What are the different relays that employed for protection of apparatus and transmission lines?

What are the different relays that employed for protection of apparatus and transmission lines?
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1 Answer

Answer :

Answer: The relays that are usually employed for protection of transmission lines include
• Over current relay
• Directional relay
• Distance relay
• Under Voltage relay
• Under-frequency relay
• Thermal relay
• Differential relay
• Phase sequence relays
• pilot relays
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Related questions

Which of the following relays is used on long transmission lines ? (a) Impedance relay (b) Mho's relay (c) Reactance relay (d) None of the above

Description : Which of the following relays is used on long transmission lines ? (a) Impedance relay (b) Mho's relay (c) Reactance relay (d) None of the above

Last Answer : (b) Mho's relay

Reactance relays are employed for Phase faults in :

Description : Reactance relays are employed for Phase faults in : (A) Short lines (B) Medium lines (C) Long lines (D) Any line

Last Answer : Reactance relays are employed for Phase faults in : Short lines

The inverse definite mean time relays are used for over current and earth fault protection of transformer against (a) heavy loads (b) internal short-circuits (c) external short-circuits (d) all of the above

Description : The inverse definite mean time relays are used for over current and earth fault protection of transformer against (a) heavy loads (b) internal short-circuits (c) external short-circuits (d) all of the above

Last Answer : (b) internal short-circuits

The single phasing relays are used for the protection of (a) single phase motors only (b) two phase motors only (c) two single phase motors running in parallel (d) three phase motors

Description : The single phasing relays are used for the protection of (a) single phase motors only (b) two phase motors only (c) two single phase motors running in parallel (d) three phase motors

Last Answer : (d) three phase motors

Discrimination between main and back up protection is provided by the use of relays which are (a) fact (b) sensitive (c) slow (d) none of the above

Description : Discrimination between main and back up protection is provided by the use of relays which are (a) fact (b) sensitive (c) slow (d) none of the above

Last Answer : (c) slow

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

State any four relays used for catenary protection. State function of each relay.

Description : State any four relays used for catenary protection. State function of each relay.

Last Answer : Relays Used for Catenary Protection: 1. MHO relay: Wrong coupling protection. 2. MHO relay: Over current protection at farthest point. 3. Over current relay: Over current protection against faults near substation 4. Under voltage relay: Protection against faults far away from substation. 

State use of any four relays for the protection of traction transformer.

Description : State use of any four relays for the protection of traction transformer. 

Last Answer : Relays for the protection of traction transformers:  Inverse time over current relay as back up protection on primary (HV side) - over current protection of transformer and other equipment.  ... .  Buchholz relay - protection from incipient earth or inter winding faults inside the transformer

For the protection of parallel feeders fed from one end, the relays used are:

Description :  For the protection of parallel feeders fed from one end, the relays used are: A) non-directional relays at the source-end and directional relays at the load-end B) non-directional relays at both the ... at the source-end and non-directional at the load-end D) directional relays at both the ends

Last Answer : For the protection of parallel feeders fed from one end, the relays used are: non-directional relays at the source-end and directional relays at the load-end

The inverse definite mean time relays are used for over current and earth fault protection of transformer against?

Last Answer : The inverse definite mean time relays are used for over current and earth fault protection of transformer against internal short-circuits.

The single phasing relays are used for the protection of?

Last Answer : The single phasing relays are used for the protection of three phase motors.

Discrimination between main and backup protection is provided by the use of relays which are?

Last Answer : Discrimination between main and back up protection is provided by the use of relays which are slow.

What are different types of principles of operation of electro-mechanical relays?

Description : What are different types of principles of operation of electro-mechanical relays?

Last Answer : Answer: Electro-mechanical relays operate by two principles. Electro-magnetic attraction and electromagnetic induction. In electromagnetic attraction relay plunger is drawn to the solenoid or an ... operation is similar to induction motor. Torque is developed by electromagnetic induction principle

Name the different kinds of over current relays.

Description : Name the different kinds of over current relays.

Last Answer : Induction type non-directional over current relay, Induction type directional over current relay & current differential relay.

