EE 1402 POWER SYSTEM PROTECTION AND SWITCHGEAR Unit II Question Bank

UNIT – II

CIRCUIT BREAKERS

PART – A (2 MARKS)

1. What is an arc?

2. Define restricting voltage.

3. Define recovery voltage.

4. Define current chopping.

5. Mention the different methods of high resistance arc interruption.

6. What is switchgear?

7. What is breaking capacity?

8. What are the functional requirements of a circuit breaker under fault condition?

9. What are the advantages of low oil circuit breaker?

10. What are the types of air blast circuit breaker?

11. What are the advantages of SF6 circuit breaker?

PART - B

1. Discuss the recovery rate theory and energy balance theory of arc interruption in a circuit breaker. (16)

2. Explain terms:

i) Restriking voltage (3)

ii) Recovery voltage (3)

iii) RRRV (3)

iv) Derive expressions for restriking voltage and RRRV. (3)

v) What measures are taken to reduce them? (4)

3. (a) What is resistance switching? (4)

(b) Derive the expression for critical resistance. (12)

4. (a) Explain the phenomenon of current chopping in a circuit breaker. (12)

(b) What measures are taken to reduce it? (4)

5. Discuss the problem associated with the interruption of

(i) Low inductive current (5)

(ii) Capacitive current and (5)

(iii) Fault current if the fault is very near the substation. (6)

6. With neat sketch, describe the working principle of an axial air blast type circuit breaker. (16)

7. (a) Discuss the operating principle of SF6 circuit breaker. (10)

(b) What are its advantages over other types of circuit breakers? (3)

(c) For what voltage range is it recommended? (3)

8. Describe construction, operating principle and application of vaccum circuit breaker. For what voltage range is it recommended? (16)

9. (a) What are the various types of operating mechanisms which are used for opening and closing of the contacts of a circuit breaker? (10)

(b)Discuss their merits and demerits. (6)

10. (a) Enumerate various types of ratings of a circuit breaker. (4)

(b) Discuss symmetrical and asymmetrical breaking capacity, (4)

(c) Making capacity (4)

(d) Short-time current capacity. (4)

11. What are the different methods of testing of circuit breakers? Discuss their merits and demerits. (16)

12. What is the difficulty in the development of HVDC circuit breaker? Describe its construction and operating principle. (16)

13. (a) What are the physical chemical and dielectric properties of SF6 Gas (8)

(b) Define switchgear. What are the essential features of switchgear (8)

14. A 3-phase alternator has the line voltage of 11kV. The generator is connected to a circuit breaker. The inductive reactance upto the circuit breaker is 5Ω/phase. The distributed capacitance upto circuit breaker between phase and neutral is 0.001 μF. Determine peak restriking voltage across the CB, frequency of restriking voltage, average rate of restriking voltage upto peak restriking voltage, maximum RRRV. (16)