Symmetrical Short circuit selection

[Budhi.Rahardjo]

Dear All,

Based on the E.T.A.P Calculation our reference is 1/2 Cycle duration short circuit as the highest value occured while symmetrical short circuit occured.In the ETAP report we have Momentary symmetrical short circuit, so in this case we should take this value Bus Bracing Capacity and Integrated Protection such as Circuit Breakers. This value will be suited to the manufacturer rating standard in the to obtain feasible selection of Symmetrical short circuit capacity.
Could any body give suggestion how to select the suitable values without considering Manufacturer Rating, but It could be adopted to the market rating capacity ?( May be with any factors ? )
THank you and appreciate for your immediate respond.

Regards,

Budhi Rahardjo

 

[physis]

I don't know if I'd be able to help. But if you could be a little more specific, and I also mean less jargon, maybe I could see what your question is more clearly. Not that maybe it's my fault that it's something I'm not that familiar with.

I'm really curious what a symetrical short circuit is.

 

[Budhi.Rahardjo]

symmetrical Short Circuit Selection

symmetrical Short Circuit Selection

Dear all,

How to select Bus Bracing Withstand Short Circuit by using E.T.A.P by ignoring manufacturer standard Rating for example :

1. Bus-Bar KA for Switchgear BUS.

2. Related Circuit Breaker KA.

Regards,

Budhi Rahardjo

 

[physis]

Well I've looked into the symmetrical and asymmetrical fault current concept, which I'd never even heard of before today, I guess I've been somewhat sheltered or something. I'm posting this link for anybodies edification just because I'm rather surprised I've never heard of this and it might be helpful to other people who aren't familiar with it.

http://www.powerstudies.com/articles/ImportanceofX-over-RRatios.pdf

Edit: Error A

 

[Budhi.Rahardjo]

symmetrical Short Circuit Selection

symmetrical Short Circuit Selection

Dear all,
Below an example of E.T.A.P Report Symm & Asym)

Table-1. Summary of Short Circuit Study
MCC VTG MOMENTARY (kA) INTERRUPTING LINE-GROUND REMARKS
V SYMM ASYM (kA) (kA)
MCC-02 480 17.723 21.710 17.723 16.267

In your link PLs check There is mentioning Symmtrical & A symmetrical KA Current !

Regards,

Budhi Rahardjo

 

[kingpb]

The 1/2 cycle symmetrical current is results from the calculation of the subtransient network, and can be used to select equipment symmetrical withstand ratings. The asymmetrical current is the symmetrical with a DC offset multiplier. The DC offset is calculated by performing separate R and X network calculations to determine an X/R ratio. From the X/R ratio a multiplying factor is used to determine the momentary peak, and asymmetrical momentary peak.

Using the "DUTY" calculation button in ETAP will provide values for each bus location printed as Momentary Duty column. this should be used to select equipment.

Within ETAP, you do not have to select specific equipment manufacturers. Simply model the system, run the analysis, and then use the Duty printout to see what equipment ratings you need to meet the available fault levels. Be sure to select the parameters for the study case. Of particular mention is the ability to use total fault on the bus, or bus through fault current. Total bus is more conservative, and IMO should be used as first pass, especially on LV systems. On MV systems, because of better relaying protection schemes, through fault is acceptable.

Hope that helps.