Induction motor drive system performance under influence of voltage sags and interruptions

Abstract

This thesis presents performance of induction motor drive system under influence of voltage sags and interruptions. The drive system consists of an induction motor and adjustable speed drive (ASD) that connected in series. Its terminal is connected to power supply through a contactor and a circuit breaker. Contactor, ASD and induction motor have being recognized as sensitive equipment to voltage sags and interruptions. Investigation was started by identifying characteristics of voltage sags. The characteristics considered are magnitude and duration of voltage sags, point on wave of sag initiation (POW), symmetrical and unsymmetrical, repetitive and multistage voltage sags as well as non-sinusoidal voltage sags. The testing results of three different contactors show that their performances are greatly influenced by magnitude, duration and POW of sag initiation. Non-sinusoidal voltage sags did not have significant influence. In general, the contactors’ sensitivity increased when the contactors were subjected to deeper and longer voltage sags. The POW influence of sag initiation on three contactors have kepekaan es almost similar against sag duration. Sensitivity of the contactors to sag duration decreases for the voltage sags with POW close to 90o. Influence of POW on the contactor was shown also in repetitive voltage sags. It tripped is slower for first voltage sag with the POW close to 90o. Testing has been carried out in various conditions on ASD such as symmetrical voltage sag (type A voltage sag), unsymmetrical voltage sags (types B, C and D), non-sinusoidal voltage sag supply and sinusoidal voltage sags with various speeds and rated loads. Rectifier diodes behaviour to conduct current are influenced by sag magnitude and sag types. Ride through of the ASD against voltage sags was greatly influenced by performance of the rectifier diodes. Type A and type C voltage sags caused all rectifier diodes were reverse biased. These two types of voltage sags caused the ASD to trip. Type A produced higher sensitivity than type C to sag magnitude.