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Relay Protection for Engineers

The document discusses various types of relays used in electrical power systems including differential, distance, percentage differential, under frequency, earth fault, and bus bar protection relays. It also discusses instrument transformers, faults that can occur in alternators, problems arising from prime mover failures in generators, and methods for protection of transmission lines, generators, transformers and bus bars. Some key points covered include the operation of differential relays, the advantages of distance relays over overcurrent relays, the need for percentage differential relays to be more stable than simple differential relays, the function of earth fault relays, and common methods used for transmission line protection.

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20EEE24 Balaji kanna M
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117 views3 pages

Relay Protection for Engineers

The document discusses various types of relays used in electrical power systems including differential, distance, percentage differential, under frequency, earth fault, and bus bar protection relays. It also discusses instrument transformers, faults that can occur in alternators, problems arising from prime mover failures in generators, and methods for protection of transmission lines, generators, transformers and bus bars. Some key points covered include the operation of differential relays, the advantages of distance relays over overcurrent relays, the need for percentage differential relays to be more stable than simple differential relays, the function of earth fault relays, and common methods used for transmission line protection.

Uploaded by

20EEE24 Balaji kanna M
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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1 What is meant by differential relay?

2 Show the difficulties of differential protection

3 Why distance relay is superior to over current protection?

4 Define biased differential beam relay

5 What is meant by reach of the distance relay?

6 What are the disadvantages of simple differential protection?

7 Why is percentage differential relay more stable than simple differential relay?

8 What is an under frequency relay?

9 Illustrate the need for instrument transformer.

10 What are the main safety devices available with transformer?

11 Why secondary of current transformer should not be opened?

12 Illustrate the advantages and limitations of Buchholz’s relay

13 What are the errors in CT?

14 Outline the function of earth fault relay.

15 Summarize the various faults that would affect an alternator.

16 Why field excitation is to be suppressed as early as possible in the event of faults in generator

swindings?

17 Illustrate the problem arising due to failure of prime mover in generator?

18 Why bus-bar protection is needed?

19 What is the cause for over speed and the necessary protection from it?

20 List the methods of protection of bus bars.

21 Summarize the common methods used for the transmission line protection.

22 Why loss of excitation must be avoided in generators?

23 Which are the common methods used for the transmission line protection.

24 Illustrate over fluxing in transformers.

PART B
1 Explain clearly with neat diagram about current balanced and voltage balanced differential
relay.

2 Demonstrate the operation of negative sequence relay with neat diagram.

3 Illustrate with a neat sketch, the working and construction of impedance relay with suitable R-X
diagram.

4 Explain the principle and operation of frequency relay with neat diagram

5 Demonstrate the protection of generator using differential and biased differential protection
scheme.

6 Illustrate with neat diagram carrier aided protection of transmission lines and various relays
associated with it

7 Explain the protective scheme employed for the bus bar with a clear diagram

8 Explain with neat diagram the application of Merz-Price circulating current principle for
protection of alternator

PART C

1 An alternator rated at 10 kV protected by the balanced circulating current system has its neutral
grounded through a resistance of 10 ohms, The protective relay is set to operate when there is an out
of balance current of 1.8 A in the pilot wires which are connected to the secondary winding of 1000/5 CT
ratio. Solve for the percentage of winding which remains unprotected and minimum value of earthing
resistance required to protect 80% of the winding.

2 A star connected, 3 phase, 10 MVA, 6.6 kV alternator has a per phase reactance of 10%. It is
protected Merz prize circulating current principle which is set to operate for fault currents not less than
175 A. Solve for the value of earthing resistance to be provided in order to ensure that only 10% of the
alternator winding remains unprotected

3 A generator is protected by restricted earth fault protection. The generator ratings are 13.2kV,
10 MVA. The percentage of winding protected against phase to ground is 85%. The relay setting is such
that it trips for 20% out of balance. Solve for the resistance to be added in the neutral to ground
connection.

4 A 6.6 KV star connected alternator has a transient reactance of 2 ohm per phase and negligible
winding resistance. It is protected by circulating current Merz-Prize protection. The alternator neutral is
earthed through 7.5 ohm resistance. The relays are set to operate when there is an out of balance
current of 1 Amp in the secondary of 500/5 Amps current transformers. Solve for the % of winding that
is protected against earth fault.

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