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Quick Start | Load Flow


Load flow is implemented so that users can start a simulation from a steady-state condition. It is an analysis to determine the voltages, currents, real and reactive power flows under a given operating condition. Given the system admittance matrix, 4 variables (P, Q, V, theta) are associated with each bus to solve two power flow equations. Therefore, for each node, at least 2 out of the 4 variables should be known to solve the equations.

For background, see IEEE Std 3002.2™-2018 Recommended Practice for Conducting Load-Flow Studies and Analysis of Industrial and Commercial Power Systems.

For the use of different HYPERSIM components in load flow analysis, see Load Flow | Configuration of Components.

1 Open the Quick Start Reference Model

Launch HYPERSIM and load the model labeled Load_Flow.ecf found under Options > Open an example model > How To.

2 Build the Model

Ensure that all pertinent values have been entered when building the model (e.g. for voltage sources, ensure that you have defined both Base voltage and impedance values). Base power and Base voltage are important if voltage or impedance value is defined in per unit.

After all the parameters are configured and all the connections are made, the model is ready for load flow execution.

Without a load flow solution, all the signals in the model would start from 0. Starting with a load flow solution in place initializes the model from steady-state values.

If you click on a bus in the example model where load flow has not yet been calculated, you will see default values in the load flow results tab.

If you click on a generator, you will see the default values in Angular frequency, Voltage, Active power and Reactive power.

3 Configure the Generation

Once the model is ready, relevant generator/source parameters must be defined so HYPERSIM can solve for them in the load flow analysis.

First, choose the bus types for generators and sources, then configure the active power, voltage, and angle as required: see below.

3.1 Determine the swing bus

There should be a source/generator that serves as the swing bus, with a given voltage and angle, to provide/absorb any mismatch between the load and generation in the system. 

Double-click on voltage source VS2, in the Load Flow tab, select the Type to be Swing. Specify Voltage to be 1 pu and Angle to be 0 deg.

Note: Remember there should be only one swing bus in a network.

3.2 Configure the other sources

Similarly, configure the other generators/sources in the model. Usually, generator bus is a PV bus because it's terminal voltage and active power are regulated by the generator controller. 

Double-click on synchronous machine SM1, in the Load Flow tab, select the Type to be PV. Specify Voltage to be 1 pu and Active power to be 30 MW.


Similarly, configure VS1, SM2 and SM3 as PV buses with the following parameters in the Load Flow tab:

ComponentTypeV (pu)P (MW)

NOTE: The unit prefix may be changed by right-clicking unit and selecting the desired prefix.

4 Entering the Bus Voltage Level

To execute the load flow, the nominal voltage level of each bus has to be specified (phase-to-phase RMS). There are multiple ways to do so:

4.1 Defining each bus individually

Double-click a specific bus and define its nominal voltage in the property window as shown in the figures below.

By default, HYPERSIM assigns it an initial value of 1kV which must be modified based on the user's case.

As an example, double-click Bus1, define the nominal voltage as 230 kV.

4.2 Defining in Netlist - Base Voltage (recommended)

If there is at least one transformer in the model, configuring the base voltages in Netlist is the easiest method. By specifying the transformer nominal voltages, it defines the voltage of all the buses connected to each side of the transformer.

  • For example, in this model, to access, click the HYPERSIM tab and click Netlist. 
  • Once the Netlist window pops up, select Base Voltage from the Views drop-down menu.

Views Menu

  • Each transformer’s primary, secondary and tertiary base voltages are already configured based on the transformers' voltage settings in the network model.

  • Specify the Primary Bus Voltage and Secondary Bus Voltage accordingly. If a tertiary bus is present, configure it as well. There is a drop-down menu with common voltage levels which you can choose from.

  • If the secondary buses of several transformers are connected together, defining one bus will automatically define the others. After the configuration, it should look like this:

  • Now if you go back to the model and double-click a bus, the nominal voltage is defined.

4.3 Defining in Netlist - Load Flow Parameters

When there is no transformer, it means all buses are at the same voltage level. You could launch Netlist, then select Load Flow Parameters from the Views drop-down menu. 

Views Menu

Then you could define the Nominal voltage of all buses. Copy and paste works here!

5 Run the Load Flow

Click HYPERSIM > Network > Load flow. 

