GE D90 Plus Instruction Manual page 190

POWER SYSTEM
CT/VT input channel configuration
Signal source settings
180
The internal grouping of current and voltage signals forms an internal source. This source
can be given a specific name through the settings, and becomes available to protection
and metering element in the D90
clearly identify them for later use. For example, in the scheme shown above, a source
configured as the sum of CT1 and CT2 can be assigned the name "Line Current".
Once the sources have been configured, they are available as selections for the choice of
input signal for the protection elements and as metered quantities.
The previous section explains how the input channels are identified and configured to the
specific application instrument transformers and the connections of these transformers.
The specific parameters to be used by each measuring element and comparator, and
some actual values are controlled by selecting a specific source.
The source is a logical group of current and voltage input channels selected by the user to
facilitate this selection. With this mechanism, a user does not have to make multiple
selections of voltage and current for those elements that need both parameters, such as a
distance element or a watt calculation. It also gathers associated parameters for display
purposes. The basic idea of arranging a source is to select a point on the power system
where information is of interest. An application example of the grouping of parameters in a
source is a transformer winding, on which a three-phase voltage is measured, and the sum
of the currents from CTs on each of two breakers is required to measure the winding
current flow.
Select the Settings > Protection > Power System > Signal Sources menu item to open the
protection sources configuration window.
Figure 159: Protection sources configuration settings
Settings are available for all three sources. The "LINE", "BKR1", and "BKR2" text items can
be replaced by with a user-defined name to uniquely identify the associated source.
It is possible to select the sum of two CTs for a protection source. The first channel
displayed is the CT to which all others will be referred. For example, the selection "J1+J4"
indicates the sum of each phase from channels J1 and J4, scaled to whichever CT has the
higher ratio.
The approach used to configure the protection sources is detailed below.
1. Specify the ratio and nominal secondary current for each CT input.
2. Specify the connection type, ratio, and nominal secondary voltage for each VT input.
3. Specify the configuration for each source, including the CTs to be summed together.
The following settings are available for each protection source.
Plus
. Individual names can be assigned to each source to
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION