optimal capacitor placement

8/10/2019 Optimal Capacitor Placement

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Optimal Capacitor Placement

NEPLAN User's Guide V5 16-1


Introduction

Purpose of this program module is to identify key locations in the radial primaryfeeders of a distribution network, where the placement of shunt capacitorsminimizes the MW losses. The program will come up with such installations,where each installation consists of

1. the bus of the primary feeders where a shunt capacitor would be located2. the MVAR size of the capacitor3. the additional reduction in MW losses (in %)

Theory

Structure of the distribution networkThe following figure shows the structure of a distribution network, its mostimportant elements and the nomenclature used in this chapter.

Subtransmissionnetwork

Voltageregulation+ meters

Primaryfeeders

Distributionsubstation

Primaryfeeder bus

Fig. 16.1 Distribution network structure


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Primary

feeder bus

Fig. 16.2 Primary feeder

Distribution systems provide power to a wide variety of load types. Resistive loads(power factor = 1.0) require no reactive power at all, while inductive loads (powerfactor < 1.0) require both active and reactive power. Inductive loads (e.g. motors)are always present so that the line current consists of a real (or resistive)component and an inductive component. Both components contribute to the MWlosses (which are proportional to the square of the current magnitude), voltagedrop and line loading (measured in A or MVA). The resistive component of thecurrent cannot be substantially reduced as this is the part of the current thatactually perfoms work (defined by demand). The reactive component of thecurrent can be reduced by installation of capacitors close to the loads. This has

the effect that the reactive power needed is generated locally and the distributioncircuits are relieved from the reactive power transfer. Effective placement of theshunt capacitors (depending on the situation) can improve the voltage profile andcan greatly reduce the losses and the line loading.

The program will propose locations for the placement of shunt capacitors with thepurpose of reduction of losses in the primary feeders. The method used for thecapacitor placement module in NEPLAN performs a maximization on the MWsavings from an installation of a shunt capacitor. Only buses on the primaryfeeders are candidate buses for capacitor location. The user has to make surethat only these buses are activated as candidate buses in the respecive list (seeparameters).

The primary feeder bus is the bus after the distribution substation (see figure16.1). There can be more than one primary feeders. Each primary feeder mustbe radial, i.e. there must be only one flow path from every node to the primaryfeeder bus (see figure 16.2). The user should select the primary feeder bus insuch a way, that all the transformers, switches etc. are behind that bus. Ideallythe primary feeders should only contain transmission lines, cables and any other

one-port elements.


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Note that only the losses of the feeder (and not transformer losses) areconsidered. No optimisation is performed in terms of costs (operating orinstallation). However, there is a number of certain parameters imposingconstraints on the installed MVar and number of installations (see Calculation

Parameters).

Calculation Parameters (CP)

The calculation parameters are entered with the help of a "Parameters" dialog,which is explained below.

Parameters

Primary FeederBus

The bus from which all primary feeders start. Make sure alltransformers and switches are behind this bus.

Switch off existingcapacitors

This option ignores the existing capacitors for the CPanalysis (they are not physically disconnected).

Suppress LFOutput

This option suppresses almost all messages (but not errorsor warnings) from the LF (load flow) calculations in the

Analysis window.

CheckOvercompensation

With this option activated the kVAR size of a capacitor willnot be higher than the Q flow (of the initial load flow) at thatline end.

Max. number ofinstallations

The maximum number of capacitors that will be installed. Ifset to 0 (zero) then the maximum number of installations isequal to the number of candidate buses selected in theCandidate Buses List.

Increment size(kVar)

Used for discretization of the rated power. The minimumincrement of kVar power.

Max. tot. kVarinstalled

The maximum total kVar rated power that should beinstalled. If set to 0 (zero) no limit is imposed.

Variable Load

Variable SlackVoltage

With this option activated the user can give a different setvoltage for the network slack for every load factor.

Min. Load Factor The minimum load factor (scaling factor) for all the loads ofthe selected partial network (same for P and Q demand)

Slack voltage In %. The set voltage of the slack bus for the minimum loadfactor

Max. Load Factor The maximum load factor (scaling factor) for all the loads of


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the selected partial network (same for P and Q demand). Ifthe minimum and maximum load factor are equal only thisload factor is considered.

Slack voltage In %. The set voltage of the slack bus for the maximumload factor

Create Capacitors

Create If set then the capacitors in the results table after acalculation will be created and connected to the network

Min. Load Factor the minimum load factor is considered for the placementand sizing of the capacitors to be created (see Results)

Max. Load Factor the maximum load factor is considered for the placementand sizing of the capacitors to be created (see Results)

Select Partial network

Partial Networklist

The user has to select one and only one of the feeded partialnetworks listed in this dialog.

Candidate Bus List

Candidate BusList

The user has to select the candidate buses for capacitorplacement. The user has to make sure that all buses behindthe primary feeder bus are unselected.

Consider forplacement

Select/Unselect option

Sort Consider Sort buses by Consider value (ascending order)Sort by ID Sort buses by Bus ID number (ascending order)Sort by Name Sort buses by Bus Names (ascending order)

Sort by Un Sort buses by nominal bus voltage (ascending order)

Results

The results of the CP Analysis can be viewed with the menu option Analysis Capacitor Placement Select results or the push button Select results.


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Installations

For every load level there is a number of proposed installations. Theseinstallations can be viewed by pressing the Results Installations button.

Load factor The load factor for the loads of the selected partial network(Note: not of the primary feeder).

Bus ID The ID number of the bus where the capacitor is placedBus Name The name of the bus where the capacitor is placedSize In kVar. The size of the capacitorLosses In MW. The losses with the capacitor connected. In the first row

with the load factor the original state losses (no installations)are shown.

Additional MWloss reduction

In % of the orig. state (load flow) MW losses. The additionalMW loss reduction that would be achieved with the capacitorconnected.

Voltage Profiles

The voltage profiles before and after the installations shown in Results Installations can be viewed by pressing the Voltage Profiles button.

Bus ID The ID number of the busBus Name The name of the busu(LF,Min) In % of the nominal bus voltage. The orig. state % voltage of

the bus for the minimum load factoru(CP;Min) In % of the nominal bus voltage. The new % voltage of the bus

for the minimum load factor and for the installation proposed forthe minimum load factor

u(LF,Max) In % of the nominal bus voltage. The orig. state % voltage ofthe bus for the maximum load factor

u(CP;Max) In % of the nominal bus voltage. The new % voltage of the busfor the maximum load factor and for the installation proposedfor the maximum load factor

optimal capacitor placement

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