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Quick Start | Load Flow
- Sylvain Ménard
- Victoria Bruny
Overview
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:
| Component | Type | V (pu) | P (MW) |
|---|---|---|---|
| SM1 | PV | 1 | 30 |
| SM2 | PV | 1 | 30 |
| SM3 | PV | 1 | 30 |
| VS1 | PV | 1 | 0 |
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.
- 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.
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)
Summary
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
Detail
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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