problem 1)a) With neat sketches, describe the high resistance and low resistance methods of arc interruption.
b) A 50 Hz, 11 kV, 3 alternator with earthed neutral has a per phase reactance of 5 and is connected to a bus bar through a circuit breaker. The distributed capacitance up to the circuit breaker between phase and neutral is 0.01 F. Find out:
(a) peak re-striking voltage across the breaker contacts
(b) frequency of oscillations
(c) average rate of rise of re-striking voltage upto the first peak.
problem 2)a) With a neat sketch, describe the process of current chopping.
b) With a neat sketch, describe peterson coil earthing.
problem 3)a) Briefly describe the following terminologies: (a) fusing current (b) arching time (c) energizing quantity (d) burden (e) under reach.
b) Briefly describe the essential qualities required of a good protection system
problem 4)a) With a neat sketch, describe the working principle of SF6 circuit breaker.
b) With a neat sketch, describe the protection scheme for a ring main system
problem 5)a) With a neat sketch, describe the operation of a Buchholz relay used for transformer protection.
b) With a neat sketch, describe the phase comparison method of carrier current protection used for transmission line protection.
problem 6)a) Briefly describe the various abnormal conditions that may occur during induction motor operation.
b) Prove that duality does exist between amplitude and phase comparators.