The voltage across a wye connected transformer coil is what fraction of the line-to-line voltage on the wye system?

In a wye (Y) connected transformer configuration, the relationships between line-to-line voltage and phase voltage are well-defined. The phase voltage, which is the voltage across each coil of the transformer, is actually a fraction of the line-to-line voltage.

To understand this in terms of their mathematical relationship, consider that in a balanced three-phase system, the line-to-line voltage is equal to the square root of three times the phase voltage. Specifically, the formula is:

Line-to-line voltage = √3 × Phase voltage.

This implies that the phase voltage can be derived from the line-to-line voltage using the equation:

Phase voltage = Line-to-line voltage / √3.

When you calculate the fraction, you'll find that phase voltage is approximately 0.577 times the line-to-line voltage, or around 58%. This is why the correct answer indicates that the voltage across a wye connected transformer coil is 58% of the line-to-line voltage on the wye system, aligning well with the principles of three-phase electrical systems.