Protection and switchgear Prepared by R.Karthi kn

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

2. Identify the protective device a)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 to a)CB b)Relay c)PT d)none of these

5. In protective apparatus trip coil in overcurrent relay is connected to a)CB b)Relay c)PT d)CT

6. In induction disc type which currents will be formed a) forward current b) Reverse current c) eddy current d) Saturation current  

7. Other name of induction disc type relay is a) shaded pole relay d) Permanent magnet relay c) mho relay d)none of these  

8. Other name of admittance relay is a) shaded pole relay d) Permanent magnet relay c) mho relay d)Watt hour meter relay  

  9. In induction cup type relay will be formed a) high torque b) high current c) low torque d)low current

10.In relay is mandatory a)High impedance b)low impedance c)zero impedance d)very high impedance

11. Relay contacts are normally made up of: a) Silver contacts b) Copper contacts c) Aluminium contacts d) Lead contacts

12. Sparking between the contacts can be reduced by inserting: a) A capacitor in parallel with the contacts b) A capacitor in series with the contacts c) A resistor in the line d) A reactor in the line

13. The contact resistance is least affected by: a) Shape of the contact faces b) Ambient temperature c) Mechanical forces applied d) Amount of surface commutation

14.  The arc voltage produced in an ac circuit breaker is always: a) In phase with the arc current b) Lagging the arc current by 90 deg c) Leading the arc current by 90 deg d) In phase opposition with the arc current

15. Breaking capacity of the circuit breaker is usually expressed in: a) MVA b) MW c) Kilo-amperes d) kV

16. Which of the following circuit breakers produce least arc energy: a) Plain oil b) Minimum oil c) Air blast d) Air break

17.  A thermal protection switch is used to provide protection against: a) Over load b) Temperature c) Short circuit d) 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 alloy b)Silver alloy c)lead d)aluminium  

22.On which of the following routine test conducted a)relay b)CB c)fuse d)CT

  23. In overcurrent relay , plug setting ranges from 50 % to a)150 b)200 c)300 d)500

24. In overcurrent relay , plug setting range is determined by a)15 steps b)35 steps c)25 steps d)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)T b)U c)E d)none of these

27.EIDMT means a) 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 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 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 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