Why Happen Over-voltage In Power System?

The Major Causes to Why Over-voltage Develop in  Power Distribution System.

The causes of happening over-voltage in power transmission system may many more reasons. In short we can define as internal causes and external causes to develop over-voltage in electrical power transmission or distribution networks. We can sum up the whole causes of over-voltage in power system in major five cause as below:

1.     Power System Surges:

If absence or poor quality devices like Relay, AVR, Auto-transformer regulator etc. are used in transmission network, the system will function as poor regulation of the power source that may cause voltage fluctuations either over or under. This type of power supply system may cause serious damage to users’ equipment, especially to electronic or computer controlled equipment;

2.     Insulation Failure:

This is the most common reason failure the insulation of conductor and cause grounding or near to grounding of the conductor. Failure takes place when there is no insulation between the line and the earth that allows the current to flow downward or earth;

3.     Arcing Ground:

This happens normally in three-phase system when there is presence of a sporadic arc in line-to-ground fault. In this case short-live oscillations are produced, if this happen continuously or again and again that would be serious problem for system cause of insulation breakdown of the connected equipment;

4.      Resonance: 

Happening resonance is bad effect for the power system. In this case when resonance occurs means when the value of the inductive resistance become equal the value of capacitive resistance, system voltage increases absurdly;

5.      External Causes:

In above mentioned causes are mainly happen internally in the system. There are many causes that may happen externally to the system and may inject over-voltage into the system. Lightning is one good example who is responsible for high magnitude of surges, leading to very serious high voltage injection to system.

What Is Internal Causes for Over-voltages?


Demonstration of Over-voltage developing in the steady system system:

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There are many internal causes for over-voltage in power distribution network, we will focus only some main causes for over-voltage that will help to over-voltage detection and selection of over-voltage protection devices like over-voltage relay, over-voltage AVS, over-voltage detection circuit specification, etc. and finally help to protect the system from over-voltage damages or over-current damages.

The definition of over-voltage may define as “the excess potential required for the discharge of an ion at an electrode over and above the equilibrium potential of the electrode”; in short- voltage in excess of the normal operating voltage of a device or system in known as over-voltage.

The major internal causes for developing over-voltage is as-
a.      Switching Operations on Unloaded Line;
b.      Sudden Opening of Loaded Line;
c.      Insulation Failure;
d.      Arcing Grounds;
e.      Resonance, etc.

Internal over-voltages actually two major groups first- for switching over voltages or Transient over operation voltages of high frequency and second temporary over-voltages.

Switching over-voltages is caused when switching operation is carried over the network system, Ferranti Effect the receiving end voltage is increased when an unloaded long line is charged or stitch ON, similarly over voltage of transient nature occurs when the primary side of the transformers or reactors is switched ON.

Temporary over-voltages may occurred due to disconnect a major load from the long line under normal or steady state condition.

What Is External Causes for Over-voltages?


The external causes of over-voltage may occur due to various reasons from atmospheric disturbances, it originates mainly due to lightning that takes the form of a surge and has no direct relationship with the operating voltage of the system network. The major cause of external over-voltage developing in system is as-
a.      Direct lightning stroke;
b.      Indirect lightning strokes;
c.      Electromagnetically induced over voltages due to lightning discharge taking place near the line, called 'side stroke';
d.      Voltages induced due to atmospheric changes along the length of the line;
e.      Electrostatically induced voltages due to presence of charged clouds nearby; &
f.       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.


What Happen Due to Over-voltage in Power Distribution Network?

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All line equipment and appliances desire the stable power supply to function properly in its long span of life. Over voltage be disposed to stress the insulation of the electrical equipment’s and possible to cause of damage to them when it frequently over-voltage hits them. Especially for electronic circuits, over-voltage is very harmful for them.

In line equipment, over voltage may cause in spark over and flash over between phase and ground at the weakest point in the distribution network and result is damages property if not the over-voltage protection devices function.
If you have more information about over-voltage, over-voltage protection and over-voltage devices, share in comments.

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