Reference setup for the calibration of power transformer loss measurement systems

A reference system is developed for the calibration of power transformer loss measurement systems (TLMs). A crucial element in such calibrations is the availability of voltage and current signals with adjustable phase close to 90°, that is power factor near to zero, in order to apply a known and stable loss or reference power to the TLM. In the new reference system, digital signal processing is used to maintain the phase relation between the voltage (up to 100 kV) applied to the TLM and the generated current (up to 2000 A). Initial results indicate that phase uncertainties of better than 20 μrad can be obtained.