Areva MiCOM P441, Technical Manual

Page: 266 / 636

P44x/EN AP/E33 Application Notes
Page 92/220 MiCOM P441/P442 & P444
2.20.1 Setting Guidelines
The inclusion of the two stages and their respective operating characteristics allows for a
number of possible applications;
•
Use of the IDMT characteristic gives the option of a longer time delay if the
overvoltage condition is only slight but results in a fast trip for a severe overvoltage. As
the voltage settings for both of the stages are independent, the second stage could
then be set lower than the first to provide a time delayed alarm stage if required.
•
Alternatively, if preferred, both stages could be set to definite time and configured to
provide the required alarm and trip stages.
•
If only one stage of overvoltage protection is required, or if the element is required to
provide an alarm only, the remaining stage may be disabled within the relay menu.
This type of protection must be co-ordinated with any other overvoltage relays at other
locations on the system. This should be carried out in a similar manner to that used for
grading current operated devices.
2.21 Circuit breaker fail protection (CBF)
Following inception of a fault one or more main protection devices will operate and issue a
trip output to the circuit breaker(s) associated with the faulted circuit. Operation of the circuit
breaker is essential to isolate the fault, and prevent damage / further damage to the power
system. For transmission/sub-transmission systems, slow fault clearance can also threaten
system stability. It is therefore common practice to install circuit breaker failure protection,
which monitors that the circuit breaker has opened within a reasonable time. If the fault
current has not been interrupted following a set time delay from circuit breaker trip initiation,
breaker failure protection (CBF) will operate.
CBF operation can be used to backtrip upstream circuit breakers to ensure that the fault is
isolated correctly. CBF operation can also reset all start output contacts, ensuring that any
blocks asserted on upstream protection are removed.
2.21.1 Breaker Failure Protection Configurations
The phase selection must be performed by creating dedicated PSL.
The circuit breaker failure protection incorporates two timers, ‘CB Fail 1 Timer’ and ‘CB Fail 2
Timer’, allowing configuration for the following scenarios: