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Buchholz's relay gives warning and protection against electrical fault inside the transformer itself.

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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 : Reactance relay is normally preferred for protection against

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

Description : A negative sequence relay is used for protection of  (1) Generator (3) Motor (2) Transformer (4) Long Transmission lines

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

Answer : A Buchholz relay can be installed on oil cooled transformers.

Description : What is phase failure relay and how it's work?

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 : What is the difference between relay and contactor?

Answer : Relay have smaller ratings. Contactor is a high rating relay.

Description : What is the difference between a switch and a relay?

Answer : Switch is simply a mechanical contact mechanism and relay is a electromagnetic switch . Switch can be direct mechanically turn on and off but relay can be operated by energising coil .

Description : main parts of Relay

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

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 : The operating time of instantaneous relay is

Answer : The operating time of instantaneous relay is 0.1 sec

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 : 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

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

Description : In the induction type directional over current relay, when a short-circuit occurs in the circuit (A) power flows in reverse direction (B) power flows in normal direction (C) directional power element does not operate (D) over current element is not energized

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

Description : A solid state relay (A) withstands voltage transients (B) does not require auxiliary dc supply (C) provide low burden on CT and P (D) does not provide earth fault protection

Answer : A solid state relay provide low burden on CT and P

Description : A reactance relay is (A) Voltage restrained directional relay (B) Directional restrained over-current relay (C) Voltage restrained over current relay (D) Directional restrained over voltage relay

Answer : A reactance relay is Directional restrained over-current relay

Answer : The torque produced in induction type relay (shaded pole structure) is inversely proportional to the square of the current.

Answer : Admittance relay is directional relay.

Answer : The relay with inverse time characteristic will operate within 5 to 10 sec.

Answer : The under voltage relay can be used for generators, busbars, transformers, motors.

Answer : Reactance relay is preferred for phase fault on short transmission line.

Answer : Induction cup relay is operated due to changes in current, voltage, impedance.

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

Answer : Overheating of relay contacts or contact born out is due to slow making and breaking of load circuit contacts, foreign matter on the contact surface, too low contact pressure.

Answer : A differential relay measures the vector difference between two or more similar electrical quantities.

Answer : Burden of a protective relay is the power absorbed by the circuit of relay.

Answer : In order that current should flow without causing excessive heating or voltage drop, the relay contacts should have low contact resistance, be clean and smooth, be of sufficient size and proper shape.

Answer : The relay operating speed depends upon the spring tension, the rate of flux built up, armature core air gap.

Description : How do relay works ?

Answer : Relay working like contact it is noise less 

Description : What is the use of Buchholz relay in transformer?

Answer : This is a transformer that is used to step up and down current. 

Description : what is reverse power relay?

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Description : Draw a neat sketch of earth fault protection of auxiliary circuit of electric loco. State the function of relay and isolating resistance.

Answer : Ans: Earth fault protection for auxiliaries in Loco: Function of relay: The earth fault occurring anywhere in the auxiliary circuit gets monitored by the relay which acts to trip the main CB. Function of ... star point to earth through a high resistance so that the relay operation is avoided.

Description : State any four relays used for catenary protection. State function of each relay.

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Description : A series resistance is added to the over-current relay in a bus bar differential protection scheme which: a. Helps to develop some voltage across it which otherwise should appear across the relay and is ... the effects of CT saturation and lowers the pickup value of the relay d. All of the above 

Answer : A series resistance is added to the over-current relay in a bus bar differential protection scheme which: a. Helps to develop some voltage across it which otherwise should appear across the relay and is ... the effects of CT saturation and lowers the pickup value of the relay d. All of the above 

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Answer : The transmission line distance protection relay having the property of being inherently directional is MHO relay

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Answer : Mho relay is usually employed for protection of long lines.

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Answer : The inverse definite mean time relays are used for over current and earth fault protection of transformer against internal short-circuits.

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Description : Which type of protection is provided on a generator to protect against stator insulation failure? A) Differential protection B) Overcurrent relay C) Thermocouple actuated alarm D) Reverse power relay

Answer : Which type of protection is provided on a generator to protect against stator insulation failure? A) Differential protection B) Overcurrent relay C) Thermocouple actuated alarm D) Reverse power relay 

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Description : Surge absorbers are used for protection against

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Description : Differential protection is used for protection against (1) Phase fault (2) Unbalanced voltage fault (3) Unbalanced Current fault (4) Overcurrent fault 

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