5.1 Load flow options

The Load Flow window opens. In the Load flow execution section, there are several load flow options and parameters:

  • Analyze: Analyze the network topology. If there are changes in the model, Analyze updates the netlist and the load flow input data.
  • Execute load flow: Execute the load flow analysis, a short load flow report will be returned to the log. This step also sets initial conditions to all the buses and components in the model. Note that the Execute Load Flow function automatically executes the Analyze function.
  • Set initial conditions: This is to Initialize conditions at the simulation start. Therefore, the simulation will start from a steady-state condition.
  • Use Qmin and Qmax limits: If this option is checked, the Q limits specified in each component's load flow tab are used as constraints when solving the load flow equations.
  • Frequency (Hz): The nominal frequency of the power system model.
  • Power base (MVA): The power base when displaying power in PU.
  • PQ tolerance (MVA): The load flow convergence tolerance.
  • Max iterations: The maximum number of iterations for the load flow algorithm to search for a convergent solution.
  • Deceleration factor: Usually set to 1 for most cases, this parameter is used only when iteration is necessary to find a solution. Decreasing its value reduces the size of the variation between two iterations.

In the report section, there are some more options:

  • Save: Save the log as a text file.
  • Print: Print the log.
  • Clear: Clear the log window.
  • Display voltage in PU: Display the voltage in PU according to the base voltages.
  • Display power in PU: Display the power in PU according to the Power base.

5.2 Input data

To verify the input data in the load flow window, click the Show button in the Input data row. A report is generated with the properties of every component and all the input parameters as shown below:

  • The first section is Bus summary where the base voltage of all buses are listed.
  • In Generation summary, all the generation buses are listed, with the bus type, load flow input parameters and Q limits. The total P and Q are calculated. 
  • If there are loads in the model, they will be listed in the section Load summary. In this example model, only shunt RLC components are used to represent loads, thus they are listed in the Shunt impedance summary. Again, the total P and Q are calculated.
  • In the two drop-down menus on the right of Input data, individual category (Generation, Load, Shunt) and component (Bus, Load) can be selected to be displayed.
  • The number of digits after the decimal points can be adjusted between 3, 6 and 9, to show more precise results.


====================  Bus summary  ====================
Bus name                    Vbase (kV rms LL) 
Bus1                           230.000
Bus10                          230.000
Bus11                          230.000
Bus12                          230.000
Bus13                          230.000
Bus14                           13.800
Bus15                           13.800
Bus16                           13.800
Bus2                           110.000
Bus3                           110.000
Bus4                           110.000
Bus5                           110.000
Bus5_1                         110.000
Bus6                           110.000
Bus7                           110.000
Bus8                           110.000
Bus9                           230.000
Total: 17 buses 

====================  Generation summary  ====================
Bus                      Component                Type            V (kV rms LL, deg)                    P (MW)          Q (Mvar)       Qmin (Mvar)       Qmax (Mvar)
Bus1                     VS1                      PV                230.000   -----                     0.000             -----          -999.000           999.000
Bus13                    VS2                      Swing             230.000 @ 0.000                     -----             -----          -999.000           999.000
Bus14                    SM2                      PV                 13.800   -----                    30.000             -----          -999.000           999.000
Bus15                    SM3                      PV                 13.800   -----                    30.000             -----          -999.000           999.000
Bus16                    SM1                      PV                 13.800   -----                    30.000             -----          -999.000           999.000
                                                                                                 ------------      ------------
Total [    5 generator(s)]:                                                                            90.000             0.000

====================  Shunt impedance summary  ====================
Bus                      Component                   Vbase (kV rms LL)        P (MW)      Q (Mvar)            
Bus10                    Load_10                        230.000              19.980        -0.000
Bus11                    Load_11                        230.000              19.980        -0.000
Bus14                    Snubber_14                      13.800               0.990        -9.991
Bus15                    Snubber_15                      13.800               0.990        -9.991
Bus16                    Snubber_16                      13.800               0.990        -9.991
Bus7                     Load_7                         110.000              19.985        -0.000
Bus9                     Load_9                         230.000              19.980        -0.000
                                                                           --------      --------
Total [    7 element(s)]:                                                    82.896       -29.973

5.3 Load flow execution

Load flow execution parameters do not need to be changed for this example. Once all input parameters have been verified, proceed to perform the load flow analysis.

Hit the Execute Load Flow button located in the upper part of the load flow window. The Result report abstract is displayed in the log window.

Warning: some elements not considered for load flow.

Load flow report
Buses          	:    17
Components     	:    29
Iteration no 1; max PQ = 0.152727 (MW); at bus Bus1
Load flow completed

==========  Result report abstract  ==========

Generation buses
Bus                           Pgen (MW)   Qgen (Mvar)            
Bus1                             0.000       -56.255
Bus13                            1.155       -60.899
Bus14                           30.000       -18.020
Bus15                           30.000       -16.303
Bus16                           30.000       -25.317
                             ---------     ---------
Total:                          91.155      -176.794

Internal voltages at generation buses
Bus                               Vint (kV rms LL, deg)
Bus1                                 228.471 @   3.529
Bus13                                228.350 @   0.067
Bus14                                 13.374 @  15.873
Bus15                                 13.417 @  18.180
Bus16                                 13.193 @  37.541

This step also sets initial conditions to all the buses and components in the model.

