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12 RAYTECH Switzerland
THREE PHASE TRANSFORMER TESTING: 8 – 0
Ratio tests on three phase transformers are carried out on a single phase
basis.
Understanding the configuration, phase relationship, and vector diagrams
is required.
A detailed explanation and description of terminal markings, phase
relationship, and vector diagrams is contained in specification: C57.12.70
American National Standard Terminal Markings and Connections for
Distribution and Power Transformers.
The tables on the following pages are guidelines for connecting and
testing three phase transformers.
Table Key:
VECTOR GROUP:
The vector group column is the IEC vector group coding. The number
indicates the phase displacement in increments of 30° of the low side
winding to the high side winding. For example a D-Y transformer with a
Vector group number of 3 would have a phase displacement of 3 x 30° or
90°. The low side winding has a lagging displacement with respect to the
high side winding.
PHASE:
The transformer phase that is being tested.
HV WINDING & LV WINDING:
The transformer connections that are selected for testing.
For example: D – Y, phase “A” would require H1 & H3 to be tested
against X1 & X2-X3
Note: (X2-X3 are jumpered together).
See charts on following pages:
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