System voltages fluctuate due to the ever-changing load consumption characteristics of customers. Voltage at the customer's premises must be maintained within a range that will permit the customer load to operate properly. The American National Standard for Electric Power Systems and Equipment Voltage Ratings (60 Hz) ANSI C84.1 provides detailed information on standard nominal system voltages and voltage ranges. This standard specifies that 120-volt alternating-current nominal voltage must be maintained between 114 and 126 volts (+/ 5 percent). There are several options available to utilize in order to stay within the desired utilization voltage range and compensate for the system load changes. The options include balancing load, increasing feeder size, applying tap-changing transformer equipment, installing capacitors, or installing voltage regulators. The concept of voltage regulation is discussed in more detail in Chap. 40. It was stated in Chap. 3 that if the substation power transformer is not equipped with load-tap-changing equipment, it is usually necessary to install voltage regulators. Voltage regulators are used to vary the source voltage to the customer by the proper amount to keep the voltage within the limits desired. Voltage regulators maintain a reasonably constant voltage at the point of utilization. Voltage regulation equipment may be installed in the substation or on a pole out on the distribution circuit.

Tap-Changing Transformers. Distribution substation power transformers or distribution line transformers may be equipped with tap-changing equipment. The distribution substation transformers (Fig. 19.1) are normally three-phase with delta-connected primary windings and wye-connected secondary windings to provide a...