Find fault levels

What it tells you. A short circuit study shows how much current flows into a fault, how large its first peak is and how much heat it causes. Use it to check switchgear ratings and to set protection. The calculation is IEC 60909-style.

Warning. The short-circuit calculation is IEC 60909-style. It is not certified. Do not use it alone to release equipment or protection settings.

Before you start

Check that the network has the data below. Select an element to see its data in the inspector.

Data	Where to enter it
Busbar Nominal voltage	Inspector, Basic data
External grid Short-circuit power max and R/X ratio max	Inspector, Short circuit
External grid Short-circuit power min and R/X ratio min, for minimum currents	Inspector, Short circuit
Machine Subtransient reactance xd″, with Short-circuit source set to Synchronous machine	Inspector, Short circuit
Transformer Short-circuit voltage, Copper losses (resistive part) and Vector group	Inspector, Basic data
Line Resistance R′ and Reactance X′	Inspector, Basic data
Motors: select a load, then switch on Asynchronous motor and enter its data	Inspector, Short circuit

A load flow is not needed first. The short-circuit calculation ignores loads and the load flow's voltages.

Set up the study

Choose the task that matches your question. Each task ends with the results open.

Find fault levels at every busbar

This shows the largest fault current at each busbar, so you can compare it with the ratings of the switchgear there.

Before you start. Enter the data in the table above for the whole network.

Select the Calculate tab.
Under Faults, select Three-phase.
Select Maximum currents.
Select Every busbar.
Select Short circuit, or press Alt+S.
In the Short circuit tab, read the Busbars table.

Compare Ik″, ip, Ib and Ith with the ratings on the equipment's datasheet. Use Ik″ for the initial current, ip for the peak withstand, Ib for the breaking capacity and Ith for the short-time withstand.

Find the fault current at one busbar

This shows how much current flows into a fault at one busbar, and how much each line and transformer feeds into it.

Before you start. Check the Short circuit group in the inspector for the sources near that busbar. That means the external grid Short-circuit power max and R/X ratio max, and the machine Subtransient reactance xd″. Check each transformer's Short-circuit voltage and Vector group under Basic data.

Select the Calculate tab.
Under Faults, select Three-phase.
Select Maximum currents.
Right-click the busbar on the diagram.
Select Short circuit at this busbar.
In the Short circuit tab, select Contributions.

You can also select the busbar, then select Short circuit at selected busbar from the command palette (Ctrl+K). To go back to every busbar, select Every busbar under Faults.

Find minimum fault currents

This shows the smallest current a fault can drive. Protection must still detect that current.

Before you start. Enter the minimum data for each external grid: Short-circuit power min and R/X ratio min. Check that Line temperature at fault end in the study case suits your lines.

Select the Calculate tab.
Under Faults, select Minimum currents.
Select the fault type your protection must detect: Three-phase, Line to line or Line to earth.
Select Every busbar, or right-click one busbar and select Short circuit at this busbar.
Select Short circuit, or press Alt+S.

Minimum currents use the grid's minimum short-circuit power and a lower voltage factor. They also use line resistance at the temperature you set. The study case's default is 80 °C.

Study earth faults

This shows the current when one or more phases touch earth. Use it to set earth-fault protection and to check earthing.

Before you start. Earth faults need zero-sequence data. Zero-sequence data describes how the network carries current through earth. Enter it in the Short circuit group of the inspector:

Line: Zero-sequence R0′, Zero-sequence X0′ and Zero-sequence B0′.
Transformer: Zero-sequence uk0, Zero-sequence uR0 and the neutral earthing resistance and reactance. Also check its Vector group under Basic data.
External grid: X0/X1 ratio and R0/X0 ratio.

Machines are unearthed in the zero sequence. An earth fault behind a delta winding reads about 0 kA.

Select the Calculate tab.
Under Faults, select Line to earth.
Select Maximum currents or Minimum currents.
Select Every busbar, or right-click one busbar and select Short circuit at this busbar.
Select Short circuit, or press Alt+S.
In the Busbars table, read Ik″ and |Z0|.

Line to earth is the only earth fault in the short-circuit study. The EMT study also has Two phases to earth. See Look at the first cycles of a fault or switching.

Run it

You can run the study from any of the tasks above, or from the Calculate tab.

Select Short circuit, or press Alt+S.
Wait for the progress bar in the status bar to finish.

The Short circuit tab opens in the results panel, and the diagram shows each busbar's current. The Output tab logs the highest Ik″ and where it occurs.

To change the other settings, press Ctrl+, to open Study case, then scroll to Short circuit. The settings you may need are in this table.

