AC motor feeding cable consequences on EMC performance of ASD

High level of conducted EMI emissions of adjustable speed drives (ASD) is one of the most difficult problems in contemporary applications. Many investigations are carried out in order to find more effective methods allowing to predict this emission at early stage of design, and therefore to predict adequate countermeasures. This paper deals with the method which allows to estimate by simulation the influence of motor feeding cable parameters on overall EMC performance of ASD. Proposed method is based on analysis of common mode (CM) impedance of motor feeding cable and motor windings which allows to determine their broadband model parameters. Motor windings are modelled by ladder circuit with an adequate number of rungs and motor feeding cable by lossy transmission line. After experimental verification of selected impedances of the evaluated model it can be successfully used for calculation of CM currents distribution at output side of frequency converter for various motor feeding cable lengths. Influence of motor feeding cable parameters on CM currents emission can be evaluated using this model, especially the cable length which depends on particular application requirements and can be determined only at ASD installation design stage.