Synchronous Generator Disturbance Provoked by Induction Motor Starting

Problem statement: This study presented an alternative procedure for the starting of large Inductions Motors (IM) in isolated generation systems. Approach: In isolated generation systems on stand-by or base load, the starting of the IM provoked sags frequently beyond the ability of the other consumers in the plant to stand. Manufacturers' solutions always recommend a supersized generator to decrease transient reactance and achieve smaller sags. These calculation procedures were based on the theory presented by Beeman (1955). Instead of supersizing the generator, a good but expensive solution, the present authors had undertaken research into how to improve the Synchronous Generators (SG's) capacity to stand the start of IM without exceeding the field and armature temperature limits and with small sags. Results: The method utilized consisted of decreasing the response time of excitation, thus increasing Ceiling Voltage (CV). The advantage of this method besides leading to a reduction in the investment involved permits retrofitting in electrical plants already installed. Tests on updated industrial equipment whose CV of a 250 kVA SG was increased from 2.7-5.4 were presented with their respective oscilographic records which show a reduction in sag from 40-34%. With this solution was possible to start a 75 HP IM without supersize the SG. Conclusion: Computational simulations in MATLAB are also given and were compared with experimental results to validate the simulations. Models in the frequency and time domains are discussed.