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Front paneI
Fig.2. Front panel of the differential relay module SPCD 3C21.
Operation
The differential relay modules are provided
indicators
with a yellow-red operation indicator. When
the differential relay module issues a tripping
signal to the circuit-breaker, the operation
indicator is lit with red light and it remains lit as
long as the tripping signal is reset.
The yellow light of the operation indicator shows
that the CB tripping is blocked by a blocking
function based on the occurrence of the second
harmonic component of the current.
The self-supervision alarm indicator shows
that the self-supervision system has detected
a permanent fault. The indicator is lit with red
light within two minutes after the fault has been
detected. At the same time the relay module
Measured
The measured values are displayed with the
data
three rightmost digits of the display. The
4
B
Load current and differential
current indicators
Setting knob and indicator for
the basic setting p
Setting knob and indicator for
the starting ratio s
Setting knob and indicator for
the error correction of the
transforming ratio of the HV
side current transformers
Setting knob and indicator for
the error correction of the
transforming ratio of the LV
side current transformers
Module type designation
Indicator
Measured data
I
The HV side load current I
1
correction setting I
into account in the display.
I
The differential current I
d
current.
I
The LV side load current I
2
correction setting I
into account in the display.
issues a control signal to the self-supervision
output relay of the protection unit. Further, in
most fault situations, a fault code showing the
nature of the fault appears on the display of the
module. At a permanent fault, the fault code,
consisting of a red figure one and a green code
number, cannot be erased from the display of
the module by resetting. The self-supervision
alarm is automatically reset when the fault
disappears, but the fault code is maintained on
the display. If the fault has disappeared, the
recorded fault code is reset from the display at
the next pressing of the STEP or the RESET
push-button. When a fault occurs, the fault
code should be written down on a piece of
paper and stated when overhaul is ordered.
relevant measured data are indicated by a
LED indicator.
as a multiple of the relay rated current. The
1
/I
of the current transformer ratio has been taken
1
n
expressed as a multiple of the relay rated
d
as a multiple of the relay rated current. The
2
/I
of the current transformer ratio has been taken
2
n
Device symbol
Self-supervision alarm indicator
Display window for set and
measured values
Display step push-button
Switchgroup for vector group,
output relay latching and
blocking mode selection
Switchgroup indicator
Reset push-button
Operation indicators
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