sensitivity Idmin. Any search for an external fault is aborted if trip request counter is greater
than zero.
6. As long as the external fault persists, an additional temporary trip condition is introduced.
This means that REFPDIF (87N) is temporarily desensitized.
7. If point P(Ibias, Idiff) is found to be above the operate-bias characteristic), so that trip
request counter is greater than zero, a directional check can be made. The directional check is
made only if Iresidual (3Io) is more than 3% of the
IBase
current. If the result of the check
means “external fault”, then the internal trip request is reset. If the directional check cannot
be executed, then direction is no longer a condition for a trip.
8. When neutral current, residual current and bias current are within some windows and some
timing criteria are fulfilled, the ratio of 2
nd
to fundamental harmonic is calculated. If it is found
to be above 40%, the trip request counter is reset and TRIP remains zero.
9. Finally, a check is made if the trip request counter is equal to, or higher than 2. If yes, and at
the same instance of time t
REFtrip
, the actual bias current at this instance of time t
REFtrip
is at
least 50% of the highest bias current Ibiasmax (Ibiasmax is the highest recording of any of the
three phase currents measured during the disturbance), then REFPDIF (87N) sets output TRIP
to 1. If the counter is less than 2, the TRIP signal remains zero.
6.4.8 Technical data
IP12661-1 v1
M13062-1 v16.1.1
Table 78: REFPDIF (87N) technical data
Function Range or value Accuracy
Trip characteristic Adaptable ±1.0% of I
n
at I ≤ I
n
±1.0% of I at I > I
n
Reset ratio >95% -
Minimum pickup, IdMin (4.0-100.0)% of IBase ±1.0% of I
n
Directional characteristic Fixed 180 degrees or ±60 to
±90 degrees
±2.0 degrees
Trip time, trip at 0 to 10 x
IdMin
Min. = 15 ms
Max. = 30 ms
-
Reset time, trip at 10 to 0 x
IdMin
Min. = 15 ms
Max. = 30 ms
-
Second harmonic blocking 40.0% of fundamental ±1.0% of I
n
1MRK 502 066-UUS B Section 6
Differential protection
175
Technical manual
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