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

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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 : 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 : 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 voltage used for suburban trains in D.C. system is usually 600 to 750 V.

Description : List standard voltage level used in India. 

Answer : Standard voltage level used in India: * Generation Voltage : 3.3KV, 6.6KV,11KV and 17.5 KV,21KV (Now a days generation voltage is in the range of 11KV- 33KV) * Primary Transmission voltage :- 220 ... voltages in India are 765 KV (750KV), 400KV, 220KV, 132KV, 110KV, 66KV, 33KV, 22KV, 11KV.

Description : An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be  (1) unaffected (2) decreased (3) increased (4) either decreased or increased depending on the direction of the DC field

Answer : An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be either decreased or increased depending on the direction of the DC field

Description : The frequencies and voltage used in Dielectric heating are (A) 10 – 30 MHz, upto 25 kV (B) 50 – 60 Hz, upto 25 kV (C) 10 – 30 MHz, upto 100 V (D) 50 – 60 Hz, 110 V – 230 V

Answer : The frequencies and voltage used in Dielectric heating are 10 – 30 MHz, upto 25 kV

Description : What equipment is used to measure voltage?

Answer : Voltmeter is used to measure voltage.

Description : Reactance relay is normally preferred for protection against

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

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

Description : State the type of insulating materials under Class Y and Class B.

Answer : The type of insulating materials under Class Y : 1. Cotton  2. Silk 3. Paper 4. Rubber 5. PVC The type of insulating materials under Class B: 1. Backelite 2. Impregnated varnish 3. Mica 4. Fiber glass 5. Asbestos 

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 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?

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

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 : 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

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 : 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 : 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 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 .

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

Description : The voltage of transmission can be regulated by  (A) Use of tap changing transformers (B) Switching in shunt capacitors at the receiving end during heavy loads (C) Use of capacitors to neutralize the effect of series reactance (D) Any of the above methods

Answer : The voltage of transmission can be regulated by  (A) Use of tap changing transformers (B) Switching in shunt capacitors at the receiving end during heavy loads (C) Use of capacitors to neutralize the effect of series reactance (D) Any of the above methods

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

Answer : The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to extinguish the arc.

Description : main parts of Relay

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

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

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

Description : what is reverse power relay?

Answer : Thereverse powerrelay is a directional protective relay that prevents power from flowing in the reverse direction. Read our article going back ... it all to be up to date. And if you do, read it anyway just to check if youreallydo!

Description : A network is said to be under resonance when the voltage and the current at the network input terminals are (A) in phase (B) out of phase (C) in phase quadrature (D) in phase, and have equal magnitudes

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Answer : Earthing switch is used for?  (A) Measuring of safety voltage (B) Protection of equipment from ground faults (C) Discharging residual energies (D) All of the above 

Description : Regulating-transformers are used in power systems for control of

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