Simulation of cable charging current and its effects on operation of low power AC drives

In Variable Frequency Drive (VFD) systems, long motor leads can have many detrimental effects, including cable charging current, overvoltage at the motor terminals, and voltage stress on power modules. Different types of AC system grounding can also interact with long motor leads to yield undesirable effects on drive operation. Analyzing models of various components of a drive system is useful to determine any potential issues prior to installation and to recommend any needed filter solutions to mitigate these issues. However, prior cable models have several shortcomings and are inadequate for fully understanding long cable effects prior to VFD system installation. In this paper, a commercially available finite element analysis (FEA) tool is applied to generate a wide frequency range model for a multi-conductor VFD cable. It is shown that this cable model can be used in a system level simulation to determine application issues for low power AC drives. The method is validated using experimental tests on selected cable, motor and drive combinations.