Air Core Reactor

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ron

ron

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Can someone suggest a name of a manufacturer.
We need to reduce calculated fault current from 150kA to below 65kA @ 480V 3ph.
A 1500kVA isolation transformer is huge, and reduces us much lower than we need.
I thought I heard that air core reactors can result in smaller footprint than in an iso xfmr.
 
Air-core reactors take up a "lot" of space - if you can put up with the noise an equivalent iron-core unit will be 1/3 to 1/4 the physical size of air-core. And you can get more reactance from iron-core (typically). I just replaced a unit on a 700 volt, 2750 hp DC drive this year. We put an iron-core unit in the bay that the old (lower rated) air-core unit was and it was about 1/3 the size of the old unit - lots of space to breath. Reactors need to be sized for voltage levels, amperage, reactance required & duty cycle. The main advantage to air-core is sound. The disadvantage is size (when compared to iron-core & amount of reactance -vs- size.
 
I don't know enough about really large feeders and short circuit current, but it seems to me that it wouldn't take much inductance to limit the short circuit current in this situation.

Assume that without your reactor, the short circuit current is infinite. And that the goal is to make the line-line short circuit less than 65KA.

This requires a reactive impedance of 277/65000 = 4.3 milliohms. Inductive impedance is given by 2 * pi * f * L, so L = 11uH.

You can get this with a few loops of your feeder cables a couple of feet in diameter. Not that the feeder cables for 1800A are small :)

-Jon
 
Jon,
I considered that, but it is not a clearly recognized method, acceptable to the AHJ, to reduce fault current.
At least a reactor is a recognized piece of equipment for the job.

Steve,
Current limiting fuses (or limiters) cannot be used to reduce fault current ... sort of, due to dynamic impedance of downstream equipment. I would need a listed tested assembly (series rating), and unfortunately static transfer switches do not seem to have a series rating with anything.

jcormack,
This is a UPS room which originally had designed in, a isolation transformer to reduce fault current. Is the difference between air and iron core that noticeable with high ambient noise anyway?
 
My guess is that air core reactors are _better_ for the application. Air core inductors don't saturate and the inductance remains constant as the current goes up.

An iron core can saturate at which point the inductance plummets and the current limiting is reduced. Also at low current levels the iron core transformer is at its maximum inductance, meaning more impedance causing voltage drop.

-Jon
 
jcormack said:
We put an iron-core unit in the bay that the old (lower rated) air-core unit was and it was about 1/3 the size of the old unit - lots of space to breath.
Click to expand...

Presumably with the only concern up front being that you had all your numbers right so you didn?t load up and saturate the core (pretty tough to saturate an air core) and/or add more heat into the room than with the air core predecessor. Am I close?
 
ron said:
Can someone suggest a name of a manufacturer.
Click to expand...

One more note having just read up the thread -

Did anyone address the question? I would shop north of the border and inquire with Hammond's Guelph facility for air core and REX in Rexdale for iron - just something about the Canadians ability with reactors I trust
 
I guess this will be a common problem I will run into, but this project is in NYC, so it has to have a NYC MEA number to make it legal.
I checked with Phoenix Electric and they are not listed with an MEA number so they don't get installed in NYC without a special dispensation from the NYC AJH g-ds.
 
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