How to use the Load Flow Simulator

Draw a single-line diagram, run a load flow, read where the power goes. Every clip on this page is the real tool, recorded while it was used.

Open the tool Start with the screen

The short version

  1. Draw or load a network

    Start from a worked network in Quick Start, or drag buses, lines, transformers, generators and loads onto the diagram.

  2. Set it up

    Select an element for its ratings and set points. The Load flow tab picks AC Newton-Raphson or DC, and the limits a result is read against.

  3. Run and read

    Press Run load flow. The diagram shows voltages, flows and loadings; the figures and tables under it give the detail.

Nothing is uploaded. The load flow runs in your browser, on PSA.js, a JavaScript port of PyPSA.

The screen

Inputs on the left, the diagram beside them, the results under it. Point at a part in the list to see where it is.

  1. Inputs

    Quick Start, save and open, then three tabs: Element, Load flow and Labels. Run load flow sits at the bottom. The chevrons fold the card to a slim Inputs rail.

  2. Parts

    Bus, node, line, transformer, generator, solar, wind, grid, load, shunt, storage and HVDC link. Under them: undo, redo and Clear.

  3. Diagram

    Your network, with the result written on it. Above it: the flow animations, Colour by and Share. In it: full screen and zoom.

  4. Results

    Four figures (convergence, losses, the voltage range, the highest loading), then Results by element and What this assumes.

Top right, Tour replays a one minute walk through the tool, and Guide opens this page.

Quick Start

Four worked networks: the WSCC 9-bus system, a 3-bus ring, a 20/0.4 kV feeder with rooftop solar, and two areas joined by an HVDC link. One click replaces the diagram and solves it.

On a phone, press Full screen under a clip and turn the phone sideways to read it.

Open the inputs, pick a network

  1. Open the inputs

    On a first visit the card is folded to a rail, so the diagram has the room. Click Inputs to open it; it stays the way you leave it.

  2. Pick a network

    Hover a button to read what it holds. A click loads it over the diagram and runs the load flow.

  • The WSCC 9-bus is a check. It reproduces the published voltages and generator outputs of Anderson and Fouad to the last digit shown.
  • Then make it yours. Change anything over the top of an example; Undo brings the last step back.

Draw a network

Buses first, then the devices on them and the branches between them. Every part takes sensible values for its voltage, so a network runs as soon as it is connected.

Two buses, a grid, a load and a line

  1. Drop a bus

    Drag Bus (a bar) or Node (a dot) onto the diagram. A new bus takes the voltage of the selected bus, or the one most buses have.

  2. Drop a device on a bus

    Drag a generator, solar, wind, Grid, load, shunt or storage onto a bus. It snaps to it.

  3. Connect two buses

    Pick Line, Transformer or HVDC link, then drag from one bus to the other. Esc stops.

  4. Run it

    Run load flow, or Ctrl Enter. The values appear on the diagram.

  • Every island needs a slack. A Grid, or a generator set to Slack, holds the voltage and takes up the balance.
  • Which end first. A transformer is drawn from its high-voltage bus; an HVDC link from its sending bus.
  • Move and arrange. Drag anything to move it, empty space to pan, scroll to zoom. The arrow keys nudge a selection, R turns a bus upright.
  • Mistakes are cheap. Undo and redo sit under the parts. Clear empties the diagram after asking, and Undo brings it back.

Edit an element

Select an element on the diagram and the Element tab shows its values: a bus's voltage, a line's type and length, a generator's control and set points, a load's demand.

3-bus ring: the town's load raised to 160 MW

  1. Select an element

    Click it on the diagram. Its name, kind and where it connects head the panel.

  2. Change a value

    Type it in. The last result stays, faded, and a note says the network changed.

  3. Run it again

    The new flows replace the faded ones.

  4. Nothing selected

    Esc, or a click on empty space, shows the network: its name, every element by kind, and any Checks to fix before it runs.

  • Standard types. Lines and transformers offer PyPSA's standard types, those matching the bus voltage first; Custom takes your own impedance and rating.
  • Duplicate, delete, deselect. The three icons beside the name, or Ctrl D, Del and Esc.
  • Its own labels. An element can show other values than the rest of its kind.

Load flow and labels

The Load flow tab sets what is solved and what a result is read against. Labels sets what the diagram writes beside each kind of element.

The method, a tighter loading limit, the labels

  1. Load flow

    AC, Newton-Raphson for voltages, angles, reactive power and losses, or DC, linear for active power only.

  2. Limits

    The lowest and highest voltage and the highest loading. They flag a bus or a branch in colour; they never change the result.

  3. Labels

    One row per kind of element, one tick per value it shows on the diagram.

  • Newton-Raphson. The tolerance, the initial guess (a DC load flow, so phase-shifting transformers converge, or a flat start), and a Distributed slack shared by dispatch or by rating.

Read the diagram

After a run, every bus carries its voltage and angle and every branch its flow. Solid arrows are active power, open arrows reactive power, moving the way it flows.

WSCC 9-bus, coloured by loading against a 60% limit

  1. Colour by

    Bus voltage, branch loading, both or nothing. Amber nears a limit, red is past it.

  2. Hover to read

    Hover or tap an element and the box under the diagram gives its values, both ends of a branch included.

  3. The flows

    Tick or untick the active and reactive power animations.

  4. Full screen

    ⤢ fills the screen with the diagram; the same button brings it back. ⟳ fits the view again.

Results

Under the diagram: the answer in four figures, then every element's values in tables, then what the result assumes.

Figures and tables

  1. Four figures

    Iterations to converge, losses and their share, the voltage range and where, and the most loaded branch.

  2. Open the tables

    Results by element opens from its chevron.

  3. Pick a table

    Buses, Branches or Devices. ⬇ CSV saves the one shown.

  • What this assumes. The last card lists what the result rests on for this network, such as the method and the slack.

Save, export and share

The tool keeps your network in this browser between visits. The rest makes something to keep or send.

Save, open and Share

  1. Save or open a file

    The two icons beside Quick Start write the whole network and its settings to a file, and read one back.

  2. Share

    The diagram as SVG, PNG or an animated GIF, a copy to the clipboard, a link that opens your network, or an embed for a web page.

  • An embed is live. It shows the diagram with its flows moving, and a reader can pan, zoom and hover it.
  • The GIF is offered after a run, while a flow animation is on.

Shortcuts

  • Ctrl Enter run the load flow
  • Ctrl Z undo
  • Ctrl Y redo
  • Ctrl D duplicate
  • Ctrl A select everything
  • Delete remove the selection
  • R turn a bus
  • ← → ↑ ↓ nudge (with Shift, further)
  • Esc stop drawing, clear the selection

Ready to run one?

Open the tool