations?

By ensuring minimal voltage induction in the system Signup and view all the answers

What is a significant drawback of using oil circuit breakers as mentioned?

They have a very high maintenance cost. Signup and view all the answers

Which of the following statements is true regarding the fault breaking current for a system with a voltage of 220 kV?

It is 31.5 kA. Signup and view all the answers

Which of the following is NOT a function of power circuit breakers?

Convert AC to DC Signup and view all the answers

What was one of the main reasons for the shift from imported to indigenous manufacturing of circuit breakers by Indian Railways?

High maintenance costs of oil circuit breakers Signup and view all the answers

What defines electrical clearance in an electrical network?

The minimum distance required between live parts and earthed material or different potentials. Signup and view all the answers

Which of the following is not considered when determining minimum electrical clearances for outdoor switchgear?

Clearance between similar potential lines. Signup and view all the answers

What is the minimum air safety clearance required for a switchgear with an impulse voltage rating of 145 kV?

1350 mm Signup and view all the answers

Which clearance is referred to as sectional clearance?

Minimum distance between unscreened live conductors and the limits of a work section. Signup and view all the answers

For a switchgear rated at 245 kV, what is the minimum clearance to earth?

1800 mm Signup and view all the answers

What is the voltage level to which the incoming supply is typically stepped down for traction substations?

25 kV Signup and view all the answers

What is the average spacing between successive substations in high-density routes?

40 to 60 km Signup and view all the answers

At what voltage does Indian Railways purchase electric power from other utility providers?

220 kV Signup and view all the answers

What aspect of transformer circuit breakers is critical for maintaining electrical safety in traction substations?

Providing a backup function to the feeder breaker Signup and view all the answers

How did the management of traction substations change for Indian Railways in the late sixties?

Began operating and maintaining their own substations Signup and view all the answers

Where is one terminal of the secondary winding of the step-down transformer connected?

To the overhead equipment (OHE) Signup and view all the answers

In a traction power supply system, which component ensures the continuity of electrical supply in case of transformer failure?

Feeder circuit breaker Signup and view all the answers

What is the maximum fault current that the newly adopted 'Zebra' ACSR conductor can withstand?

31.5 KA Signup and view all the answers

What is the diameter of the rigid type bus bar that can carry a continuous current of 1530 Amps?

50 mm Signup and view all the answers

What type of conductors are the bushing type CTs mounted on the primary and secondary side of traction transformers primarily designed for?

Differential protection Signup and view all the answers

What is the minimum height requirement for the 25 KV bus bar installation?

3800 mm Signup and view all the answers

Which conductor was used in earlier electrification schemes before the 'Zebra' ACSR conductor?

Aluminium spider conductor Signup and view all the answers

What is the primary purpose of lightning arresters in a power supply system?

Protect against over-voltages Signup and view all the answers

What is the tension range that is maintained in the strung bus system?

500 to 900 kgf Signup and view all the answers

Which type of bus bar is used on the HV side of traction substations?

Strung type bus bar Signup and view all the answers

What is the continuous current capacity of the rigid type bus before upgrades?

960 Amps Signup and view all the answers

How are the support insulators for the rigid type bus bar positioned?

At a distance not exceeding 3 m Signup and view all the answers

What characteristic of an ideal arrester ensures minimal current during normal operation?

High impedance Signup and view all the answers

Which type of lightning arrester is designed with a series gap for protection?

Rod gap type Signup and view all the answers

Which of the following is NOT a consideration when selecting a lightning arrester?

Color of the apparatus Signup and view all the answers

What is one advantage of Zinc oxide gapless lightning arresters?

Greater energy absorption Signup and view all the answers

What is the recommended maximum installation distance for a lightning arrester relative to the protected apparatus?

10 meters Signup and view all the answers

What is the purpose of having a lower breakdown voltage for a lightning arrester compared to the equipment in the substation?

To ensure effective protection Signup and view all the answers

Which of the following types of lightning arresters is considered outdated due to complexity?

Conventional value type Signup and view all the answers

What is an important feature of a lightning arrester when considering its performance under environmental conditions?

Better sealing arrangement Signup and view all the answers

Which voltage level is critical when assessing a lightning arrester's power frequency flashover voltage?

Maximum line voltage Signup and view all the answers

How does the response speed of Zinc oxide gapless lightning arresters compare to other types?

Faster due to elimination of series gap Signup and view all the answers

What is the main function of the interrupter in a traction substation?

To break the load current while being non-automatic Signup and view all the answers

What is typically located between adjacent traction substations to separate different phases?

Neutral section Signup and view all the answers

Which task is NOT performed by the feeder circuit breakers in a traction substation?

Acting as back up protection for transformer breakers Signup and view all the answers

What type of circuits does a paralleling interrupter connect at each subsectioning post?

