IDMTL relay tripping of main incoming circuit breakers

Overcurrent and earth fault protection by means of inverse definite minimum time lag (IDMTL) relay tripping has been a standard solution for many years. In this case study the author examines the application of IDMTL relays for the tripping of LV main incoming circuit breakers as applied to installations in Hong Kong. The requirements imposed by the local supply companies and the consequent difficulties in achieving discrimination between the MICB protection and that on outgoing circuits are discussed.<
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