What is differential protection?

What is differential protection? 
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1 Answer

Answer :

It is the current balance type protection, in which vector difference between current entering the winding is used for relay operation. 
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Related questions

Explain differential protection?

Description : Explain differential protection?

Last Answer : Differential protection is based on the fact that any fault within an electrical equipment would cause the current entering it, to be different, from that leaving it. Thus, we can compare the two ... phase or both and issue a trip output if the difference exceeds a pre- determined set value.

What are the problems in bus zone differential protection?

Description : What are the problems in bus zone differential protection?

Last Answer : Large number of circuits, different current levels for different circuits for external faults. Saturation of CT cores due to dc component and ac component in short circuit currents. The saturation ... the bus makes circuit complicated. Setting of relays need a change with large load changes.

What are the problems arising in differential protection in power transformer and how are they overcome?

Description : What are the problems arising in differential protection in power transformer and how are they overcome?

Last Answer : 1. Difference in lengths of pilot wires on either sides of the relay. This is overcome by connecting adjustable resistors to pilot wires to get equipotential points on the pilot wires. 2. ... harmonic restraining unit is added to the relay which will block it when the transformer is energized.

What is the coverage of differential protection for SUT?

Description : What is the coverage of differential protection for SUT?

Last Answer : Covers from 230 kV bushing to 6.6 kV breaker end.  

Why differential protection for PHT motors?

Description : Why differential protection for PHT motors?

Last Answer : For more than 2500 kW motors it is required to provide differential protection. It is biased Relay against internal phase fault or earth fault very fast. Insensitive to starting current and stalling current. 

Why delta – delta CT’s are used for star – star transformer differential protection?

Description : Why delta – delta CT’s are used for star – star transformer differential protection?

Last Answer : Say primary neutral is not solidly earthed. Then for any earthfault on secondary terminal, the primary current distribution is so for external fault, the differential is likely to operate if sequence current ... into relay. The 2:1:1 distribution is possibly only for core type or delta tertiary.

Why inter-turn protection is provided along with differential protection in generator?

Description : Why inter-turn protection is provided along with differential protection in generator?

Last Answer : Inter-turn protects two separate windings from the fault of the generator.  

For which of the following ratings of the transformer differential protection is recommended ? (a) above 30 kVA. (b) equal to and above 5 MVA (c) equal to and above 25 MVA (d) none of the above

Description : For which of the following ratings of the transformer differential protection is recommended ? (a) above 30 kVA. (b) equal to and above 5 MVA (c) equal to and above 25 MVA (d) none of the above

Last Answer : (b) equal to and above 5 MVA

Large internal faults are protected by (a) merz price percentage differential protection (b) mho and ohm relays (c) horn gaps and temperature relays (d) earth fault and positive sequence relays

Description : Large internal faults are protected by (a) merz price percentage differential protection (b) mho and ohm relays (c) horn gaps and temperature relays (d) earth fault and positive sequence relays

Last Answer : (a) merz price percentage differential protection

Explain the “Differential Protection Scheme” used for alternators with neat labeled diagram.

Description : Explain the “Differential Protection Scheme” used for alternators with neat labeled diagram.

Last Answer : Differential Protection Scheme for Alternator: Figure shows the differential protection provided to 3 phase alternator. Here identical CTs are placed on both sides of 3 phase alternator and ... causing its operation. Relay sends trip signal to the CB, thereby alternator circuit is tripped.

Explain differential protection scheme for busbars with neat sketch.

Description : Explain differential protection scheme for busbars with neat sketch.

Last Answer : Differential Protection Scheme for Bus bar:  Under normal conditions, the sum of the currents entering the bus bar zone is equal to those leaving it and no current flows through the relay ... of these currents will flow through the relay coil causing opening of circuit breaker of bus-bar.

List two limitations of Differential-Protection scheme for transformer.

Description : List two limitations of Differential-Protection scheme for transformer.

Last Answer : Limitations of Differential Protection Scheme of Transformer:  1) Due to the magnetization characteristics of the CTs used, the ratio errors change with respect to the circulating currents.  2) ... & improper operation.  5) Inrush of magnetizing current may lead to inadvertent operation.

Explain differential protection of busbar.

Description : Explain differential protection of busbar.

Last Answer : Differential protection Scheme for bus bar: Under normal conditions the sum of the currents entering the bus bar zone is equal to those leaving it and no current flows through the relay ... . The difference of these currents will flow through the relay coil causing opening of circuit breaker.

