Lower Cost Solution for Medium Voltage Heater Control: An Affordable Evolution Using Variable Voltage Transformers

Power electronic devices are the standard solution for lowvoltage (LV) heater control; however, cost and harmonic issues are amplified for medium-voltage (MV) heater applications. To provide an MV alternative at a significantly lower cost, this article details modifications and testing that will evolve part-range and load-tap-changing voltage regulators into full-range variable voltage transformers (VVT) for MV heater control. From the initial minor modifications that converted autotransformers into 16-tap isolation transformers, the development moves on to the inclusion of secondary base windings that bring 32 taps into play for refined control. Three-phase solutions and the addition of MV interrupters from the utility industry provide an economical solution for a stand-alone MV heater operation that avoids the harmonic issues of other heater control technologies.