Which type of transformer connection is used when dealing with supply-circuit voltages of 206 volts for equipment rated at 220 volts?

The selection of Group II transformer connection is appropriate when working with supply-circuit voltages that are close to the equipment's rated voltage. In this context, a supply-circuit voltage of 206 volts is close to the nominal requirement of 220 volts for the equipment. Group II connections are specifically designed to accommodate systems where the voltage is slightly below the equipment's rating but still within acceptable limits for efficient operation.

This type of transformer connection allows for the use of step-up transformers to increase the voltage to the desired level while providing a reliable means of voltage transformation for systems operating around that threshold. It ensures that the equipment will function properly without the risk of under-voltage conditions that could lead to suboptimal performance or damage.

Understanding these connections helps in selecting the proper transformer type to ensure compatibility with nominal voltage ratings while maintaining operational efficiency.