GE D90 Plus Instruction Manual page 147

CHAPTER 7: PROTECTION
Current inputs
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
For three-phase channel groups, the number of the lowest numbered channel identifies
the group. For example, J1 represents the three-phase channel set of J1, J2, and J3, where
J is the slot letter and 1 is the first channel of the set of three channels. The first channel in
the group is identified as phase A, the second channel as phase B, and the third channel as
phase C.
Select the Settings > Protection > Power System > AC Inputs - Current menu item to
open the current inputs configuration window.
Figure 105: Current inputs configuration settings
The current inputs configuration window allows the user to specify the parameters for
each current input (represented by the module slot position letter). The
Auxiliary CT Ratio settings are used for calculation of primary metering values and for ratio
matching when multiple CT inputs are added within a source. The
settings are used to derive secondary current values from per-unit
Auxiliary CT Nominal
settings used in protection elements. This setting will typically be "1 A" or "5 A", depending
on the hardware. However, the user may enter an alternate value. For example, if a value
of "4 A" is chosen, an instantaneous overcurrent element with a pickup of 2 pu. would
operate at 8 A primary.
Since the phase CTs are connected in a wye (star) configuration, the calculated phasor
sum of the three phase currents (IA + IB + IC = neutral current = 3I0) is used as the input for
the neutral overcurrent elements. In addition, a zero-sequence (core-balance) CT which
senses current in all of the circuit primary conductors, or a CT in a neutral grounding
conductor may also be used.
The following current input settings are available.
Connection
Range; 3-Phase, 1-Phase
Default: 3-Phase
This setting specifies the connection for the F7 current input. If configured to "3-Phase",
then current inputs F7 through F9 are grouped as a three-phase bank and only the
phase CT settings are available; the F8 and F9 columns will not be displayed. If the F7
connection is configured as "1-Phase", then the auxiliary CT settings will be shown for
the F7 through F9 current inputs and the F8 and F9 columns will be displayed.
This setting is fixed to "3-Phase" for the 5VT/7CT and 4VT/4CT/1SCT modules.
Phase CT Ratio
Range: 1 to 65000 in steps of 1
Default: 1
This setting specifies the phase CT ratio for the corresponding current input. It is used for
calculation of primary metering values and for ratio matching when multiple CT inputs
are added within a source.
POWER SYSTEM
Phase CT Ratio and
and
Phase CT Nominal
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