Using a 120/240V-12/24V Group I transformer, what voltage is supplied to equipment rated for 220 volts when the supply-circuit voltage is 206 volts and Diagram 4 is used?

To understand why 227 volts is the correct voltage supplied to equipment rated at 220 volts in this scenario, we need to consider the operation of the transformer and its implications on voltage regulation.

A Group I transformer is designed for applications where the secondary voltage is derived from a primary voltage with a specific ratio. In this case, the primary side operates at 120/240 volts while the secondary operates at 12/24 volts. When the supply-circuit voltage is lower than the nominal (in this case, 206 volts instead of the expected 240 volts), the output voltage on the secondary side will also be proportionally reduced due to the transformer's ratio.

Using the transformer's characteristics, the output is not exactly equal to the rated output because the input voltage is less than the nominal value. Thus, the output voltage calculated based on the supply-circuit voltage would lead to a proportional decrease relative to the difference in supply voltage.

By applying the transformer’s voltage ratio to the actual supply voltage (206 volts), we arrive at an output that reflects the effective drop, resulting in approximately 227 volts provided to the equipment.

This calculation displays the relationship between input and output voltages through the transformer under less-than-ideal conditions, illustrating that