Power System Protection (EX-701) - Important Questions

Explain the process and significance of using symmetrical components to simplify fault analysis in power systems, especially unsymmetrical faults.

Explain the different types of faults in a power system, their causes and effects on system stability.

Derive an expression for the fault current of a double line to ground fault.

Determine the time of operation of an IDMT over-current relay given plug setting, time multiplier setting, CT ratio and fault current using the relay characteristic curve.

Explain the operating principle of impedance / distance / directional relays and show their characteristics on the R-X plane.

Explain the construction, principle of operation and applications of induction disc type and induction cup type relays, including reset to pick-up ratio.

Explain the meaning of PILOT in power line protection and how power line carrier protection is implemented.

Explain busbar protection schemes, including differential protection and frame-leakage protection, and their importance.

Determine the required CT ratio on the high-voltage side for Merz-Price differential protection of a star-delta three-phase transformer given the CT ratio on the low-voltage side.

List and explain the different types of protection schemes for alternators.

Explain the types of air blast circuit breakers, their operating principles and areas of application, including which type is less affected by current chopping.

Explain the rating of circuit breakers and the factors/criteria considered in their selection.

Explain the construction, operating principle, ratings and applications of SF6 and vacuum circuit breakers. Compare their selection criteria.

Explain comparators and level detectors and their functions in electronic / static relays.

Write short notes on any two of the following: (i) Microprocessor-based protection schemes (ii) HRC fuses and their applications (iii) Security and reliability in protection (iv) Theory of current interruption.