TYPE-TESTING OF A MEDIUM VOLTAGE SWITCHGEAR

Abstract

MV switchgear has a great impact on the reliability of electric power distribution delivery in substations and industrial power plants. VEO Oy is developing VEO-Vector, a new MV switchgear. It is designed to meet the requirements of the international IEC 62271-200 standard for metal-enclosed switchgear.

In order to meet the requirements it has to pass the type-tests specified by the standard. All type-tests included in the standard has been explored in this thesis and by comparing the attributes and the technical data of the switchgear to the standard specifications, the type-tests to be performed on VEO-Vector have been ascertained. The content of the tests, test parameters and the criteria to pass the tests are explained.

Since the content of the switchgear varies depending on its the rated current and the components desired by the customer, the switchgear might have a great variety of de-signs. According to the standard only the most critical variant needs to be type-tested. The most critical variants have been calculated for the temperature-rise and short-circuit withstand tests. For the temperature-rise tests the busbar materials, cross-sectional areas, rated current and the effects due to skin and proximity effects have been taken into account. The estimated temperature-rise is obtained by comparing the heat generated by the conductors and heat losses from their surfaces due to convection and radiation. Considering the short-circuit withstand tests, the most critical design is estimated by taking into account both the thermal and mechanical criteria. The calculations are based on data and formulas from scientific articles, master’s theses and various technical publications.

The mandatory type-tests to be performed on the VEO-Vector was found despite the standard’s challenging expressions and explanations. The calculation of the most critical variants was also successful and in both temperature-rise and short-circuit withstand calculations one switchgear type was found to be more critical than others.