This master's thesis investigates the effects on the medium voltage circuit breaker on the supply side by certain power electronic converters. In particular, the case of a variable frequency drive powering an induction motor is considered and the effect of this converter on the circuit breaker parameters are observed and analyzed. Since,powerelectronicconvertersdonotfollowthenormsofconventionalloads,they have highly variable and different characteristics and therefore their influence on the supplyvoltageandcurrentarealsounconventional.Thevariablefrequencydriveunder consideration is a combination of a rectifier and an inverter which uses an open loop pulse width modulation (PWM) scheme which are coupled together by means of a series inductance and DC link capacitance. Also, analysis is made as to which component within the converter influences the supply parameters and how their variations influences the supply. Investigations and simulations are carried out by means of the PSIM software. Therefore, this thesis investigates the possibilities of adverse effects the converter has on the circuit breaker performance and attempts to provide some recommendations to mitigate these effects.