10 questions
Q.1. (a) State various types of faults in the system and explain methods of calculating short circuit fault currents under different fault conditions. [8]
(b) What are Current Transformers (CTs)? Describe the ratio and phase angle error in CTs. Also discuss about their reasons and remedies. [8]
Q.1. (a) What are the essential qualities of protection? [8]
(b) Define the terms - (i) Burden (ii) Pickup (iii) Reset (iv) Operating time. [8]
Q.2. (a) What are the HRC fuses? How these are different in construction from ordinary fuses? Also explain the applications of HRC fuses. [8]
(b) What do you understand by time multiplier setting and plug multiplier setting in an over current relay? Explain with the help of relay characteristics. Show why an IDMT characteristic is chosen in preference to simple inverse time characteristic. [8]
Q.2. (a) Explain the construction, principle of operation and working of a thermal relay with a suitable schematic diagram. [8]
(b) Explain the term directional relay. Give the 90 degree method of connecting directional relays. [8]
Q.3. (a) Explain various types of faults that occur in an electrical generator. [8]
(b) Explain generator differential protection scheme for stator protection. [8]
Q.3. (a) Explain loss of excitation protection scheme and unbalanced loading protection. [8]
(b) Explain prime mover protection scheme for a generator with reverse power relay operating characteristics. [8]
Q.4. (a) Describe the principle of Merz Price system of protection applied to a power transformer. What are the shortcomings of this scheme and how they are overcome? [8]
(b) Describe a Buchholz relay and discuss its merits and drawbacks. [8]
Q.4. Explain the effect of inrush magnetizing current on the protective system of transformers. Why does desensitizing of relay not provide satisfactory protection to the transformer? What is the principle of harmonic restraint? [16]
Q.5. (a) Compare among the following relays - (i) Impedance (ii) Reactance (iii) Mho. [8]
(b) What are the types of faults that are likely to occur in a three-phase induction motor? If a motor is not fully loaded, is it necessary to provide protection against single phasing? Explain why. [8]
Q.5. (a) Explain three stepped distance protection of transmission lines. [8]
(b) Explain various faults associated with 3-phase induction motors. How motor is protected against these faults? Write a brief note. [8]