The class of surge arrester to be applied on a system depends upon the importance and value of the protected equipment, the impulse insulation level, and the expected discharge currents the arrester must withstand.
Station class arresters are designed for protection of equipment that may be exposed to significant energy due to line switching surges and at locations where significant fault current is available. They have superior electrical performance because their energy absorption capabilities are greater. Station class arresters are the top choice for protecting valuable equipment where high reliability operation is required.
Intermediate class arresters are designed to provide economic and reliable protection of medium voltage class electrical power equipment. Intermediate arresters are commonly used for the protection of dry-type transformers, for use in switching and sectionalizing equipment and for the protection of URD cables.
Distribution class arresters can be found on smaller liquid-filled and dry-type transformers 1000 kVA and less. These arresters can also be used for application at the terminals of rotating machines below 1000 kVA, if available in the proper voltage rating. The distribution arrester is often used out on exposed lines that are directly connected to rotating machines.
Secondary class arresters are utilized for voltages 999V or less. These are applied in low-voltage distribution systems, electrical appliances, and low-voltage distribution transformer windings.