Now, if you double-click source VS1, the Amplitude and Angle are updated.

If you double-click on SM1, the Angular frequency, Voltage, Active power and Reactive power are updated to load flow solution values.

If you double-click on a bus, the data in Load Flow Results tab are updated based on the load flow solution. Take Bus14 as an example:

5.4 Result data

To view a more detailed load flow report, click Show button in the Result data row. The display options are the same as Input data.

  • In Bus report, for each bus, the voltage and angle, as well as Pgen, Qgen, Pload, Qload, Pshunt and Qshunt are displayed in Summary. In Detail, the load flow towards every connected bus is shown. As an example:
Node Bus11 (no 2)
             V (kV rms LL, deg)            Pgen (MW)   Qgen (Mvar)    Pload (MW)  Qload (Mvar)   Pshunt (MW) Qshunt (Mvar)
               240.687 @ -0.174               0.000         0.000         0.000         0.000        21.880         0.000
   Source                   Destination              Component                        P (MW)      Q (Mvar)            
   Bus11                    Bus10                    L1_7                           -20.795        -9.013
   Bus11                    Bus12                    L1_8                            -1.085         9.013

  • In Generation report, the V, angle, P and Q of each generation bus are listed, as well as the internal voltage and angle of the source (behind internal impedance).
====================  Generation report  ====================
Bus                      Component                Type           Vbase (kV rms LL)            V (kV rms LL, deg)              P (MW)      Q (Mvar)         Vint (kV rms LL, deg)                 I (kA peak LG, deg)    
Bus1                     VS1                      PV                      230.000             230.000 @ 3.474                 0.000       -56.255             228.471 @ 3.529                       0.200 @ 93.474       
Bus13                    VS2                      Swing                   230.000             230.000 @ 0.000                 1.155       -60.899             228.350 @ 0.067                       0.216 @ 88.914       
Bus14                    SM2                      PV                       13.800              13.800 @ 12.859               30.000       -18.020              13.374 @ 15.873                      2.071 @ 43.851       
Bus15                    SM3                      PV                       13.800              13.800 @ 15.175               30.000       -16.303              13.417 @ 18.180                      2.020 @ 43.697       
Bus16                    SM1                      PV                       13.800              13.800 @ 34.487               30.000       -25.317              13.193 @ 37.541                      2.323 @ 74.648       
                                                                                                                         ----------    ----------
Total [    5 generator(s)]:                                                                                                  91.155      -176.794

  • In Load report, all the load information are listed. In this example, there are only Shunt RLC components and no load component. Thus Load report doesn't not appear.
  • In Shunt report, all the shunt information are listed.
====================  Shunt report  ====================
Bus                      Component                   Vbase (kV rms LL)           V (kV rms LL, deg)               P (MW)      Q (Mvar)
Bus10                    Load_10                              230.000             240.098 @ 0.556                21.773         0.000
Bus11                    Load_11                              230.000             240.687 @ -0.174               21.880         0.000
Bus14                    Snubber_14                            13.800              13.800 @ 12.859                0.990        -9.991
Bus15                    Snubber_15                            13.800              13.800 @ 15.175                0.990        -9.991
Bus16                    Snubber_16                            13.800              13.800 @ 34.487                0.990        -9.991
Bus7                     Load_7                               110.000             111.513 @ -19.549              20.539        -0.000
Bus9                     Load_9                               230.000             235.678 @ 2.111                20.979        -0.000
                                                                                                             ----------    ----------
Total [    7 element(s)]:                                                                                        88.141       -29.973

  • In the end, a Summary is displayed.
============================  Summary  ============================
                                 P (MW)            Q (Mvar)      
Generation total                91.155            -176.794
Load total                       0.000               0.000
Shunt total                     88.141             -29.973
Difference                       3.014            -146.821

NOTE: If mistakes were made while entering input parameters for various circuit components (e.g. wrong voltage for a three-phase bus), an error message appears. When the user attempts to execute the load flow, it warns the user that input parameters are not correct and indicates which parameters are at fault.

The load flow parameters can also be viewed in Netlist - Load Flow Parameters.

The updated values are used by HYPERSIM once the simulation is launched to start from steady-state conditions.

Additional Information

To get the software to automatically run a load flow analysis before the start of the simulation, tick the Perform load flow and set initial conditions at simulation start box in the load flow window.

Qmin and Qmax refer to the lower and upper bound of the reactive power already defined in the generator properties (see Load Flow tab in the component’s properties window).

If the Q box is ticked in the load flow window, the results of the analysis will be included in the defined interval.

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