Sel SEL-787 - Page 102

4.16
SEL-787 Relay Instruction Manual Date Code 20150130
Protection and Logic Functions
Basic Protection
The Complete List of Compensation Matrices (m = 1 to 12)
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 sequence (ABC
or ACB). The following brief review discusses the nature of various
connections, their phase shifts, and the reference motion for selection WnCTC
based on system phase rotation. This review primarily explains the flexibility
the relay offers in selecting the WnCTC settings for your application.
Although the relay offers flexibility in choosing compensation settings, there
are combinations that are preferable over others. The last section of the review
concludes with an overview of preferred WnCTC settings for different
transformer connections.
Winding Connection Review
Figure 4.7 shows the three basic winding connections, consisting of a wye
connection and the two possible delta connections.
CTC 1
1
3
-------
1 –1 0
0 1 –1
–1 0 1
= CTC 2
1
3
---
1 –2 1
1 1 –2
–2 1 1
=
CTC 3
1
3
-------
0 –1 1
1 0 –1
–1 1 0
= CTC 4
1
3
---
–1 –1 2
2 –1 –1
–1 2 –1
=
CTC 5
1
3
-------
–1 0 1
1 –1 0
0 1 –1
= CTC 6
1
3
---
–2 1 1
1 –2 1
1 1 –2
=
CTC 7
1
3
-------
–1 1 0
0 –1 1
1 0 –1
= CTC 8
1
3
---
–1 2 –1
–1 –1 2
2 –1 –1
=
CTC 9
1
3
-------
0 1 –1
–1 0 1
1 –1 0
= CTC 10
1
3
---
1 1 –2
–2 1 1
1 –2 1
=
CTC 11
1
3
-------
1 0 –1
–1 1 0
0 –1 1
= CTC 12
1
3
---
2 –1 –1
–1 2 –1
–1 –1 2
=