The Add | Load Region command in the DS Relays Window displays a specified load region on the complex plane. This is designed as an aid to avoid load encroachment on distance relay characteristics.
TO DISPLAY A LOAD REGION:
1. Select the Add | Load Region command.
Note: This command is dimmed and cannot be execute if a load region is already being displayed. To add a new load region, you must first delete the existing load region with the Delete | Load Region command.
A dialog box will appear asking for the load region parameters.
2. Enter the load in Amperes or MVA.
If you choose to characterize the load by amperes, enter the load current as the line’s rating, adjusted by the appropriate multiplier. Please refer to the PRC-023-3 Standard for details.
If you choose to characterize the load by MVA, the load MVA must be computed using the adjusted load current, the nominal kV and per-unit voltage factor.
Note: If the relay group is on a transmission line that has a nonzero value in the Rating field, the Load current is initialize to1.5 times the line’s current rating. The line rating used for this purpose is the one that was selected in the Check | RELAY LOADABILITY COMMAND dialog box.
3. Enter the minimum power factor of the load. A lagging power factor is assumed. If the “line angle” is known, the power factor is equal to the cosine of the line angle. A line angle of 30 degrees -- which is equivalent to a power factor of 0.866 -- is required by the PRC-023 Standard.
4. Enter the load’s nominal kV and per-unit value.
A voltage that is lower than one per-unit will make load encroachment more likely. A value of 0.85 per-unit is required by the PRC-023 Standard.
5. Click on “Forward load region” or “Reverse load region” to show the load region to the right or to the left of the origin.
6. Press Show to display the load region.
The cone-shape load region will appear on the DS Relays Window.
7. Remove the load region from the distance relay window.
Select the Edit | Load Region command.
The previous dialog box will appear.
Press Hide.
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