See Also
The Bus Marginal Loss Sensitivities Dialog is used to calculate and display the sensitivity of a real power loss function, PLosses, to bus real and reactive power injections. Stated mathematically, the display calculates d PLosses/d Pi and d PLosses/d Qi , where Pi and Qi are the real and reactive power injections at bus i, respectively.
Stated less formally, the display indicates how losses would change if one more MW or Mvar of power were injected at bus i. Simulator can calculate the losses for a bus relative to losses in the bus’ island or area, to losses in a select group of areas, or, if the bus belongs to a super area, to losses in the bus’ super area. How Simulator computes the losses is governed by the value of the Loss FunctionType option.
The Loss Function Type may assume one of the following six values:
Do Not Calculate Bus Loss Sensitivities
No Losses are calculated because a loss function is not specified.
Each Electrical Island
Existing loss Sensitivities: Losses are calculated with respect to the losses in bus’ island. If the power system consists of only one island, losses are computed with respect to the total system losses.
Island Loads: Losses are calculated with respect to the losses in the island load buses.
Injection Group:. Losses are calculated with respect to the losses in island load buses that correspond to the injection group buses of the participation objects that correspond to the island.
Each Area
Losses are calculated with respect to the total losses for the area containing bus i. This is probably the most common loss function because usually one is concerned with minimizing losses for a particular area rather than for the entire case.
Use Area Loss Reference: Losses are calculated as explained before but with respect to a reference. The choices are Existing loss sensitivities directly, Area’s Bus’ Loads, Injection Group, or a specific bus.
Each Area or Super Area
Losses are calculated with respect to the total losses for the area containing bus i if bus i does not belong to a super area, and with respect to the total losses for the super area containing bus i if bus i does belong to a super area. When a case contains Super Areas this is more commonly done. When Simulator calculates loss sensitivities internally for use in the Economic Dispatch or the Optimal Power Flow calculation, this is the option which is used.
Use Super Area Loss Reference: Losses are calculated as explained before but with respect to a reference. The choices are Existing loss sensitivies directly, Super Area’s Bus’ Loads, Injection Group, or a specific bus.
Areas Selected on Loss Sensitivity Form
Losses are calculated with respect to the total losses for a group of areas, specified in the Selected Areas table.
User-Specified
If you select User-Specified as the loss function type, the values last calculated using a different loss function type will become fixed. Thus you can force the loss sensitivities to remain constant when used in other features and tools of Simulator.
In steady-state power system operation, total generation must always equal total load plus losses. Therefore, the real power injection at a single bus cannot be changed arbitrarily; it must be met by a corresponding change somewhere else in the system so that the total power remains balanced. In other words, the change in power injection must somehow be absorbed. How the injection is absorbed depends on the Loss Function Type. If the Loss Function Type is Each Island, the injection is absorbed by the island slack. For the Each Area and Selected Areas loss functions, the injection is absorbed at the area tie-lines.
The loss sensitivities are calculated by modeling an injection of power at a bus and then assuming that this injection is absorbed by the island slack bus. The sensitivity then shows how much the losses (for the region of interest) increase when you transfer 1 MW at the injection bus to the island slack. The "region of interest" is what was chosen as Island, Each Area, or Selected Areas.
Therefore, the "absolute numbers" given by the loss sensitivity dialogs are not directly meaningful because we are always assuming that the absorbing point is the island slack bus. What is meaningful is the "difference" between sensitivity numbers.
Example:
Assume the sensitivities are calculated to be
Bus A Loss MW Sensitivity = -0.04 = Asens
Bus B Loss MW Sensitivity = -0.02 = Bsens
Bus C Loss MW Sensitivity = +0.03 = Csens
Using these we can then look at the sensitivity of generic transfers between these buses by using "superposition".
Consider the following change in injections modeling a transfer of power from Bus A to Buses B and C.
Bus A injection = +10 MW = AMW
Bus B injection = - 6 MW = BMW
Bus C injection = - 4 MW = CMW
An estimate of the change in losses can then be calculated as
Loss Change = (AMW)(Asens) + (BMW)(Bsens) + (CMW)(Csens)
= (+10)(-0.04) + (- 6)(-0.02) + (- 4)(+0.03)
= -0.4 MW
The Bus Marginal Loss Sensitivities Dialog houses the following controls:
Selected Areas Table
This table is used only when the Loss Function Type is set to Selected Areas; otherwise, it is ignored. Left-click on the Include field to include or exclude areas from the loss function.
Calculate Marginal Loss Sensitivities Button
Once the loss function type has been specified, click this button to calculate the bus marginal loss sensitivities and update the Bus Marginal Loss Sensitivities table.
Bus Marginal Loss Sensitivities Table
This table shows the bus marginal loss sensitivities for all buses with valid Area/Zone/Owner filters. The Bus Marginal Loss Sensitivities Table is a type of Case Information Display and thus exhibits features and behavior similar to all other case information displays. It has a local menu from which you can choose to find out more about a particular bus. You can sort records by any of the listed fields by clicking on the column headings. The table contains the following fields:
Number, Name: Number and name of the bus.
Area Number, Area Name: Number and name of the bus’ area.
Loss MW Sens:. Sensitivity of the loss function to an increase in the real power injection (generated power assumed positive) at the bus.
Penalty Factors: Computed penalty factor of each bus.
MVR Sens:. Sensitivity of the loss function to an increase in the reactive power injection (generated power assumed positive) at the bus.
If using the Integrated Topology Processing add-on, an Only show the primary bus for each superbus checkbox will be available for this table. Checking this box will limit the buses show to only those that are primary buses. This provides a quick means of removing the clutter of redundant data. The primary buses and superbuses are determined from the base case topology.
Just Generators Marginal Loss Sensitivities Table
This table shows the bus marginal loss sensitivities for only the generator terminal buses with valid Area/Zone/Owner filters. This table is otherwise identical to the displayed values and table operation as the Bus Marginal Loss Sensitivities Table described above.
Areas Marginal Loss Sensitivities Table
This table shows the Areas Energy/Loss ref String and Energy/Loss Ref Type used for the losses references when the Use Area Loss Reference option is selected.
Super Areas Marginal Loss Sensitivities Table
This table shows the Super Areas Energy/Loss ref String and Energy/Loss Ref Type used for the losses references when the Use Super Area Loss Reference option is selected.