Which of the following devices will receive voltage surge first travelling on the transmission line ? (a) Lightning arresters (b) Relays (c) Step-down transformer (d) Switchgear

Description : Which of the following devices will receive voltage surge first travelling on the transmission line ? (a) Lightning arresters (b) Relays (c) Step-down transformer (d) Switchgear

Last Answer : (a) Lightning arresters

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

If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of wood C. inject small amounts of CO2 into the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents

Description : If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of ... the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents

Last Answer : Answer: A

When the master switch for the winch shown in the illustration is in the 'off' position, and the line & safe switches are closed, which of the listed relays should be energized? EL-0102 A. 'DB' & '2T' B. 'DB' & '4M' C. 'FR-B.O.' & 'LV' D. '1M' & '1A'

Description : When the master switch for the winch shown in the illustration is in the 'off' position, and the line & safe switches are closed, which of the listed relays should be energized? EL-0102 A. 'DB' & '2T' B. 'DB' & '4M' C. 'FR-B.O.' & 'LV' D. '1M' & '1A'

Last Answer : Answer: C

Motor controllers are seldom troubled by grounds because ________________. A. cabinet heaters always keep internal components dry B. special insulation is used on wire for vital circuits C. shock mounts on controller panels greatly reduce vibration D. contactors and relays are mounted on nonconducting panels

Description : Motor controllers are seldom troubled by grounds because ________________. A. cabinet heaters always keep internal components dry B. special insulation is used on wire for vital circuits C. ... on controller panels greatly reduce vibration D. contactors and relays are mounted on nonconducting panels

Last Answer : Answer: D

A faulty 'function generator' shown in the illustration may prevent _____________. EL-0095 A. proper pitch control from both the 'bridge' and 'engine room thrust levers' B. the 'split potentiometer's' ability to control pitch C. the pitch meter from indicating accurately D. relays #2 and/or #3 from energizing

Description : A faulty 'function generator' shown in the illustration may prevent _____________. EL-0095 A. proper pitch control from both the 'bridge' and 'engine room thrust levers' B. the 'split potentiometer ... control pitch C. the pitch meter from indicating accurately D. relays #2 and/or #3 from energizing

Last Answer : Answer: A

When power is restored after a complete power failure, a steering gear pump motor will ____________. A. have to be restarted B. have to be reset C. restart automatically D. trip its overload relays

Description : When power is restored after a complete power failure, a steering gear pump motor will ____________. A. have to be restarted B. have to be reset C. restart automatically D. trip its overload relays

Last Answer : Answer: C

Power necessary to operate the horn relay shown in the illustration ____________. EL-0093 A. comes from each station's magneto B. is supplied from a 115 volt source C. is conducted through the relay's contacts D. also lights lamps 'R' and 'T'

Description : Power necessary to operate the horn relay shown in the illustration ____________. EL-0093 A. comes from each station's magneto B. is supplied from a 115 volt source C. is conducted through the relay's contacts D. also lights lamps 'R' and 'T'

Last Answer : Answer: A

As shown in the illustration, when the 'speed control' system is in 'SPLIT' _______________. EL-0096 A. Relays #1, #5 and #8 are not used B. the 'slew rated controller' is grounded through Relay #6 C. the RPM 'function generator' and 'thrust levers' have no control D. the 'E/P converters' are bypassed and air is fed directly to the governors via the 'load sharing valve'

Description : As shown in the illustration, when the 'speed control' system is in 'SPLIT' _______________. EL-0096 A. Relays #1, #5 and #8 are not used B. the 'slew rated controller' is grounded through Relay ... E/P converters' are bypassed and air is fed directly to the governors via the 'load sharing valve'

Last Answer : Answer: C

The division of the kilowatt load between two AC generators operating in parallel is controlled by the settings and characteristics of the _____________. A. voltage regulators B. field rheostats C. reverse power relays D. prime mover governors

Description : The division of the kilowatt load between two AC generators operating in parallel is controlled by the settings and characteristics of the _____________. A. voltage regulators B. field rheostats C. reverse power relays D. prime mover governors

