Effects of Short Circuit Fault Currents on Power System

Effects of Short Cicuit Fault Currents on Power System

 

Short circuit fault current depends on the power circuit voltage and configuration, method of neutral connections (solidly grounded, resistance grounded, reactance grounded and ungrounded), presence of the regulating devices (such as shunt reactor, series reactor, shunt and series capacitors and FACT devices), and the speed of disconnection of the faulted circuit section. Different types of short circuit currents can effect the power system in different manners. It is known that, the flow of short circuit currents incident to the occurrence of inter phase short circuits near the generating units frequently results in substantial disturbance to normal operation of the power system. The short circuit may have the effects on the power system: 

 

Effect of Fault Current on Power System

  • The heavy currents due to the short circuit currents results in the excessive heating of the lines, cables and windings resulting in melting down of the above and even can result in fire or explosion
  • Sometimes the short circuit takes the form of the arc that may cause considerable damage to the elements of the power system. For example an arc on an over-head transmission lines if not cleared quickly will burn the conductors causing it to break resulting in long time interruption of the supply
  • Unsymmetrical short circuit faults (such as line to ground, phase to phase, double phase to ground) introduce unbalance in the symmetrical circuits of the power system
  • Stability of the power system may be adversely affected and can even lead to complete shutdown or cascade tripping of the power system
  • Damage to other apparatus in the power system due to short circuit currents may be caused due to the over-heating and also due to abnormal mechanical stresses or forces set up by the fault
  • A reduction in the voltage in power system due to faults will be sometimes be so large that the relays having pressure coils tends to fail
  • There may be an interruption in the power supply to the consumers when power circuits or generating units are switched out with resultant outage of the connected consumer equipment and in number of cases formidable breakdowns
  • Due to short circuits in the power system, there may be considerable reduction in the voltage on the healthy feeders connected to the system having fault. This may result in drawing of abnormal high currents by the motors or the operation of no load coils of the motors. In the latter case there will be considerable loss in the industrial output due to the outage of the motors and other drives
  • Sometimes in an interconnected systems, when a fault develops it is followed by a fall in voltage and frequency. This may result in loads such as motors which normally takes the power from the supply will start to feed or deliver the power to the fault locations. During the faults, induction motors and synchronous motors feed the fault.

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