Fault Current Calculations

1 Medium Voltage Times / Factors

Trip. Time MV (s):

This can be seen in the alarm report of the result. Sort on the alarm fuse tripping time to view all sections having a too long tripping time. This parameter is valid for the MV network.

 

2 Low Voltage Times / Factors

Trip. Time Feeder (s):

This time is used for the control of the tripping times for LV feeder conductors.

 

Trip. Time Service (s):

This time is used for the control of the tripping times for LV service conductors.

 

Voltage short. calc. V:

This parameter gives the assumed short circuit voltage for an earth fault LV short circuit. If no voltage is specified the feeding voltage will be used through the transformer ratio.

 

3 C-Factors

To evaluate tripping conditions in LV networks regarding different safety regulations you are able to reduce the LV bus bar feeding voltage used as base value for the short circuit calculation. First decide how the fuse is used, as both overload and short circuit protection or as short circuit protection only.

Then decide the voltage reduction factor for each conductor and protection type.

 

Feeding Cable Overload and shc. protection

Press this button if the fuse is to act both as overload and short circuit protection for feeder conductors.

 

Feeding Cable Short Circuit

Press this button if the fuse is to act as short circuit protection only for feeder conductors.

 

Service Cable Overload and shc. protection

Press this button if the fuse is to act both as overload and short circuit protection for service conductors.

 

Service Cable Short Circuit

Press this button if the fuse is to act as short circuit protection only for service conductors.

 

C-Factor OH Free Line

Factor for voltage correction of fault currents when controlling the tripping time condition and the line type is an OH free line.

 

C-Factor Cable Overload and shc.protection

Factor for voltage correction when the fuse is used both as overload and short circuit protection.

 

C-Factor Cable Short Circuit

Factor for voltage correction when the fuse is used as short circuit protection only.

 

Note! The parameters above are used unless the corresponding values are given in fuse code list.

 

4 C-factors for LV busbar in substation

Voltage factors for the protection against three-phase short-circuit at LV busbar in secondary substation.

 

C-factor 1

Voltage factor which is used when short-circuit power at the busbar is lower than the threshold value or when the threshold value is not specified.

 

Skmin (MVA) for C-factor 2

Threshold value of short-circuit power (MVA) at the busbar. It is required when using both C-factor 1 and C-factor 2.

 

C-factor 2

Voltage factor which is used when short-circuit power at the busbar is higher than the threshold value. This factor is usually the lower factor.

 

Notes: 

   • Today these C-factors are used only when calculating Ik3 transformer upside for LV busbar and Tripping time trf-up device for transformer in secondary substation.

   • When the C-factors are not specified, the default value 1 is used.

 

 

5 Neutral Point

Neutral Point capacitive correction

If a neutral point correction value is given this value will be used as neutral point current instead of calculating the difference between the inductive current of the Earthing transformer and the capacitive Conductor generated current. This value is used for calculating exposed voltage due to earth faults in the medium voltage network.

 

Fuse types

In these fields you give the fuse types to be used when a safety calculation is to be performed. It is advisable to add a series of IEC fuses in the fuse codelist as these often represent the minimum requirement for a fuse. The field displayed comes from the Make field of the fuse code list.

 

Description of the concept of the type of fuses in the parallel form:

If there are necessary incoming data then the calculation will be done for maximum allowed (proposed) fuses, based on the specification type of fuses.

 

Description of the High and Low voltage Fuse types concept

If these fuse types are available in the codelist the result presentation will present calculation data based in these proposed fuses.

The rated data for the fuse types should be defined in the codelist ELFUSETYPE_CL.

In order to get a collected “package”, for the fuses to be interpolated in, the fuses time-current curves, must be of the same make (MAKE) and of the same Rated voltage (RATED_VOLTAGE).

 

In the example below, the combination Rated current 1 kV and Manufacturer IEC FUSE-LINK contains 20 cohesive curves (2-1250 A rated current).

 

Calculation Result relating to fuse types

 

 

7 Neutral conductor

Here you can indicate whether the neutral conductor should be seen as intact during the short circuit or broken both in a faulty parallel conductor and in a possibly disconnected conductor.