Setting	What it does
Minimum time delay	Sets the time from the fault to the first contacts parting, for Ib. The default is 0.1 s.
Short-circuit duration	Sets how long the current flows, for Ith. The default is 1 s.
Peak factor method	Chooses how ip is found. The default is Method C (equivalent frequency).
LV voltage tolerance	Chooses 6 % or 10 % for networks at or below 1 kV. The default is 10 %.
Fault resistance and Fault reactance	Adds an impedance in each faulted phase, such as an arc. Zero means a bolted fault.
Line temperature at fault end	Raises line resistance for minimum currents. The default is 80 °C.

Methods are described in the engine description.

Read the results

The top of the Short circuit tab shows the fault type, Maximum or Minimum, the peak factor method and the location. The Busbars table has these columns.

Column	What it shows
Busbar and Un	The busbar and its nominal voltage in kV
Ik″	The initial short-circuit current, in kA
ip	The peak short-circuit current, in kA
Ib	The breaking current, in kA. It appears only for Three-phase and Maximum currents.
Ith	The thermal equivalent current over the Short-circuit duration, in kA
Sk″	The short-circuit power, in MVA
κ, R/X and c	The peak factor, the fault loop's resistance to reactance ratio and the voltage factor

The columns |Z1| and |Z0| give the fault impedances in ohms. |Z0| appears for Line to earth only, and reads open when there is no path to earth.

Select Contributions to see the current each branch carries into a single fault. It lists Branch, I from and I to, the current at each end in kA. I from is at the from or HV end. The tab appears only for one busbar.

To sort, filter or chart the table, see Work with results.

Check your results

Power. For a three-phase fault, Sk″ equals √3 times Un times Ik″. Check one row with a calculator.
Near the source. Fault levels fall as you move away from the external grid and the large machines.
Maximum against minimum. The minimum Ik″ at a busbar must be lower than the maximum. If it is not, check the minimum data.
Peak against initial. ip equals κ times √2 times Ik″. At 20 kV in Riverside, 1.847 times 1.414 times 18.397 kA is 48.05 kA.
Contributions. The currents of the branches that feed the fault should add up to a little more than Ik″. They do not add exactly, because their phases differ.
A known figure. Compare with the utility's quoted fault level at the point of connection.

To compare with another tool, see Check PowerStudio against your own tool.

If something goes wrong

What you see	What it means	What to do
Ik″ reads 0.000 kA for Line to earth	The busbar has no earth path in the model, for example behind a delta winding	Check the transformer's Vector group. Remember that machines are unearthed.
The zero-sequence impedance column reads open	The zero-sequence network has no path to earth	Add earth data, or an earthed transformer, near that busbar.
The message No busbar could be faulted	The study found no busbar it could fault	Read the warnings above the table. Check that the network has a source.
No Ib column	Ib is shown only for Three-phase with Maximum currents	Select those two options and run it again.
No Contributions tab	You faulted every busbar	Select one busbar with Short circuit at this busbar.
A warning pill about a converter or 2 units at a busbar	A source is left out of the contributions, or only the first unit is used	Read the warning. See the engine description.
The pill Calculated before the last edit	You changed the network after the calculation	Run Short circuit again.

Two limits apply to every result. The study does not calculate the steady-state current Ik. It takes Ith with n equal to 1, as pandapower does.

Try it on the Riverside sample

The Riverside sample is a 110/20/0.4 kV distribution network. It opens with a three-phase fault set at Hilltop, not at every busbar.

Select the Help tab.
Under Samples, select Riverside distribution.
Select the Calculate tab.
Under Faults, check that Three-phase and Maximum currents are on, then select Every busbar.
Select Short circuit.
Read the Busbars table. The highest Ik″ is 18.397 kA at Riverside 20 kV. Its ip is 48.047 kA and its Sk″ is 637.3 MVA.
Check the power. The square root of 3 times 20 kV times 18.397 kA is 637.3 MVA.
Look at Riverside 110 kV. Its Sk″ is 3034.4 MVA, slightly above the grid's Short-circuit power max of 3000 MVA. The CHP unit adds the difference.
Right-click Hilltop on the diagram, then select Short circuit at this busbar.
Select Contributions. Ik″ at Hilltop is 3.920 kA. The Overhead line Riverside–Hilltop carries 2.535 kA. The CHP unit transformer carries 1.541 kA at its HV end.

For minimum currents, return to the Faults group, select Minimum currents and Every busbar, and run it again. Ik″ at Brook Farm falls from 2.068 kA to 1.729 kA.

For earth faults, select Line to earth, Maximum currents and Every busbar, and run it again. Hilltop reads 4.450 kA and Mill Lane reads 9.172 kA. Hilltop CHP 6.3 kV reads 0.000 kA. The CHP unit transformer has a delta winding on that side, so no earth current can flow there.

The IEEE 14-bus sample has few earth paths. Its earth-fault currents are small, and at Bus 8 the result is 0.000 kA.