Investigation on the impact of thermal stress on a combined 220 kv instrument transformer

Summary

A combined 220 kV instrument transformer has been investigated for its thermal behaviour. Therefore multiple tests based on the rated thermal current of the transformer were made. Furthermore, partial discharge measurements, loss factor measurements as well as Karl Fischer titration and dissolved gas analysis were frequently done to investigate the effects on the insulation system. The performed investigations were accompanied with FEM-simulations. The evaluation of the performed measurements based on the given values of manufactures (nameplate) and the standard IEC 61869 and IEC TR 60943 show that the quality of the electrical contacts dominate the thermal behavior as well as the temperature distribution. Furthermore, different degradation processes like the formation of impurity layers, hot contacts and loss of contact pressure have been observed. The overall contact resistance has been approximated with thermal FEM-simulation.

Additional informations

Keywords

instrument transformer, thermal stress test, contacts, simulation