Write down limitation of differential protection of transformer.

Description : Write down limitation of differential protection of transformer.

Last Answer : Limitations of differential protection of transformer: 1) Due to the magnetization characteristics of the CTs used, the ratio errors change with respect to the circulating currents. 2) The pilot wires ... current (higher imbalance) due to which accuracy of sensing & operation is decreased. 

A series resistance is added to the over-current relay in a bus bar differential protection scheme which:

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 

Last 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 

An AC generator operating in parallel loses its excitation without tripping the circuit breaker. This will __________. A. not affect the faulty generator due to the compensation of the other generators B. cause the slip rings to melt C. cause a low voltage differential to develop between the armature and the bus D. cause high currents to be induced in the field windings

Description : An AC generator operating in parallel loses its excitation without tripping the circuit breaker. This will __________. A. not affect the faulty generator due to the compensation of the other generators B. ... between the armature and the bus D. cause high currents to be induced in the field windings

Last Answer : Answer: D

Which of the following operating characteristics for DC motors is considered to give high starting torque? A. series B. shunt C. cumulative-compound D. differential-compound

Description : Which of the following operating characteristics for DC motors is considered to give high starting torque? A. series B. shunt C. cumulative-compound D. differential-compound

Last Answer : Answer: A

Figure 'A' of the diagram shown in the illustration represents a ______________. EL-0092 A. differential transformer B. saturable reactor C. synchro system D. magnetic amplifier

Description : Figure 'A' of the diagram shown in the illustration represents a ______________. EL-0092 A. differential transformer B. saturable reactor C. synchro system D. magnetic amplifier

Last Answer : Answer: C

Basic operating characteristics of the operational amplifier such as gain and stability are the function of its _____________. A. differential input stage B. power output stage C. feedback circuit D. supply voltages

Description : Basic operating characteristics of the operational amplifier such as gain and stability are the function of its _____________. A. differential input stage B. power output stage C. feedback circuit D. supply voltages

Last Answer : Answer: C

To provide its unique characteristics to analog circuits, the operational amplifier is made up of a/an ______________. A. voltage amp, current amp and output amp B. input amp, power amp and output amp C. scaling amp, power amp and voltage amp D. differential amp, voltage amp and output amp

Description : To provide its unique characteristics to analog circuits, the operational amplifier is made up of a/an ______________. A. voltage amp, current amp and output amp B. input amp, power amp and output amp C. scaling amp, power amp and voltage amp D. differential amp, voltage amp and output amp

Last Answer : Answer: D

Mention any 2 applications of differential relays.

Description : Mention any 2 applications of differential relays.

Last Answer : Protection of generator and generator-transformer unit: protection of large motors and bus bars

What is biased differential bus zone reduction?

Description : What is biased differential bus zone reduction?

Last Answer : The biased beam relay is designed to respond to the differential current in terms of its fractional relation to the current flowing through the protected zone. It is essentially an over-current ... coil. The restraining coil produces a bias force in the opposite direction to the operating force.

Mention any two applications of differential relay.

Description : Mention any two applications of differential relay.

Last Answer : Protection of generator & generator transformer unit; protection of large motors and busbars .

Why high impedance circulating current differential?

Description : Why high impedance circulating current differential? 

Last Answer : Under through faults, CT’s of different phases saturates differently. Net spill current will operate low impedance CAG relay, so high impedance scheme with CAG relay and stabilising resistor used. 

Why generator differential provided?

Description : Why generator differential provided? 

Last Answer : For generator phase to phase faults and 3 phase faults. 

Will main generator differential relay pick up for generator earth faults?

Description : Will main generator differential relay pick up for generator earth faults? 

Last Answer : No earth fault current limited to 5A, while differential setting is 10%. 

What is a differential amplifier? Also, explain CMRR.

Description : What is a differential amplifier? Also, explain CMRR.

Last Answer : Differential Amplifier: The amplifier, which is used to amplify the voltage difference between two input-lines neither of which is grounded, is called differential amplifier. This reduces the amount of noise ... , CMRR would be infinite because in that case common mode voltage gain would be zero.

Inverse definite minimum time lag relay is also called ___________ (A) pilot relay. (B) differential relay. (C) over current relay. (D) directional overcurrent relay.

