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what is a coil 'group" in a shell form transformer?

what is a coil 'group" in a shell form transformer?

what is a coil 'group" in a shell form transformer?

(OP)
The following description is provided for a 700MVA 345kv/25kv wye/delta shell form transformer;

Quote:

This...transformer design is the typical design concept that McGraw Edison used in their
three phase transformers. It has two parallel low voltage circuits and each parallel is connected in
delta. The closing of the delta was performed at the bottom of the low voltage bushings. Each
phase has four low voltage coil groups that are connected in parallel; each group has four pancake
coils. Two of the LV groups of each phase form one of the LV delta circuits.
The high voltage winding is comprised of two coil groups that are connected in series. The
winding group connected to the high voltage line bushings H1, H2 and H3, is designated as the
“line” group while the high voltage group connected to the H0 neutral bushing, is designated as
the “ground” group. Each high voltage group has ten pancake coils.
The low voltage coil groups enclose each of the high voltage groups on each phase, to form what
is known as a 4 H-L (high to low) spaces shell design.
Most of it makes sense except the concept of a "group".
On the high voltage side for example we have 20 pancake coils in series, formed into two "groups".
What is it about them that associates them with a group: are the coils in a group physically adjacent?

=====================================
(2B)+(2B)' ?

RE: what is a coil 'group" in a shell form transformer?

My guess is that it relates to manufacture. That's a pretty big transformer, and the LV coils will be substantial both in cross section and mass, so the coil assemblies may well be manufactured as separate blocks which only meet when they are on the core. Without the mechanical support afforded by the core the full winding assembly is probably unmanageable.

RE: what is a coil 'group" in a shell form transformer?

pete, Iam not a shell type transformer expert.But I guess the following as arrangement.Windings are arranged horizontally on core limb as below:

L-H-LL'-H-L' Each letter forms a bunch of pancake coils forming as a group.L-L goes one LV circuit and other L'-L' forms another parallel circuit which are taken to LV bushings.

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