Current Transformer
4 - 33
CT RatioV (with Voltage)
Use the CTRatioV test card to measure a current transformer’s ratio. To do so,
from the 2kV AC output feed a voltage of up to 500V to the transformer’s
secondary side.
The preferred method for CT ratio measurement is current injection using the
CTRatio test card. However, on CTs such as some GIS CTs or bushing CTs on
power transformers where the primary current path is not accessible, the
method described in this section is the only solution.
Both the amplitude of the injected test voltage as well as amplitude and phase
angle of the voltage on the transformer’s primary side are measured. The
measurements taken are the basis for the calculation of the actual ratio and the
deviation from the nominal ratio.
To measure the CT ratio using the CTRatioV test card, connect the 2kV AC
output to the CT’s secondary winding and the V2 AC input to the main
conductors, for example, on a power transformer to the transformer’s bushings
of different phases.
Figure 20:
Setup for testing the
ratio and polarity by
measuring the voltage
ratio
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