The Constant Voltage Transformer (CVT) for Mitigating Effects of Voltage Sags on Industrial Equipment

Abstract

Electric quality problems associated with power interactions between distribution and industrial process control systems can be prevented. Surveys of large users that buy power at the transmission and distribution voltages turn up relatively few complaints about the quality of their incoming power, while surveys of small users connected at secondary voltages tum up numerous complaints about the quality of their incoming power. Three major changes in the characteristics of customer loads and power distribution systems have altered the nature of the power quality equation: (I) greater sensitivity of devices and equipment to electric power variations, (2) the interconnection of sensitive loads in extensive networks and automated processes, and (3) an increase in loads that use power electronics in some type of power conversion configuration [1][2]. This paper presents applications of the constant-voltage transformer (CVT) for mitigating the effects of electric service voltage sags on industrial equipment in an oil refinery. Unlike conventional transformers, the CVT or ferro-resonant transformer allows the core to become saturated with magnetic flux, which maintains a relatively constant output voltage during input voltage variations such as undervoltages, overvoltages, and harmonic distortion.