how do you manually calculate the f 3

[kunkuta]

how do you manually calculate the fault level at a substation for big multi source network for the purpose of specifying CTs, CVTs, Transformers, Circuit Breakers, earthing transformers.

 

[Juzu]

Yuo can find examples for this calculations in the ABB manual.

 

[rtrimblepe]

Which ABB manual?

 

[ipb]

I also want to know. Where I can download the ABB manual?
Thanks a lot!

 

[MDom]

Iknow SE manual

http://www.cn.co.kr/cnuser/power/power/pdf/ect158.pdf

with an example of fault level calculation at the end of it.
It is "Cahier technique # 158. Calculation of short-circuit currents" (English)
Best regards

 

[RajT]

It is not something simple that can be explained in a discussion forum. My advise is to buy a good book on power system studies, study it and one day all will be apparent.

 

[SidiropoulosM]

The general method used for manual calculation is based on a Thevenin representation of the power network, which is modeled as a single voltage source E in series with an impedance Z, as seen from the point of the fault. For three phase faults, the fault MVA in per unit is simply 1/Z, where Z is also expressed in per unit. For single line to ground faults, the positive, negative and zero sequence networks are interconnected in series and the fault current is equal to 3E/(Z1+Z2+Z0). In general, for any unbalanced faults you must employ positive, negative and zero sequence representations. For a multi source network and for the purpose of specifying equipment ratings, it is not advisable to rely on manual calculations. Any power flow program will compute the fault levels at any bus in your system. Michael Sidiropoulos
Transmission Planning Engineer

 

[scottf]

I know it's just being picky, but you don't need to know the fault level to specify a CCVT, as it's not a relevant parameter.

 

[jbartos]

Suggestion: References:
1. IEEE Std 141-1993 IEEE Recommended Practice for Electric Power Distribution for Industrial Plants, (Red Book)
2. Donald Beeman, Industrial Power Systems Handbook, McGraw-Hill Book Company, Inc., 1955

 

[19gabi50]

Manual calculation of short-circuit current in a complex network may be difficult to perform. Any network configuration can be reduced to a simple equivalent scheme, usually referred to as "positive-sequence equivalent diagram". It consists of an equivalent e.m.f. (E – line to neutral) and equivalent positive –sequence impedance (Z). In simplified calculations, the latter is replaced with the reactance (X). Then, the three-phase, steady state short-circuit current at the fault location is the ratio E to X.
Knowing the branches' reactances the current in each branch can be calculated.
This approach might be applicable only for three-phase faults and provides reliable values for switchgears, current transformers, and cables sizing. In general, it is not possible to calculate in this way: subtransient, transient and aperiodic components.
The case becomes much more complicated for phase-to-phase and phase-to-ground faults. Besides, negative and homopolar-sequence network must be considered, the latter for phase to ground fault only. Symmetrical current components (positive, negative and homopolar-for phase to ground fault only) must be calculated and then the phase current at the fault location, based on symmetrical components.
Much care should be exercised when calculating the equivalent reactances: all must be calculated at a base voltage, usually the normal operating voltage at the fault location, transformers' connection must be also considered and so on.
Useful information can be found here:

http://www.schneiderelectric.com,

CT-158.
Manual calculation of short-circuit current in complex networks is difficult and time consuming.
There are available many programs that accurately solve the problem. I would recommend EDSA, SIMULINK/MATLAB and ABB DOC win.

 

[GRPatel]

Perhaps, you can calculate fault level of each source and then add up. This could be the simplest to get the idea of order of fault level. I assume that you are interested in steady state fault current.