These transformers are used to supply variable speed drives (VSD) for motor control. A VSD typically injects a whole spectrum of harmonics into the supply lines, and the transformer design needs to accommodate these harmonics. A converter transformer is typically rated at 100% capacity, while a distribution transformer is typically rated at 80% capacity. VSD drives are based on power electronics and usually require a neutral line; hence, the most common vector group is DYn11, i.e., a delta primary with a star secondary with the neutral point brought out.