Transformer Connection code

asked Oct 21 '1

Kaustubh
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As part of TPL007, I am performing GIC studies at our 345/138kV (Auto Transformers). I had a question regarding the connection codes of auto- transformers.

PSS/E documents state :

Vector Group: YNa0 Type = Core CC= 18,

Vector Group: YNa0 Type = Shell CC= 21

What is the difference between CC = 18 and CC = 21 ?

18 = Series path, ground on each side. 21 = Series path, no ground on each side.