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Dear Madam/Sir,

My question is: How the Vector group of step - up transformer to be written? For example:

A. Step - up transformer rating: 1000kVA Primary (Input) voltage: 0.4kV Secondary (output) voltage: 354kV

B. For the sep - down transformer 1000kVA/35/0.4kV, Vector group; Dy11 - no question). In the transformer books, we can only see transformer group of step-down transformer.

When we say "step - up transformer," How the connection group to be defined: Voltage vector of HV 35kV to be taken for reference or Voltage vector of LV 0.4kV and how it to be written:

I can not understand what is wrong, what is right:

- some people say: y/D11 is right (1) - other people say: D/y11 is right (2)

Please be so kind to let me know what is wrong: (1) or (2).

I will be very thankful to your help.

Thank you and best wishes.