Areva MiCom P120, Техническое руководство

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P12x/EN AP/A96 Application Guide
Page 60/80
MiCOM P120/P121/P122/P123
All the settings are available in the AUTOMAT.CTRL/CB supervision menu.
SETTING RANGE
MENU TEXT
MIN MAX
STEP SIZE
CB Supervision
CB Open S’vision No Yes
CB Open Time 50 ms 1 000 ms 50 ms
CB Close S’vision No Yes
CB Close Time 50 ms 1 000 ms 50 ms
CB Open Alarm ? No Yes
CB Open NB 0 50 000 1
Σ
Amps (n) ?
No Yes
Σ
Amps (n)
0 4 000 E6 1 E6
n 1 2 1
t Open Pulse 100 ms 5 000 ms 100 ms
t Close Pulse 100 ms 5 000 ms 100 ms
The circuit breaker condition monitoring counters will be updated every time the relay issues
a trip command. In cases where the breaker is tripped by an external protection device it is
also possible to update the CB condition monitoring. This is achieved by allocating one of the
logic inputs or via the communication to accept a trigger from an external device.
24.2 Setting guidelines
24.2.1 Setting the
Σ
I
n
Thresholds
Where overhead lines are prone to frequent faults and are protected by oil circuit breakers
(OCB’s), oil changes account for a large proportion of the life cycle cost of the switchgear.
Generally, oil changes are performed at a fixed interval of circuit breaker fault operations.
However, this may result in premature maintenance where fault currents tend to be low, and
hence oil degradation is slower than expected.
The
Σ
I
n
counter monitors the cumulative severity of the duty placed on the interrupter
allowing a more accurate assessment of the circuit breaker condition to be made.
For OCB’s, the dielectric withstand of the oil generally decreases as a function of
Σ
I
2
t. This
is where ‘I’ is the fault current broken, and ‘t’ is the arcing time within the interrupter tank (not
the interrupting time). As the arcing time cannot be determined accurately, the relay would
normally be set to monitor the sum of the broken current squared, by setting
n = 2.
For other types of circuit breaker, especially those operating on higher voltage systems,
practical evidence suggests that the value of
n = 2 may be inappropriate. In such
applications n ’ may be set to 1.
An alarm in this instance may be indicative of the need for gas/vacuum interrupter HV
pressure testing, for example.
It is imperative that any maintenance programme must be fully compliant with the switchgear
manufacturer’s instructions.