Subject 2018 Question Paper — Government College of Engineering and T…

The 2018 Subject previous year question paper (Government College of Engineering and Technology, Jammu), with every question and its marks.

Instructions

Attempt five questions in all selecting at least two questions from each Section.
Assume missing data if any.
All questions carry equal marks.

selecting at least two questions from each Section

Q1. (a) Show that a travelling wave moves with a velocity of light on the overhead line and its speed is proportional to $1/\sqrt{E_r}$ on a cable with dielectric material of permittivity $E_r$. (b) Explain reflection and refraction at a T-junction. [20 marks]
Q2. (a) Determine the time of operation of a IA, 3 s over-current relay having plug setting of 125 per cent and a time multiplier of 0.6. The supplying CT is rated 400 : 1 A and fault currently is 4,000 A. The relay characteristic curve is given below: | PSM | 1.3 | 2 | 4 | 8 | 10 | 20 | |---|---|---|---|---|---|---| | Time of operation ( in second) | 30 | 10 | 5 | 3.3 | 3 | 2.2 | (b) Explain rotor fault protection against loss of excitation and rotor earth fault. [20 marks]
Q3. Describe a directional over-current relay. Explain where and why would you prefer directional current relay. What do you understand by $30^0$ connection and $90^0$ connection. Explain with diagram. [20 marks]
Q4. (a) A 6,600 volt 3-phase turbo-alternator has a maximum continuous rating of 2,000 kw at 0.8 p.f. and its reactance is 12.5%. It is equipped with Merz Price circulating current protection which is set to operate at fault currents, not less than 200 amperes. Find what value of the neutral earthing resistance leaves 10% of the windings unprotected. (b) Explain the parallel feeder and ring mains protection of feeders. [20 marks]

selecting at least two questions from each Section

Q5. (a) Explain the current zero interruption theories. (b) Explain the interruption of low inductive current chopping. [20 marks]
Q6. (a) An 11 KV, 500 MVA circuit breaker suddenly closes on to a fault. Determine (i) the symmetrical breaking current (ii) the asymmetrical breaking current assuming 50% dc component (iii) the peak making current (iv) the short-time current rating. (b) Explain the construction of $\text{SF}_6$ breaker with diagram. [20 marks]
Q7. (a) What are the different types of testing of circuit breakers? (b) Explain the protection of Power Stations and sub-stations against Direct Strokes. [20 marks]
Q8. Write short notes on the following: (a) Surge diverter (b) Effectively grounded (c) Surge Absorber. [20 marks]