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Interruption of large currents by relay requires arc suppressing blow out coils, wide separation of the opened contacts, high speed opening of contacts.

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Answer : In a single phase power factor meter the phase difference between the currents in the two pressure coils is exactly 90°.

Answer : For handling greater currents induction wattmeters are used in conjunction with current transformers.

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Answer : Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.

Description : How eddy currents are generated?

Description : The purpose of the restraining coil in a biased differential relay is  (A) To reduce CT saturation during fault.  (B) To increase the sensitivity of the relay.  (C) To match the transformation ratio.  (D) To limit the spill current through the relay during heavy external fault.

Answer : d

Description : A relay used for protection of motors against overload is :  (A) Impedance relay (B) Electromagnetic attraction type (C) Thermal relay (D) Buchholz's relay

Answer : A relay used for protection of motors against overload is : Thermal relay

Description : A relay has a rating of 5 A, 2.2 sec IDMT and a relay setting of 125% TMS = 0.6. It is connected to a supply circuit through a C.T. 400/5 ratio. The fault current is 4000 A. The operating current of the relay is

Answer : A relay has a rating of 5 A, 2.2 sec IDMT and a relay setting of 125% TMS = 0.6. It is connected to a supply circuit through a C.T. 400/5 ratio. The fault current is 4000 A. The operating current of the relay is 6.25A

Description : The operating time of instantaneous relay is

Answer : The operating time of instantaneous relay is 0.1 sec

Description : What is the difference between relay and contactor?

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Answer : A negative sequence relay is used for protection of Generator 

Description : Buchholz relay is  (1) located in the conservator tank  (2) located in the transformer tank itself  (3) connected in the pipe connecting main tank of transformer and conservator  (4) installed in the circuit breaker

Answer : Buchholz relay is connected in the pipe connecting main tank of transformer and conservator 

Description : To prevent mal-operation of differentially connected relay while energizing a transformer, the relay restraining coil is based with  (1) second harmonic current  (2) third harmonic current  (3) fifth harmonic current  (4) seventh harmonic current

Answer : To prevent mal-operation of differentially connected relay while energizing a transformer, the relay restraining coil is based with  second harmonic current 

Description : Reactance relay is normally preferred for protection against

Answer : Reactance relay is normally preferred for protection against earth faults

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Answer : In the induction type directional over current relay, when a short-circuit occurs in the circuit power flows in reverse direction

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Answer : Admittance relay is directional relay.

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Answer : Relay working like contact it is noise less 

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Answer : Coil, plunger, contacts, springs, connecting terminals and enclosure.

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Answer : Buchholz relay is used as a safety device with respect to which of the following? A) Audio transformers B) Oil filled power transformers C) Air core transformer D) None of these

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Answer : The current zero interruption, in oil and air blast circuit breakers, is achieved by lengthening of the gap, cooling and blast effect.

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Answer : Construction of Buchholz Relay: It takes the form of a domed vessel placed in the connecting pipe between the main tank and the conservator. The device has two elements. The upper element ... manner that it senses the sudden violent movement of oil/gas from transformer tank to conservator. 

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Description : With a neat sketch, explain the working of Thermal relay.

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