optimal distribution network

8/10/2019 Optimal Distribution Network

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Optimal Distribution Network

NEPLAN User's Guide V5 7-1


Calculation Parameters (ODN)

The dialog box for the calculation parameters appears after having selected"Calculation - Optimal Distribution Network - Parameter...".

Voltage: Voltage level of distribution network in kV

Load data: The minimum and maximum active and reactive power of

loads are either fixed by means of load factors or 2 loadingdata files (.ndb).

Calculationmodel:

2 states:to get the extreme values of the load flow results,only the minimum and the maximum load state areconsidered.

Automatic:the number of load states to be considered is fixedautomatically.

Optimization: Normal switching, N-1 calculation.:selection, if the objectivefunctions are optimized regarding the normal network

operation or regarding line failures (N-1-security check). Ifnothing is selected, only an evaluation of the network is done.

Opt. MV/LV-trans. Tap:the MV/LV-transformer taps areoptimized. This concerns only the optimal transformernominal voltage calculation.

Valuation initialnetwork:

Selection, if the load flow results are shown only for thenormal network operation or also for the (N-1)-security checkare shown. If at least 1 (N-1)-optimization is selected, the(N-1)-security check results are shown.

Results: Value setting: if this option is active the input data of thenetwork is modified according to the optimization.

Graphical:after the calculation the result window appearsautomatically. This window also appears after havingselected "Calculation - Optimal Distribution Network -Chart...".

The user defined voltage limits appear and can be changed if the menu option"Calculation - Load Flow - Reference Voltages..." is selected. In this calculation

module only the limits of node voltages of the considered voltage level (mediumvoltage level) are used. The procedure chooses for the calculation and the


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7-2 NEPLAN User's Guide V5

graphical results from the user defined limits and from the predetermined normthe stricter rules. The user defined limits have the default values 95% and 105%.

Graphical Results

The graphical results window appears after having selected "Calculation -OptimalDistribution Network - Chart...". The value to be shown can be selected with themenu option "Results". Only results of the considered voltage level are shown.

Chart Parameters

The parameter window appears after having selected "Chart - Parameters...".

Select nodes /elements:

All nodes/elements: results of all nodes/ elements of theconsidered voltage level are shown.

Result list:only results of selected nodes/ elements areshown.

Node list,element list:result list for nodes/ elements

Title: User defined title

Default title: The default title is shown. If this option is not selected, theuser defined title is shown. If this option is not selected and"Title" has no entry, no title is shown.

Grid: Grid on/ off

Black/white: Black/white on/ off

Ymin: User defined lower limit of y-axis. If the field is empty, thevalue is fixed automatically.

Ymax: User defined upper limit of y-axis. If the field is empty, thevalue is fixed automatically.

Show names: Node names/ element names are shown/ not shown on x-axis

Show nodenames:

If this option is selected and element values are shown, notonly the element names but also the node names areshown. This option has only an influence, if "Show names"is selected.


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Chart Representation

Node Voltages

The fat bars show the value ranges of node voltages for the normal networkoperation. The overlying thin bars show the value ranges of the (N-1)-securitycheck. The results of the (N-1)-security check are only shown if the calculationparameter "N-1 calculation" in "Valuation initial network" is selected or if at leastone (N-1)-calculation was performed.

Line Currents, Element Loadings

The results of the normal operation case and of the (N-1)-security check(maximum line currents/ maximum element loadings) are represented as parallelbars. The results of the (N-1)-security check are only shown if the calculation

parameter "N-1 calculation" in "Valuation initial network" is selected or if at leastone (N-1)-calculation was performed.

Voltage Limits

The voltage limits in the normal operation case are shown as dashed lines. Thevoltage limits in the exceptional case (N-1-security check) are shown as plainlines.

Text Results

Text File

The calculated optimal values are listed in a text file if the load flow parameter"Text file" is selected ("Calculation - Load Flow - Parameters..."). The text file is

shown after having selected the menu option "Results - List - Last Calculation...".It can also be opened by an external text editor.

