Which variable represents the line-to-line voltage in a WYE transformer?

• A. EP
• B. EL
• C. IL
• D. IP

Answer: (A)

Line-to-line voltage is the voltage measured between two lines, not from a line to neutral. In transformer notation, the primary winding’s line-to-line voltage is denoted by E with a subscript P, meaning it is the voltage across two lines on the primary side. This is the value that defines the primary line-to-line rating. In a Wye connection, each phase has a line-to-neutral voltage, and the line-to-line voltage between two lines is related to that phase voltage by a factor of √3, but the symbol used for the primary line-to-line voltage is E_P. The other symbols typically refer to the secondary line-to-line voltage or to currents, so they don’t represent the primary line-to-line voltage in this context. Therefore, the line-to-line voltage on the primary side is represented by E_P.