SGP

 Important Question For GTU Exam

1	Define following terms in context to protective relay (i) Reliability (ii) Selectivity (iii) Discrimination
2	Discuss time and current grading schemes of over current protection.
3	Discuss the working principle of an induction relay and also derive an expression for the torque produced by it.
4	What problems, if any, do you anticipate in applying conventional differential protection to a transmission line?
5	Select CT ratios and determine the TMS, and Plug setting of the IDMT relays at location O and A, for the over-current protection of radial feeder shown in Fig.1. The characteristic of IDMT relay is given in the Table-2. Minimum fault currents at each point are given Table-1. Maximum load current from each bus are indicated in the
6	Draw logic diagram for implementing 3-step distance protection scheme using impedance relay.
7	Explain the line trap units for carrier-aided protection of transmission line.
8	Explain the behaviour of Merz–Price protection during normal load, external fault and internal fault condition.
9	What are the advantages of carrier current protection scheme?

10	Draw the flow chart for implementing over current protection scheme using numerical relay.
11	With the help of schematic block diagram, explain the realization of transformer protection using numerical protection.
12	Analyze the performance of the CT by drawing its equivalent circuit and vector diagram. Also differentiate between protective CT and measuring CT.
13	Which are the types of SF6 circuit breaker? With neat diagram, explain the working of Puffer type SF6 circuit breaker.
14	Determine the plug setting and % bias setting to permit 25% overload for 50 MVA, 132 kV/66 kV, delta-star transformer. The CT ratios on delta and star side is 300/5 and 1200/5 respectively.
15	Discuss necessity of Back up protection and types of backup protection in brief
16	Explain Slepian’s theory of arc interruption
17	Discuss the difficulties in implementing HVDC circuit breaker.
18	To obtain complete damping of transient oscillations analyze the critical value of shunt resistance. Also draw transient oscillations for different values of R.
19	Define reach, under reach, and over reach of the relay.
20	A 50 Hz, 13.6 kV, 3-phase alternator with grounded neutral has inductance of 12 mH per phase and is connected to busbar through a circuit breaker. The capacitance to earth between the alternator and the location of circuit breaker is 0.03μF per phase. Neglect the resistance of the alternator. calculate the following: i)  Maximum value of restriking voltage across the contacts of circuit breaker. ii)  Frequency of transient oscillations iii)  Maximum value of RRRV
21	What are incipient faults? Discuss in detail the type of protection provided in transformer to cater to such type of faults.
22	Differentiate between longitudinal and transverse differential protection in context to generator protection
23	What causes loss of prime mover? Can a generator be allowed to run with its prime mover lost? If not, why?
24	Explain ratio error and phase angle error in CTs.
25	Why is protection of an induction motor against reversal of phase sequence required?
26	Define following terms (i) Recovery voltage (ii) Re-striking voltage (iii) RRRV. Derive an expression for the restiking voltage in terms of system inductance and capacitance.
27	Explain current chopping in brief.

28	Explain auto reclosing
29	Explain following terms: symmetrical breaking current, asymmetrical breaking current & making current as applied to circuit breaker and show how these currents can be determined from oscillograms taken during short circuit tests on a three phase circuit breaker.
30	Write short note on vacuum circuit breaker
31	List the properties of SF6 gas and its advantages over other arc quenching medium.
32	Explain the physics of arc phenomena. On what factors does the arc phenomenon depends?
33	An air- blast CB designed to interrupt a transformer magnetizing current of 15A (rms) chops the current at an instantaneous value of 12A. The value of L and C in the circuit are 8H and 0.009μF. Find the voltage that appears across the circuit breaker. Assume that the inductive energy is transformed to capacitance.
34	List and explain various protections used for an induction motor.
35	Explain following : harmonic restrain relay, reactance relay, impedance relay, mho relay
36	List the different types of circuit breaker.
37	With neat sketch explain constructional features and working principal of IDMT relay.