Condition monitoring thermal properties of a 20A hydraulic-magnetic MCB

Abstract

Heat is one of the major causes of degradation which can cause a reduction in performance, reliability and life span of miniature circuit breakers (MCBs) [1]. In order to diagnose the condition of electrical equipment, the thermal stress of that equipment should be known [2]. Due to the compact design of MCB’s it is important to minimize or dissipate the heat that builds up inside MCBs during normal use. With time electrical components and contact surfaces heats up and begin to deteriorate, this increase in heat is often a product of increased electrical resistance which is a result of degradation [3]. Infrared thermography is a condition monitoring technique that can be applied to electrical distribution boards but because of design limitations MCBs are stacked next to each other on a rail in a panel allowing a direct view only from the front. Is the surface temperature of the MCB a reflection of the internal degradation or are there other factors that need to be considered to accurately diagnose the MCB? The following methodology for the exploratory study was followed to determine the heat profile after degradation, a 20A hydraulic-magnetic MCB was switched 9000 times at rated voltage and current. The volt drop across the conduction path as well as thermal images of the front and sides were taken after every 500 switching operations, after the MCB was allowed to heat up for 1 hour at rated current. When comparing the surface temperature rise above ambient of the three sides the results shows that the number of operations does not influence the surface temperature of the front and the left (hydraulic magnetic unit) as much as the right (conduction path). The aim of this paper is to use a lumped model and compare with empirical infrared thermographic results relating to the condition of MCBs and to: Define the MCB surface heat distribution after a number of switching operations at rated current. Determine whether the frontal surface temperature of the MCB is an accurate indicator of internal degradation. Determine a field methodology to determine degradation and to anticipate failure of MCBs? Due to the construction of the MCB the front, left and right sides give different heat patterns that complicate matter with regards to determining the correct internal health state of the MCB