Horn Gap Lightning Arrestor

 

 A Horn gap arrester is a protective device used in electrical power systems to safeguard transformers, insulators, and transmission lines from high-voltage surges caused by lightning. It uses an air gap that arcs over during a surge, diverting the excess voltage safely to the ground. 

Construction and Parts

• Horn-Shaped Electrodes: Two metal rods shaped like horns, separated by a small distance. The gap gradually widens as it moves upward.
• Series Resistance: Connected to one side to limit the flow of follow-through current after the surge has discharged.
• Choke Coil: Connected to the line side; it offers low reactance to normal frequencies but high reactance to high-frequency transients, preventing surges from entering the protected equipment.
• Porcelain Insulators: Used to mount the horns safely on the poles. [1, 2, 3]

Working Principle

Under normal operating voltages, the air gap acts as an insulator, preventing current from jumping between the horns. When a high-voltage surge occurs, the voltage breaks down the air insulation, creating an electrical arc. 

Due to the heat generated by the arc and the magnetic effects of the current, the arc travels upward, progressively widening the gap. Once the gap becomes too wide for the voltage to sustain the arc, it extinguishes on its own.

Advantages and Disadvantages

• Advantages: It is inexpensive, simple to design, and the arc can be extinguished automatically without human intervention.
• Disadvantages: The clearing time for the arc can be relatively slow (around a few seconds), which may lead to system disturbances. Additionally, factors like wind or dust can alter the breakdown voltage.