Description : Inverse definite minimum time lag relay is also called ___________ (A) pilot relay. (B) differential relay. (C) over current relay. (D) directional overcurrent relay.

Last Answer : Ans: B Inverse definite minimum time lag relay characteristic is inverse but minimum time is fixed. The operating time is inversely proportional to the magnitude of actuating quantity.

Emulsifier protection is associated with: a) Grounding protection b) Dielectric strength protection of cables and conductors c) Lightning protection d) Fire protection

Description : Emulsifier protection is associated with: a) Grounding protection b) Dielectric strength protection of cables and conductors c) Lightning protection d) Fire protection

Last Answer : Ans: D

Where automatic restart does not present a hazard after a power failure, Coast Guard Regulations (46 CFR) require motor controllers for auxiliaries vital to the propelling equipment to be provided with ________________. A. overload protection B. low voltage protection C. low voltage release D. reverse current protection

Description : Where automatic restart does not present a hazard after a power failure, Coast Guard Regulations (46 CFR) require motor controllers for auxiliaries vital to the propelling equipment to be provided ... overload protection B. low voltage protection C. low voltage release D. reverse current protection

Last Answer : Answer: C

Which of the spaces listed is defined as a 'location requiring an exceptional degree of protection' when considering the installation of shipboard electrical equipment? A. Machinery space B. Chart room C. Console room D. Accommodation space

Description : Which of the spaces listed is defined as a 'location requiring an exceptional degree of protection' when considering the installation of shipboard electrical equipment? A. Machinery space B. Chart room C. Console room D. Accommodation space

Last Answer : Answer: A

The wiring diagram for the motor starting circuit shown in the illustration indicates ______________. EL-0007 A. resistance starting B. reduced voltage starting C. low voltage protection D. low voltage release

Description : The wiring diagram for the motor starting circuit shown in the illustration indicates ______________. EL-0007 A. resistance starting B. reduced voltage starting C. low voltage protection D. low voltage release

Last Answer : Answer: C

Which of the following statements is true concerning the motor controller diagram shown in the illustration? EL-0023 A. Terminal 'T2' is hot only on high speed. B. Both indicating lights will be lit on both high and low speeds as they are connected to the common lead when the motor is running. C. Overload protection is provided for high speed operation only. D. 'L2' is always connected to 'T2' whenever the motor is running.

Description : Which of the following statements is true concerning the motor controller diagram shown in the illustration? EL-0023 A. Terminal 'T2' is hot only on high speed. B. Both indicating lights will be lit on ... high speed operation only. D. 'L2' is always connected to 'T2' whenever the motor is running.

Last Answer : Answer: D

The purpose of the automatic bus transfer shown in the illustration is to ___________. EL-0014 A. stepdown voltage to the lighting distribution panel B. provide emergency power to the lighting distribution panel C. energize the emergency switchboard from the main switchboard D. provide overcurrent protection to the lighting distribution panel

Description : The purpose of the automatic bus transfer shown in the illustration is to ___________. EL-0014 A. stepdown voltage to the lighting distribution panel B. provide emergency power to ... emergency switchboard from the main switchboard D. provide overcurrent protection to the lighting distribution panel

Last Answer : Answer: B

Component F in the illustrated device is for _________. EL-0033 A. short circut protection B. latching the trip unit closed after resetting the breaker C. overload protection D. providing a flexible connection between the input terminal G and the tripping unit E

Description : Component F in the illustrated device is for _________. EL-0033 A. short circut protection B. latching the trip unit closed after resetting the breaker C. overload protection D. providing a flexible connection between the input terminal G and the tripping unit E

Last Answer : Answer: C

A fuse will 'blow' if _____________. A. an electric motor is stopped suddenly by opening a switch B. the flow of current to the protection device is reversed C. the electrical current exceeds the rated value of the fuse D. unequal resistors are connected in parallel

Description : A fuse will 'blow' if _____________. A. an electric motor is stopped suddenly by opening a switch B. the flow of current to the protection device is reversed C. the electrical current exceeds the rated value of the fuse D. unequal resistors are connected in parallel

Last Answer : Answer: C

Periodic testing of circuit breakers is necessary to assure that a correctly rated and properly installed unit _________________. A. can trip faster as it increases in age B. will continue to provide the original degree of protection C. does not exceed its interrupting capacity D. be able to withstand at least 125% of applied voltage

