When voltage increases then current also increases then why we need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only?

When voltage increases then current also increases then why we need of over voltage relay and over current relay? Can we
measure over voltage and over current by measuring current only?
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1 Answer

Answer :

No. We cannot sense the over voltage by just measuring the current only because the current increases not only for over voltages but
also for under voltage (As most of the loads are non-linear in nature).So, the over voltage protection & over current protection are completely
different.
 Over voltage relay meant for sensing over voltages & protect the system from insulation break down and firing. Over current relay
meant for sensing any internal short circuit, over load condition, earth fault thereby reducing the system failure & risk of fire. So, for a better
protection of the system. It should have both over voltage & over current relay.
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Related questions

When voltage increases then current also increases then what is the need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only?

Description : When voltage increases then current also increases then what is the need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only?

Last Answer : No. We can't sense the over voltage by just measuring the current only because the current increases not only for over voltages but also for under voltage (As most of the loads are non-linear in ... So, for a better protection of the system. It should have both over voltage & over current relay.

You have installed a Zener diode in parallel with a load. While measuring the voltage across the Zener diode it is found that it does not change as the current through the load increases. This means that the Zener diode __________. A. is working as it should B. is shorted C. is open D. does not regulate as it should

Description : You have installed a Zener diode in parallel with a load. While measuring the voltage across the Zener diode it is found that it does not change as the current through the load increases. This means that the ... is working as it should B. is shorted C. is open D. does not regulate as it should

Last Answer : Answer: A

What is the difference between over voltage relay and over current relay?

Description : What is the difference between over voltage relay and over current relay?

Last Answer : A:The current increases not only for over voltages but also for under voltage(As most of the loads are non-linear in nature). So,the over voltage protection & over current protection are completely ... , for a better protection of the system.It should have both over voltage & over current relay.

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.

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

Equal power factors on paralleled AC generators are maintained by an automatic _____________. A. voltage regulator B. reverse power relay C. reverse current relay D. governor control switch

Description : Equal power factors on paralleled AC generators are maintained by an automatic _____________. A. voltage regulator B. reverse power relay C. reverse current relay D. governor control switch

Last Answer : Answer: A

If a magnetic controller relay fails to drop out when the coil voltage is removed from the relay, the probable cause may be _____________. A. excessive spring tension B. overvoltage C. excessive current D. welded contacts

Description : If a magnetic controller relay fails to drop out when the coil voltage is removed from the relay, the probable cause may be _____________. A. excessive spring tension B. overvoltage C. excessive current D. welded contacts

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

What is the advantage of CMM relay over normal Inv. O/C current relay?

Description : What is the advantage of CMM relay over normal Inv. O/C current relay?

Last Answer : Inv. O/C relay under protects at low current and over protects at high currents. CMM: accounts for both +ve and -ve sequence currents i.e. Single phasing / unbalance supply conditions ... closely matched to motor heating characteristic. So it is better than thermal overload relay also. 

Why IDMT over current relay is always used as backup?

Description : Why IDMT over current relay is always used as backup?

Last Answer : Because setting has to be 200% to emergency loading and TMS be large to grade with feeder. Therefore very slow for internal faults/terminal faults/uncleared LV faults. 

Purpose of Over current & earth fault relay; type- CAG

Description : Purpose of Over current & earth fault relay; type- CAG  

Last Answer : This relays are designed for instantaneous phase or earth fault protection and instantaneous high set over current protection.; A standard hinged-armature unit forms the basic movement for this relay. It consists an ... to the end of the core while the other arm to operate a set of contacts.  

Purpose of Directional inverse Over current & earth fault relay; type- CDD

Description : Purpose of Directional inverse Over current & earth fault relay; type- CDD

Last Answer : Directional phase or earth fault protection of ring-mains, parallel transformers, transformer feeders, parallel feeders etc., employing the time graded principle.; This relay comprises an inductive ... induction disc unit. The directional unit is normally provided with voltage polarising coils. 

Purpose of over current relay (Inverse); type- CDG

Description : Purpose of over current relay (Inverse); type- CDG  

Last Answer : It is a self powered inverse time over current and earth fault relay, used for selective phase and earth fault protection in time graded systems for A.C. machines, transformers, feeders ... it rotates the driving torque increases and offsets the changing restraining torque of the control spring. 

What is the characteristic of inverse time over current relay?

Description : What is the characteristic of inverse time over current relay?  

Last Answer : If the fault current increases the time of the operation of the relay will be decreases.  

