Short Circuit

This section allows users to configure parameters for short circuit analysis that are valid throughout the project.

INFO

The options defined here are used for all short-circuit calculations carried out in this project. This also includes other features that require this calculation, such as D-A-CH-CZ and VDE AR-N connection requests, the protection calculation and others.

The calculation options defined on the Short Circuit page fall back to this configuration when the page is left or reloaded.

Zero Sequence Impedance

The zero sequence impedances are derived from the positive sequence impedances. Choose factor 1 for a conservative calculation. For lines, the actual zero sequence impedance can also be defined directly in the grid model. When this value is set, the factor here has no effect.

Details

The zero sequence impedance represents the soil's eletrical impedance for the short circuit types 'Single-phase to ground' and 'Two-phase to ground'. The zero sequence impedance of lines and connections that don't have an explicit zero sequence impedance defined are calculated using this factor. For a conservative analysis, use factor 1.0. The zero-sequence impedance of the overlying grid is neglected ($R_{(0)Qt}=0\mathrm{\Omega }$)

Voltage Tolerance

The voltage tolerance affects how the voltage correction factors $c_{min}$ and $c_{max}$ of low voltage buses are set. During the short circuit calculation, the min/max current and power values are calculated using the bus voltages, scaled with the voltage factors $c_{min}$ and $c_{max}$. The factors models temporal voltage fluctuations, voltage deviation due to tap changers or load/generation. The c-factor on low voltage buses depends on the voltage tolerance:

Tolerance	$c_{min}$	$c_{max}$
6%	0.95	1.05
10%	0.9	1.1
IEC 60909-0 2001	0.95	1.1

Medium and high voltage buses are not affected by this setting. They always have a voltage tolerance of $c_{min}$ = 1 and $c_{max}$ = 1.1.

TIP

For a conservative analysis, use a voltage tolerance of 10%.

Short Circuit Duration

The short circuit duration is used to calculate the thermally equivalent currents $I_{th}$.

Branch Temperature

The branch temperature defines the temperature of the line at the end of the short circuit (after the time defined in Short Circuit Duration). This affects the minimum short circuit values.

Warm lines have a higher impedance, which leads to smaller minimal short circuit currents. It is important that the minimal currents are not too small such that protection devices (e.g. fuses) work properly. For a conservative analysis, use 160°.

Generator Contribution

Generators can feed three phase short circuits that occur nearby. Depending on their connection type, they contribute to a greater or lesser extent to the short circuits:

• Direct: No contribution
• Inverter: 1x rated current
• Synchronous Machine: 8x rated current
• Asynchronous Machine: 6x rated current
• Converter: 1x rated current
• left blank: No contribution (Direct connection is assumed)

The rated currents of the generators are calculated using their active power assuming them to be connected by a three-phase connection.