Appendix; Description - GE 469 Instruction Manual

Two-Phase CT Configuration

Description

GE Multilin

8 Appendix

Two-Phase CT Configuration
This appendix illustrates how two CTs may be used to sense three phase currents.
The proper configuration for the use of two CTs rather than three to detect phase
current is shown. Each of the two CTs acts as a current source. The current that
comes out of the CT on phase A flows into the interposing CT on the relay marked A.
From there, the current sums with the current that is flowing from the CT on phase
C which has just passed through the interposing CT on the relay marked C. This
'summed' current flows through the interposing CT marked B and from there, the
current splits up to return to its respective source (CT). Polarity is very important
since the value of phase B must be the negative equivalent of A + C in order
for the sum of all the vectors to equate to zero. Note that there is only one
ground connection as shown. If two ground connections are made, a parallel path
for current has been created.
A B
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Motor Management Relay
C
:5
:COM
:5
:COM
:5
:COM
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A
B
C
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