Areva MiCOM P441, Technical Manual

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P44x/EN AP/E33 Application Notes
Page 160/220 MiCOM P441/P442 & P444
Certain circuit breakers, such as oil circuit breakers (OCB’s) can only perform a certain
number of fault interruptions before requiring maintenance attention. This is because each
fault interruption causes carbonising of the oil, degrading its dielectric properties. The
maintenance alarm threshold (N° CB Ops Maint) may be set to indicate the requirement for
oil sampling for dielectric testing, or for more comprehensive maintenance. Again, the
lockout threshold (N° CB Ops Lock) may be set to disable autoreclosure when repeated
further fault interruptions could not be guaranteed. This minimises the risk of oil fires or
explosion.
4.7.4 Setting the Operating Time Thresholds
Slow CB operation is also indicative of the need for mechanism maintenance. Therefore,
alarm and lockout thresholds (CB Time Maint / CB Time Lockout) are provided and are
settable in the range of 5 to 500ms. This time is set in relation to the specified interrupting
time of the circuit breaker.
4.7.5 Setting the Excessive Fault Frequency Thresholds
A circuit breaker may be rated to break fault current a set number of times before
maintenance is required. However, successive circuit breaker operations in a short period of
time may result in the need for increased maintenance. For this reason it is possible to set a
frequent operations counter on the relay which allows the number of operations (Fault Freq
Count) over a set time period (Fault Freq Time) to be monitored. A separate alarm and
lockout threshold can be set.
4.7.6 Inputs/Outputs for CB Monitoring logic
4.7.6.1 Inputs
Reset Lock Out
Provides a reset of the CB monitoring lock out (all counters & values are reset)
Reset All Values
Provides a reset of the CB monitoring (all counters & values are reset)
4.7.6.2 Outputs
I^Maint Alarm
An alarm maintenance is issued when the maximum broken current (1
st
level) calculated by
the CB monitoring function is reached
I^Lock Out Alarm
An alarm Lock Out is issued when the maximum broken current (2nd level) calculated by the
monitoring function is reached
CB Ops Maint
An alarm is issued when the maximum of CB operations is reached [initiated by internal (any
protection function) or external trip (via opto)] (1st level:CB Ops Maint)
CB Ops Lockout
An alarm is issued when the maximum of CB operations is reached [initiated by internal or
external trip] (2nd level:CB Ops Lock)
CB Op Time Maint
An alarm is issued when the operating tripping time on any phase pass over the CB Time
Maint adjusted in MiCOM S1 (slowest pole detection calculated by I< from CB Fail logic)
CB Op Time Lock
An alarm is issued when the operating tripping time on any phase pass over the CB Time
Lockout adjusted in MiCOM S1 (slowest pole detection calculated by I< from CB Fail logic)