Finite element analysis modeling and experimental verification of reflected wave phenomena in variable speed machine drive cables

Modern variable frequency drives (VFDs) are employed in various industry applications. The machine windings may be subject to large overvoltage, called reflected wave phenomena (RWP), if long cables are used or fast voltage rise times are implemented in the VFD system. The overvoltage places high electrical stress on the machine terminal windings, in the long term resulting in the winding insulation degradation and eventually a complete insulation breakdown. Several methods were proposed to model the RWP overvoltage based on the transmission line theory to study how various factors affect the RWP. The accurate acquisition of the electrical characteristics of the cable for the RWP models however proved to be difficult. This work proposes to use a 2D finite element analysis (FEA) model to simulate the electrical characteristics of the power cable under test. The characteristics are then used to construct a two-port network in a circuit simulation of RWP. The accuracy of the modeling technique is experimentally verified by measuring the voltage overshoots using cables of different lengths and under different switching frequencies and duty cycles. The simulation results are found to closely match the experimental findings after adopting a compensation method.