It used to be the case that transformers of different vector groups were used on distribution systems.
The majority of our network was constructed with DY1 transformers, but there are numerous areas which still have DY11. When replacing a DY11 transformer where we cannot re-align the phasing as there are 3 phase customers being fed off the transformer, we use a DY1 transformer but swap the yellow and blue phases on both the HV and LV sides.
There are areas of the UK distribution network where there are a variety of different vector group, and this might explain the different configuration of the OHL.
Ian
Edited to correct spelling etc
[This message has been edited by ianh (edited 07-06-2004).]
