Analysis and evaluation of ageing phenomena of high-power LV and HV fuses due to longterm operation

Fuses in the high and low voltage range are considered reliable and unobtrusive during their service life. This means that fuses are sometimes used within an application for decades. However, experimental investigations show that fuses are subject to ageing effects. The results based on the investigations show that critical situations may arise while fuses degradate due to ageing. The paper presents analyses on low-voltage and high-voltage AC fuses with the aim of examining their state of ageing at the end of their service time. The test sample consisted of about 180 LV fuses and 20 HV back-up fuses, all of them aged 35 and over. Investigations were made on their optical condition, resistances, time-current characteristics, thermal behaviour and switching behaviour in the range of their minimum to their maximum breaking current. It was found that the behaviour of the samples studied differs, sometimes considerably, from the nominal behaviour of as-new fuses which is defined by recognised state-of-the-art type tests ([1], [2], [3] et al.). The discrepancy between nominal and observed behaviour is traced to deterioration.