Description : Periodic testing of circuit breakers is necessary to assure that a correctly rated and properly installed unit _________________. A. can trip faster as it increases in age B. will continue to provide ... not exceed its interrupting capacity D. be able to withstand at least 125% of applied voltage

Last Answer : Answer: B

The 'reset' contacts of the master switch shown in the illustration provides the winch controller with ___________. EL-0102 A. low voltage release B. overload protection C. low voltage protection D. high power factor correction

Description : The 'reset' contacts of the master switch shown in the illustration provides the winch controller with ___________. EL-0102 A. low voltage release B. overload protection C. low voltage protection D. high power factor correction

Last Answer : Answer: C

The speed of a series wound winch motor is controlled by ____________. A. varying the voltage applied to the motor B. the weight of the load on the cargo boom C. overcurrent protection devices in the motor D. a hydraulic speed-limiting governor

Description : The speed of a series wound winch motor is controlled by ____________. A. varying the voltage applied to the motor B. the weight of the load on the cargo boom C. overcurrent protection devices in the motor D. a hydraulic speed-limiting governor

Last Answer : Answer: A

The circuit shown in the illustration represents a ________. EL-0090 A. battery charging circuit B. synchronous exciter C. depth sounding unit D. cathodic protection system

Description : The circuit shown in the illustration represents a ________. EL-0090 A. battery charging circuit B. synchronous exciter C. depth sounding unit D. cathodic protection system

Last Answer : Answer: D

Which of the listed items will stop a motor due to a reduction in voltage and restart it when the voltage is restored to normal? A. Low voltage protection circuit B. Non-renewable link fuse C. Renewable link fuse D. Low voltage release circuit

Description : Which of the listed items will stop a motor due to a reduction in voltage and restart it when the voltage is restored to normal? A. Low voltage protection circuit B. Non-renewable link fuse C. Renewable link fuse D. Low voltage release circuit

Last Answer : Answer: D

Impressed current cathodic protection is used on vessels instead of _________________. A. fire alarm systems B. repeated painting C. sacrificial zincs D. vacuum tube degaussing systems

Description : Impressed current cathodic protection is used on vessels instead of _________________. A. fire alarm systems B. repeated painting C. sacrificial zincs D. vacuum tube degaussing systems

Last Answer : Answer: C

In an impressed current cathodic protection system, the anode is ____________. A. connected to the hull and deteriorates with time B. insulated from the hull and does not waste away C. connected to the hull but does not waste away D. insulated from the hull but deteriorates with time

Description : In an impressed current cathodic protection system, the anode is ____________. A. connected to the hull and deteriorates with time B. insulated from the hull and does not waste away C. connected to the hull but does not waste away D. insulated from the hull but deteriorates with time

Last Answer : Answer: B

The amount of current flow required for the cathodic protection of a vessel is dependent upon the _________. A. amount of bare steel surface B. speed of the ship through the water C. temperature of the water D. all of the above

Description : The amount of current flow required for the cathodic protection of a vessel is dependent upon the _________. A. amount of bare steel surface B. speed of the ship through the water C. temperature of the water D. all of the above

Last Answer : Answer: D

The purpose of a magnetic relay is to _____________. A. open a circuit only in the event of overload B. remotely open and close contacts C. provide overcurrent protection during starting D. relay voltages at increased power

Description : The purpose of a magnetic relay is to _____________. A. open a circuit only in the event of overload B. remotely open and close contacts C. provide overcurrent protection during starting D. relay voltages at increased power

Last Answer : Answer: B

RC time constant characteristics, as shown in the illustration, are important in _____________. EL-0086 A. bridge rectifiers for alternator excitation B. timing and pulse shaping circuits C. transistor power amplifier biasing D. motor controller overload protection

Description : RC time constant characteristics, as shown in the illustration, are important in _____________. EL-0086 A. bridge rectifiers for alternator excitation B. timing and pulse shaping circuits C. transistor power amplifier biasing D. motor controller overload protection

Last Answer : Answer: B

The purpose of a motor undervoltage protection device is to _____________. A. prevent high armature current when power is restored B. start the motor at a very low voltage C. trip the load off the motor in case of fire D. protect personnel from low voltage shocks

Description : The purpose of a motor undervoltage protection device is to _____________. A. prevent high armature current when power is restored B. start the motor at a very low voltage C. trip the load off the motor in case of fire D. protect personnel from low voltage shocks

Last Answer : Answer: A