Anna University Chennai 2005-1st Sem B.E Electrical and Electronics Engineering VESTER EE338 - PROTECTION AND SWITCHGEAR - Question Paper

ANNA UNIVERSITY :: CHENNAI – 600 025
MODEL ques. PAPER
VI - SEMESTER
B.E. ELECTRICAL AND ELECTRONICS ENGINEERING
EE338 - PROTECTION AND SWITCHGEAR
Time: 3hrs Max. Marks: 100
ans all ques.
PART – A (10 x two = 20 Marks)
1. Differentiate ranging from a fuse and a protective relay.
2. describe the subsequent terms as related to protective relaying: (a) pick-up
current, (b) reset value and (c) reset ratio.
3. elaborate the various kinds of faults and abnormal conditions expected in an
alternator?
4. elaborate the requirements of line protection?
5. describe (a) arc voltage, (b) restriking voltage, (c) recovery voltage and (d)
breaking capacity of a circuit breaker.
6. What is the importance of arc resistance? On which factor does it depend?
7. A three-phase oil circuit breaker is rated at 1500 A, 1000MVA and 33kV obtain
(a) rated symmetrical breaking current, (b) making capacity.
8. Suggest a suitable option of circuit breakers for the subsequent voltage ranges:
(a) 3.3kV to 33kV, (b) 400kV to 760kV.
9. What is Peterson coil? What protective functions are performed by this
device?
10. Differentiate ranging from a surge diverter and surge absorber.
PART B – (5 x 16 = 80 Marks)
11. With a neat sketch discuss the Merz-Price circulating current scheme for
protection of alternators. (16)
12.a) discuss the principle of a distance relay, stating clearly the difference ranging from
electromagnetic version of an impedance relay and a mho relay. Your ans
should include typical schematics the characteristics of these relays in an R-X
diagram.
(OR)
12.b)i) provide the block diagram of a typical microprocessor based protective relay for
motor protection. (8)
ii) elaborate the typical protective functions that can be built into the relay? (8)
13.a) A star connected, three phase, 10 MVA, 6.6kV alternator has a per phase
reactance of 10%. It is protected by a Merz-Price circulating current protection
which is set to operate for fault currents not less than 175 A. compute the
value of earthing resistance to be given in order to ensure that only 10% of
the alternator winding remains unprotected. (16)
(OR)
13.b)i) discuss current chopping phenomenon. (6)
ii) explain the different methods of arc quenching in circuit breakers. (10)
14.a)i) Derive an expression for restriking voltage and rate of rise of restriking
voltage (RRRV) in terms of system voltage, inductance up to the fault location
and bushing to earth capacitance of the circuit breaker. (8)
ii) For a 132KV system, the reactance up to the fault location and bushing
capacitance are three ohms and 0.015µF respectively. compute the maximum
value of RRRV. (8)
(OR)
14.b) In a 132kV systems, the reactance and capacitance up to the location of the
circuit breaker is 5O and 0.02µF respectively. A resistance of 500 O is
connected across the contacts of the circuit breaker. Determine
(i) natural frequency of oscillations (4)
(ii) frequency of damped oscillations (4)
(iii) critical value of resistance (4)
(iv) the value of resistance which will provide frequency of damped
oscillations which is equal to 1/4th the natural frequency (4)
15.a)i) define the construction and the operation of metal oxide surge arrester?(10)
ii) elaborate its advantages over conventional arrester and its drawbacks? (6)
(OR)
15.b) discuss the following:(i) Earthing screen (8)
(ii) Overhead ground wires (8)
-----

Earning:   Approval pending.