Device KA rating verification study 2

[ksupriya]

Device KA rating verification study should be done based on bus fault or Branch fault current?

 

[waross]

Possibly the expected fault current that will pass through the device being verified.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[krisys]

Supriya,

For a liberally designed (sized) system, it is a good engineering practice to use the bus fault current. This would be a conservative approach.

Some smart guys may argue other way around. There is no harm using the branch fault current.

However, while performing the relay coordination, you should take the appropriate branch currents.

 

[X49]

To me, "branch fault current" implies that this is the fault current downstream of the overcurrent device (i.e. at the load). The fault current available at the load could be much lower than the fault current available at the breaker.

You should use the fault current that is present either at the overcurrent device, or on an upstream bus if you want to be conservative.

 

[davidbeach]

If you're looking at a single source, radial system then bus fault is clearly the only value to look at.

But in a multi-sourced, networked system then you have to look at what the maximum is from each side and base your choice on that. For instance, if you consider a generator breaker; it needs to interrupt the system contribution for a generator fault or the generator contribution for a system fault, but it can't see the total fault current.

 

[veritas]

Was the OP's question focussed on protective devices or actual items of plant such as cables, switches?

 

[Parchie]

As far as my eyes tell me, he/she's asking wrt "devices".

 

[TusharB]

Hi Supriya,

I think using of branch fault current will be more appropriate in case of evaluation of devices. The branch fault current will be a pass through current passing through the respective devices in case of Fault. The devices 'KA' rating, can be compared with the branch fault current & devices can be evaluated.

regards,

Tushar Borole

 

[ksupriya]

Thank you all.

Can anyone elaborate more on this topic with the help of attached single line diagram.

If we want to evaluate KA rating for PD-3, then which fault current should be considered, the one appearing at the bus PANEL or the fault current going through the branch i.e. CBL-4?

 

[ksupriya]

Single line diagram related to my previous post:

 

[EverGreen1231]

ksupriya,

Branch fault would be most appropriate, I would think. The current produced can be compared with the ratings of the devices and the protective device settings modified accordingly.

-Glenn

 

[LionelHutz]

I would use the Panel value. You can't control where the fault occurs on the output of PD-3.

 

[VTer]

I use the bus fault level . At the cable terminal of the PD-3, fault current will be essentially the same at the available bus fault current which is the worst case scenario.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla

 

[wroggent]

Definitely bus value

 

[ksupriya]

Thank you everyone.

So, that means bus fault KA value should be considered for all its outgoing feeder breakers?
Please advice.

 

[davidbeach]

Yes.

 

[Strogoff]

davidbeach! I'm sorry but I can't notify you in any other way. You have written the What are good references for a Power Engineer? FAQ. If you are able to alter it, plesae, write in it that the famous Edith Clarke books are now available online at the hathitrust.org .

 

[davidbeach]

Thanks, but there is a link with the FAQ to facilitate sending comments to the FAQ author.

 

[LionelHutz]

Yes. Generally you use the fault current available when shorting the input terminals to a device. In your single line, it shows the breaker PD-3 connected directly to the bus called Panel so the fault current at this bus is used.