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Contents
Features ..............................................................................................................1
Description of function .........................................................................................2
Signal abbreviations ............................................................................................3
Front panel ..........................................................................................................4
Operation indicators ............................................................................................4
Measured data ....................................................................................................4
Settings ...............................................................................................................5
Vector group matching ........................................................................................6
Recorded information ..........................................................................................8
Main menus and submenus of settings and registers .........................................9
Technical data ...................................................................................................10
Event codes .......................................................................................................11
Remote transfer data .........................................................................................12
Description of
function
Fig.1. Block diagram of the single phase differential relay module SPCD 3C2_.
The differential relay modules SPCD 3C21,
SPCD 3C22 and SPCD 3C23 measure the
phase currents I1 and I2 on either side of the
power transformer, their differential current Id
and a possible second harmonic component of
the differential current.
A certain angular displacement exists between
the currents of the HV and the LV side of the
protected power transformer depending on
the transformer vector group. The angular
matching of the displacement is based on
phase shifting and on subtraction of phase
currents attenuated with a factor √3. Because
of the phase angle matching all currents must
be routed to each differential relay module.
When, at rated load, the secondary currents of
the current transformers are lower than the
rated current of the relay they can be matched
without steps and separately on either side of
the power transformer.
2
C
U1 / U2 / U3
I
A
I1/In
I
I1
B
Y
I
C
I
a
I2/In
I
I2
b
Y
I
c
SG1/1...6
2f
10...20%Id
SG1/8
Id=I1-I2
P%
+
-
I1+I2
Ib=
S%,Ib
2
Id>>
0.5x
Ib<0.33xId
0.1 x In
t =100ms
t
1
0.1 x In
S
R
0.2 x In
&
0.2 x In
As the differential current exceeds the set
starting level the differential relay module issues
a signal TS for the output relays, unless the
blocking signal BS OUT of the relay module
itself or a blocking signal BS IN from the
cooperating differential relay modules are alert.
The starting value is defined by the basic
setting p, the starting ratio s and the bias
current Ib according to the characteristic curve.
Upon operation, the operation indicator Id> of
the relay module is lit with red colour. The
indication is maintained when the protection
stage resets and it can be reset with the
RESET push-button.
The differential relay module measures the
second harmonic component of the differential
current. If the second harmonic component
exceeds the set blocking level the operation of
the differential current stage Id> is blocked. At
the same time the module issues a blocking
signal BS OUT for the other differential relay
&
1
1
&
&
SG1/7
&
S
R
STEP+RESET
S
RESET
R
BS OUT
Ihr>
Y
BS IN
TS
1
Id>
R
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