Over voltage due to Internal causes.
When there is sudden change in circuit conditions of the power system, oscillation are produced due to the capacitance and inductance of the circuit and there is increase in voltage. this voltage is may be double the system voltage.
There are different Types of internal cause of over voltage.
1. Switching surge
2. Arcing ground
1. Switching surge: When power system us subjected to
“The load or without the load there are some voltage produced due to switching operations this is called switching surge”
Switching on and off the unloaded lines : when switch is on the traveling wave are produced. This wave travels over the line and come back to the supply end without changing the polarity. This may happened for the very short time duration. Same for the switch off, voltage become double before becoming zero.
switching on and off of loaded line: increase in voltage of the line when the loaded line is switched on or off. When switched on, voltage 2 Zo x i is produced in line at time. Where Zo is neutral impedance o the line. And it is given by the square root of ratio of inductance to the capacitance.
current chopping : when the low value of current is interpreted in the circuit breaker, the current become immediately zero before coming to its natural zero condition due to the powerful air blast. Is called current chopping. It can be removed by resistance switching.
Auto reclosing of CB : when we close or open the circuit beaker. The high voltage produced for short time due to the line charge. Also produced due to the interruption of current due to the fault and short circuit, switching on of the magnetizing current.
2. Arcing ground : This happens when there is presence of a sporadic arc in line-to-ground fault belonging to three-phase system. Here, short-live oscillations are produced in the system due to some changes in the voltage and the current load. This phenomenon may lead to serious problems like breakdown of the insulation and may harm equipment connected to the power system.
3.Resonance : This one occurs when the value of the inductive resistance in the power system becomes equal with the value of capacitive resistance. at the Power frequency there is no possibility of producing resonance in the normal condition as the value of Xc and Xl are not equal at the same frequency.
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