A design tool to protect industrial long cable PWM ASD systems against over-voltage problems

This work presents a proposed tool to be utilized in design for long cable adjustable speed drive (ASD) systems. It allows coordination between the inverter, the motor and the cable type and length in order to protect the motor against over-voltages due to the reflected wave. Detailed mathematical formulas describing the transient voltage and current along the cable are first developed in the frequency domain. Then, by applying the boundary conditions at the cable ends and assuming a lossless cable, delay equations are developed in time domain. Using these equations, an appropriate simulation scheme has been built, using SimPowerSystems (SPS) and Simulink of Matlab software, to compute the high frequency over-voltages (and their associated currents) at the ends of the feeding cable. The proposed tool has been applied to an industrial 5 kVA ASD prototype using a 4-wire shielded long cable. It includes simulation results and experimental validations.