How to choose surge arrester to protect electrical equipment
Surge arrester is a vital protective precaution in power system. Its sole purpose is to protect the delicate electrical equipment like generator, transformer and equipments in substation. A direct fault is likely to happen rarely but any indirect fault in out side transmission line which create traveling wave will cause severe harm to the indoor or out door equipments.
So special care should be take in to consideration to choose a surge arrester as per protection level and costing. After all surge arrester protects the equipments which are considered to be the heart of electrical system.
Things to consider to choose surge arrester
01. MCOV value in kV
MCOV – Maximum Continuous Operating Voltage (MCOV) provided by the manufacturer. The surge arrester’s MCOV must be greater than (or equal to) the service voltage of the network in consideration.
The choice of a surge arrester should take into consideration the voltage between the conductors and the earth (phase to neutral voltage) whereas in general the service voltage of the network is given in phase to phase voltage.
02. Voltage & Current – supplied level of protection
The effectiveness of surge arrester protection is measured by the residual voltage, at the surge arrester terminals, while a given current is flowing through it. Typically, the level of protection is defined by a pair of values (for example 80 kV/10 kA).This voltage value must be in range of withstand value of the equipment.
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The margin must be at least 20% and should take the surge arrester’s installation mode and cabling into account. Ineffective cabling can lead to voltages in the equipment’s terminals that are considerably higher than the surge arrester’s residual voltage, due to voltage drops in stray impedencies.
03. Thermal withstand
It aims at guaranteeing the non-destruction of the surge arrester in the case of a long impulse (greater than the normalised test impulse). This performance is given by a current impulse withstand.