Estimating the temperature rise of load break switch contacts in enclosed MV switchgear

Abstract

Medium-voltage (MV) switchgear experiences a rise in temperature during normal operation due to ohmic losses in conductors and contacts. If the temperature rise is too high, the switching device may be degraded. The focus of this study is to find a value for the total heat transfer coefficient that may be applied to estimate the temperature of critical parts (open/close contact) of the load break switch (LBS) in an enclosed MV switchgear, relative to the surrounding air (inside the enclosure) for future design. The values for the total heat transfer coefficient (including all transfer mechanisms) showed a relatively strong dependence on the surface emissivity and the actual design of the switch, but were less dependent on temperature changes within the relevant temperature range. Based on authors' findings, it is reasonable to assume that the total heat transfer coefficients may be applied in a first approximation of the temperature rise of an LBS contacts relative to the surrounding air inside an enclosure. Further refinement could be obtained by taking the actual design of the switch into consideration, especially details influencing the emissivity and design elements influencing the heat conduction to adjacent conductor parts.