Variable voltage transformers for medium voltage heater control

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