A New Generation of On-Site Test Systems for Power Transformers

Abstract

The presented mobile on-site test system enables the performance of high voltage routine tests at power transformers up to 500 MVA. As per IEC 60076 the different routine tests require different voltages, currents, load conditions and especially different frequencies. In order to generate frequencies of 50/60 Hz and >100 Hz transformer factories have been using motor-generator- sets for the different dielectric tests. Considering the needs for on-site testing of power transformers the heavy weight and bulky dimensions, the attrition of rotating machine parts, the costly service and last but not least a limited range of the output frequency make the use of motor-generator- sets for site application very impractical. The experience of more than one decade using modern frequency converters at on-site resonant test systems for cables and GIS has led to the idea to realize the testing of power transformers with static frequency converters. The described test system consists of a combined test system for induced / no-load losses and applied voltage tests according to IEC 60076-3 based on a power electronic static frequency converter. The three phase converter works at a frequency range of 40...200 Hz. It is connected to a compensation unit, an adaptation transformer and a HV filter for the induced voltage and no-load losses tests. During induced voltage tests also partial discharge measurements down to 30...50 pC are possible. The realization of the applied voltage test is basically founded on the proven principle of resonant circles with variable frequency. Due to the compact design of the system it can be installed inside a 40-ft container and, if necessary, a separate 20-ft container for applied voltage testing.