Relay Settings in Traction Systems

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Questions and Answers

What is the correct formula for calculating Y given impedance Z?

Y = Z x 1.25 x Cos(delta-delta)

Y = Z / 1.25 x Cos(delta-delta)

Y = Z x Cos(delta-delta) / 1.25

Y = Z x 1.25 / Cos(delta-delta) (correct)

What percentage of the continuous current rating of the traction transformer does the current setting of the instantaneous over-current relay correspond to?

250%

100%

200% (correct)

150%

Under what condition should the impedance setting of the relay be set to Y?

When Z is less than Y (correct)

When Z is between X and Y

When Z equals Y

When Z is greater than Y

What factor accounts for the CT and relay errors and transient over-reach in the setting of the instantaneous over-current relay?

1.25 Signup and view all the answers

What represents the overload condition considered in the critical impedance setting?

50% of the traction transformer Signup and view all the answers

What is the maximum torque angle of the YCG-14 relay?

125 degrees Signup and view all the answers

What is the primary factor used to determine the critical impedance setting for the relay?

Rated current of the transformer Signup and view all the answers

Which of the following angles is indicated as the load angle when calculating the relay settings?

40 degrees Signup and view all the answers

How is the impedance setting of the English - Electric make YCG-14 relay calculated?

K1 K2 (K3 + K4) Signup and view all the answers

In which operational configuration is double line operation applied?

From the sectioning post to the adjoining feeding post Signup and view all the answers

For the IDMT over current relay to permit overloading of the traction power transformer, what should the current setting correspond to?

150% of rated current Signup and view all the answers

What is the typical operation time range for the IDMT relay during an earth fault on the 25 kV bus?

0.4 to 0.5 sec Signup and view all the answers

The relay settings must ensure protection when which of the following occurs?

When one feeder breaker is taken out for maintenance Signup and view all the answers

When can Z be set for the relay?

If Z lies between X and Y Signup and view all the answers

What percentage of the rated current of the traction power transformer is the current setting for the restricted earth fault relay on the low voltage side?

10% Signup and view all the answers

What is the relationship between the impedance settings of a Mho relay relative to Y, X, and Z?

Must not exceed Z and should be minimum Y or maximum X Signup and view all the answers

How should the higher impedance setting be determined for WPC relays at TSS-1?

By calculating individually for each side Signup and view all the answers

What is the factor that limits the relay not to operate under overload conditions?

The impedance setting must be lower than Z Signup and view all the answers

What role does the IDMT overcurrent relay serve in the traction substation protection scheme?

Feeder protection relay backup Signup and view all the answers

What percentage does the high voltage side restricted earth fault relay's current setting correspond to?

10% Signup and view all the answers

What is the purpose of setting the instantaneous element of the IDMT relay to correspond to 1.25 times the fault current?

To avoid operation of the relay for 25 kV bus faults Signup and view all the answers

Which setting is used to accommodate overloading of the traction transformer with the IDMT relay?

150% of the rated current Signup and view all the answers

For time grading with the IDMT relay, what is the typical operating time selected for earth faults?

0.8 to 0.9 seconds Signup and view all the answers

What should the percentage bias setting of the biased differential relay account for?

Tap changing on traction transformer and CT saturation levels Signup and view all the answers

What is the suggested operating current setting for the biased differential relay?

40% Signup and view all the answers

What is the recommended action if mal-operations of the biased differential relay are noted during through faults?

Consider a higher setting for the operating current Signup and view all the answers

What is the initial time multiplier setting recommended for the biased differential relay?

1 Signup and view all the answers

What is the percentage allowance that should be made for CT saturation levels under through-fault conditions?

7.5 to 15% Signup and view all the answers

Which factor is NOT a cause for the biased differential relay to remain inoperative?

Normal loading variation Signup and view all the answers

What should be considered if mal-operations of the relay occur on magnetizing inrush but not on through faults?

Increase the time multiplier setting Signup and view all the answers

What must be true for the relay not to operate under specified overload conditions?

The impedance setting must be lower than the critical impedance setting. Signup and view all the answers

If the critical impedance setting is calculated as Z, what should the relay's impedance setting range be?

Between X and Y. Signup and view all the answers

What is the significance of the maximum torque angle in calculating relay settings?

It influences the relay's impedance setting directly. Signup and view all the answers

In the absence of an operating feeder breaker, how should the impedance setting be determined?

Use the higher of the two calculated values from both sides. Signup and view all the answers

What is the minimum impedance setting for the Mho relay in relation to Y?

The setting can be higher than X but lower than Z. Signup and view all the answers

What is the impact of the load angle of 40 degrees on the relay calculations?

