Megger presents the CTER-91 portable test sets designed to perform excitation, ratio and polarity tests on current transformers using the voltage-comparison method.
The lightweight test sets are ideal for testing bushing CTs mounted inside transformers or switchgears. They can also be used to perform saturation, ratio and polarity tests without changing test lead connections in addition to ensuring overload and short-circuit protection.
Model CTER-91 current transformer excitation, ratio and polarity test sets employ advanced technology to provide a variable voltage output and precision instrumentation for testing single and multiratio CTs. All three tests, excitation, ratio and polarity can be performed without changing any leads.
Current transformers can be tested in their equipment configuration including being mounted in transformers, oil circuit breakers or switchgears. It is necessary for the equipment to be totally isolated from the electrical system prior to testing.
Model CTER-91 test sets provide a variable voltage output and digital instrumentation for measuring the excitation voltage and excitation current that result as the voltage applied to the CT under test is increased. As the CT under test begins to saturate, a large increase in current will be detected for a small increase in voltage.
The ratio test is performed by comparing a voltage applied to the secondary winding to the resulting voltage produced on the primary winding.
Polarity of the current transformer under test is determined by special circuitry that divides the voltage applied to the secondary winding by either 10 or 100 depending on switch position, adding the result to the primary voltage. An increase in magnitude indicates correct polarity, and a decrease shows incorrect polarity.
Key features of CTER-91 test sets:
- Voltmeter can be used to measure external voltages up to 600 volts AC
- RUN/HOLD switch freezes readings on instruments when switched to the HOLD position
- Low range of 40 volts is provided for CTs that saturate at low voltages
- Provides a high range of 1000 volts
- Zero-start interlock is incorporated to minimise the possibility of energising the CT under test with a sudden high voltage