Schweitzer Engineering Laboratories SEL-787 - Page 93

4.15
Date Code 20081022 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Basic Protection
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 WnCTC 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 WnCTC
based on system phase rotation.
Winding Connection Review
Figure 4.7 shows the three basic winding connections, consisting of a wye
connection and the two possible delta connections.
CTC 5()[]
1
3
-------
–1 0 1
1 –1 0
0 1 –1
•=CTC6()[]
1
3
---
–2 1 1
1 –2 1
1 1 –2
•=
CTC 7()[]
1
3
-------
–1 1 0
0 –1 1
1 0 –1
•=CTC8()[]
1
3
---
–1 2 –1
–1 –1 2
2 –1 –1
•=
CTC 9()[]
1
3
-------
0 1 –1
–1 0 1
1 –1 0
•=CTC10()[]
1
3
---
1 1 –2
–2 1 –1
1 –2 1
•=
CTC 11()[]
1
3
-------
1 0 –1
–1 1 0
0 –1 1
•=CTC12()[]
1
3
---
2 –1 –1
–1 2 –1
–1 –1 2
•=