Reactor Sizing

[EE7860]

I came across late 50's low voltage MCCs and noticed all of the MCCs have reactors(current limiting) in series (between the incoming from the transformer to the line side of MCC) or MCC feeding another MCC. There are no nameplate or information available what so ever. Is there a way i can approximate the size of the reactor either by measuring voltage and current? if so what will be the better way to do it?
Regards.

 

[dpc]

In theory, you could measure the current flowing into the reactor and the voltage drop across it.

It might be safer to take one out of service and do this under controlled conditions with appropriate test equipment.

 

[ePOWEReng]

You should be able to derive the value of the inductance from the properties too (radius, # of turns, wire size).


ePOWEReng

http://www.ess-engineering.com

 

[burnt2x]

You are inserting a reactor so that you can reduce fault currents from a higher short-circuit rated bus I_SChigh to a lower SC rate bus I_SClow!
Having said that, all you need to do is find the difference in the short-circuit rating of the source bus and the supplied bus short circuit rating(in kA). With your bus voltage, you can calculate for the value of the reactance X_L(assuming a pure inductive reactor) by dividing the rated bus voltage by the difference in short circuit amps. Be sure to use per phase values to arrive at the value of the reactance. Now you have the inductance L:
L =X_L/(2 X Pi)X freq)

 

[scottf]

ee7860-

The only true way to find the inductance rating of the reactor is to measure the inductance, either by taking out of service and using an RLC meter or by taking inservice measurements of voltage and current. Note you'll need to get the phase angle as well.

You won't be able to tell the short-time current rating of the reactor from this measurement or the continuous current rating. If you're wanting to buy more reactors for a new install, then, as burnt2x said, you can figure ratings based on the formulas given. Note that when you size the reactor, use the short-time rating after the reactor is installed and not the rating prior to install...this could save some big $. I see people all the time over-rate current limiting reactors as they use the available fault current without the reactor for rating the reactor itself.