Power Factor Correction Capacitor + Electric Arc Furnace Transformer 3

[edison123]

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 ?

 

[edison123]

correction

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

 

[gordonl]

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?)

 

[DanDel]

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

 

[edison123]

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 " ?

 

[jbartos]

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.\\\

 

[busbar]

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.

 

[RAMConsult]

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.

 

[edison123]

jb, busbar , RAMConsult,

Thanks for your good tips. They were useful.

 

[rbulsara]

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

 

[jbartos]

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

 

[jbartos]

Suggestion: Visit

http://www.cooperpower.com/Products/Systems/Setup/summer98.pdf

for Harmonic Measurements article by Frank DeCesaro

http://www.cooperpower.com/Products/Systems/Setup/summer96.pdf

for:
1. Ferroresonance article
2. Arc furnace article

http://grouper.ieee.org/groups/harmonic/iharm/docs/ih519.pdf

for: Arc furnaces interharmonics