Current Transformer
4 - 21
Use the test card RWinding to measure the resistance of a current
transformer’s secondary winding. To do so, open the circuit as shown in Figure
13, and inject DC current from the CPC 100 6A DC output into the transformer’s
secondary winding. Currents higher than 6 A are not needed for measuring CTs.
It is recommended to perform all winding resistance measurements with the
CP SA1 connected to the CPC 100 VDC input sockets to protect yourself and
CPC 100 from high-voltage hazards. The CP SA1 must be used for
measurements using 400A DC output. Before using CP SA1, you can check its
functionality by following the test procedure in ”CP SA1” on page 17-14. If the
CP SA1 is defective, contact OMICRON electronics sales office (for ordering
information, see ”Ordering Information for CP SA1” on page 17-14). Before
disconnecting the test leads, short-circuit the transformer’s terminals first and
then remove the wirings to CPC 100.
VDC input measures the voltage generated at the transformer’s secondary
winding. From that value the winding resistance is calculated.
Due to the significant time span needed for the transformer’s inductance to
reach its saturation, this test evaluates the deviation of measured values within
a time interval of 10 seconds. The winding resistance is continually measured
and stored in CPC 100 internal memory. The calculated difference between the
maximum and minimum measured values in % within the last 10 seconds is
displayed.
Furthermore this test comprises the option to take a temperature compensation
for copper (Cu) into consideration (refer to page 4-24).
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