Voltage Regulators - Specifications & Selection

When selecting a tap changing voltage regulator, select a model which adjusts its taps at the zero current point of the output wave. There are some models which make their regulating adjustment at the zero crossing of the voltage. These units may cause a transient to be generated except when they are powering a linear or non-electric load. Also important is the number of taps provided. A good quality regulator will have at least 4 taps below normal voltage, and 2 taps above normal voltage for a total of 7 steps. The taps are usually set for 4% to 10% steps depending on the manufacturers design. Response time is very important in selecting a voltage regulator. It should be no more than 1 or 2 cycles. Tap changers are limited to this because they look for the zero crossing. Remember, the total response time must include not only response but also sense time. Some manufacturers occasionally publish only the time tap change and not include the 1 or 2 cycles of sense time. A major advantage of a Tap Changer is its low impedance.

In selecting a ferroresonant regulator, sometimes called a constant voltage transformer, sizing is very important. These units can only supply 125% to 200% of their rated load. So, if the inrush or starting current of a printer, or series of devices for instance, is very high, then the transformer would not be able to supply the correct voltage. For this reason, these devices should be oversized if they are to provide for heavy starting or inrush currents. The ferroresonant transformer will maintain a constant voltage on the output for voltage swings generally ranging from minus 20% to plus 40%. These units are usually very reliable since they contain no moving parts. They do contain capacitors which may need replacing periodically.