Areva MiCOM P441, Technical Manual

Page: 272 / 636

P44x/EN AP/E33 Application Notes
Page 98/220 MiCOM P441/P442 & P444
2.21.3 Typical settings
2.21.3.1 Breaker Fail Timer Settings
Typical timer settings to use are as follows:
CB Fail Reset Mechanism tBF time delay Typical delay for 2½ cycle
circuit breaker
Initiating element reset CB interrupting time + element
reset time (max.) + error in tBF
timer + safety margin 50 + 50 + 10 + 50
= 160 ms
CB open CB auxiliary contacts
opening/closing time (max.) +
error in tBF timer + safety
margin 50 + 10 + 50
= 110 ms
Undercurrent elements CB interrupting time +
undercurrent element operating
time (max.) + safety margin 50 + 25 + 50
= 125 ms
Note that all CB Fail resetting involves the operation of the undercurrent elements. Where
element reset or CB open resetting is used the undercurrent time setting should still be used
if this proves to be the worst case.
The examples above consider direct tripping of a 2½ cycle circuit breaker. Note that where
auxiliary tripping relays are used, an additional 10-15 ms must be added to allow for trip
relay operation.
2.21.3.2 Breaker Fail Undercurrent Settings
The phase undercurrent settings (I<) must be set less than load current, to ensure that I<
operation indicates that the circuit breaker pole is open. A typical setting for overhead line or
cable circuits is 20% In, with 5% In common for generator circuit breaker CBF.