Power Systems

 Q.1.      What is meant by short-circuit ?

Ans: When conductors of diiferent phase come in contact with each other , alarge amount of current flows in one or more phase.

      Q.2.      What is the difference between a short-circuit and an over load?

Ans: When short circuit occurs the voltage is reduced to zero and a abnormally high magnitude of current flows through the network through to the fault point. On the other hand overload means when the load greated than the designed value have been imposed on the system. In this case the voltage at the overload point becomes low but cannot be zero.

      Q.3.      What are the sources of short-circuit power in power system?

Ans: There are three sources of short-circuit.

1.       Synchronous generators

2.       Synchronous condensers or motors

3.       Induction motors

      Q.4.      What is meant by fault level?

Ans:  When fault occurs at a point in the power system, the corresponding MVA is referred to as the fault level at that  point.

      Q.5.      What are the different types of fault which occur in power system?

Ans:  The most common and dangerous faults that occur in power system are short-circuit or shunt faults such as L-G,L-L,L-L-G,L-L-L  and L-L-L-G faults. Others are series type fault as one conductor open fault and two conductor open fault.

      Q.6.      Which fault do not have zero sequence current?

Ans: L-L or L-L-L-G don’t have zero sequence components.

      Q.7.      Which fault causes a greater electromagnetic interference  between power line and nearby communication line?

Ans: Single phase to ground fault due to heavy unbalancing of line currents, causes a greater electromagnetic interference  between power line and nearby communication line.

      Q.8.      Name the different faults that occur in an over headed transmission line.

Ans: Different faults that occur in an overheaded transmission line are:

1.       Single phase to ground

2.       Phase to phase

3.       Two phases to ground

4.       Phase to phase and third phase to ground

5.       All the three phases shorted  , and

6.       All the three phases to ground

      Q.9.      Which fault occurs more in over head transmission line?

Ans: Single phase to ground(L-G) occurs more frequently in over headed transmission line.

    Q.10.    Name the fault in which all the three sequence currents are present and equal to each other.

Ans: In L-G fault all the three sequence currents are present and are equal to each other.