What is protective relay?

What is protective relay?
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1 Answer

Answer :

It is an electrical device designed to initiate the isolation of a part of the electrical installation, or to operate an alarm signal, in the event of abnormal condition or a fault. In simple words relay is an electrical device that gives signal to isolation device (eg: Circuit Breaker) after sensing the fault and helps to isolate the fault system from the healthy electrical system
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Related questions

A three-phase, induction-type motor experiences an open in one phase. Which of the listed automatic protective devices will prevent the machine from being damaged? A. Overspeed trip B. Thermal overload relay C. Three-pole safety switch D. Magnetic blowout coil

Description : A three-phase, induction-type motor experiences an open in one phase. Which of the listed automatic protective devices will prevent the machine from being damaged? A. Overspeed trip B. Thermal overload relay C. Three-pole safety switch D. Magnetic blowout coil

Last Answer : Answer: B

The boundary of the protective zone is determined by the (A) Location of CT (B) sensitivity of relay used (C) Location of PT (D) None of these

Description : The boundary of the protective zone is determined by the (A) Location of CT (B) sensitivity of relay used (C) Location of PT (D) None of these

Last Answer : Ans: B The boundary of the protective zone is determined by the sensitivity of relay used. If the relay is more sensitive, the protective zone will be increased.

Burden of a protective relay is the power (a) required to operate the circuit breaker (b) absorbed by the circuit of relay (c) developed by the relay circuit (d) none of the above

Description : Burden of a protective relay is the power (a) required to operate the circuit breaker (b) absorbed by the circuit of relay (c) developed by the relay circuit (d) none of the above

Last Answer : (b) absorbed by the circuit of relay

Define the following terms with respect to protective relays i) Relay time ii) Reset current iii) Plug setting multiplier and iv) Time setting multiplier

Description : Define the following terms with respect to protective relays i) Relay time ii) Reset current iii) Plug setting multiplier and iv) Time setting multiplier

Last Answer : 1) Relay Time: The time interval between occurrence of fault and closure of relay contacts.  2) Reset Current: The value of current below which the relay resets and comes back to ... The adjustment arrangement provided for setting the operation time of relay is known as Time setting multiplier. 

Draw a neat labeled diagram to show protective system for AC traction and give the function of each relay used in it.

Description : Draw a neat labeled diagram to show protective system for AC traction and give the function of each relay used in it. 

Last Answer : Protective system for AC traction:  Function Of Each Relay: For transformer -  Inverse time over current relay- as back up protection on primary (HV side) over current ... against faults near substation  Under voltage relay - protection against faults far away from substation

Burden of a protective relay is the power?

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

The harmonic currents in a power transformer does not cause increase in: a) Secondary voltage b) Core loss c) Copper loss d) Magnetic interference with protective relays

Description : The harmonic currents in a power transformer does not cause increase in: a) Secondary voltage b) Core loss c) Copper loss d) Magnetic interference with protective relays

Last Answer : Ans: A

Routine maintenance of dry-type transformers should include ______________. A. preventing the entrance of water from broken pipe lines steam lines B. keeping protective surfaces and insulating bushings free of dirt and conductive debris C. periodic testing of insulation resistance with a megger D. all of the above

Description : Routine maintenance of dry-type transformers should include ______________. A. preventing the entrance of water from broken pipe lines steam lines B. keeping protective surfaces and insulating bushings free of ... debris C. periodic testing of insulation resistance with a megger D. all of the above

Last Answer : Answer: D

Complete controller maintenance includes _____________. A. periodic testing of protective devices B. checking for loose or worn contacts and weak springs C. maintaining a sufficient supply of spare parts D. all of the above

Description : Complete controller maintenance includes _____________. A. periodic testing of protective devices B. checking for loose or worn contacts and weak springs C. maintaining a sufficient supply of spare parts D. all of the above

Last Answer : Answer: D

A commutator's protective oxide film can be destroyed by _________________. A. periods of low humidity B. very low brush current density C. improper brush grade D. all of the above

Description : A commutator's protective oxide film can be destroyed by _________________. A. periods of low humidity B. very low brush current density C. improper brush grade D. all of the above

Last Answer : Answer: D

A common type of protective covering used on electrical conductors is _____________. A. plain paper B. fibrous braid C. silver sheathing D. babbitt sheathing

Description : A common type of protective covering used on electrical conductors is _____________. A. plain paper B. fibrous braid C. silver sheathing D. babbitt sheathing

Last Answer : Answer: B

What is meant by protective angle? Give its value for reliable operation?

