protection and switchgear prepared by r.karthi kn
TRANSCRIPT
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Protection and switchgear
Prepared by R.Karthi kn
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1. Identify the inductive elementa)Transistor b)Transformer c)diode d)none of these
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2. Identify the protective devicea)CB b)Relay c)both A & B d)none of these
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3. Identify the element that subjected to more faults
a )motor b) busbar c)diode d) Transformer
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4. In protective apparatus CT is connected toa)CBb)Relayc)PTd)none of these
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5. In protective apparatus trip coil in overcurrent relay is connected to
a)CBb)Relayc)PTd)CT
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6. In induction disc type which currents will be formed
a) forward currentb) Reverse currentc) eddy currentd) Saturation current
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7. Other name of induction disc type relay isa) shaded pole relayd) Permanent magnet relayc) mho relayd)none of these
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8. Other name of admittance relay isa) shaded pole relayd) Permanent magnet relayc) mho relayd)Watt hour meter relay
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9. In induction cup type relay will be formeda) high torqueb) high currentc) low torqued)low current
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10.In relay is mandatorya)High impedanceb)low impedancec)zero impedanced)very high impedance
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11. Relay contacts are normally made up of:a) Silver contactsb) Copper contactsc) Aluminium contactsd) Lead contacts
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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
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13. The contact resistance is least affected by:a) Shape of the contact facesb) Ambient temperaturec) Mechanical forces appliedd) Amount of surface commutation
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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
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15. Breaking capacity of the circuit breaker is usually expressed in:a) MVAb) MWc) Kilo-amperesd) kV
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16. Which of the following circuit breakers produce least arc energy:a) Plain oilb) Minimum oilc) Air blastd) Air break
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17. A thermal protection switch is used to provide protection against:a) Over loadb) Temperaturec) Short circuitd) Over voltage
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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.
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19. Sulphur hexafluoride is a(A) Conductor of electricity(B) Semi-conductor(C) Inactive gas(D) Dielectric.
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20. As the force on contact is increased, the contact resistance will
(A) increase linearly(B) increase exponentially(C) remain unaltered(D) decrease.
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21. The arcing contacts in a circuit breaker are made of
a)copper tungsten alloyb)Silver alloyc)lead d)aluminium
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22.On which of the following routine test conducted
a)relayb)CBc)fused)CT
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23. In overcurrent relay , plug setting ranges
from 50 % toa)150b)200c)300d)500
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24. In overcurrent relay , plug setting range is determined by
a)15 stepsb)35 stepsc)25 stepsd)none of these
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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
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26.The upper magnet in induction type overcurrent relay is shaped
a)Tb)Uc)Ed)none of these
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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
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28 Overload relays are of…… type.(a) induction(b) solid state(c) thermal(d) electromagnetic(e) all above
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29. Magnetic circuit breaker has ______ trip action.(a) delayed(b) instantaneous(c) both of the above(d) none of the above
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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
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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
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32. Directional relays are based on flow of(a) power(b) current(c) voltage wave(d) all of the above
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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
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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
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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
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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
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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
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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
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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
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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