Step response test of a Russian PT-125C (ПТ 125-2сер) type rotary converter.

Allways wanted to check how accurate these devices can maintain their fixed output frequency of 400Hz in case of load applied. In this test full load ~2Arms/phase (green power resistor bank on the left) is applied to the output via a manually enabled relay. Meters from left are: output Voltage, Frequency, input Current. Unit seems to reacts quite fast to the full load step, no-load Frequency of 401Hz drops to only 397Hz. This technology was developed in the sixties and still runs reliable.