Last Answer : Answer: D

Line losses in a distribution circuit are kept to a minimum by __________. A. adding rubber insulation conductors to the circuit B. using higher current and lower voltage C. increasing the number of thermal relays in the circuit D. using higher voltage and lower current

Description : Line losses in a distribution circuit are kept to a minimum by __________. A. adding rubber insulation conductors to the circuit B. using higher current and lower voltage C. increasing the number of thermal relays in the circuit D. using higher voltage and lower current

Last Answer : Answer: D

On an engine throttle control system, the auxiliary control circuits are provided with devices to prevent excessive overtravel of the pilot valve by the synchronous motor. These devices are called _________________. A. overlap sensors B. limit switches C. overtravel relays D. proximity switches

Description : On an engine throttle control system, the auxiliary control circuits are provided with devices to prevent excessive overtravel of the pilot valve by the synchronous motor. These devices are called _________________. A. overlap sensors B. limit switches C. overtravel relays D. proximity switches

Last Answer : Answer: B

Motor controllers are seldom troubled with grounds because _____________. A. the auxiliary contacts have a high resistance connection B. the contactors and relays are mounted on a nonconducting panel C. the resistor banks are composed of individual series-connected units D. there are separate switches for the motor and the control

Description : Motor controllers are seldom troubled with grounds because _____________. A. the auxiliary contacts have a high resistance connection B. the contactors and relays are mounted on a nonconducting panel ... individual series-connected units D. there are separate switches for the motor and the control

Last Answer : Answer: B

The alarm system for an engine order telegraph uses small selsyn motors attached to the indicators. The alarm sounds when the rotors are _____________. A. in synchronous position, no current is flowing, and the relays are open B. in synchronous position, no current is flowing, and the relays are closed C. not synchronized, current is flowing, and the relays are open D. not synchronized, current is flowing, and the relays are closed

Description : The alarm system for an engine order telegraph uses small selsyn motors attached to the indicators. The alarm sounds when the rotors are _____________. A. in synchronous position, no current is flowing, ... and the relays are open D. not synchronized, current is flowing, and the relays are closed

Last Answer : Answer: D

Which of the following statements represents the main difference between a relay and a contactor? A. Contactors control current and relays control voltage. B. A relay is series connected and a contactor is parallel connected. C. Contactors can handle heavier loads than relays. D. Contactors are made from silver and relays are made from copper.

Description : Which of the following statements represents the main difference between a relay and a contactor? A. Contactors control current and relays control voltage. B. A relay is series connected and a contactor ... loads than relays. D. Contactors are made from silver and relays are made from copper.

Last Answer : Answer: C

How relays are connected in the power system?

Description : How relays are connected in the power system?

Last Answer : Answer: The relays are connected to the power system through the current transformer (CT) or potential transformer (PT).

Mention some of the applications of Directional Over-Current relays?

Description : Mention some of the applications of Directional Over-Current relays?

Last Answer : 1. Double end fed power system 2. Single end fed system of parallel feeders 3. Ring main feeder system

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 are over and under current relays?

Description : What are over and under current relays?

Last Answer : Overcurrent relays are those that operate when the current in a line exceeds a predetermined value. (eg: Induction type non-directional/directional overcurrent relay, differential overcurrent relay)whereas ... in a circuit/line drops below a predetermined value.(eg: differential over-voltage relay)

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.

Why 86.1 and 86.2 relays are used?

Description : Why 86.1 and 86.2 relays are used?

Last Answer : All electrical protection is wired to 86.1 and under voltage protection is wired to 86.2 relay for automatic restoration in EMTR. 

Why 2 types of earth fault relays in 6.6 kV side of transformers?

Description : Why 2 types of earth fault relays in 6.6 kV side of transformers?

Last Answer : I – Trips 6.6 kV breakers only. It gives primary protection for 6.6 kV bus bars. I1 – Trips the both HT and LT breakers. It acts as a backup to ref and also acts as backup to bus bar earthfault relay. 

