Portable unit for performing excitation, ratio and polarity tests on current transformers. All three tests can be performed without changing test lead connections. The current transformers can be tested while mounted in transformers, oil circuit breakers or switchgear - without moving bushings and CTs. Using the voltage-comparison method, the CTER-91 provides a variable-voltage output up to 1000 volts and precision instrumentation for testing single and multi-ratio CTs. Output: 0 to 1000 V in four ranges. Digital voltage and current meters. Overload and short circuit protection.