Protection Method of Magnetic Energy Recovery Switch Applied to Series Compensation in Power Systems

Abstract

Series compensation in transmission systems is efficient for improved utilization of the grid. However, during faults, large over-currents will result and necessary protection must be installed. This increases the costs significantly. A power flow controller called the magnetic energy recovery switch (MERS) is investigated. The configuration consists of four active switches and a small dc capacitor. It is characterized by a large steady-state voltage-current operating range. A special capability of the configuration is the possibility to conduct current in two parallel arms when the voltage across the capacitor is zero. It can be found that this increases the over-current capability of the device to almost the double. A protection method utilizing the active switches is suggested. By applying simple control, parallel conduction mode can be reached quickly after fault occurs. Small scale experiments demonstrate simple implementation and successful operation. Additionally, large scale system investigations show that the influence of the protection method on the required semiconductor rating is low. This indicates the potential for significant protection cost reductions.