Series connected circuit breaker discrimination - prevents complete tripping of all series connected switches on supply side of switch closest to fault

摘要

For a fault (K2) at the load (L1), the nearest switch (S3) contacts part in response to the instantaneous overcurrent release. After a set time a blocking signal is sent to the series connected switches (S2,S1) to prevent the main trips from operating. The closest switch (S3) continues its fault clearing action and the main trip operates. When the contacts are fully open the blocking signal is cancelled. There is a brief time delay between the onset of blocking and the main trip operation to prevent complete opening due to transient faults. The contacts of the series connected switches begin to open due to the high speed release action. The main trip action is however blocked, and on cancellation of the block, and clearing of the fault current by the close up switch (S3), their contacts again close.