TOP Switchgear Protections Multiple choice Questions and Answers pdf

11.    Relays can be designed to respond to changes in
(a)     resistance, reactance or impedance
(b)     voltage and current
(c)    light intensity
(d)    temperature
(e)    all above
Ans: e

12.    Overload relays are of...... type.
(a) induction 
(b) solid state
(c) thermal 
(d) electromagnetic
(e) all above
Ans: e

13.    Thermal overload relays are used to protect the motor against over current due to
(a) short-circuits 
(b) heavy loads
(c) grounds 
(d) all of the above
Ans: b

14.    Magnetic circuit breaker has ______ trip action.
(a)     delayed 
(b)     instantaneous
(c)    both of the above
(d)    none of the above
Ans: b

15.    D.C. shunt relays are made of
(a)    few turns of thin wire
(b)    few turns of thick wire
(c)    many turns of thin wire
(d)    many turns of thick wire
Ans: c

16.    The relay operating speed depends upon
(a)     the spring tension
(b)     the rate of flux built up
(c)    armature core air gap
(d)    all of the above
Ans: d

17.    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
Ans: d

18.    Circuit breakers usually operate under
(a)     transient state of short-circuit current
(b)     sub-transient state of short-circuit current
(c)    steady state of short-circuit current
(d)    after D.C. component has ceased
Ans: a

19.    Circuit breakers are essentially
(a)     current carrying contacts called electrodes
(b)     arc extinguishers
(c)    circuits to break the system
(d)    transformers to isolate the two systems
(e)    any of the above
Ans: a

 20.  The current zero interruption, in oil and air blast circuit breakers, is achieved by
(a)    lengthening of the gap
(b)    cooling and blast effect
(c)    both (a) and (b)
(d)    deionizing the oil with forced air
(e)     none of the above
Ans: c

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