Effect of induction motors and other loads on voltage dips: theory and measurements

Voltage dips at the terminals of sensitive equipment are often due to faults that occur at a much higher voltage level. Even though the load current is small compared to the fault current, the changes in load current during and after the fault still make that the voltage at the equipment terminals is different from the voltage at the faulted voltage level. This paper discusses the change in the shape and magnitude of the voltage dip during its propagation from the faulted voltage level down to the equipment terminals. Both balanced and unbalanced voltage dips are discussed by presenting theoretical considerations and measurements. A quantitative model is derived for induction-motor load; for other types of load a qualitative analysis is given. Studies of voltage-dip propagation due to symmetrical and non-symmetrical faults can be simplified using symmetrical components and the related dip characteristics "characteristic voltage" and "PN-factor".