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Power Factor Correction Capacitor + Electric Arc Furnace Transformer
3

Power Factor Correction Capacitor + Electric Arc Furnace Transformer

Power Factor Correction Capacitor + Electric Arc Furnace Transformer

(OP)

My client, a steel manufacturer, has an electric arc furnace transformer with power correction capacitors connected on the incoming HV side. During power outage, he has noticed heavy inrush currents and voltage spikes for a very short period. I know that in ac induction motor connected permanently with power factor correction capacitor, heavy inrush currents and high voltages occur during power outage due to induction generator effect created by still rotating motor. Will such phenomenon occur in a transformer-capacitor circuit also ? I reason that transformer being a static unit, there is no stored energy to produce to such transient inrush currents and voltages. Or am I wrong ?

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

(OP)
correction

read "electric arc furnace transformer with power correction capacitors" as
"electric arc furnace transformer with power factor correction capacitors".

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

Particularly with vacuum contactors you have to watch out for switching transients, and resonance with your caps.  During a power outage with an "infinite" load connected I can't think of a reason. (or for an induction motor?)

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

Where and how were the heavy inrush currents and voltage spikes seen during the power outage?

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

(OP)
Thanks gordon1 and DanDel,

I will post that information the moment I get it. In the mean time, you got any ideas about my question "whether the arc furnace trafo with parallel power factor correcting caps will behave like an induction motor (or rather induction generator) on power loss  " ?

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

Suggestion to edison123 (Electrical)    Sep 5, 2003 marked ///\\\
 I reason that transformer being a static unit, there is no stored energy to produce to such transient inrush currents and voltages.
///The transformer also contains energy (See SMETs) that will be exchanging with capacitor stored energy (energy oscillation) until fully damped by resistances.\\\
 Or am I wrong ?
///Visit
http://www.afrlhorizons.com/Briefs/Dec01/ML0009.html
http://www.energy.ca.gov/distgen/equipment/energy_storage/energy_storage.html
for SMESs, which are in essence large magnetic coils holding energy.
etc. for more info.\\\

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer


Edison—your client may be experiencing a ferroresonant condition in capacitor-transformer interaction at some point during voltage decay.  A search on ferroresonance in Forum238 should yield significant discussion and references.  Without some instrumentation to monitor the affected system, causes and effects may remain speculative.
  

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

Arc furnaces go through different modes of operation depending upon the temperature and stage of the 'charge' being processed.  It is bascially a short circuit with time-varying electrical parameters, not at all like a clearly defined device such as a motor.  For an interesting analysis, check this paper which has oscillographs of voltage, current and admittance based upon actual tests:

http://www.pserc.wisc.edu/cgi-pserc/getbig/publicatio/2000public/heydt_korea2000.pdf

You may find that your customer is not having a problem.

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

(OP)
jb, busbar , RAMConsult,

Thanks for your good tips. They were useful.

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

As busbar indicated, ferroresonance is a likely reason, specially the power outage starts with single phasing.

RE: Power Factor Correction Capacitor + Electric Arc Furnace Transformer

Suggestion: The arc furnaces are nonlinear loads. The nonlinear loads cause different resonances than linear resonant circuits. One of them is the ferroresonance.

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