Basler BE1-CDS220, Instruction Manual

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13-10 Testing And Maintenance BE1-CDS220
Sidebar 13-1. Testing With Internal Phase and I0 Compensation
When the internal phase and zero sequence compensation feature of the BE1-CDS is used, confusing
test results can occur unless the compensation is taken into consideration. The best way to illustrate how
the BE1-CDS relay performs internal phase compensation and thus, what to expect under test situations,
is by looking at an application example. The application below shows a delta/grounded-wye transformer
with wye connected CTs. The currents flowing into and out of the transformer and reflected through the
CTs are shown for this configuration.
H1
H2
H3
X1
X2
X3
A
B
C
a
b
c
I
C1
-I
A1
I
B1
-I
C1
I
A1
-I
B1
I
C2
I
B2
I
A2
I
A1
-I
B1
I
B1
-I
C1
I
C1
-I
A1
I
A2
I
B2
I
I
A2
’ - (I
B2
’
)
I
B2
’ - (I
C2
’
)
I
C2
’ - (I
A2
’
)
INTERNAL PHASE
COMPENSATION
BE1-CDS
I
A1
’-I
B1
’ - (0)
I
B1
’-I
C1
’ - (0)
I
C1
’-I
A1
’ - (0)
D2857-08.vsd
05-05-00
C2
I
C1
I
B1
I
A1
Isolating the box marked BE1-CDS, we see that, for the A phase 87 element, the relay subtracts the
measured Ib from the measured Ia on the transformer wye side to compensate for the measured IA-IB
delta currents that are flowing in the line phases on the transformer delta side. Remember that these
currents are the compensating currents when the relay is in service for this application.
Under a test scenario, any set of balanced, 180
°
out of phase, single-phase, input currents that we apply
to the two phase A connections will result in balanced currents in the 87A element. But, the 87C element
will also see a compensating -IA2 current that will cause it to operate. Table 13-7 shows the compensated
currents that with the various compensation settings will be applied to each 87 phase element.
The relay can also remove the zero sequence component of the current if a zero sequence source exists
on an input that is not delta compensated. When this compensation is applied during testing, it has a
similar effect as subtracting I0 from the phases not under test. This also causes them to operate.
It is this compensating effect that you must be aware of in order to understand what operations and
targets to expect when testing a BE1-CDS relay with internal phase compensation settings. To prevent
unwanted phases from tripping during the slope test which starts from a balanced condition, delta test
injection connections are recommended as shown in Table 13-11 and Figures 13-4 to 13-11.
Tables 13-8 through 13-10 also show what equation to use to calculate the test points for the minimum
pickup (minpu) and slope tests for each possible configuration of compensation.