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 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

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

Considering the function of the circuit shown in the illustration, what is the purpose of supplying the thrust lever potentiometers with both (+) and (-) 15 volts? EL-0095 A. To select which lever (bridge or engine room) is active. B. So the circuit can differentiate between ahead and astern commands. C. To provide an alternate voltage supply if the other fails. D. So as to automatically select the position of Relay #

Description : Considering the function of the circuit shown in the illustration, what is the purpose of supplying the thrust lever potentiometers with both (+) and (-) 15 volts? EL-0095 A. To select which ... alternate voltage supply if the other fails. D. So as to automatically select the position of Relay #

Last Answer : Answer: B

During its operation, loud buzzing and resultant welding of contacts of a magnetic relay may be caused by __________. A. overheating of the contactor coil B. low voltage on the operating coil C. low insulation resistance to ground D. lubrication of the contact bearing points

Description : During its operation, loud buzzing and resultant welding of contacts of a magnetic relay may be caused by __________. A. overheating of the contactor coil B. low voltage on the operating coil C. low insulation resistance to ground D. lubrication of the contact bearing points

Last Answer : Answer: B

The timer element found in a reverse power relay obtains its operating torque via _____________. A. line voltage B. the main bus C. electromagnets D. a separate battery source

Description : The timer element found in a reverse power relay obtains its operating torque via _____________. A. line voltage B. the main bus C. electromagnets D. a separate battery source

Last Answer : Answer: C

Low voltage releases as used in some shipboard motor starter and control equipment will have which of the following characteristics? A. They trip circuit contactors when the motor starts to overspeed. B. They require manual resetting upon restoration of normal voltage. C. They use a phase sensitive relay to trip contacts in series with the holding coil of the starter. D. They allow the motor to restart upon restoration of normal voltage.

Description : Low voltage releases as used in some shipboard motor starter and control equipment will have which of the following characteristics? A. They trip circuit contactors when the motor starts to overspeed. B. ... coil of the starter. D. They allow the motor to restart upon restoration of normal voltage.

Last Answer : Answer: D

A constant output voltage from an AC generator is maintained by the _____________. A. prime mover governor B. exciter generator C. voltage regulator D. reverse power relay

Description : A constant output voltage from an AC generator is maintained by the _____________. A. prime mover governor B. exciter generator C. voltage regulator D. reverse power relay

Last Answer : Answer: C

Regarding an AC generator connected to the main electrical bus; as the electric load and power factor vary, a corresponding change is reflected in the generator armature reaction. These changes in armature reaction are compensated for by the __________ A. governor speed droop setting B. voltage regulator C. balance coil D. phase-balance relay

Description : Regarding an AC generator connected to the main electrical bus; as the electric load and power factor vary, a corresponding change is reflected in the generator armature reaction. These changes in ... . governor speed droop setting B. voltage regulator C. balance coil D. phase-balance relay

Last Answer : Answer: B

What is use of lockout relay in ht voltage?

Description : What is use of lockout relay in ht voltage?

Last Answer : Answer:A lock-out relay is generally placed in line before or after the e-stop switch so the power can be shut off at one central location. This relay is powered by the same electrical source as ... allows the control power for multiple machines to be locked out by the turn of a single key switch.

If reading AC current with the illustrated device and unsure of the range as a precaution , the first step should be to _________. EL-0047 A. secure power and test for voltage B. disconnect the lead to be tested and connect the meter in series C. connect the meter to measure resistance and use Ohm's law to calculate current D. unable to safely measure current with the device

Description : If reading AC current with the illustrated device and unsure of the range as a precaution , the first step should be to _________. EL-0047 A. secure power and test for voltage B. disconnect the ... resistance and use Ohm's law to calculate current D. unable to safely measure current with the device

Last Answer : Answer: A

A multimeter can be used to measure _____________. A. resistance B. voltage C. current D. all of the above

Description : A multimeter can be used to measure _____________. A. resistance B. voltage C. current D. all of the above

Last Answer : Answer: D

A galvanometer is an instrument used to measure ___________. A. thickness of galvanized metal B. resistance of electrical wiring insulation C. very small amounts of current or voltage D. quantity of galvans in an electric circuit

Description : A galvanometer is an instrument used to measure ___________. A. thickness of galvanized metal B. resistance of electrical wiring insulation C. very small amounts of current or voltage D. quantity of galvans in an electric circuit

Last Answer : Answer: C

A megohmmeter is used to measure _____________. A. voltage B. dielectric strength C. current D. power

Description : A megohmmeter is used to measure _____________. A. voltage B. dielectric strength C. current D. power

