A methodology to identify electrical ageing of winding insulation systems

Forced by the high requirements on modern variable speed controlled drives, power electronics are used to achieve the specific requirements on accuracy and dynamics. These properties are realized by fast switching converters, which result in voltages and currents with high slew rates. As a consequence, these rise times or slew rates lead to high frequency phenomena throughout the electrical drive. High frequency electrical traveling waves superimpose in the electrical machine, in the supply cables and in the power inverter. Based on this superimposition, high overvoltage occurs at different locations in the electrical drive systems [1]. These high voltage waves result in high electrical fields, which load the insulation by various ageing mechanisms [2]. Therefore, ageing of insulation in low voltage machines is influenced by a combination of the dominant factors: thermal, mechanical, electrical ageing and the interaction of their impacts. For this reason, high frequency phenomena in electrical drives lead to failures, e.g. in the winding system of electrical machines. This paper presents a methodology to identify the electrical load of insulation systems of machine windings. The methodology is based on the use of a high voltage generator. Here, a voltage generator is presented, which is used to identify the electrical ageing procedure for different winding topologies.