Soft Reclosing of an Industrial Power Network Using an Inverter-Controlled Energy-Storage System

We describe a process for using inverter-coupled local energy storage to support a part of the network in an industrial power system following a momentary outage, and then transfer the loads to the utility source in a transient-free manner. This process, called “Soft-Reclosing,” eliminates a number of problems and minimizes the losses encountered by industries due to power outages and momentary interruptions. Consequential damages, scrap losses, and motor-starting inrush currents that cause voltage dips in nearby load centers, and breaker reclosing transients are avoided through the use of this method. The soft-reclose process is accomplished by supplying the plant with a voltage/frequency ramp while the network operates in islanded mode, then reclosing the service-entrance breaker when the plant network is matched in phase and voltage to the utility grid. Voltage and frequency acceleration of the network are controlled by the inverter according to the characteristics of the connected loads. The method is tested with simulation using the power system network which is representative of a plastic/rubber manufacturing plant. The results show a significant reduction in current spikes, voltage dips, motor torque, speed, power factor fluctuations, and most important, process downtime compared to a conventional manual restart process.