Voltages to ground in load-commutated inverters

Load-commutated inverter (LCI) drives are well suited to the starting and variable-speed operation of large fans, pumps, and compressors used in the petroleum industry. The origin and magnitude of the voltages to ground found in these types of drives are introduced and explained. The voltage to ground in most of the LCI circuit depends on bridge firing angles and can reach a maximum value as high as 2.4 p.u. (per unit) of rated. An analysis of this phenomenon and an algorithm for predicting the magnitude of the voltage as a function of machine voltage, and bridge firing angles is presented. Test results are included for validation of the analysis. How system grounding and DC link reactance can be used to reduce the magnitude of the elevated voltage to ground and transfer it to less devices is discussed