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what is reverse power relay?

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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!
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Description : The device which allows reverse power flow and withstands highest switch frequency is (A) GTO (B) MOSFET (C) IGBT (D) Inverter grade SCR

Answer : The device which allows reverse power flow and withstands highest switch frequency is MOSFET

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

Description : What happens when you reverse the direction of the current in an electromagnet?

Answer : When  you  reverse  current  direction  in  an  electromagnet,  the magnetic  poles  will  also  change.

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Description : What is the difference between forward and reverse bias?

Answer : Forward bias is a PN junction bias which allows current to flow through the junction. Forward bias decreases the resistance of the depletion layer. Reverse bias is a PN junction bias that allows only ... Positive polarity on the n-type material and negative polarity to the p-type material.

Description : A diode in which the change in reverse bias voltage varies the capacitance is called as A) Varactor diode B) Switching diode C) Tunnel diode D) Zener-diode  

Answer : A diode in which the change in reverse bias voltage varies the capacitance is called as Varactor diode

Description : How can we reverse the direction of rotation of synchronous motor?

Answer : By reversing supply phase sequence we can reverse the direction of rotation of synchronous motor.

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Answer : In cut-off region of BJT both the emitter-base junction and collector-base junction are reverse biased.

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

Description : main parts of Relay

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

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 : What is the difference between relay and contactor?

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

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 .

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 : 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 

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 

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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

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

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

Description :

Answer : Admittance relay is directional relay.

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

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

Description :

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

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

Description :

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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.

Description :

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

Description :

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.

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

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

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

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Answer : Acc to Ohms law V=IR but it is only applicable when our resistance R is constant, as in case of transformer we take impedence which is equivalent to resistance is not constant it varies with system parameters that why Ohms law not applicable in case of transformer

Description :

What is the value of capacitance required to improve power factor from 0.7 to 0.9. Given that:

Real power = 50 W

Vrms of the source = 120

Frequency = 50 Hz  


#powerfactor


Description : What are the basic requirements of locating wind power plant ?

Answer : The basic requirements of locating wind power plant:  1) The site should be selected where winds are strong i.e. where pressure of wind is high and there is continuity. 2) Wind pressure ... the turbine which can affect the system's overall performance. 10)Possibility to connect to power grid. 

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Answer : What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 500 Hz (frequency) source of the same voltage:  (A) Eddy Current and Hysteresis losses will be ... will be too much high  (C) Transformer may start to smoke and burn  (D) No effect

Description : What is the power factor when a single phase watt meter operating on 200 V and 5 A for 5 hours makes 2016 revolutions and the meter constant in revolution is 420? A) 0.04 B) 1.04 C) 0.96 D) None of these

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