It alters the critical impedance setting formula. Signup and view all the answers

Why must the relay settings account for both feeder sides separately?

To provide redundancy in case of maintenance. Signup and view all the answers

What role does the critical impedance setting play in the operation of the relay?

It establishes a threshold to prevent undesired operation. Signup and view all the answers

When the calculated value of Z is less than Y, what should be the action regarding the relay settings?

Set the relay at Y. Signup and view all the answers

What is one of the factors that can cause the relay not to operate during overload conditions?

Setting below the critical impedance. Signup and view all the answers

What is the role of the IDMT overcurrent relay in the traction substation protection scheme?

It serves as a backup protection to feeder relays. Signup and view all the answers

How should the current setting for the restricted earth fault relay on the high voltage side be established?

10% of the rated current of the traction power transformer. Signup and view all the answers

What is indicated by the maximum torque angle of the YCG-14 relay?

The angle beyond which the relay may not function correctly. Signup and view all the answers

What is the effect of selecting a current setting corresponding to 150% of the rated current for the IDMT relay?

It allows the transformer to operate under overloading conditions. Signup and view all the answers

How is the impedance setting of the WPC relay determined at TSS-1?

By determining and adopting the higher value of two separately calculated impedances. Signup and view all the answers

What primary aspect must the impedance setting formula K1 K2 (K3 + K4) account for in the YCG-14 relay?

The plug board and potentiometer settings. Signup and view all the answers

What percentage does the restricted earth fault relay current setting correspond to on the low voltage side?

10% Signup and view all the answers

Which factors contribute to the relay not operating under overload conditions?

Relay errors, transient overreach, and high voltage conditions. Signup and view all the answers

What is indicated by the time-multiplier setting of the IDMT relay?

The duration before the relay activates upon fault detection. Signup and view all the answers

What is the primary purpose of setting the instantaneous element of the IDMT relay to correspond to 1.25 times the fault current?

To avoid relay operation for 25 kV bus faults at the traction substation Signup and view all the answers

What current setting percentage is recommended for the IDMT relay to accommodate overloading of the traction transformer?

150% of its rated current Signup and view all the answers

Which percentage mismatch should be considered in the biased differential relay settings due to tap changing on traction transformers?

7.5% to 15% Signup and view all the answers

For maintaining time grading with the IDMT relay on the 25 kV side, what operating time is typically chosen for earth faults?

0.8 to 0.9 seconds Signup and view all the answers

What is the suggested operating current setting for the biased differential relay?

40% Signup and view all the answers

What action should be taken if mal-operations of the biased differential relay are observed during through faults?

Increase the operating current setting Signup and view all the answers

What is the initial time multiplier setting recommended for the biased differential relay?

1.0 Signup and view all the answers

What operational condition should the percentage bias setting for the biased differential relay account for?

All of the above Signup and view all the answers

What should be considered when mal-operations of the biased differential relay occur only on magnetizing inrush but not on through faults?

Increase the time multiplier setting Signup and view all the answers

What range should the initial bias setting of the biased differential relay consider for through-fault conditions?

7.5% to 15% Signup and view all the answers

What is the relationship between critical impedance setting and the rated full load PT ratio?

It is equal to the rated full load PT ratio divided by the transformer current. Signup and view all the answers

Under which condition should the Mho relay be set to Y?

When Z is less than Y. Signup and view all the answers

What happens if the calculated value of Z is greater than Y?

The relay may be set to Z. Signup and view all the answers

What is the importance of the maximum torque angle in the context of relay settings?

It sets the critical impedance value for relay operation. Signup and view all the answers

What condition must be satisfied for Z to be set to the relay?

Z must lie between X and Y. Signup and view all the answers

What happens if Z is set above the calculated Z?

The relay settings will need adjustment. Signup and view all the answers

In the critical impedance setting, what load angle may be taken for calculations?

40 degrees Signup and view all the answers

What is the effect of selecting a higher impedance setting for the Mho relay?

Decreased sensitivity to overloads. Signup and view all the answers

When might the relay settings be calculated for both sides of the feeding post?

When maintenance is performed on one feeder. Signup and view all the answers

What must be considered if the impedance setting is not to exceed Z?

The derived value of impedance must accommodate overload. Signup and view all the answers

What is the purpose of setting the instantaneous element of the IDMT relay to 1.25 times the fault current?

To prevent relay operation for 25 kV bus faults Signup and view all the answers

What should the current setting of the IDMT relay correspond to in relation to overloading of the traction transformer?

150% of the rated current Signup and view all the answers

What is the recommended time multiplier setting for the IDMT relay during an earth fault on the 25 kV bus?

0.8 to 0.9 seconds Signup and view all the answers

What should the percentage bias setting of the biased differential relay account for?

