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

Purpose of Directional inverse Over current & earth fault relay; type- CDD
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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 disc over current unit with wound shading coils and a directional high speed induction cup unit. The cup-unit contact is wired across the shading coils so that no torque is exerted on the disc of the over current unit until the cup unit contact closes. The inductive disc unit is thus directionally controlled and it operates only when the current flows in the tripping direction. The directional unit is a high speed, low inertia four pole induction cup movement designed to give a high, steady and non-vibrating torque. its current coil is connected in series with the operating coil of the induction disc unit. The directional unit is normally provided with voltage polarising coils. 
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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.

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

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

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Last Answer : (b) internal short-circuits

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Description : Explain construction and operation of induction type directional over current relay.

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Description : In induction type directional over current relay the driving torque is due to interaction of magnetic fields derived from (A) current in the potential coil (B) both voltage and current in the ... (C) directional element and non-directional element (D) non-directional element and the trip circuit

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Description : How generator earth fault relay works? 

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

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Last Answer : Answer: B

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Description : What are the features of directional relay?

Last Answer : High speed operation; high sensitivity; ability to operate at low voltages; adequate short-time thermal ratio; burden must not be excessive.

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Description : Action carried out by the relay and circuit breaker during fault condition?

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

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Description : Which of the following statements is incorrect? (a) Station batteries are used to operate relay only (b) The lightning arresters are basically surge diverters (c) An impedance relay has maximum fault current when fault occurs near the relay (d) A high speed relay has an operation of 1 to 2 cycles

Last Answer : (a) Station batteries are used to operate relay only

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Last Answer : (b) 5 to 10 sec

The relay with inverse time characteristic will operate within?

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Description : Why earth fault current of generator should not be reduced below 5A? 

Last Answer : To limit over voltage due to neutral shift.  

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Description : Why not high resistance for earth fault than using grounding transformer & resistor 0.45 ohms?

Last Answer : It is mechanically unwide. Difficult to manufacture.  

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Description : What is the direction of current through the load resistor in the circuit shown in the illustration? EL-0085 A. Always from point 'Z' to the grounded end. B. Always from the grounded end to ... on the instantaneous polarity at point 'W'. D. It cannot be determined without a directional ammeter.

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relay is preferred for phase fault on short transmission line. (a) Induction type (b) Reactance (c) Impedance (d) None of the above

Description : relay is preferred for phase fault on short transmission line. (a) Induction type (b) Reactance (c) Impedance (d) None of the above

Last Answer : (b) Reactance

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Description : Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

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Description : Purpose of Local breaker back-up relay; type -CTIG

Last Answer : To safe guard against the drastic consequences of failure to clear faults rapidly, many power supply authorities install 2 independent systems of protection for major transmission lines. There remains however the ... reset, which enables the time delay to be set closer to the breaker trip-time. 

If a relay fails to operate for a fault within its reach, it is said to

Description : If a relay fails to operate for a fault within its reach, it is said to

Last Answer : If a relay fails to operate for a fault within its reach, it is said to Under reach

Which relay is preferred for phase fault on short transmission line?

Last Answer : Reactance relay is preferred for phase fault on short transmission line.

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.

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.

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. 

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?

Description : 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?

Last 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 ... , for a better protection of the system. It should have both over voltage & over current relay.

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

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

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

What is the purpose of anti-pumping relay?

Description : What is the purpose of anti-pumping relay?

Last Answer : When closing signal is continuously existing even after the closing of the breaker the anti-pumping relay will be picked up and it will not allow the breaker to close back in case of tripping of the breaker. 

What is the purpose of the earth fault indication on the switch board?

Description : What is the purpose of the earth fault indication on the switch board?

Last Answer : It detects and indicates phase to earth fault on a circuit.

When earth fault occurs: a) voltage potential at the earth mat increases due to grounding b) voltage potential at the earth mat decreases due to grounding c) voltage potential at the earth mat remains zero irrespective of fault d) none of the above

Description : When earth fault occurs: a) voltage potential at the earth mat increases due to grounding b) voltage potential at the earth mat decreases due to grounding c) voltage potential at the earth mat remains zero irrespective of fault d) none of the above

Last Answer : Ans: A

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. 

The purpose of stacking elements on an antenna. A. Sharper directional pattern B. increased gain C. Improved bandpass D. All of these

Description : The purpose of stacking elements on an antenna. A. Sharper directional pattern B. increased gain C. Improved bandpass D. All of these

Last Answer : D. All of these