Schweitzer Engineering Laboratories SEL-387E - Selecting the Correct Values of Wnctc for each Winding; Winding Connection Review

3-16 Protection Functions Date Code 20080110
SEL-387E Instruction Manual
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9CTC
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10CTC
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11CTC
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12CTC
The matrices for odd values of
m (1, 3, 5, 7, 9, 11) are similarly constructed, as are the matrices
for even values of
m (2, 4, 6, 8, 10, 12). Also, [CTC( m )] equals the minus of [CTC( m ± 6)],
because these matrices represent shifts separated by exactly 180 degrees.
Selecting the Correct Values of WnCTC for Each Winding
The process of choosing the correct W n CTC setting value for each winding involves a complete
knowledge of the transformer winding connections and phase relationships, the CT connections,
and the system phase rotation (ABC or ACB). The following brief review discusses the nature of
various connections, their phase shifts, and the reference motion for selecting W
n CTC based on
system phase rotation.
Winding Connection Review
Figure 3.8 shows the three basic winding connections, consisting of a wye connection and the two
possible delta connections.