Tap changing and CT characteristics Signup and view all the answers

If mal-operations of the biased differential relay are observed during switching in of the power transformer, what adjustment should be made?

Increase the time multiplier setting Signup and view all the answers

What operating current setting should be taken for the biased differential relay?

40% Signup and view all the answers

What is the suggested allowance for percentage mismatch due to CT saturation levels under through-fault conditions?

7.5 to 15% Signup and view all the answers

When mal-operations of the biased differential relay are observed on through faults, what should be considered?

Increasing the operating current setting Signup and view all the answers

What is the implication of setting the time multiplier setting of the biased differential relay to 1?

It provides normal operating time Signup and view all the answers

Which condition should the percentage bias setting of the biased differential relay effectively negate?

Differential currents from tap changing Signup and view all the answers

What is the allowed load current for the instantaneous over-current relay if the current setting corresponds to 200% of the continuous current rating of the traction transformer?

160% of the rated load current Signup and view all the answers

What is the time-multiplier setting range for the IDMT over current relay during an earth fault on the 25 kV bus?

0.4 to 0.5 sec Signup and view all the answers

Which setting is typically used to provide backup protection to feeder protection relays in traction substations?

IDMT over current relay Signup and view all the answers

What is the maximum torque angle of the English - Electric make YCG-14 relay?

125 degrees Signup and view all the answers

In the WPC relay, how should the impedance settings be determined?

Individually for each side and adopting the higher value Signup and view all the answers

What percentage of the rated current does the restricted earth fault relay on the low voltage side correspond to?

10% of the rated current Signup and view all the answers

What percentage does the current setting for the IDMT relay on the traction power transformer need to allow for overloading?

150% of the rated current Signup and view all the answers

What should the impedance setting formula for the English - Electric make YCG-14 relay account for?

K1 K2 (K3 + K4) Signup and view all the answers

What current setting is advised for the restricted earth fault relay on the high voltage side?

10% of the rated current Signup and view all the answers

The relay operation time for an earth fault should be set to achieve what goal?

Operation within 0.4 to 0.5 sec Signup and view all the answers

Study Notes

Appendix V: Guidelines for Relay Settings

Guidelines for calculating relay settings at traction sub-stations and sectioning posts are presented.

Ohm Impedances

Values for calculating relay settings are provided for single and double track overhead line equipment (OHE) with and without return conductors:
- Single track OHE without return conductor: 0.4127∠70° Ohm/km
- Double track OHE without RC: 0.24∠70° Ohm/km
- Single track OHE with RC: 0.702∠70° Ohm/km
- Double track OHE with RC: 0.43∠70° Ohm/km
Booster transformer impedance is added at a rate of 0.15 Ohm per booster transformer.

Feeding Post: Feeder Protection

Distance Protection using 'Mho' Relay Type YCG 14

Electromechanical 'Mho' relays are used for protection against catenary-to-earth faults.
Maximum torque angle for this relay is 75°.
Impedance setting for single-line sections is 1.25 times the impedance of the OHE between the feeding post and the adjacent feeding post.
A 1.25 factor is used to account for errors in the relays, current transformers (CTs) and potential transformers (PTs).
Formulas are provided for calculating relay settings that consider the CT and PT ratios and the angle of the OHE impedance.
Impedance setting calculation for double-line sections involves calculating the single-line impedance of the OHE and using specific formulas to arrive at the relay impedance settings.

Instantaneous Over-current Protection

This relay is for primary protection against catenary-to-earth faults near feeding posts.
Current setting is about 200% of the continuous current rating of the traction transformer.
This setting allows for CT and relay errors and transient overreach.

Wrong Phase Coupling Protection using Offset MHO Type YCG 14 (English-Electric Make)

Impedance setting (K₁, K₂, K₃, and K₄) of the YCG-14 relay is given by a specific formula involving plug board and potentiometer settings.
Maximum torque angle of the relay is 125°.
Forward offset is around 10% of K₃ K₄.
Relay will operate if the 25kV voltage lags compared to the voltage at another nearby substation.

Sectioning Posts: Under-Voltage Protection

Under-voltage protection is provided for extended feeding: Opening a bridging interrupter when the OHE voltage falls below a safe operating value.

Sample Calculations for Relay Settings

Examples provide specific details (traction power transformer ratings, CT and PT ratios, line impedance, etc.) and use the calculations to determine relay settings for different parts of the system.

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Description

This quiz focuses on the guidelines for calculating relay settings at traction substations and sectioning posts. It covers the necessary impedances for single and double track overhead line equipment and the distance protection using Mho relay type for feeder protection. Test your knowledge on these important electrical concepts.