A resonant transformer for high voltage testing of generator stators
A partial core transformer has been designed such that its magnetising reactance has been matched to a generator stator insulation capacitance. The reactive current drawn by the stator insulation is provided by the transformer magnetisation This means that the supply only has to provide the real power losses of the transformer and in practice any mismatch between the magnetisation current and the stator capacitance. A high voltage inductor was designed and used in the testing of a generator at a New Zealand power station. It supplied 115kVAr of reactive power compensation at 23kV. The inductor was turned into a resonant transformer by the addition of a low voltage primary. A laboratory test showed that the required high voltage of 23kV could be obtained from energising the primary at 285V at 60A or at a rating of about 1/7th the load. A further resonant transformer was then designed for a 334kVAr capacitor load to test generator stators at 31.5kV. This transformer was supplied from a nominal 400V supply and gave a gain in kVA of 16. The transformer has a finished weight of approximately 300kg.