Interview Questions.

Question 1. What Are The Common Types Of Generator Faults?

Answer :

The commonplace types of faults occurring in synchronous generators are:

Stator winding faults (segment to section faults, segment to earth faults, inter flip faults), Rotor winding faults (conductor to earth faults, open circuit faults, inter turn faults), failure of high mover, failure of the field, unbalanced loading, over loading, over-voltage at generator terminals, over-speed, air flow failure, lack of excitation.

Question 2. For What Type Of Faults Does Differential Protection Is Provided?

Answer :

Differential safety responds to the phasor difference among two or more electric quantities. It operates for the inner faults arise in mills or transformers. For outside faults differential safety does no longer perform.

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Question three. What Is The Disadvantage Of Ordinary Differential Protection?

Answer :

When differential relaying is used for safety, the CTs at each sides of the generator winding need to be of identical accuracy. Otherwise if the CT mistakes are excessive it's going to cause the mal-operation of the relay. To guard against such disadvantages percent differential safety is employed.

Question 4. Why It Not Necessary To Provide Over-voltage Protection In Turbo-alternator?

Answer :

The over voltage occurs when the top mover velocity increases because of surprising lack of the weight on the generator and the speed manage governors in case of turbo-generators are very touchy to the velocity versions and consequently generator over voltage of massive duration or value does now not typically occur. This is the purpose why mills aren't provided with over voltage protection

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Question 5. Why It Is Necessary To Suppress Field Immediately After Disconnection Of Faulty Alternator From The System?

Answer :

In the occasion of fault at the generator windings even though the generator circuit breaker is tripped, the fault is non-stop to fed so long as the excitation will exist because the emf is triggered within the generator. Hence it is important to suppress the sector right now after disconnecting the faulty generator from the gadget

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Question 6. Why It Is Not Necessary To Provide Protection For Turn To Turn Fault In Alternator?

Answer :

The coils of the contemporary alternators are single flip and therefore it isn't necessary to offer protection for turn to turn faults

Question 7. Why Large Alternator Is Grounded With Large Resistance?

Answer :

Large capacity of alternators are typically supplied with resistance grounding. High cost of resistor is hooked up to the neural direction to the ground. If the generator is delta linked, then it is grounded with the help of zig-zag transformer or (Delta-Star) transformer such that a high resistor is connected among the impartial point and the ground. Resistance grounding is furnished on the way to limit the quick circuit modern-day flowing throughout earth fault to stator winding for you to offer safety against mechanical stresses and melting of winding for the duration of Line to Ground short circuit. In large mills fault cutting-edge is limited as little as 10 to 15 amperes at some stage in quick circuit.

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Question eight. What Is Advantage Of Using Percentage Differential Relay Protection?

Answer :

It does no longer require CTs with air gaps or unique balancing features
It lets in a low fault placing for use and this guarantees most protection of the windings
It guarantees whole balance under the most intense thru fault situations
Question nine. Explain Differential Protection?

Answer :

Differential safety is usually supplied for the device or organization of equipments which can be to be blanketed in opposition to internal faults. They are the number one safety structures (operates quicker) for any internal faults going on in the protection sector.

Under healthy conditions the currents at each ends of the windings could be identical. EMF induced inside the secondaries of the CATs may be identical and so no cutting-edge flows through the working coil of the relay. When an earth fault or section to phase fault takes place the circumstance no longer holds desirable and the differential contemporary flows via the relay operating coils makes the relay to perform. Relay operates for the faults occurring inside the quarter of safety.

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Question 10. Why Over Current Protection Is Not Necessary For Modern Generators?

Answer :

Over Current protection isn't always requisite for modern-day alternators because those are capable of withstanding a entire short circuit at their terminals for sufficient time without a good deal over heating and damage.

Question eleven. Which Type Of Relays Are Used For The Merz-charge Protection System For Alternator?

Answer :

Merz-Price safety is differential safety provided for the alternator. The relays used within the Merz-Price protection gadget of alternator are instantaneous electro-magnetic type protection

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Question 12. What Type Of Protection Is Provided For The Generators Against Over Heating Of The Generator Stator?

Answer :

Resistance temperature detector

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