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The prerequisites to be able to perform a calculation with load calibration is:
- A network that has the correct topology (connected correctly, correct switch state on switch distribution)
- Correct loads and effects on consumption- and Production plant
- Either Measured current- or Power values (Apparent or active) for bay.
Measurement values can be added on incoming and/or outgoing bays and on bays on the downside of the transformer in stations.
Maximum number of iterations, number
The number of calculations that can maximum be performed during the load calibration. If the maximun number is reached before the convergence criteria is reached, the calculation is canceled and present the latest calculation as result. The user will get a notification about reached accuracy.
Convergence criteria, all measuring points, %
Indicated in percent and refers to the mean of the ratio between measured currents and calculated currents for all measuring points. If the ratio in percent is less or equal to the stated convergence criterion, the calibration is terminated and the result is presented.
Convergence criteria, individual measuring points, %
Indicated in percent and refers to the ratio between measured current and calculated current for an individual measuring point. If the ratio in percent for all individual measurement points is less or equal to the stated convergence criterion, the calibration is terminated, after which the result is presented.
Manage power loads, on/off
Option to exempt power-based load from calibration. Energy loads will always be included in the calibration, but with this choice one can determine how power loads that are either on connection points or are summed on Bus Bars should be handled. If the checkbox is marked, the power loads are calibrated, if the checkbox is unmarked, power loads are treated statically in the calibration.
Parameters for meshed networks
Under Parameters for meshed networks there are two available options:
- Merge of measured points.
- Meshes included in calibration.
1.A normal load flow calculation is performed. Estimated currents corresponding to all measuring points are identified.
2.For each measuring point, all underlying imported loads are identified. There may be measurement points on several levels. There may therefore be measuring points that lie below another measuring point in the feeding order. The result is a list of the "islands" that each of the measurement points form. If there are islands in islands, this will also be handled.
3.For each island (measuring point), a correction factor is calculated, which corresponds to an increase or decrease in the load level in order to achieve a desired current. The correction factor is calculated from the difference between measured and calculated value for current / power. If one has chosen not to calibrate power loads, the proportion of power load for each island will be identified and the correction factor will be calculated from the fact that the power load part is static. This means that when only the energy loads are to be corrected, a "larger" factor will be needed for the desired result.
4.The stated loads are corrected based on calculated correction factors and then a new load calculation is performed. If the convergence criterion or the maximum number of iterations is achieved, the calibration is interrupted, after which the result is presented to the user. Otherwise, please go back to paragraph 2. above.
Masked nets are not completely handled and the calibration is therefore performed with a simplified model. Instead of performing a load calculation per iteration, two calculations are performed.
First, a load calculation is performed when the meshes are included and from this calculation the sections where the current is lowest are identified. To get a radial network, the lines with the lowest current are then disconnected before a new load calculation is performed. From calculation number 2, the correction factor for each island is calculated and otherwise the calibration takes place as for radial networks.
This method works well on nets where the stitches lie far out of the feed point. In the case of meshes near the feed point, for example, in case of several parallel and joined sections from one outgoing group to a common point in the network, it is advisable to merge these groups during the calibration and calibrate them as a single measurement.
Existing solution for inserting current or power values
Example on how to add a current value in a bay:
1.Find a measure value for the bay. The value usually comes from an outside measurement value database.
2.Open the attribute form for a bay.
3.Open the Bay measurement tab.
4.Press Add.
5.Make sure to enter a Measurement grouping. The format should be a number. The number should be unique for each load calibration performed.
6.Enter the current that should be used during calibration in the Measured current field
7.After tracing the network to be used for load calibration, enter the loads to consider in the Load values tab.
8.In the bay measurement dialog found in the Load calibration tab, enter the ID used as Measurement grouping when adding measure values for the bay.
9.Finally, check the box Activate load calibration in the tab Load calibration before pressing Start network calculation.
When the calibration is converged or terminated due to the maximum number of itterations achieved, the last load calculation will be read to the dpPower Analyzer as a normal calculation. Printing detailed information regarding the calculation process can be obtained as an additional report from the results archive.
The report is found by opening the Result/administration dialogue adn right-click on the calculation to open the right click menu and select Show extra report.
Example on logging from calibration.
LOAD CALIBRATION
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Measure point : ÄT13/LÄT13-B Current : 95.0 A
Measure point : ÄT13/LÄT13-B Current : 46.0 A
Measure point : ÄT13/LÄT13-B Current : 25.0 A
Lap : 1 Total difference : 27.24 %
Measure point : ÄT13/LÄT13-B Calculated current : 85.87 A Difference : 9.61 %
Measure point : ÄT13/LÄT13-B Calculated current : 46.32 A Difference : 0.69 %
Measure point : ÄT13/LÄT13-B Calculated current : 42.86 A Difference : 71.44 %
Lap : 2 Total difference : 1.74 %
Measure point : ÄT13/LÄT13-B Calculated current : 95.28 A Difference : 0.29 %
Measure point : ÄT13/LÄT13-B Calculated current : 45.84 A Difference : 0.34 %
Measure point : ÄT13/LÄT13-B Calculated current : 23.85 A Difference : 4.59 %