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

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Description :

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 :

The operating time of instantaneous relay is

Answer :

The operating time of instantaneous relay is 0.1 sec

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Air blast circuit breakers for 400 kV power system are designed to operate in 50 millisecond.

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Circuit breakers usually operate under transient state of short-circuit current.

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For power factor correction, synchronous motors operate at no-load and greatly over-excited fields.

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3X3 inverse of matrix short trick

Answer :

3X3 inverse of matrix short trick

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Description :

For a given matrix inverse of a matrix is

Answer :

For a given matrix inverse of a matrix is https://youtu.be/gL8Q6IQjTHY

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Description :

What is the inverse of reactance?

Answer :

Inverse of reactance is Susceptance .Unit of Susceptance is Siemens.

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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

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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

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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

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Description :

What is the difference between relay and contactor?

Answer :

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

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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 

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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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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 

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Description :

Reactance relay is normally preferred for protection against

Answer :

Reactance relay is normally preferred for protection against earth faults

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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

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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

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Description :

Answer :

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

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Description :

Answer :

Admittance relay is directional relay.

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Description :

Answer :

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

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Answer :

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

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Description :

Answer :

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

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Description :

Answer :

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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Description :

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.

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Description :

Answer :

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

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Description :

Answer :

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

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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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Description :

Answer :

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

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Description :

How do relay works ?

Answer :

Relay working like contact it is noise less 

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Description :

What is the use of Buchholz relay in transformer?

Answer :

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

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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 .

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Description :

If a relay fails to operate for a fault within its reach, it is said to

Answer :

If a relay fails to operate for a fault within its reach, it is said to Under reach

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Description :

Draw and explain the characteristic of UJT. 

Answer :

UJT Characteristics: The UJT characteristic is emitter voltage versus emitter current characteristic, as shown in the figure. There three operating regions in UJT  1.Cut off region: For ... in IE will place the device into saturation and hence after valley point there is valley point. 

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Description :

The unit heat rate characteristic of a thermal power unit shows :  (A) Heat input per kWh of output versus the megawatt output of unit  (B) Heat input per kW of output versus the megawatt output of unit  (C) Heat input per kWh of output versus the megawatt hour output of unit  (D) Heat input per kW of output versus the megawatt hour output of unit

Answer :

The unit heat rate characteristic of a thermal power unit shows : Heat input per kWh of output versus the megawatt output of unit 

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Description :

Which of the following statements is not characteristic of a static magnetic field? (A) It is solenoidal. (B) It is conservative. (C) It has no sinks or sources. (D) Flux lines are always closed.

Answer :

Which of the following statements is not characteristic of a static magnetic field? (A) It is solenoidal. (B) It is conservative. (C) It has no sinks or sources. (D) Flux lines are always closed.

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Description :

Which diode exhibits negative resistance characteristic? (A) LED (B) Zener (C) Tunnel diode (D) PN diode

Answer :

Which diode exhibits negative resistance characteristic? (A) LED (B) Zener (C) Tunnel diode (D) PN diode

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Description :

Answer :

Speed torque characteristic of a repulsion induction motor is similar to that of a D.C. compound motor.

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Description :

With fault clearing time, the transient stability of a power system

Answer :

With fault clearing time, the transient stability of a power system decreases

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Description :

ln HRC fuse the time between cut-off and final current zero is called

Answer :

ln HRC fuse the time between cut-off and final current zero is called the arcing time

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Description :

Answer :

The time of closing the cycle, in modern circuit breakers is 0.003 sec.

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Description :

Describe over current relay with time-current characteristic.

Answer :

Over current relay with time-current characteristics:- 1. Definite time over current relay: Operating time is constant, the relays operates after a predetermined time when the current exceeds the pickup ... of fault current and definite time characteristics at higher values of fault current.

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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

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Description :

For a frequency of 200 Hz, the time period will be?

Answer :

For a frequency of 200 Hz, the time period will be 0.005 s.

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Description :

Draw a typical time-current characteristic for IDMT relay. 

Answer :

Time-Current Characteristic for IDMT Relay:

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Description :

main parts of Relay

Answer :

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

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Description :

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

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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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Description :

Answer :

A Buchholz relay can be installed on oil cooled transformers.

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Description :

Answer :

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

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