Why Arc Horn are used in High Voltage Transmission Line?

Arcing horns are used to protect the transmission conductors, insulators, transformers bushings and other transmission equipments from lightning high voltages, transient voltages and surge voltages. Arc horns are working under the principle of arcing.

Arcing Horn is basically projected conductors used to protect the Insulators in High Voltage Transmission Line from damage during flashover.

Over voltage on Transmission Line may occur due to various reasons like lightning strike, sudden load variation, fault etc. 

Due to this high voltage a flash over may take place which will shatter the Insulator. 

To prevent Insulator from such an occurrence, it is very important that flashover do not take place through the Insulator.

 Arcing Horn serves this purpose by providing a bypass flashover the high voltage across the insulator using air as a conductive medium.

Arc horns are consisting of two small conductors which are placed in transmission lines and Earth point typically two end of the protecting equipments (insulator).

In High voltage transmission system, the insulator provides the physical separation between the conductors with some distances. 

Here the air around the insulator become ionized due to the electrical field caused by high voltages. 

The spark gap between the horn conductors are maintained to avoid the arc Under Normal condition. 

During lightning condition, the voltage in the transmission conductors are increased. Hence this high voltage ionizes further the air surrounding insulator. 

Due to this ionization process, further free electron starts flows in the form of sparks through the air and it forms a flashover. By the way, the high voltages are suppressed.

The presence of the arcing horns necessarily disturbs the normal electric field distribution across the insulator due to their small but significant capacitance. 

More importantly, a flashover across arcing horns produces an earth fault resulting in a circuit outage until the fault is cleared by circuit breaker operation. 

For this reason, non-linear resistors known as varistors can replace arcing horns at critical locations.

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