Description : What is meant by protective angle? Give its value for reliable operation?

Last Answer : Protective angle is the vertical angle through the ground wire axis and the line passing from the ground wire axis to the outermost phase conductor. Its value for reliable protection is taken equal to 20-30 degrees

What are the functions of protective relays

Description : What are the functions of protective relays

Last Answer : To detect the fault and initiate the operation of the circuit breaker to isolate the defective element from the rest of the system, thereby protecting the system from damages consequent to the fault.

What are the protective parameters to changeover AVR auto to manual?

Description : What are the protective parameters to changeover AVR auto to manual? 

Last Answer : a. PT supply fail. b. Auto pulse fail. c. Supply of limiter fail. d. Supply of auto channel fail. e. Regulated supply fail. f. High auto reference. 

In accordance with Coast Guard Regulations (46 CFR), each battery operated relay-controlled lantern must _____________. A. be readily portable B. contain a dry cell battery having a minimum capacity of 10 amp hours C. have an automatic battery charger to maintain the battery in a fully charged state D. all of the above

Description : In accordance with Coast Guard Regulations (46 CFR), each battery operated relay-controlled lantern must _____________. A. be readily portable B. contain a dry cell battery having a minimum capacity of ... automatic battery charger to maintain the battery in a fully charged state D. all of the above

Last Answer : Answer: C

As shown in the illustration, once the "LV" relay is energized for operation, what contacts must remain closed to maintain the "LV" relay energized when the control lever is moved away from the "off" or "stop" position? A. "DBa" contact. B. Reset contacts. C. Upper set of "LVa" contacts. D. Lower set of "LVa" contacts.

Description : As shown in the illustration, once the "LV" relay is energized for operation, what contacts must remain closed to maintain the "LV" relay energized when the control lever is moved away from the "off" or "stop" ... . B. Reset contacts. C. Upper set of "LVa" contacts. D. Lower set of "LVa" contacts.

Last Answer : Answer: C

The division of the reactive KVA load between paralleled AC generators is initiated by the ______________. A. prime mover governors B. voltage regulators C. phase balance relay D. proportioner

Description : The division of the reactive KVA load between paralleled AC generators is initiated by the ______________. A. prime mover governors B. voltage regulators C. phase balance relay D. proportioner

Last Answer : Answer: B

The schematic diagram shown in the illustration uses symbol 'A' to represent a/an _________. EL-0011 A. non-renewable fuse link B. circuit breaker coil C. overload relay coil D. thermal overload heater

Description : The schematic diagram shown in the illustration uses symbol 'A' to represent a/an _________. EL-0011 A. non-renewable fuse link B. circuit breaker coil C. overload relay coil D. thermal overload heater

Last Answer : Answer: D

Diesel generators #1 and #2 are operating in parallel at near full load capacity. Diesel generator #1 suddenly trips out mechanically due to low lube oil pressure. The reverse power relay functions properly and trips generator #1 electrically off the bo A. Start the emergency generator. B. Ascertain cause of the low lube oil pressure. C. Strip the board of all nonvital circuits. D. Secure alarms, reset reverse power relay, and restart #1 engine.

Description : Diesel generators #1 and #2 are operating in parallel at near full load capacity. Diesel generator #1 suddenly trips out mechanically due to low lube oil pressure. The reverse power relay functions ... all nonvital circuits. D. Secure alarms, reset reverse power relay, and restart #1 engine.

Last Answer : Answer: C

When an operating motor is connected to the controller shown in the illustration, the a path of current flow through the circuit is ____________. EL-0010 A. 'L1', stop button, start button, coil 'CR', 'L2' B. 'L1', stop button, 'CR' and 'M' contacts, 'M' coil, 'OL contacts, the 'CR' coil in parallel, 'L2' C. 'L1', stop button, jog button, 'CR' contact, 'CR' relay, 'L2' D. 'L1', stop button, start button, 'CR' contact, 'M' contact, 'CR' coil, 'L2'

Description : When an operating motor is connected to the controller shown in the illustration, the a path of current flow through the circuit is ____________. EL-0010 A. 'L1', stop button, start button, coil 'CR', 'L2' B. 'L1' ... L2' D. 'L1', stop button, start button, 'CR' contact, 'M' contact, 'CR' coil, 'L2'

