scheider electric MiCOM P746, Техническое руководство

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Operation P746/EN OP/G31
MiCOM P746 (OP) 5-
7
OP
The check zone is the sum of all the current nodes entering and leaving the substation
(feeders).
Scheme differential current = sum of all differential current feeder nodes:
i
diff
(t) CZ =
⏐Σ
i
diff
⏐
The Check Zone will operate as the Zone element.
1.2.4 Tripping Criteria
A trip signal for a zone will be issued:
1. If the fault is detected in the zone AND
2. confirmed by the check zone AND
3. confirmed by the phase comparison.
For a fault to be detected, 4 trip criterions and 4 (optional) must be met; these criterions are:
For the Zone:
•
If 2 consecutive calculations are above (ID>2) and k × Ibias
•
Confirmation of the phase comparison algorithm
•
Optional Voltage criteria (U< or V1< or V2> or 3V0>)
For the Check Zone:
•
If 2 consecutive calculations are above (IDCZ>2) and kCZ × Ibias
1.2.5 Current Circuit Supervision
During normal operation the differential current in the scheme should be zero or negligible.
Any anomaly is detected via a given threshold
I
D
>1.
A biased differential element is used to supervise the current circuit. A differential current will
result if the secondary circuit of a CT becomes open circuited, short circuited; the amplitude
of this current is proportional to the load current flowing in the circuit monitored by the faulty
current circuit.
The setting is chosen to be as low as possible (minimum suggested setting is 2% of the
biggest CT primary winding) but also allow for standing differential current for example due
to CT mismatch and varying magnetising current losses. 5 to 20% is a typical application
range.
The element is typically time delayed for 5 seconds (set greater than the maximum
clearance time of an external fault). Instead the time delay allows the relevant protection
element (which should be substantially faster) to clear the fault instead i.e.
I
D
>2 in the case
of an internal phase fault.
1.3 Additional protection
1.3.1 Dead Zone protection (DZ)
On a feeder, if the isolators or the breaker is open, a dead zone (or end zone) is said to exist
between the open element and the CT. The P746 can protect this zone with the Dead Zone
protection. This is a simple time delayed overcurrent and earth fault element which is only
active when a dead zone is identified in the local topology.