Manufacturing economical solution for overvoltage transient problem on machine terminal

This contribution research on economical possible solutions for manufacturing an external device as a remedy for overvoltage transients on machine terminals. The overvoltage source could be lightening , faults or switching , or a Variable Frequency Drive (VFD) including a pulsewidth modulation (PWM) inverter with Insulated Gate Bipolar Transistor (IGBT) as pulse generator which is overvoltage source on this investigation.The connected cable between Variable Frequency Drive and the machine leads both wave travelling and mismatching of input impednce of cable and machine due to IGBT switches with very fast output signals risetimes. Overvoltage surge on machine terminal would lead dielectric system breakdown in stator winding of machines without suitable protection. For mismaching study ,Input impedance of electric machine and cable at high signal fre- quencies requires a complicated Common Mode and Differential Mode test ,However , High frequency simulation models for power cables and machines, are the key factors for appropriate analyzing of the overvoltage problem in PWM drives. Time and frequency domain of machines in high frequency is explained briefly in section ”motor frequency response” [section 3.2.3]. Also the proposed model help for simulation of overvoltage on inverter fed machine .Transmission line models are generally lead to calculate the voltage distributions flow through the cable. There are various solution ,such as inverter output filter is proposed for PWM inverter or using better insulation for winding machine which needs more cost and cause manufacturer think about low cost solutions. The alternative approach of surge protection in this thesis is adding Metal Oxide Varistor (MOV) with ZNO non-linear ceramic resistors parallel with machine terminal. This methode is concluded from surge arrester resistors which protect application of high Voltage (HV) transmission and distribution systems. Varistor mitigates repetitive overvoltages with an increasing rise time of the impulses occurring at the machine terminal. The main concern is sizing the varistors for low voltage machines ,because of lack ofthe industrial Metal Oxide resistance can adopt to low voltage machines. However theoritical and industrial sizing is investigated in section 5. The simulation study and experiment result will show the reflection of the progressive and regressive voltage wave at the machine terminal and also solutions effect on simulation will expressed in section 6.