Rod Gap Lightning Arrester

Lightning arrestor is connected between the line and earth. It is a protective device which conducts the high voltage surges (due to both direct and indirect stroke) on the power system to the ground and protects the equipments connected to it.Rod gap is the simplest form of Lightning arrester used for the protection of electrical apparatus.

Construction: It consists of two 1·5 cm rods, which are bent at right angles with a gap in between. One rod is connected to the line and the other rod is connected to earth. The distance between gap and insulator (P) must be greater than one-third of the gap length so that the arc may not reach the insulator and damage it. The gap length is so adjusted that breakdown of air should occur at 80% of spark- over voltage in order to avoid cascading of very steep wave fronts across the insulators.The string of insulators for an over head line or the bushing of transformer has rod gap across it.

Figure shows the rod gap across the bushing of a transformer.

Working: Under normal operating conditions, the gap does not conducting. When a high voltage surge occur on the line, the air breaks and the surge current is conducted to earth. In this way, excess charge on the line due to the surge is conducted to earth without causing  any damage to the insulator and equipments.

Limitations:

• After surge over, arc in the gap maintained by the normal supply votage leading short circuit effect.
• Due to change in climate, affect the performance of this arrester.
• When excessive heat produced, it will damage the rods or melted.