480V Current Limiting Reactors
480V Current Limiting Reactors
(OP)
A customer has several 800A rated or larger Motor Control Centers with 22,000A bus bracing and 39,000A available short circuit current. Has anyone had success using reactors at this voltage level to get the fault current down to an acceptable value. If so, can you recommend a manufacturer? Any other suggestions?






RE: 480V Current Limiting Reactors
But you're talking about a fair amount of reactance to get that level of reduction.
It's not the best solution, but sometimes it's the most practical.
You could also look at adding an upstream breaker that had a series rating with downstream breakers.
RE: 480V Current Limiting Reactors
RE: 480V Current Limiting Reactors
RE: 480V Current Limiting Reactors
Check with the manufacture of the MCC, for the short circuit bracing test X/R ratio. Is this test ratio within the new X/R parameters with these reactors.
RE: 480V Current Limiting Reactors
RE: 480V Current Limiting Reactors
For an 800A MCC, the necessary reactor will have less than 5 volts drop at full load and energy losses of about 500W. A 1200A unit has even lower drop with about 1000W loss.
X/R ratios are not much of a concern for several reasons.
RE: 480V Current Limiting Reactors
http://www.ch.cutler-hammer.com/unsecure/cms1/TB04300003E.PDF
RE: 480V Current Limiting Reactors
RE: 480V Current Limiting Reactors
Current limiting fuses are not much help at these levels of fault current.
///Have you checked with
http://www.bussmann.com
http://www.ferrazshawmut.com
etc.? The Utilities use current limiting fuses to reduce the danger of large short circuit currents by limiting the short circuit currents to very low short circuit current levels all the time. I do too.\\\
RE: 480V Current Limiting Reactors
As RonSharp said, in UL regions the fuse must have been type tested in combination with that particular circuit breaker. Circuit breaker manufacturers publish lists of tested combinations.
http://geindustrial.com/industrialsystems/wizards/seriesratings/home.htm
RE: 480V Current Limiting Reactors
RE: 480V Current Limiting Reactors
I am assuming that you have done a comprehensive system fault study to determine Ik" & Sk" at your MCC's to determine where your fault current contributions are coming from (SKM Power*Tools or similar).
If the high fault current rating Ik" is largely due to contributions from rotating electromagnetic machines (motor), the contribusion from these sources is approx S/X"d in kVA (ie LRC) for a cycle or so (where S = motor rated kVA).
Note - typically X"d = 0.167 for smaller induction machines (X"d FLC/LRC).
However, if you are using a lot of VSD's (not soft-starts with contactor bypass) the fault current contribution will be significantly lower due to SCR commutation failure when the bus voltage level collapses (speak to your VSD manufacturer - I am not a power electronics man).
Hope this helps
_______________________________________
Colin J Flatters BSc(Hons) IEng MIEE MIIE
Electrical Engineer / Project Manager
Email - cflatters@colin7.demon.co.uk.