Patent ID: 7102866

Claim:
In an electrical power line system of the type comprising radially connected power line sections, wherein a first electrically upstream one of the line sections is connectable to a power source, a protection system comprising: at least one relay installed proximate at least the upstream end of each line section to protect that line section, each relay having an associated circuit breaker, the relays being provided with a first set of accelerated overcurrent functions and a second set of under-current/under-voltage functions, the relays being directional and the first and second sets of functions being time graded in reverse to each other, the first and second sets of functions being distributed amongst the relays such that if an under-current/under-voltage function in a second relay located downstream of a first relay triggers operation of a circuit breaker associated with the second relay, an accelerated overcurrent function in the first relay triggers accelerated operation of a circuit breaker associated with the first relay, thereby to isolate from the power source the line section that the first relay protects.