Control transformers are designed to withstand short duration
overloads with minimal output voltage drop.
Motor starter solenoid coils draw six to eight times as
much current when they are closing as is required to hold
them closed.
Constant output voltage transformers or voltage regulating
transformers produce a nearly constant output
voltage, even though the input voltage may not be constant.
The voltage supplied by the utility typically will
fluctuate up and down a few percent during the day. This
voltage fluctuation is of little concern except for certain
equipment, such as electronic computers. Installing a
constant output voltage transformer to supply sensitive
equipment will eliminate undesirable voltage fluctuations.
Special filters can also be added to these transformers
to eliminate voltage spikes and electrical noise
caused by other equipment operating on the electrical
system, Figure 14-12.