Last Answer : Answer: B

A loss of field excitation to an AC generator while operating in parallel will cause it to ____________. A. absorb more and more load due to decreased armature reaction B. lose its load due to the inherent speed droop built into the governor C. smoke and overload due to field flashover as residual field flux changes polarity D. lose its load, begin to motorize, trip out on reverse power relay, and possibly overspeed

Description : A loss of field excitation to an AC generator while operating in parallel will cause it to ____________. A. absorb more and more load due to decreased armature reaction B. lose its load due to ... polarity D. lose its load, begin to motorize, trip out on reverse power relay, and possibly overspeed

Last Answer : Answer: D

An alternator operating in parallel begins to vibrate severely and eventually trips out on the reverse power relay. The cause of the vibration was a result of ______________________. A. the dropping of load by that alternator B. overspeeding of the vibrating alternator C. the alternator was operating out of synchronism D. flashover at the alternator collector rings

Description : An alternator operating in parallel begins to vibrate severely and eventually trips out on the reverse power relay. The cause of the vibration was a result of ______________________. A. the ... C. the alternator was operating out of synchronism D. flashover at the alternator collector rings

Last Answer : Answer: C

In order to safely carry out repairs to a generator circuit breaker, it must be isolated from the bus. This is accomplished by opening the _____________. A. reverse power relay B. bus disconnect link C. generator bus fuse connections D. power directional relay

Description : In order to safely carry out repairs to a generator circuit breaker, it must be isolated from the bus. This is accomplished by opening the _____________. A. reverse power relay B. bus disconnect link C. generator bus fuse connections D. power directional relay

Last Answer : Answer: B

A diesel driven emergency generator is prevented from being paralleled with the ship's service generators by __________. A. an electrical interlock system B. an automatic paralleling trip switch C. the synchronizing oscilloscope D. the reverse current relay

Description : A diesel driven emergency generator is prevented from being paralleled with the ship's service generators by __________. A. an electrical interlock system B. an automatic paralleling trip switch C. the synchronizing oscilloscope D. the reverse current relay

Last Answer : Answer: A

Which of the listed procedures is the best way to tell if a motor has become overloaded? A. Measure the current flow and compare it with the motor full load current flow as shown on the nameplate. B. Feel the motor and judge by the temperature. C. Watch for telltale signs of smoke coming from the motor. D. Periodic opening of the O/L relay coil

Description : Which of the listed procedures is the best way to tell if a motor has become overloaded? A. Measure the current flow and compare it with the motor full load current flow as shown on the nameplate. ... Watch for telltale signs of smoke coming from the motor. D. Periodic opening of the O/L relay coil

Last Answer : Answer: A

Why is it a good practice to have the frequency of the incoming alternator adjusted slightly higher than that of the loaded alternator when paralleling two alternators? A. This allows the oncoming machine to accept load immediately. B. This prevents the machine from floating on the line. C. The reverse power relay is prevented from activating. D. All of the above.

Description : Why is it a good practice to have the frequency of the incoming alternator adjusted slightly higher than that of the loaded alternator when paralleling two alternators? A. This allows the oncoming machine to ... line. C. The reverse power relay is prevented from activating. D. All of the above.

Last Answer : Answer: D

As shown in the illustration, what is responsible for maintaining the "LV" relay energized when the master switch handle is moved away from the "off" position? EL-0102 A. "DBa" contact. B. Reset contacts. C. Upper set of "LVa" contacts. D. Lower set of "LVa" contacts.

Description : As shown in the illustration, what is responsible for maintaining the "LV" relay energized when the master switch handle is moved away from the "off" position? EL-0102 A. "DBa" contact. B. Reset contacts. C. Upper set of "LVa" contacts. D. Lower set of "LVa" contacts.

Last Answer : Answer: C

Which component is responsible for energizing solenoid 'B1-B2' and releasing the brake for the winch motor shown in the illustration? EL-0102 A. Contactor '3M' B. A spring not shown in the schematic diagram C. Resistor 'B2-R1' D. Relay 'FR-B.O.'

Description : Which component is responsible for energizing solenoid 'B1-B2' and releasing the brake for the winch motor shown in the illustration? EL-0102 A. Contactor '3M' B. A spring not shown in the schematic diagram C. Resistor 'B2-R1' D. Relay 'FR-B.O.'

