33
5.1.4.5. Phase discontinuity protection
The phase discontinuity protection detects phase unbalance between phases I
L1
,I
L2
and I
L3
, caused by a broken conductor, for instance. The difference between the
minimum and maximum phase currents is calculated as follows:
Δ=
−
()
×I
II
ax
max min
m
I
%100
(3)
When the current difference exceeds the set start value of the phase discontinuity
stage, ΔI>, the stage will generate a start signal after a ~100 ms’ start time. When the
set operate time at definite-time characteristic elapses, the stage will generate a trip
signal. The stage will be reset in 70 ms after the current difference has fallen below
the set start value of the stage.
The phase discontinuity protection will be inhibited when all phase currents fall
below 0.1 x I
n
.
It is possible to block the tripping of the phase discontinuity stage by applying a
digital input signal to the relay.
Stage ΔI> can be set out of operation in SGF3. This state will be indicated by dashes
on the LCD and by “999” when the set start value is read via serial communication.
5.1.4.6. Circuit-breaker failure protection
The circuit-breaker failure protection (CBFP) detects situations where the trip
remains active although the circuit breaker should have operated.
If a trip signal generated via output PO1 is still active and the current has not been
cut off on expiration of the CBFP set operate time, the CBFP generates a trip signal
via output PO2.
The CBFP is not triggered in case of:
*
Thermal alarm
*
Thermal trip
*
External trip
The CBFP can also be selected to be triggered externally by applying a digital input
signal to the relay. In this case, the CBFP generates a trip signal via output PO2 if
the current has not been cut off on expiration of the set operate time.
External triggering is inhibited when all phase currents fall below 12 percent of the
rated current, I
n
.
Internal triggering is selected by activating the CBFP in SGF and external triggering
by activating the CBFP in SGB. Both triggering options can be selected at the same
time.
Feeder Protection Relay
Technical Reference Manual
REF 610REF 610
1MRS755310
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