Protection and switchgear Prepared by R.Karthi kn

Protection and switchgear

Prepared by R.Karthi kn

1. Identify the inductive elementa)Transistor b)Transformer c)diode d)none of these

2. Identify the protective devicea)CB b)Relay c)both A & B d)none of these

3. Identify the element that subjected to more faults

a )motor b) busbar c)diode d) Transformer

4. In protective apparatus CT is connected toa)CBb)Relayc)PTd)none of these

5. In protective apparatus trip coil in overcurrent relay is connected to

a)CBb)Relayc)PTd)CT

6. In induction disc type which currents will be formed

a) forward currentb) Reverse currentc) eddy currentd) Saturation current

7. Other name of induction disc type relay isa) shaded pole relayd) Permanent magnet relayc) mho relayd)none of these

8. Other name of admittance relay isa) shaded pole relayd) Permanent magnet relayc) mho relayd)Watt hour meter relay

9. In induction cup type relay will be formeda) high torqueb) high currentc) low torqued)low current

10.In relay is mandatorya)High impedanceb)low impedancec)zero impedanced)very high impedance

11. Relay contacts are normally made up of:a) Silver contactsb) Copper contactsc) Aluminium contactsd) Lead contacts

12. Sparking between the contacts can be reduced by inserting:a) A capacitor in parallel with the contactsb) A capacitor in series with the contactsc) A resistor in the lined) A reactor in the line

13. The contact resistance is least affected by:a) Shape of the contact facesb) Ambient temperaturec) Mechanical forces appliedd) Amount of surface commutation

14. The arc voltage produced in an ac circuit breaker is always:a) In phase with the arc currentb) Lagging the arc current by 90 degc) Leading the arc current by 90 degd) In phase opposition with the arc current

15. Breaking capacity of the circuit breaker is usually expressed in:a) MVAb) MWc) Kilo-amperesd) kV

16. Which of the following circuit breakers produce least arc energy:a) Plain oilb) Minimum oilc) Air blastd) Air break

17. A thermal protection switch is used to provide protection against:a) Over loadb) Temperaturec) Short circuitd) Over voltage

18. In a circuit breaker the current which exists at the instant of contact separation is known as

(A) re striking current(B) surge current(C) breaking current(D) recovery current.

19. Sulphur hexafluoride is a(A) Conductor of electricity(B) Semi-conductor(C) Inactive gas(D) Dielectric.

20. As the force on contact is increased, the contact resistance will

(A) increase linearly(B) increase exponentially(C) remain unaltered(D) decrease.

21. The arcing contacts in a circuit breaker are made of

a)copper tungsten alloyb)Silver alloyc)lead d)aluminium

22.On which of the following routine test conducted

a)relayb)CBc)fused)CT

23. In overcurrent relay , plug setting ranges

from 50 % toa)150b)200c)300d)500

24. In overcurrent relay , plug setting range is determined by

a)15 stepsb)35 stepsc)25 stepsd)none of these

25.The main function of a fuse is to(a) protect the line(b) open the circuit(c) protect the appliance(d) prevent excessive current

26.The upper magnet in induction type overcurrent relay is shaped

a)Tb)Uc)Ed)none of these

27.EIDMT meansa) Extra inverse current definite minimum time b) Enormous inverse current definite minimum time c) Extremely inverse current definite minimum time d) Efficient inverse current definite minimum time

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

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

30. 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

31. 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

32. Directional relays are based on flow of(a) power(b) current(c) voltage wave(d) all of the above

33. A differential relay measures the vector difference between(a) two currents(b) two voltages(c) two or more similar electrical quantities(d) none of the above

34. When a transmission line is energized, the wave that propagates on it is(a) current wave only(b) voltage wave only(c) both (a) and (b)(d) power factor wave only

35. The voltage appearing across the contacts after opening of the circuit breaker is called______voltage.(a) recovery(b) surge(c) operating(d) arc(e) none of the above

36. Ionization in circuit breaker is facilitated by(a) high temperature(b) increase of mean free path(c) increasing field strength(d) all of the above

37. In a circuit breaker the basic problem is to

(a) maintain the arc(b) extinguish the arc(c) transmit large power(d) emit the ionizing electrons

38. Shunt capacitance is neglected while considering(a) short transmission line(b) medium transmission line(c) long transmission line(d) medium and long transmission lines

39. The interaction between a transmission line and communication line is minimized by(a) transposing transmission as well as communication lines(b) increasing the height of the trans-mission line tower(c) increasing the distance between the two lines(d) all of the above

40. Which of the following statements is incorrect ?(a) Lightning arrestors are used before the switchgear(b) Shunt reactors are used as compensation reactors(c) The peak short current is (1.8 xV2) times the A.C. component(d) The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance