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:
- Explain role of protection in a power system. What are
the fundamental requirements of protective relaying?
- Discuss the role of back up protection. What is the
various method of giving back up protection?
- Discuss briefly the following:
(a) Pick up
(b) Selectivity
(c) Stability
(d) Flag indicator
(e) Burden of relay - What do you mean by PSM and TMS? Explain how these
factors are affecting the relay operation?
- Explain the working principle of induction type
electromagnetic relay.
- 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:
- What do you understand by amplitude comparator and
phase comparator?
- Describe the principle of operation of impedance type
distance relay and explain its characteristic of V-I and R-X planes.
- With a neat diagram explain the principle of static
differential relay.
- With the help of neat sketches describe the principle of
current comparator and voltage comparator used in distance protection.
- Explain the integration type phase comparator with
rectifier type AND gate.
- 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:
- 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.
- What is Merz-Price voltage protection scheme? How does
it prefer feeder? Explain it with a neat diagram.
- 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:
- Explain the phenomenon of arc formation and its
characteristic. Discuss different theories given for the arc extinction.
- 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.
- 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:
- Classify circuit breakers. Explain the basic difference
between bulk oil circuit breaker and minimum oil circuit breaker with neat
sketch.
- 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.
- 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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