Answer :
The inverse definite mean time relays are used for over current and earth fault protection of transformer against internal short-circuits.
asked
Mar 20, 2018
by
anonymous
Description : The operating time of instantaneous relay is
Answer :
The operating time of instantaneous relay is 0.1 sec
asked
May 3, 2018
by
anonymous
Answer :
Air blast circuit breakers for 400 kV power system are designed to operate in 50 millisecond.
asked
Mar 20, 2018
by
anonymous
Answer :
Circuit breakers usually operate under transient state of short-circuit current.
asked
Mar 19, 2018
by
anonymous
Answer :
For power factor correction, synchronous motors operate at no-load and greatly over-excited fields.
asked
Mar 20, 2018
by
anonymous
Description : 3X3 inverse of matrix short trick
Answer :
3X3 inverse of matrix short trick
asked
Sep 7, 2019
by
anonymous
Description : For a given matrix inverse of a matrix is
Answer :
For a given matrix inverse of a matrix is https://youtu.be/gL8Q6IQjTHY
asked
Jul 26, 2019
by
anonymous
Description : What is the inverse of reactance?
Answer :
Inverse of reactance is Susceptance .Unit of Susceptance is Siemens.
asked
Jan 7, 2018
by
anonymous
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
asked
May 8, 2018
by
anonymous
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
asked
May 8, 2018
by
anonymous
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
asked
May 3, 2018
by
anonymous
Description : What is the difference between relay and contactor?
Answer :
Relay have smaller ratings. Contactor is a high rating relay.
asked
May 2, 2018
by
anonymous
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
asked
May 1, 2018
by
anonymous
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
asked
Apr 30, 2018
by
anonymous
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
asked
Apr 29, 2018
by
anonymous
Description : Reactance relay is normally preferred for protection against
Answer :
Reactance relay is normally preferred for protection against earth faults
asked
Apr 29, 2018
by
anonymous
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
asked
Apr 28, 2018
by
anonymous
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
asked
Apr 28, 2018
by
anonymous
Answer :
The torque produced in induction type relay (shaded pole structure) is inversely proportional to the square of the current.
asked
Mar 20, 2018
by
anonymous
Answer :
Admittance relay is directional relay.
asked
Mar 20, 2018
by
anonymous
Answer :
The under voltage relay can be used for generators, busbars, transformers, motors.
asked
Mar 20, 2018
by
anonymous
Answer :
Reactance relay is preferred for phase fault on short transmission line.
asked
Mar 20, 2018
by
anonymous
Answer :
Induction cup relay is operated due to changes in current, voltage, impedance.
asked
Mar 20, 2018
by
anonymous
Answer :
Interruption of large currents by relay requires arc suppressing blow out coils, wide separation of the opened contacts, high speed opening of contacts.
asked
Mar 20, 2018
by
anonymous
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.
asked
Mar 20, 2018
by
anonymous
Answer :
A differential relay measures the vector difference between two or more similar electrical quantities.
asked
Mar 19, 2018
by
anonymous
Answer :
Burden of a protective relay is the power absorbed by the circuit of relay.
asked
Mar 19, 2018
by
anonymous
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.
asked
Mar 19, 2018
by
anonymous
Answer :
The relay operating speed depends upon the spring tension, the rate of flux built up, armature core air gap.
asked
Mar 19, 2018
by
anonymous
Description : How do relay works ?
Answer :
Relay working like contact it is noise less
asked
Dec 30, 2017
by
anonymous
Description : What is the use of Buchholz relay in transformer?
Answer :
This is a transformer that is used to step up and down current.
asked
Dec 17, 2017
by
anonymous
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 .
asked
Dec 17, 2017
by
anonymous
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
asked
May 12, 2018
by
anonymous
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.
asked
Sep 5, 2018
by
anonymous
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
asked
Apr 30, 2018
by
anonymous
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.
asked
Apr 28, 2018
by
anonymous
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
asked
Apr 28, 2018
by
anonymous
Answer :
Speed torque characteristic of a repulsion induction motor is similar to that of a D.C. compound motor.
asked
Mar 20, 2018
by
anonymous
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
asked
Apr 27, 2018
by
anonymous
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
asked
Apr 26, 2018
by
anonymous
Answer :
The time of closing the cycle, in modern circuit breakers is 0.003 sec.
asked
Mar 20, 2018
by
anonymous
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.
asked
Jul 21, 2019
by
anonymous
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
asked
Apr 29, 2018
by
anonymous
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.
asked
Mar 24, 2018
by
anonymous
Description : Draw a typical time-current characteristic for IDMT relay.
Answer :
Time-Current Characteristic for IDMT Relay:
asked
Jun 23, 2020
by
anonymous
Description : main parts of Relay
Answer :
Coil, plunger, contacts, springs, connecting terminals and enclosure.
asked
Aug 28, 2019
by
anonymous
Description : What is phase failure relay and how it's work?
asked
Aug 12, 2019
by
anonymous
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
asked
Apr 28, 2018
by
anonymous
Answer :
A Buchholz relay can be installed on oil cooled transformers.
asked
Mar 19, 2018
by
anonymous
Answer :
Buchholz's relay gives warning and protection against electrical fault inside the transformer itself.
asked
Mar 19, 2018
by
anonymous