Causes of Over voltage in Power System


Causes of Over voltage in Power System

Increase in voltage for the very short time in power system is called as the over voltage. it is also known as the voltage surge or voltage transients. The voltage stress caused by over voltage can damage the lines and equipment’s connected to the system, There are two types of causes of over voltage in power system.
1. Over voltage due to external causes
2. Over voltage due to internal causes

Transient over voltages can be generated at high frequency (load switching and lightning), medium frequency (capacitor energizing), or low frequency.

over voltage
Example of over voltage
  • Over voltage due to external causes:

This cause of over voltage in power system is the lightning strokes in the cloud.
Now, how lightning strokes are produced. So when electric charges get accumulated in clouds due to thunder Strom caused due to some bad atmosphere process.

This type of over voltages originates from atmospheric disturbances, mainly due to lightning. This takes the form of a surge and has no direct relationship with the operating voltage of the line.

It may be due to any of the following causes:

A) Direct lightning stroke
B) Electromagnetically induced over voltages due to lightning discharge taking place near the line, called ‘side stroke’.
C) Voltages induced due to atmospheric changes along the length of the line.
D) Electrostatically induced voltages due to presence of charged clouds nearby.
E) Electrostatically induced over voltages due to the frictional effects of small particles like dust or dry snow in the atmosphere or due to change in the altitude of the line.

The potential between the clouds and earth breaks down and lightning flash takes place between the cloud and ground when this voltage becomes 5 to 20 million volts or when the potential gradient becomes 5000V to 10000V per cm.

There are two types of lightning strokes.
1. Direct lightning strokes
2. Indirect lightning strokes


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