Stability Increasing of Rolling Mills Electric Drives in Case of Voltage Sags by Using Static VAR Compensator

The article presents the results of research aimed at ensuring the stable operation of rolling mills electric drives in conditions of frequent occurrence of external voltage sags. The high sensitivity of frequency converters (FC) with active rectifiers (AR) to the asymmetry of the supply voltage is an operation's specificity of this electric drives. This fact can lead to a FC-AR system's shutdown due to current inrush exceeding the protection response settings and a decrease in the voltage level in the DC- link. A review of existing ways to solve this problem showed the following: modern voltage sags damping methods in-plant grids, aimed at improving the stability of the electric drives of rolling mills, envisage the control systems modernization for active rectifiers or the usage of external energy storage devices. In some cases, the possibilities of such measures are limited, especially with deep voltage sags (more than 20%). Thus, the paper presents a new approach to solving the issues of compensation of voltage sags in the in-plant grids of compact metallurgical plants. This approach is based on the usage of available reactive power reserves of static var compensators (SVCs) operating in combination with electric arc furnaces (EAFs).