STS and induction motors

Industrial plants with a high amount of induction motor load can run into problems following short interruptions of the supply or voltage sags. After the voltage has recovered, the high current drawn by the motors can cause voltage collapse. The case study presented in this article shows that the static transfer switch (STS) can provide a solution to this problem by transferring the loads to an alternative healthy supply within some milliseconds from the occurrence of the disturbance. However, this case study has also shown that the time needed for transferring the load is dependent on the type of disturbance and the instant when it occurs, and the transfer time is, in general, higher with an induction motor load, as compared with static load. For plants with a high percentage of motor load, a specific performance study should be carried out to assess if the installation of the STS actually improves the power quality for the plant.