Arc fault protection is a relatively new technique employed for the fast clearance of arcing faults on BUS bars and within metal clad switchgear and associated cable boxes. The arc is detected using an optical sensor and the signal input to a protection device which also monitors the load current on the system. A trip signal can be achieved in less than 1ms using arc detection only or within 15ms when using overcurrent check. This is considerably faster than a traditional IDMT overcurrent relay and provides additional protection from the onset of arcing faults with relatively low fault currents.
Arguably the greatest risk of arc fault damage exists at the CB cable termination and in the CB chamber itself due to the slow clearance times of the IDMT feeder protection. The CB cable termination is particularly at risk to ingress of moisture and rodent damage.
The problem of arc faults is most prevalent in older metal clad switchgear which already has operational protection systems.
The Arc Fault Interface Module (ARC Module), described in this document is designed to connect one or two optical arc fault sensors to a protection relay status input.
Refer to the 1S30 Technical Bulletin for details on the arc fault sensor.