The CTER-91 test set is a lightweight, portable unit for performing excitation, ratio and polarity tests on current transformers using the voltage-comparison method. Utilizing the latest technology, Model CTER-91 provides a variable voltage output and precision instrumentation for testing single and multi-ratio CTs. All three tests – excitation, ratio and polarity – can be performed without changing any leads. Current transformers can be tested in their equipment configuration, such as being mounted in transformers, oil circuit breakers or switchgear. It is necessary for the equipment to be totally isolated from the electrical system prior to testing.