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Protection
functions
Phase overcurrent
protection
Earth-fault protection
Contact outputs of
the protection
8
The overcurrent unit of the combined overcur-
rent and earth-fault relay module SPCJ 4D29
has two operation stages, a low-set stage I> and
a high-set stage I>>. The overcurrent unit meas-
ures the three phase currents of the protected
system. The unit can also be used for two or
single phase measurement.
When a phase current exceeds the set start value
of the low-set overcurrent stage, the overcurrent
stage starts, simultaneously starting the corre-
sponding timing circuit. When the set or calcu-
lated operate time has elapsed, a trip command
is delivered. Correspondingly the high-set over-
current stage starts when its start value is ex-
ceeded. As the high-set stage starts it starts its
timing circuit and trips when the set operate
time has elapsed.
The low-set stage of the overcurrent unit can be
given definite time characteristic or inverse defi-
The combined overcurrent and earth-fault relay
module SPCJ 4D29 also includes a non-direc-
tional two-stage earth-fault protection unit. The
earth-fault unit measures the residual current or
neutral current of the protected system.
When the residual current exceeds the set start
value of the low-set earth-fault stage, the earth-
fault stage starts, simultaneously starting the
corresponding timing circuit. When the set or
calculated operate time has elapsed, a trip com-
mand is delivered. Correspondingly the high-
set earth-fault stage starts when its start value is
exceeded. As the high-set stage starts it stars its
The tripping signal of the feeder terminal is
wired to the OPEN output. Double-pole or
single-pole circuit breaker control can be used
for opening and closing of the circuit breaker.
Single-pole circuit breaker control is used as
standard. If double-pole circuit breaker control
is to be used the interconnections of terminals
96-97 of the OPEN circuit and terminals 98-99
of the CLOSE circuit shoud be removed, see
nite minimum time (IDMT) characteristic. The
high-set stage of the overcurrent unit can be set
to operate instantaneously or it can be given
definite time characteristic.
By appropriate configuration of the output relay
matrix the start signals can be obtained as con-
tact functions. The start signals can be used, for
instance, as blocking signals for cooperating
protection relays.
The combined overcurrent and earth-fault relay
module contains one external control input,
which is activated by an external control voltage
applied to the input CHANNEL 8. The influ-
ence of the external blocking signal on the relay
module is determined by the selector switches of
the relay module. The control input can be used
for blocking one or more of the protection stages
or for carrying out a trip command by means of
an external control signal.
timing circuit and trips when the set operate
time has elapsed.
The low-set stage of the earth-fault unit may be
given definite time characteristic or inverse defi-
nite minimum time (IDMT) characteristic. The
high-set stage of the earth-fault unit operates
with definite time characteristic.
The operation of the two earth-fault stages can
be blocked by feeding a control voltage to the
external control input CHANNEL 8 of the
feeder terminal.
Fig. 5.2. The trip OPEN circuit is continuously
supervised by means of the constant current
injection principle. The feeder terminal has five
signalling contacts, one of which is the common
internal relay failure (IRF) output. Four signal-
ling outputs, SIGNAL 1...4, can be used to
indicate starting or tripping of the protection,
see chapter "Signal diagram".
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