Metal Oxide Lightning Arrester:

Metal oxide lightning arrester belongs to the new generation of station metal oxide surge arresters developed by General Electric Co. in 1976. This is useful for the protection of systems rated 2.4 to 400 kV against overvoltages. Such an arrester consists of a stack of Zenox^TM disks mounted in a sealed porcelain housing. Each disk is wedged in place with silicone rubber which offers heat transfer and protection against physical damage. On the end faces of each disk, a conducting surface is applied to assure proper contact and uniform current distribution.

Zenox valve elements are made of a specially formulated compound of zinc oxide and small amounts of other selected metal oxides. The ingredients arc mixed in powdered form pressed to form a disk, and fired at high temperature resetting in a dense polycrystalline ceramic. Under electric stress, the inter granular layers conduct resulting in highly nonlinear characteristics. The degree of non-linearity is much more than that in the thyrite arrester.

The Metal oxide lightning arrester is designed in accordance with the metal oxide standard IEEEC 62.11 and IEC TC-37. A change in the arrester current of 0.1 A to 10⁴ A results in a voltage change of 54%. Under normal operating conditions, the current conducted does not exceed 1 mA. When the surge reaches the arrester, it conducts only current necessary to restrict the voltages.

Advantages:

Such an arrester is simple in construction and has superior energy absorption capability, better surge protection, more stable protective characteristics and substantial reduction in overvoltage across the equipment as compared to thyrite arrester.