A transformer rated at 69000-7200/12470Y would connect as which type to a 69000 volt 3-phase 3-wire system?

The transformer specified, rated at 69000-7200/12470Y, indicates that it has a primary winding designed for a high voltage range (69,000 volts) and a secondary winding of 7,200 volts with a grounded secondary (indicated by the "Y"). When connecting to a 69,000-volt three-phase, three-wire system, the most suitable configuration is the delta connection because it is commonly used for high-voltage applications.

In a delta connection, each phase of the transformer is connected, forming a closed loop with each phase providing voltage across the load without requiring a neutral. This arrangement is beneficial for balancing loads and ensuring stable operation in three-phase systems. It also facilitates the transmission of high voltages while reducing the need for a ground reference, which is typically necessary in a wye connection.

The choice of a delta configuration is particularly advantageous when the source (the high-voltage side of the transformer) is also a three-phase delta system or when the system is ungrounded. In contrast, the wye configuration would require a neutral and may not be effective in all high-voltage applications or in systems lacking a neutral point.

Understanding these configurations and their applications helps linemen determine the appropriate transformer connections