OPTIMAL SWITCHING FOR MINIMIZING LOSSES IN SYNERGEE SIMULATION

OPTIMAL SWITCHING FOR MINIMIZING LOSSES IN SYNERGEE SIMULATION
What is Optimal Switching in the electrical distribution system?

Optimal switching
SynerGEE's optimal switching application is a powerful tool that helps you find the best operating state for feeder switches. The application accounts for exceptions, low voltages, demands, and other objectives. It is easy to use and produces a clear and understandable summary report with suggested switching operations.

Application operation
The optimal switching tool finds the local extreme for a single objective. The analysis starts with a base load-flow run with switches in their pre-analysis state. From all available switching pairs it finds the switching pair that would result in the best evaluation of the objective. A switching pair is one open switch and one closed switch combination. The tool performs the switching operation, runs a new load-flow, then repeats the process until no switching pairs result in an improvement of the objective. As such, the operations are cumulative.

The SynerGEE approach, called local optimization, optimal switching reaches a solution through successively realizable states. SynerGEE avoids a second approach, known as global optimization, in which the objective may be found by initially opening all switches and then reconnecting the system. Global optimization tends to lead to theoretical results that are not very practical, for the following reasons.

• Getting from the base state to a global optimum state may require cumbersome switching plans and contingency studies.

• A global state may be unachievable without causing an outage.

• Reaching a global state can be expensive in terms of line crew time.

A clear benefit of the local method used by optimal switching is the ease of actual implementation of the results. You can apply results in the model or in the actual system in a step-by-step fashion, without losing any loads or customers. You may implement as many recommendations as desired. For instance, if a report lists eight switching operations, you may look at the various items within the report and decide to apply only the first three operations. Keep in mind that the results are generated in a cumulative manner according to performance, and should be implemented in order. If you had eight recommended operations, you could choose to implement operations 1, 2, and 3, but implementing 1, 3, and 7, for instance, would produce unpredictable results, irrelevant to the analysis you performed.

Optimal switching does not make changes to the network model; it simply reports recommendations. All switching operations involve all phases of the relative sections. The analysis includes all selected feeders. The program ignores switches tied to feeders that are not selected in the current view.

 A feeder "owns" all sections to which it is electrically tied. Therefore, a section's feeder may change many times during an analysis.

Objectives
Optimal switching may be set up to toggle switches to achieve one of the following objectives. These objectives are independent and evaluated for all feeders selected within the view used to invoke the application.

• Minimize losses—Switches are toggled to reduce the total kW loss for all selected feeders.

• Improve lowest voltage—Switches are toggled in order to obtain the best low voltage for all sections in all feeders being analyzed. The section having the lowest voltage may change from the original run and the summary as successive switching operations are evaluated and performed.

• Minimize number of exceptions—Loading and voltage exception counts are minimized through switching operations. The total count from all feeders being analyzed is considered.

• Minimize feeder demand—This selection allows optimal switching to find the lowest total kVA demand for all feeders being analyzed. Since the total for all feeders is considered, the demand for particular feeders could conceivably increase and be offset by a reduction in the demand on other feeders.

• Minimize feeder kVA imbalance—Percent kVA imbalance calculations are made for each feeder. Switching operations are performed to reduce the average of all feeder imbalance values.

• Minimize substation transformer loading—Switching operations are made to reduce the total loading on all substation transformers. If no substation transformers are in the selected feeders, loading on all primary transformers is considered.

• Equate loading—Switches are toggled to move load so that the total load is distributed more evenly among the feeders. The analysis results table lists values for all of these options, regardless of which objective was selected for optimization.

Constraints
In optimal switching, the application is constrained by the requirement to improve the single objective. It also recognizes a maximum number of switching operations, which you can specify. Voltage and loading constraints are in place to disallow any switching operation that would result in a device loading exceeding the loading limit or a section voltage falling under the voltage limit.

Application output
SynerGEE's optimal switching tool produces a report with the components of a load-flow analysis, including a standard heading and message summary. It also produces a detailed load-flow report and switch summary.

source: synergee technical reference