Two lines in a double track section Signup and view all the answers

What is the function of transformers located in traction substations?

To convert high voltage from supply lines to suitable levels for traction Signup and view all the answers

How many types of circuit breakers are typically provided at each traction substation?

Six, including both transformers and feeder circuit breakers Signup and view all the answers

In an emergency situation, how does the bridging interrupter assist in traction substations?

Facilitates power feed from an adjacent substation Signup and view all the answers

What is the purpose of the subsectors created between substations?

To facilitate easier maintenance and isolation of sections Signup and view all the answers

What significant structure is provided at each sectioning post to allow for emergency feed?

Bridging interrupter with an under voltage relay Signup and view all the answers

Study Notes

Traction Substation Spacing and Location

Substation spacing depends on permissible voltage drop at the farthest point.
Factors influencing voltage drop include anticipated traffic, future traffic projections, and gradients of the section.
Calculations consider normal and extended feed conditions, train combinations, loads, speeds, track parameters, and feed zone length.
Calculations ensure voltage at the farthest end remains within permissible limits.
Alternatively, power requirement can be calculated based on average specific energy consumption for goods and passenger trains in level or lightly graded sections.

Specific Energy Consumption

Goods trains: 11 kWh/1000 GTKM
Passenger trains: 19 kWh/1000 GTKM
Medium/heavily graded sections require figures based on trials.

Power Requirement Formula

P = Q x (2Lo) x W / (1000 x H x CosØ)
2 x Lo = Sub-station covering area for double track line (km)
W = Weight of a train in tones
Q = Energy consumption rate (kWh/1000 GTKM)
H = Headway in minutes during peak time (assumed)
CosØ = Power Factor (lagging)

Traction Substation Considerations

Availability of reliable power supply lines close to railway lines.
Willingness of electric supply authorities to extend high-voltage transmission lines.
Tariff rates for power supply.
Traffic volume and gradients of the section.
Future traffic estimations.
Whether a single or double line section.

Traction Power Supply System

Indian Railways purchase electric power from state electricity boards.
Regional grids typically provide power at 220/132/110/66 kV.
Power is stepped down to 25 kV AC using step-down transformers.
Primary winding is connected across two phases of the three-phase system.
One terminal of the 25 kV secondary winding is connected to overhead equipment (OHE).
The other terminal of the 25 kV secondary winding is solidly earthed and connected to the running rails.

Typical Traction Substation Layout

Includes two transformers
Each transformer supplies one OHE.
Multiple breakers are provided for each side of the transformer.
Feeder breakers provide normal and abnormal operating conditions.
Circuit breakers act as backup to feeder breakers.
Interrupters, or load switches, control the supply to the tracks.
Dead zones (neutral sections) are used to separate phases.

Traction Power Transformer Characteristics

Most important and costly piece of substation equipment.
Initial electrification used 7.3 and 10 MVA.
Current electrification uses higher capacity transformers (13.5, 20, or 30 MVA).
Traction transformers handle frequent short circuits and load fluctuations.
Higher voltage ratings and current handling capacity are required typically.

Circuit Breakers

Next in importance to the transformer.
Crucial for controlling and performing power system functions.
Purpose is to carry rated currents, isolate faulty sections, interrupt load currents, handle capacitive and small inductive currents.
Oil breakers were traditionally used, SF6 and vacuum breakers are increasingly used in new projects.
Cost of upkeep and maintenance impacts breaker selection.

Rated Short-Circuit Breaking Current

Varies between 1,000 MVA to 10,000 MVA depending on the proximity of the generating station
Breakdown current rating is influenced by voltage class

Substation Insulation Coordination

Insulators, transformers, and busbars all must be adequately insulated to prevent flashovers.
Insulation levels are determined by maximum voltage and distances expected to maintain safe operating conditions.

Insulators Technical Specifications

Creepage distances are designed to accommodate various pollution levels.
Creepage distance is designed to be 25mm/kV.

Lightning Arresters

Protect substation equipment from lightning surges and overvoltages.
Various types are available (rod gap, expulsion, conventional, zinc oxide).

Earthing System

Critical component in traction substation to prevent high resistance to ground.
Multiple earth electrodes should be used.
Earthing system protects people working in the substation, and equipment from faults.
Earthing system size is influenced by fault current and corrosion.
The minimum number of earth electrodes is calculated based on the fault current.

Co-ordination Table of Circuit Breakers

Provides relationships between equipment ratings for proper operation.
Matching circuit breaker components for reliable system operation.

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Description

This quiz covers the spacing and location of traction substations, focusing on the permissible voltage drop at the farthest point. It delves into the calculations related to power requirements for both goods and passenger trains, including specific energy consumption and how various factors influence these metrics.