Surge arresters are called lighting arresters or lightning diverter in the past, this name was based on their primary function of protecting electrical insulation from lightning strikes on the system. But now surge arrester are also called surge protection device (SPD) or transient voltage surge suppressor (TVSS).
Definitions
Surge arresters are an electrical device, which protect electrical equipment from over-voltage transients or spikes caused by external or internal events like lightning, switching etc.
Surge arresters are voltage limiting devices, which is used to protect electrical insulation from voltage spikes(surges) in the power systems. Surge arresters are protection device, which is used to protect electrical equipment from surges or lightning.
Surge arresters are the equipment which sacrifice themselves to protect other costly equipment like transformers in the system.
Working principles of surge arresters
When a high voltage surge traveling along the conductor and reaches the point at which a surge arrester installed, It diverting the extra voltage into the earth wire, rather than flowing through the electronic devices, while at the same time allowing the normal voltage to continue along its path. As soon as the system voltage drops below to the predetermined value, then insulation between the conductor and the ground is restored and transmission of current flow to the ground stops.
Installation
Surge arresters are installed in parallel to the power systems or on the main service or near to the electric meter. They should be placed as close as possible to the equipment, that is to be protected.
Types of surge arrester
Metal oxide surge aresters (MOSA)
METAL OXIDE SURGE ARESTERS (MOSA) is mostly used in protection of devices. It is a type of surge arrester that comprises of number of solid zinc oxide disc, so that it is also called zinc oxide surge arrester. This discs are arranged one by one to form a cylindrical stack. the number of zinc oxide discs used per surge arrester depends upon the voltage rating of the system this stack is kept inside a cylindrical housing of polymer or porcelain. Then the stack is placed inside the housing and highly pressed by heavy spring load attached to end cap at top. the equipment connection terminal for line is projected from top cap and connection terminal for earth is protected from the bottom cap.
Zinc Oxide (ZnO):
It is an inorganic compound and odourless. It is a white solid powder, which is insoluble in water.it has highly non-uniform current voltage(I-V) Characteristics and this property makes zinc oxide very suitable for designing gap less zinc oxide surge arrester for surge protection.
Working principles of zinc oxide surge arrester
The normal operation is defined as condition when no surge is presented and the surge arrester is subjected to normal system voltage only, for which it is made for.
The nonlinear resistance of the block is an inherent bulk property and consists of mainly zinc oxide with relatively small amount of several additives of the other metal oxide like alumina, antimony try oxide, bismuth try oxide.