3
The directional neutral overcurrent relay mod-
ule SPCS 3C4 measures the residual voltage U
0
and the active component I
0
cos
ϕ
or the reactive
component I
0
sin
ϕ
of the neutral current I
0
. The
phase angle
ϕ
is the phase displacement between
the measured voltage and current.
The module starts, generating a start signal SS1
or SS2, if I
0
cos
ϕ
or I
0
sin
ϕ
exceeds the set start
value I
ϕ
> or I
ϕ
>>, and the neutral voltage
simultaneously exceeds the selected start voltage
value. The operation indicator of the stage which
starts is lit with yellow light. If the situation
persists long enough, the stage which started
also operates generating a trip signal TS1 or
TS2. Simultaneously, the yellow operation in-
dicator of the concerned stage turns red. The
operation indicators can be given self-reset or
manual-reset mode of operation. If the manual
reset mode of operation has been selected the
operation indicator can be reset by pushing the
RESET push button or by remote control via
the SPA bus using the command V101 or V102.
The operation of the low-set stage I
ϕ
> can be
blocked by routing a blocking signal BTS1 to
the stage. In the same way the operation of stage
I
ϕ
>> is blocked by means of the blocking signal
BTS2. The external blocking signals are con-
figured by means of switchgroup SGB located
on the PC board of the relay module.
If the directional neutral overcurrent relay mod-
ule is cooperating with auto-reclose relay mod-
ule, switchgroup SGB is additionally used for
the selection of start initiation signals for the
auto-reclose module. See also paragraph "Signal
diagram" in the general manual of the different
protection relays.
The direction of operation of the stages is se-
lected with switch SG1/1. The low-set stage I
ϕ
>
operates in the forward direction only, the high-
set stage I
ϕ
>> can be set to operate in either
direction (see fig. 4).
The start value of the residual voltage is selected
with switches SG1/7 and SG1/8. Four alterna-
tive start values are available.
The operation characteristics of the module are
presented in Fig. 4. If the system to be protected
is resonant earthed or solidly or nearly solidly
earthed, the operation characteristic to be se-
lected is I
0
cos
ϕ
, whereas I
0
sin
ϕ
is selected for
the protection of isolated neutral systems.
The operation characteristic, I
0
sin
ϕ
or I
0
cos
ϕ
,
can be selected manually by means of switch
SG1/3 on the front panel of the relay module,
when SG1/2 = 0. If SG1/2 = 1, the operation
characteristic can be remotely controlled irre-
spective of the position of switch SG1/3. By
bringing a control signal named BACTRL to
the 0 state the operation characteristic will be
I
0
sin
ϕ
. When the control signal BACTRL is in
the 1 state, the operation characteristic is I
0
cos
ϕ
.
If the operation characteristic is to be automati-
cally controlled, the change from I
0
sin
ϕ
to
I
0
cos
ϕ
or vice versa is initiated by an auxiliary
contact of the disconnector of the earthing coil.
The setting range of the operation time t> of the
low-set stage I
ϕ
> is selected with switch SG1/5.
Two setting ranges are available.
The setting range of the start current of the high-
set stage I
ϕ
>>, i.e. 5...40% x I
n
or 1...8% x I
n
, is
selected with switch SG1/6. Additionally the
operation of the high-set stage can be set out of
function by selecting the setting
∞
, infinite.
The operation outputs TS1 and TS2 of the two
stages are provided with a so called latching
function (switch SG1/4). If selected, the opera-
tion output and thus the output relay will re-
main energized, although the signal which caused
operation disappears. The stages are reset by
pushing the STEP and RESET push buttons
simultaneously or by remote control via the SPA
bus using the command V101 or V102. See also
table (for switchgroup SG3) on page 9 in chap-
ter "Selector switches".
The residual voltage and neutral current inputs
are provided with effective filters by means of
which harmonics of the energizing quantities
are suppressed, see Fig. 1.
Description of
operation
dB 10
0
-10
-20
-30
-40
-50
-60
0 1 2 3 4 5 6 7
f / f n
Fig. 1. Filter characteristics of the energizing
inputs of the relay module SPCS 3C4.
