A New Solution for Harmonics Generated by VSDs

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A New Solution for HarmonicsGenerated by Variable Speed DrivesIn addition to its harmonic mit-igating capabilities, this widespectrum harmonic filter helpsprotect a VSD from transientovervoltages caused by capacitorswitching and other fast changingloads. It is suitable for virtuallyany application involving a VSDor similar 3-phase, 6-pulse diodebridge rectifier load. Harmonic ProblemsThe front-end diode bridge recti-fiers of 3-phase, 6-pulse static powerconvertors (ac-dc), such as those foundin variable speed drives, are considerednonlinear because they draw current ina non-sinusoidal manner. The currentharmonics they generate are definedby the following formula:h= np 1Where:h= the Harmonics Generated n= any integer (1, 2, 3, etc.)p= the rectifier pulse numberA simple 6-pulse rectifier (p =6) is shown in Figure 1. Withoutany harmonic treatment, the totalharmonic current distortion (THID)of this rectifier would be in the100-140% range with the predomi-nant Harmonics being the 5thand7th.

A New Solution for Harmonics Generated by Variable Speed Drives In addition to its harmonic mit-igating capabilities, this wide spectrum harmonic filter helps

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