Last Answer : Answer: A

If the centrifugal switch or relay used for cutting out the starting winding of a split-phase induction motor fails to open once the motor is in operation, the _____________. A. motor will overspeed B. starting winding will burn out C. motor will immediately stall under load D. motor torque will be above normal at rated speed

Description : If the centrifugal switch or relay used for cutting out the starting winding of a split-phase induction motor fails to open once the motor is in operation, the _____________. A. motor will overspeed B ... C. motor will immediately stall under load D. motor torque will be above normal at rated speed

Last Answer : Answer: B

The winch shown in the illustration operates in any of the positions with the master switch in the 'lower' direction, but will not 'hoist' in any of the master switch hoist positions. Which of the listed faults could be the cause? EL-0102 A. Master switch contact 'MS3' may have defective springs. B. Contactor '3M' coil could have an open winding. C. Contact '2M' in the power circuit may be badly corroded. D. Series relay 'FR' may be open.

Description : The winch shown in the illustration operates in any of the positions with the master switch in the 'lower' direction, but will not 'hoist' in any of the master switch hoist positions. Which of the listed faults ... '2M' in the power circuit may be badly corroded. D. Series relay 'FR' may be open.

Last Answer : Answer: A

When paralleling two AC generators, the synchroscope selector switch and frequency meter switch should be set up to sense the frequency of the _____________. A. bus B. generator on the line C. oncoming generator D. bus transfer relay

Description : When paralleling two AC generators, the synchroscope selector switch and frequency meter switch should be set up to sense the frequency of the _____________. A. bus B. generator on the line C. oncoming generator D. bus transfer relay

Last Answer : Answer: C

The motor starts when the start button in the illustration is pushed, but stops when the button is released the trouble is _________. EL-0007 A. the incorrect thermal overload coil B. a faulty 'M' coil C. a dirty contact on the Disc.Sw. at 'L3' D. a faulty holding relay contact

Description : The motor starts when the start button in the illustration is pushed, but stops when the button is released the trouble is _________. EL-0007 A. the incorrect thermal overload coil B. a faulty 'M' coil C. a dirty contact on the Disc.Sw. at 'L3' D. a faulty holding relay contact

Last Answer : Answer: D

The contacts operated by the D.C. relay coil shown in the illustration are located in the schematic diagram prints at coordinates ____________. EL-0100 A. '41Y' on this page B. '52M52M' and '52H35M' C. '57R' on this page D. '52N' on page '57R'

Description : The contacts operated by the D.C. relay coil shown in the illustration are located in the schematic diagram prints at coordinates ____________. EL-0100 A. '41Y' on this page B. '52M52M' and '52H35M' C. '57R' on this page D. '52N' on page '57R'

Last Answer : Answer: C

The operating torque of the upper induction disc-type element, or timer element, of an AC reverse power relay is obtained from ____________. A. the main bus B. a separate battery source C. line voltage D. electromagnets

Description : The operating torque of the upper induction disc-type element, or timer element, of an AC reverse power relay is obtained from ____________. A. the main bus B. a separate battery source C. line voltage D. electromagnets

Last Answer : Answer: D

The purpose of the reverse power relay, provided on a ship's service alternator panel, is to trip the circuit in the event of ______________. A. main circuit overload B. high power transfer C. generator overspeeding D. alternator motorization

Description : The purpose of the reverse power relay, provided on a ship's service alternator panel, is to trip the circuit in the event of ______________. A. main circuit overload B. high power transfer C. generator overspeeding D. alternator motorization

Last Answer : Answer: D

The vertical dotted line connecting the small circular symbols at coordinates '05L', '09L', '13L', '21L', '25L', etc., shown in the illustration, indicate that all _______________. EL-0100 A. contacts are operated by the same relay coil B. screw connections are on terminal board 'TB2' C. wires are grounded at both ends of the line D. wires have a common shield

Description : The vertical dotted line connecting the small circular symbols at coordinates '05L', '09L', '13L', '21L', '25L', etc., shown in the illustration, indicate that all _______________. EL-0100 A. contacts are ... board 'TB2' C. wires are grounded at both ends of the line D. wires have a common shield

Last Answer : Answer: B

A reverse-current relay will prevent AC generator motorization by ____________. A. automatically redirecting the load B. automatically speeding up the prime mover C. tripping the panel board main switch D. tripping the generator circuit breaker

Description : A reverse-current relay will prevent AC generator motorization by ____________. A. automatically redirecting the load B. automatically speeding up the prime mover C. tripping the panel board main switch D. tripping the generator circuit breaker

Last Answer : Answer: D

In the illustration, if one of the devices labeled 'TURB' should fail the ___________. EL-0003 A. device labeled 'EXC' will drive the alternator B. device labeled 'BKR' for that alternator should automatically open because of the reverse power relay C. operator must open all the devices labeled 'BKRS' to reduce the load on the remaining turbo-alternator D. emergency generator should automatically start and be placed on line to supply emergency load centers

