Temperature Rise in MV Switchgears: the Role of Loose Busbar Joints

Abstract

The identification of the different causes of a Medium Voltage (MV) switchgear failure is a complex task. Among the conditions contributing to failure, thermal cycling due to loose joints and electrical components may act as a trigger for fault. This paper presents an experimental analysis of temperature variation taking place in 27 different points of a MV switchgear and originating from loose mechanical and electrical joints in the busbars, compared to the normal operating condition. The loose joints -due to improper installation, vibrations, or ageing of components -are obtained by applying a controlled clamping below the recommended operational value of 45 Nm torque, to six busbar joint screws (two for each phase). Results show that when the applied clamping goes below 10% of the recommended value, temperature does not rise significantly in points other than the loose ones, while the main circuits exhibit a detectable variation of their electrical resistance.