What is Dy11y11?

Postcode for Kidderminster in the West Midlands, UK.

Also a vector group (connection configuration) of a 3-phase transformer.D - Means Delta Wound Primary

Y - Means Wye (Star) Wound Secondary

11 - Is the phase shift between the two windings. The 11 refers to 11 on a clock face, hence 30 degrees.