Result File

The extreme values of the node voltages and the element loadings are listed in aresult file if the load flow parameter "Result file" is selected ("Calculation - LoadFlow - Parameters..."). The result file can be used by external programs (e.g. MS-Excel).


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Error File

Comments and error messages are listed in the error file. It is always shown if theload flow parameter "Iteration caracteristics" is selected ("Calculation - Load Flow- Parameters... - Iteration Data...")

Theory

The module Optimal Distribution Network optimizes the operation of distributionnetworks regarding different objective functions. Distribution networks have

usually meshes but they are radially operated. In the normal operation casenetwork losses can be minimized selecting optimal separation points. In case ofelement failures some portion of the system may be out of service and can beresupplied by changing the separation points. Dispersed generators may feedenergy into the distribution system. The HV/MV-transformers usually have voltagecontrol with possibly active compounding. The MV/LV-transformers have novoltage control, but their taps can be changed by hand mostly.

Normal Operation and (N-1)-Security Check

It is distinguished between the optimization of the system in the normal operationcase and in the case of line failures.

Valuation of Normal Operation

Several load flow calculations are performed in order to estimate the value rangesof the node voltages and the element loadings. The number of load flowcalculations is dependent on the selection of the calculation parameter"Calculation model". The results are value ranges of the node voltages and themaximum loadings of the elements (lines, cables, transformers).

Valuation by (N-1)-Security Check

The (N-1)-security check simulates a failure for each element of the consideredvoltage level. If some part of the system is out of service because of this failure,the procedure changes the network topology in order to resupply this part and tominimize losses (optimal separation points procedure). An evaluation of the newnetwork state is done after each failure. The results are value ranges of the nodevoltages and the maximum loadings of the elements (lines, cables, transformers).


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Optimization

The four optimization procedures are performed in the predetermined order andindependently of each other. The calculated optimal values of the precedingoptimization procedure are taken on.

Optimal Separation Points

Network losses of the high load case are minimized applying the optimalseparation points procedure in accordance with chapter "Optimal SeparationPoints".

Compounding

The goal is to aligne the value ranges of the MV-nodes reducing the big ones and

increasing the small ones. The procedure changes iteratively the compoundingdata of the HV/MV-transformers if their voltage control and their compounding areactive. The predetermined values Umin and Umax remain constant and thevalues Imin and Imax are changed. The smaller the range between Umin andUmax is, the lower is the influence of the compounding on the node voltages.

Cosphi-Values of Cosphi-Controlled Generators

The control input "Cosphi oper" of cosphi-controlled generators with type "Cosphiconstant" is changed. The goal is to find feasible values as close as possible to 1

in order to minimize network losses. If the voltage range of the correspondingnode amounts more than 80% of the range between the upper an lower voltagelimit, the cosphi-value is changed so that the generator consumes inductivereactive power. "Cosphi oper" must not leave the feasible domain defined by"Cosphi lim1" and "Cosphi lim2".

Transformer Nominal Voltages

The goal is to set the nominal voltages of the voltage controlled HV/MV-transformers as high as possible, in order to minimize network losses. The node

voltage limits are considered. If the calculation parameter "opt. MV/LV-trans. tap"is active, the taps of the MV/LV-transformers are changed too. The procedureproceeds iteratively. It is only successful if the HV/MV-transformers have asufficiently big number of tap steps and a sufficiently big magnitude of theadditional voltage per tap step.

Voltage Limits

On the low voltage level voltages must be within the limits +6% and -10% in thecase of normal operation and +6% and -15% in the exceptional case. These limitsare converted to the medium voltage level under consideration of the voltage dropin the low voltage network (5%) and over the MV/LV-transformer. This yields the


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allowed voltage range of each MV-node. The procedure chooses for thecalculation and the graphical results from the user defined limits and from thepredetermined norm the stricter rules. The user defined limits have the defaultvalues 95% and 105%.

The voltage limits are always shown in the graphical result window. However, theyare only considered by the last optimization procedure (transformer nominalvoltages).

optimal distribution network

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