Minimum Short Circuit Calculation IEC 363

[Beo81]

According to IEC Standard, maximum and minimum short circuit levels should be calculated.

I am using EDSA, and can not see that there is a module for calculating minimum values. There is however the 30-cycle steady-state calculation, can this be used?

What do I need to do in order to get correct minimum values?

Thank you all

 

[tem1234]

I'm not used with IEC and EDSA, But to calculate the minimum value, you should insert a fault impedance, like 20 to 40 ohm.

In the software i use, you cannot add a fault impedance if you calculate in ANSI mode, but you can if you are in NON-ANSI mode. Maybe something similar in EDSA?

 

[Kiribanda]

Be081,

Maximum and minimum short circuit levels correspond to the maximum and minimum infeed at the Utility coupling point.The Utility has got these two values depending on their operating modes and contingency plans.If you have your own generation method then maximum corresponds to when all generators are running and minimum corresponds to when one generator is running.So there is no seperate model for these two conditions in any program.

tem1234,
What you have suggested is the limiting fault current by inserting a fualt impedance and not the maximum and minimum conditions depending on Utility operating modes,

 

[7anoter4]

IEC 60909 state the way to calculate the maximum and the minimum short-circuit currents by using the voltage factor cmax and cmin according to voltage level. See [for instance]:

http://www.sueng.co.kr/pds/technical/IEC_요약본.pdf

chpt.5.3" Voltage Factor c."

 

[Beo81]

Thanks.

I read sometime ago that in order to calculate minimum currents in IEC, 3xIn for generators should be used.

And in EDSA`s IEC tab for generators, there is an input called "Ikd/I0". And if one calculates 30-cycle the corresponding short circuit would be approx 3xIn. (If Ikd/I0 is set to 3 of course).

Another way would be to insert an utility with 3xIn for one generator as short circuit contribution.

I did both these methods as an example, and they do create same results on primary side of transformers. As for secondary low voltage side of transformers, the "utility-method" gives much lower values. (7kA in generator 30-cycle method and 5 kA with utility method).

This makes me question what method to use for calculating minimum currents. Any thoughts?

 

[xxjohnh]

Minimum is when the entire system is operating in a minimum configuration fault level. Main use is in motor starting calculations.
Same value for the devices.

 

[MikiBg]

Beo81,
Looks like you mixed up a change of scc in time and because of network parameters configuration/state.
For one fixed fault scenario, you will have decreasing of fault current in time, and you can calculate several values which differs in nature and amount (initial symmetrical, peak, steady state, breaking current...).
Each of these values depends of fault scenario, so for instance, to calculate max values, you should take into account higher voltages from sources (utility and generators), and lower impedances (transformers in parallel, "cold" impedances of cables,...). To calculate min values, do the opposite.