Effects of Short Circuit Faults on Power System:

Depending upon power circuit voltage and configuration, method of neutral connection, presence of regulating devices and the speed of disconnection of the faulted circuit section, various types of short circuits may differently influence the power system as a whole. It is well known that the flow of heavy short-circuit currents incident to the occurrence of interphase short circuits near the generating units frequently results in substantial disturbance to normal operation of power system. The effects of short circuit faults on power system may have any of the following consequences:

1. The heavy currents due to short circuit cause excessive heating which may result in fire or explosion.

2. Sometimes the short circuit takes the form of an arc that may cause considerable damage to the elements of the power system. For example, an arc on an overhead power line, if not cleared quickly, will burn the conductor severely causing it to break, resulting in a long time interruption of the supply.

3. Unsymmetrical short-circuit faults (such as line to ground, phase to phase, double phase to ground) introduce unbalance in otherwise symmetrical circuits. As a result of asymmetry the currents of the network will be unbalanced though generated emfs are balanced. Since the voltages at the various points of the network are obtained by subtracting from the emf the corresponding voltage drops and these in turn depend on the current it follows that the voltages (phase and line) throughout the system will be unbalanced.

4. Stability of the power system may he adversely affected and even the complete shutdown of the power system may occur.

5. Damage to other apparatus in the system may be caused due to overheating and due to abnormal mechanical forces set up.

6. A marked reduction in the voltage which may sometimes be so large that relays having pressure coils tend to fail.

7. There may be an interruption in power supply to consumers when power circuits or generating units are switched out with resultant outage of connected consumer equipment and in a number of cases formidable breakdowns.

8. There may be a considerable reduction in voltage on healthy feeders connected to the system having fault. This may cause either an abnormally high current being drawn by the motors or the operation of no-voltage coils of motors. In the latter case considerable loss of industrial production may result as the motors will have to be restarted.

9. Sometimes in an interconnected system, when a fault develops, it is accompanied by a fall in voltage or frequency, with the result that other loads such as motors, which normally take power from the supply, starts feeding the faults and from the fault point of view, they may be termed as sources of power.

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