Ac Modules - GE D90 Plus Instruction Manual

CHAPTER 3: INSTALLATION

AC modules

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D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
An AC module has voltage inputs on channels 8 through 12 inclusive. Channel 10 is
intended for connection to a source that represents phase A voltage of the power system
(produced by a VT or CVT). Likewise, channel 11 is intended for connection to phase B, and
channel 12 is intended for connection to phase C. The phase voltage channels are used for
most metering and protection purposes.
Channels 8 and 9 are intended for connection to single-phase sources. In the D90
of these inputs are typically used to measure the voltage on the side of the breaker
opposite to the line terminal. Each of these channels is labeled as an auxiliary voltage (VX).
The auxiliary voltage channels are used as inputs for synchrocheck, but can also be used
for auxiliary undervoltage or overvoltage elements.
An AC module has current inputs on channels 1 through 7 inclusive. In a single breaker
application, channel 1 is intended for connection to a source representing the phase A
current of the power system (produced by a CT). Likewise, channel 2 is intended for
connection to phase B, and channel 3 is intended for connection to phase C. In a breaker-
and-a-half application, channels 1 through 3 are connected to the phase A, B, and C
currents from one breaker, while channels 4 through 6 are connected to the phase A, B,
and C currents from the second breaker. The phase current channels are used for most
metering and protection purposes.
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 may 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.
ELECTRICAL INSTALLATION
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