Medium Voltage Application Guide

13681.A
SWITCHGEAR
Medium Voltage Contactors
Contactors are a 3-pole load break switch with minimal short circuit making and breaking current
capacity. Back-up short circuit protection fuses must be used; the contactor manufacturer will
specify the maximum allowable fuse size. The switching contacts are sealed inside the vacuum
interrupters and mechanical operation uses the magnetic technique.
Medium voltage contactors are suitable for high frequency switching (>10,000 operations), with continuous AC3
current ratings greater than 800 A and rated voltages from 1 kV to 12 kV. Manufacturers provide standard
utilisation category ratings which can be matched to a specific application and the required number of operations.
Indoor contactors can be fixed or withdrawable style. Withdrawable style contactors can usually house primary
protection fuses.
Withdrawable style contactor
Fixed style contactor
Construction
Medium voltage contactors usually consist of:
flame retardant plastics to house the vacuum interrupters (and fuses, in the case of a withdrawable
contactor)
metal chassis (and truck, in the case of a withdrawable contactor)
busbars for main power circuit connections (or cluster style power connections, in the case of a
withdrawable contactor)
magnetic and mechanical linkage components, for operation of the vacuum interrupter contacts
auxiliary circuit components such as auxiliary contacts, truck position contacts, undervoltage or shunt trip
coils, interlock coil etc
Page 96 Medium Voltage Application Guide 710-12280-00A