Where are the following relays used?

Description : Where are the following relays used?  

Last Answer : a) Very inverse b) extremely inverse relays c) definite time O/C Relay d) instantaneous O/C Relay.  a) Very Inverse - Used where inverse protection reduces substantially as distance from source ... relay - to get higher grading margin. Disadvantage - Under minimum generation it may not operate. 

Mention the initial commissioning checks on CT’s, PT’s and relays.

Description : Mention the initial commissioning checks on CT’s, PT’s and relays.

Last Answer : Commissioning checks on CT a) Terminal marking correctness. b) Polarity of terminals. c) Insulation resistance between primary and secondary. d) Insulation resistance between primary to earth and secondary ... h) Burden check of relay. i) Primary injection test. j) Secondary injection test. 

Mho relay is usually employed for protection of

Description :  Mho relay is usually employed for protection of (A) Short lines (B) Medium lines (C) Long lines (D) Any line

Last Answer : Mho relay is usually employed for protection of long lines.

What are different types of circuit breakers employed in thermal power plant?

Description : What are different types of circuit breakers employed in thermal power plant?

Last Answer : Answer: For low voltage operation 415/220V vacuum circuit breakers or air break circuit breakers are employed. For voltage ratings about 6.6kV and beyond SF6 circuit breakers are employed.

What are the different Generator Protections employed in Thermal Power Plants?

Description : What are the different Generator Protections employed in Thermal Power Plants?

Last Answer : Answer: Faults in the windings, Over load protection, Over heating of windings or bearings, Over speed protection, Loss of Excitation protection, Motoring operation protection, Inadvertent ... , out of step operation protection, sub-synchronous oscillations protection and earth fault protection

What are different insulators employed in substations?

Description : What are different insulators employed in substations?

Last Answer : Some of the insulators employed in substations are: Pin insulators Post insulators Strain insulators Suspension insulators Hallow apparatus insulators Dead-end insulators Solid core insulators

What are different types of circuit breakers employed in thermal power plant?

Description : What are different types of circuit breakers employed in thermal power plant?

Last Answer : For low voltage operation 415/220V vacuum circuit breakers or air break circuit breakers are employed. For voltage ratings about 6.6kV and beyond SF6 circuit breakers are employed.

What are the different Generator Protections employed in Thermal Power Plants?

Description : What are the different Generator Protections employed in Thermal Power Plants?

Last Answer : Faults in the windings, Over load protection, Over heating of windings or bearings, Over speed protection, Loss of Excitation protection, Motoring operation protection, Inadvertent energisation ... , out of step operation protection, sub-synchronous oscillations protection and earth fault protection

The leakage current in the transmission lines is referred to as the a) Resistance b) Radiation c) Conductance d) Polarisation

Description : The leakage current in the transmission lines is referred to as the a) Resistance b) Radiation c) Conductance d) Polarisation

Last Answer : Ans: C

Why Earth Wire is provided in the overhead transmission lines?

Description : Why Earth Wire is provided in the overhead transmission lines?

Last Answer : Earth wire is provided above the overhead transmission lines for protection against lightning strokes. The ground wire or earth wire protects the phase conductors or line conductors by attracting itself the ... traveling waves set in the lines by acting a short circuit secondary of the line current

Why, when birds sit on transmission lines or current wires doesn't get shock?

Description : Why, when birds sit on transmission lines or current wires doesn't get shock?

Last Answer : It's true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock. so ... is grounded..So that means that human who touch the line closes the circuit between phase and neutral.

Why, when birds sit on transmission lines or current wires doesn't get shock?

Description : Why, when birds sit on transmission lines or current wires doesn't get shock?

Last Answer : A:Its true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock.. so if a human ... the air. If he is standing on the ground then touching the line (phase) he will get a shock.

The regulation of Short Transmission lines depends up on a) Distance of line b) Frequency c) Power factor d) All

Description : The regulation of Short Transmission lines depends up on a) Distance of line b) Frequency c) Power factor d) All

Last Answer : Ans: Power factor