3.7
Other measurements
Starting from the internal and external measurements, the test set computes derived measurements, according to the
test selection.
The following table lists the available measurements (the accuracy is the sum of voltage, current and possibly angle
accuracy):
No.
Parameter
AC outputs
Derived from
Formula
Units
1
Ratio (Rat)
CT or VT or PT
I
out
, I
in
or
V
out
, V
in
Rat=I
out
/I
in
Rat=V
out
/V
in
-
2
Polarity
CT or VT or PT
ϕ I
out
, I
in
or
ϕ V
out
, V
in
K => ϕ < 10 °
-
3
Burden
CT and VT
V
out
, I
out
VA=IN
2
·V
out
/I
out
VA
4
Saturation knee
CT
V
out
, I
out
VKn, Ikn: according to the
standards
V, A
5
Resistance
CB and others
I
out
, V
out
R=V
out
/I
out
Ω
6
Impedance
CT and VT insulation test
I
out
, V
out
Z=V
out
/I
out
Ω
7
Short circuit impedance
PT test
I
out
, V
out
Z=V
out
/I
out
H
Table 34 - Available measurements
The following table lists the parameters for the CT, VT and PT ratio measurement:
Range
Resolution
Ratio range
Typical accuracy
Maximum accuracy
0÷9,999
1
0.8÷166
0.20%
0.40%
167÷1,666
0.25%
0.50%
1,667÷9,999
0.30%
0.60%
Table 35 - Parameters for CT, VT and PT ratio measurement
For the polarity test, the phase shift between the two parameters is tested. Answer is OK if phase shift is less than 10 °.
The ratio and the polarity are checked also for non-conventional transformers through IEC61850-9-2LE protocol.
For the burden test, the result is the product of voltage and current; the accuracy depends upon the VA range. The
following table lists the parameters for the burden test:
Test voltage
[V]
Test current
[A]
VA range
[VA]
Resolution
[VA]
Typical accuracy
Maximum accuracy
%
%
%
%
130
3
3,000
0.05
±0.1
±0.1
±0.2
±0.2
30
2
300
0.01
±0.1
±0.1
±0.2
±0.2
10
1
30
0.005
±0.1
±0.1
±0.2
±0.2
3
1
3
0.001
±0.2
±0.1
±0.3
±0.2
Table 36 - Parameters for the burden test
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