Last Answer : Answer: B

An ammeter should be used to measure ___________. A. the voltage between two points in a circuit B. circuit continuity C. current flow in a circuit D. total or partial circuit resistance

Description : An ammeter should be used to measure ___________. A. the voltage between two points in a circuit B. circuit continuity C. current flow in a circuit D. total or partial circuit resistance

Last Answer : Answer: C

An ohmmeter can be used to measure ____________. A. current flow in a circuit B. voltage between two points in a circuit C. circuit continuity D. power

Description : An ohmmeter can be used to measure ____________. A. current flow in a circuit B. voltage between two points in a circuit C. circuit continuity D. power

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

Power necessary to operate the horn 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 a relay coil D. also lights lamps 'R' and 'T'

Description : Power necessary to operate the horn 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 a relay coil D. also lights lamps 'R' and 'T'

Last Answer : Answer: B

Will rotor earth fault relay operate for earth fault in main exciter winding or RCU Diode Bridge also?

Description : Will rotor earth fault relay operate for earth fault in main exciter winding or RCU Diode Bridge also? 

Last Answer : Yes. 

A short in the shunt field of a DC motor is best located by _____________. A. visual inspection of the commutator B. applying AC voltage to each field coil and measuring the voltage drop across each field coil C. using a growler and hacksaw blade D. isolating each coil from the others and using a megohmmeter

Description : A short in the shunt field of a DC motor is best located by _____________. A. visual inspection of the commutator B. applying AC voltage to each field coil and measuring the voltage drop across ... using a growler and hacksaw blade D. isolating each coil from the others and using a megohmmeter

Last Answer : Answer: B

When using a multimeter for resistance measurements, it should be calibrated by clipping the loose ends of the leads together and _____________. A. setting the instrument pointer at 'zero' ohms B. adjusting the line voltage to calibrate the instrument C. plugging each end of one test lead into the plus and minus terminals D. using a special purpose resistance measuring instrument (a bridge)

Description : When using a multimeter for resistance measurements, it should be calibrated by clipping the loose ends of the leads together and _____________. A. setting the instrument pointer at 'zero' ohms B. ... the plus and minus terminals D. using a special purpose resistance measuring instrument (a bridge)

Last Answer : Answer: A

When troubleshooting a lead-acid storage battery, a weak or dead cell is best detected by _________________. A. measuring and comparing all cells' specific gravity B. taking an open circuit voltage test of individual cells C. visually inspecting the electrolyte levels of each cell D. taking each cell's temperature with a calibrated mercury thermometer

Description : When troubleshooting a lead-acid storage battery, a weak or dead cell is best detected by _________________. A. measuring and comparing all cells' specific gravity B. taking an open circuit ... electrolyte levels of each cell D. taking each cell's temperature with a calibrated mercury thermometer

Last Answer : Answer: A

Which of the following statements is true concerning a stepdown transformer in an operating AC power circuit? A. Voltage and current will both be increased. B. Voltage and current will both be decreased C. Voltage decreases as current increases. D. Voltage increases as current decreases.

Description : Which of the following statements is true concerning a stepdown transformer in an operating AC power circuit? A. Voltage and current will both be increased. B. Voltage and current will both be decreased C. Voltage decreases as current increases. D. Voltage increases as current decreases.

Last Answer : Answer: C

When the voltage remains constant, and the resistance increases in a series circuit, current flow _____________. A. decreases B. remains the same C. increases D. increases by the square

Description : When the voltage remains constant, and the resistance increases in a series circuit, current flow _____________. A. decreases B. remains the same C. increases D. increases by the square

Last Answer : Answer: A

When the voltage remains constant and the resistance is increased in a series circuit, the flow of current _____________. A. increases by the square of the original value B. increases C. remains the same D. decreases

Description : When the voltage remains constant and the resistance is increased in a series circuit, the flow of current _____________. A. increases by the square of the original value B. increases C. remains the same D. decreases

Last Answer : Answer: D

Induction cup relay is operated due to changes in (a) current (b) voltage (c) impedance (d) all of the above

Description : Induction cup relay is operated due to changes in (a) current (b) voltage (c) impedance (d) all of the above

Last Answer : (d) all of the above

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should (a) have low contact resistance (b) be clean and smooth (c) be of sufficient size and proper shape (d) have all above properties

Description : In order that current should flow without causing excessive heating or voltage drop, the relay contacts should (a) have low contact resistance (b) be clean and smooth (c) be of sufficient size and proper shape (d) have all above properties

Last Answer : (d) have all above properties

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should?

Last 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.

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