Description : In the illustration, if one of the devices labeled 'TURB' should fail the ___________. EL-0003 A. device labeled 'EXC' will drive the alternator B. device labeled 'BKR' for that ... -alternator D. emergency generator should automatically start and be placed on line to supply emergency load centers

Last Answer : Answer: B

The timer element of a reverse power relay cannot be energized unless _____________. A. the power flow is the same as the tripping direction B. the power flow is the opposite to the tripping direction C. the movement of the disk is damped by a permanent magnet D. one generator is motorized

Description : The timer element of a reverse power relay cannot be energized unless _____________. A. the power flow is the same as the tripping direction B. the power flow is the opposite to the tripping direction C. the movement of the disk is damped by a permanent magnet D. one generator is motorized

Last Answer : Answer: A

The small circular symbols to which wire '52N57E' is connected at coordinates '57L' and '57P' shown in the illustration represent ___________________. EL-0100 A. relay contact solder points B. wire wrap connections C. terminal board screws D. switch contact terminals

Description : The small circular symbols to which wire '52N57E' is connected at coordinates '57L' and '57P' shown in the illustration represent ___________________. EL-0100 A. relay contact solder points B. wire wrap connections C. terminal board screws D. switch contact terminals

Last Answer : Answer: C

When troubleshooting a motor controller, all indications are that a relay coil should be energized. If there were no magnetic pull, with rated voltage measured across the coil, the most probable cause would be that the _________________. A. coil is open B. control fuse is open C. auxiliary contact in series with the coil is defective D. relay armature is stuck

Description : When troubleshooting a motor controller, all indications are that a relay coil should be energized. If there were no magnetic pull, with rated voltage measured across the coil, the most probable cause ... open C. auxiliary contact in series with the coil is defective D. relay armature is stuck

Last Answer : Answer: A

When troubleshooting motor controllers, a shorted relay or contactor coil is often indicated by _______________. A. a resistance reading of 'infinity' on an ohmmeter B. charred insulation and/or a blown control fuse C. a reading of 'zero' on a megger from one of the coil's leads to ground D. a higher-than-normal voltage reading across the winding

Description : When troubleshooting motor controllers, a shorted relay or contactor coil is often indicated by _______________. A. a resistance reading of 'infinity' on an ohmmeter B. charred insulation and/or a blown ... of the coil's leads to ground D. a higher-than-normal voltage reading across the winding

Last Answer : Answer: B

The devices located at coordinates '49W' in the illustration represents a/an _________. EL-0100 A. A.C. motor B. A.C. relay coil C. D.C. motor D. D.C. buzzer

Description : The devices located at coordinates '49W' in the illustration represents a/an _________. EL-0100 A. A.C. motor B. A.C. relay coil C. D.C. motor D. D.C. buzzer

Last Answer : Answer: B

Vessel pitch can be controlled by either the 'bridge or engine room thrust lever' shown in the illustration; but only with one engine on the line whether in 'cruise or maneuver' mode. The cause is most likely a faulty relay _____________. EL-0095 A. #1 B. #2 C. #3 D. #4

Description : Vessel pitch can be controlled by either the 'bridge or engine room thrust lever' shown in the illustration; but only with one engine on the line whether in 'cruise or maneuver' mode. The cause is most likely a faulty relay _____________. EL-0095 A. #1 B. #2 C. #3 D. #4

Last Answer : Answer: D

The device at coordinates '63/1' in the illustration represents a/an _____________. EL-0100 A. A.C. buzzer B. A.C. motor C. D.C. motor D. D.C. relay coil

Description : The device at coordinates '63/1' in the illustration represents a/an _____________. EL-0100 A. A.C. buzzer B. A.C. motor C. D.C. motor D. D.C. relay coil

Last Answer : Answer: D

If Relay #5 changed contact position grounding the 'auto' input to the 'pitch controller module', pitch control would be effected by the _________________. EL-0095 A. pitch feedback potentiometer B. Engine room thrust split potentiometer C. Engine room thrust lever only D. Bridge thrust lever only

Description : If Relay #5 changed contact position grounding the 'auto' input to the 'pitch controller module', pitch control would be effected by the _________________. EL-0095 A. pitch feedback potentiometer B. Engine room thrust split potentiometer C. Engine room thrust lever only D. Bridge thrust lever only

Last Answer : Answer: B