GE D90 Plus Instruction Manual page 65

CHAPTER 3: INSTALLATION
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PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Channel 7 can be used for either of two purposes. First, it can be connected to a CT that is
directly measuring system ground current. It can also be connected to the CT residual
circuit of a parallel line.
If connected to the CT residual circuit of a parallel line, the input provides a signal for zero-
sequence mutual coupling compensation for the distance element. If this compensation is
required, the zero-sequence current from the parallel line (3I_0) measured in the direction
of the zone being compensated must be connected to the ground input CT of the CT bank
configured as the distance source.
Verify that the connection made to the relay nominal current of 1 A or 5 A matches the
secondary rating of the connected CTs. Unmatched CTs can result in equipment damage
or inadequate protection.
The CT secondaries should be connected to the AC terminals of the D90
shorting-type test switch or shorting-type terminal blocks in order to facilitate safe
withdrawal of the AC module.
There are no internal ground connections on the current inputs. Current transformers with
1 to 50000 A primaries and 1 A or 5 A secondaries may be used.
CT connections for both ABC and ACB phase rotations are identical as shown in the typical
wiring diagram.
The exact placement of a zero-sequence core balance CT to detect ground fault current is
shown below. Twisted-pair cabling on the zero-sequence CT is recommended.
Figure 24: Zero-sequence core-balance CT installation
The phase voltage channels are used for most metering and protection purposes. The
auxiliary voltage channel is used as an input for features such as synchrocheck, volts per
hertz, and auxiliary undervoltage.
A typical AC module wiring diagram is shown below. Substitute the tilde "~" symbol with
the slot position of the AC module.
ELECTRICAL INSTALLATION
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