ABSTRACT
The control of the tap changer in a transformer or step-voltage regulator is essentially the same. Unless stated otherwise, the use of the term “transformer” in this chapter applies equally to step-voltage regulators. A principal argument for the use of single-phase regulators is that the voltages of the three phases are controlled independently, whereas a three-phase transformer or regulator controls the voltage of all phases based on knowledge of the voltage of only one phase. The voltage of the primary system is unimportant to the load-tap-changing (LTC) control. The system will always include a voltage transformer or other means to drop the system voltage to a nominal 120 V for use by the control. The principle upon which line-drop compensation is based is that there is one concentrated load located a sufficient distance from the LTC transformer for the voltage drop in the line to be meaningful.
