Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
The influence of defects on the winding insulation resistance to operational loads inherent for variable frequency drive
Abstract
The relevance of the work is determined by the need to study the healing impregnated through damages to interturn insulation of low-voltage windings of variable frequency drives. The objective of the work: to investigate the effect of electrothermal stresses arising from variable frequency drive systems on the average time before the breakdown of electric insulation of low-voltage windings of electric machines. The method of research: testing low-voltage interturn insulation of windings of the variable frequency drive (VFD) on physical samples. Results. The authors found out that the use of VFD control systems based on the pulse-width modulation increased the level of operating electrical loads. It was also discovered that the electro-thermal character of insulation aging dominates. In this case, special attention should be paid to the presence of defects in the insulation of the wires. The definition of the average time to breakdown twists with marked defects under the influence of temperature and high-frequency modulated voltage was made in this work. For the tests used the corona resistance materials: wire PETD2K 180 and varnish KO-916K. Even the presence of defects on one turn leads to significant re duction of the average time to the breakdown of the system «varnish - winding wire». For a number of cases it was discovered the interturn closure is possible at distances exceeding the limit for normal operating conditions. For more severe electric loads on the winding insulation characteristic of the pulse-width modulation (PWM), the impregnation might not provide the required «healing» through damages in enamel insulation. For windings of modern variable-speed drives it is recommended to use only corona resistant materials, winding wires with minimum insulation defects in particular.
