HV Power transformer connection type

[PKJENNY]

Hi,

Want to get some advices on HV transformer connection type.
I see two different transformer connections in 2 different projects which are just nearby.
One is having a YY transformer (110kV), another one has a DY transformer (66kV).
I'm not sure why the design is such different given a similar site and location.
What's the design consideration in general to come up with this?
Could any transmission side engineer advise me?
Thanks a lot.

 

[bacon4life]

The GE publication The-whys-of-wyes provides good info on why to choose each configuration.

Your application also matters. Do you have a load, a generation site, or a mix of load and generation? Increased distributed generation is make wye-delta-wye transformers more attractive.