I'm curious to know what standards/guidelines I can refer to for OC protection of capacitors. Particularly, I have a overhead pole-mounted type single phase capacitor bank, all I know is that the capacitor is rated 2400V with 75KV BIL ratings. Curious to know how to size the fuse for this.
overcurrent protection for capacitors
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ron
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How much capacitance is it rated for? There might be a manufacturer label on it with FLA.
FLA = 100 kvar/2.4 kv = 42 amps.
The NEC says 1.35 FLA but I don't think it is not referring to your installation.
Call mfg and get a suggestion or Goggle may get you an answer.
Single phase is a little different. Usually the installation is 3 phase.
Tell me something about the reason you are installing the caps.
T
T.M.Haja Sahib
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If the fuse is sized at 42 amps,it is liable to blow on energizing the capacitor.So use a fuse rated at 42x1.35=56.7amps or 60amps fuse.
iceworm
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I'm just guessing bob's question matches up with mine.
Cap banks for power factor correction on single phase installations are sufficiently rare that I have never seen one.
Other than some utility applications or long, low power feeder applications, 2400V single phase is pretty uncommon.
So, paralleling bob's question: What is the application for this 2400V single phase? What is it about this single phase application that requires pf correction?
This won't help you any, but I am pretty curious - just for my own education.
ice
I'm sorry if I may have caused confusion to every body from the beginning. We do have a 3-phase system, and we are using 3 of these single-phase capacitors to achieve the 3-ph application.
iceworm
Curmudgeon still using printed IEEE Color Books
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Okay. That sounds better. Again just curious; Is this 2400D or 4160/2400Y? I've seen a few 2400D and a lot more 4160/2400Y.
ice
We have a 2400V delta ungrounded system.
iceworm
Curmudgeon still using printed IEEE Color Books
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This is better. Here's what I have so far.
The installation is 300kvars delta connected across a 2400V ungrounded delta syste.
This gives a capacitive curent of 72A.
As for 2008 (2011) NEC, Art 460.8A requiring conductor ampacity 135% FLA - it does not apply. There is no matching article in Part II, Over 600V.
Now let's look at OCP. The governing NEC article is 460.25. And this refers to IEEE 18-1992.
As others have noted: The NEC isn't a design guide. And this is a perfect example. I think the NEC is pretty clear - it acknowledges this is not a cookie cutter design. For Cap Bank installations above 600V, you have an engineering problem.
So, to answer your original question:
IEEE 18 is now at -2002 (and I don't have a copy of -1992)
Other standards are IEEE 1036 Guide for Applictions of Shunt Power Capacitors, IEEE Std C37.99-2000 (capacitor bank protection) and IEEE Std C37.48-2005 (external capacitor fuses)
And there is another reference to a C37.xx on fuse characteristics (that i don't recall but is likely referenced in the others).
Aren't you glad you picked an easy one? :happysad:
ice
The installation is 300kvars delta connected across a 2400V ungrounded delta syste.
This gives a capacitive curent of 72A.
As for 2008 (2011) NEC, Art 460.8A requiring conductor ampacity 135% FLA - it does not apply. There is no matching article in Part II, Over 600V.
Now let's look at OCP. The governing NEC article is 460.25. And this refers to IEEE 18-1992.
As others have noted: The NEC isn't a design guide. And this is a perfect example. I think the NEC is pretty clear - it acknowledges this is not a cookie cutter design. For Cap Bank installations above 600V, you have an engineering problem.
So, to answer your original question:
IEEE 18 is now at -2002 (and I don't have a copy of -1992)
Other standards are IEEE 1036 Guide for Applictions of Shunt Power Capacitors, IEEE Std C37.99-2000 (capacitor bank protection) and IEEE Std C37.48-2005 (external capacitor fuses)
And there is another reference to a C37.xx on fuse characteristics (that i don't recall but is likely referenced in the others).
Aren't you glad you picked an easy one? :happysad:
ice
Last edited:
Wow, these are some truly great information on capacitors. Thanks a lot!
stew
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my 2011 handbook has a full paragraph on how to calculate the current of each bank. I assume you would then multiply by 1.35 to get the correct protective device.
beanland
Senior Member
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- Vancouver, WA
Manufacturer Information
Manufacturer Information
Normally a capacitor will not overload, it will fail. The fuse is there to protect the capacitor from exploding. The choice of fuse is based on the available short circuit current and the presence of any other capacitors nearby. It is not a simple issue. Cooper Power sells capacitors and expulsion fuses and has good information on the correct sizing of fuses based on voltage and capacitor size. When all else fails, check the manufacturer literature.
BTW, when installed indoors or where very high fault currents are present, current limiting fuses are required.
Manufacturer Information
Normally a capacitor will not overload, it will fail. The fuse is there to protect the capacitor from exploding. The choice of fuse is based on the available short circuit current and the presence of any other capacitors nearby. It is not a simple issue. Cooper Power sells capacitors and expulsion fuses and has good information on the correct sizing of fuses based on voltage and capacitor size. When all else fails, check the manufacturer literature.
BTW, when installed indoors or where very high fault currents are present, current limiting fuses are required.
T
T.M.Haja Sahib
Guest
Only internal fuses in HT capacitor with series-parallel connected elements could prevent the HT capacitor from exploding in case of any short of series element in it.External fuse is provided for clearing external shorts such as short in the terminals of the capacitor.If this fuse sized at 1.35 also does not hold on energizing the capacitor,its size may be increased to 1.5 times the capacitor rated current in your case.
Cooper Power's Electrical Distribution-System Protection manual has a good section on medium voltage capacitor fusing. The manual is available for $50 at http://www.delzer.com/v5fmsnet/OeCa...enunodseq=&FromFav=&PmSess1=39&pos=CPSDLC&v=7
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