Thursday, 27 June 2013

SWITCH GEAR AND PROTECTION (utu previous question papers)

SWITCH GEAR AND PROTECTION
SEM-VII, 2012-13
B.TECH EXAMINATION
UTTARAKHAND TECHNICAL UNIVERSITY
(UTU)

Time: 3 Hours
Total Marks: 100
Note: Attempt all the questions.

Attempt any four parts of the followings:
  1. Explain role of protection in a power system. What are the fundamental requirements of protective relaying?
  2. Discuss the role of back up protection. What is the various method of giving back up protection?
  3. Discuss briefly the following:
    (a) Pick up
    (b) Selectivity
    (c) Stability
    (d) Flag indicator
    (e) Burden of relay
  4. What do you mean by PSM and TMS? Explain how these factors are affecting the relay operation?
  5. Explain the working principle of induction type electromagnetic relay.
  6. What is Buchholz relay? Which equipment is protected by it? For what type of fault is it employed? With neat diagram discuss its working principle.
Attempt any four parts of the followings:
  1. What do you understand by amplitude comparator and phase comparator?
  2. Describe the principle of operation of impedance type distance relay and explain its characteristic of V-I and R-X planes.
  3. With a neat diagram explain the principle of static differential relay.
  4. With the help of neat sketches describe the principle of current comparator and voltage comparator used in distance protection.
  5. Explain the integration type phase comparator with rectifier type AND gate.
  6. Explain what is meant by distance protection. What arrangement is made to make the delay measure positive sequence impedance only for L-L and 3φ fault?
Attempt any two parts of the followings:
  1. Illustrate the basic feature of 3-zone stepped distance protection scheme for long transmission line, employing mho characteristic of zone 1 and 2, with an offset mho characteristic for zone 3.
  2. What is Merz-Price voltage protection scheme? How does it prefer feeder? Explain it with a neat diagram.
  3. Discuss the problem of wire-pilot differential relaying. Why is wire-pilot relaying scheme used for short lines? Discuss with necessary diagram the principle of operation of Translay feeder protection scheme.
Attempt any two parts of the followings:
  1. Explain the phenomenon of arc formation and its characteristic. Discuss different theories given for the arc extinction.
  2. In a short-circuit test on a 3 pole, 110 kV, circuit breaker p.f of the fault was 0.4, the recovery voltage was 0.95 times the full line value. The breaking current was asymmetrical. The frequency of oscillation of restriking voltage was 15000 c/s. Estimate the average rate of rise of restriking voltage. The neutral is grounded and fault involves earth.
  3. What are the type test and routine tests? Explain the equipment required and methods of testing for circuit breakers and switchgear.
Attempt any two parts of the followings:
  1. Classify circuit breakers. Explain the basic difference between bulk oil circuit breaker and minimum oil circuit breaker with neat sketch.
  2. The neutral point of a 3φ 20 MVA, 11 kV alternator is earthed through a resistance of 5Ω, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 1000/5. What is the percentage of winging protected? Also calculate the earthing resistance required to protect 90% of the winding.
  3. Write short technical notes on any two of the following:
    (a) Generator - transformer unit protection
    (b) Auto reclosing circuit breaker
    (c) Vacuum circuit breakers.
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