Low Power Factor in Arc Furnace Application

How are you measuring the PF? Do you have a separate power meter, or are you using the power company's meter to judge PF.

Maybe the new meter is more accurate than the old meter, and that's why your bills have gone up.

Are you getting separate billing for Arc Furnace usage? Or is all of the electrical usage on this one meter for all of the facility? The reason I ask is there something else that is causing the high PF readings. Do you have other large motors such as air compressors running off the utility lines. More info needed.

I might suggest asking your utility company to help you with this. Here in the states our utilities are very helpful with this issues.

I see you are relying on the Utility meters, but for the $ involved you should probably have independent measurements, and a power study done for your plant to identify what items contribute to the poor PF.

First of all I do not have any experience on Arc Furnace and comments below are from other experiences - so all members please excuse me if my comments are not valid.

In case the Furnace Load is not steady but fluctuating - and capacitors are fixed (not switched on and off with load variation) most probably your Power Factor of 0.65 is Capacitive.

Pl check for (-) sign with Power Factor Reading on your Energy meter.

As we know discharging time of HT Capacitors (33kV or 11kV) is long (in minuets which can be seen on the name plate of capacitor), these are not suitable for variable load to effectively control the power factor.

In such case it is better to install a step down transformer and either STATCON (static inverter type capacitor/ Inductor). Or one can use switched LT Inductors and Capacitors.

LT Capacitors to improve power factor when furnace on load. Inductors to balance HT Capacitors installed as part of Harmonic Filters.

Please make out sketch of SLD , showing incoming feeder,Capacitor feeder,furnace feeder.Please also show the CTs and instruments connected therein .

Now you mentioned the measured values with respect to each instrument.

In India most of the EBs charge the HT consumers based on energy consumed and maximum demand .They also charge penalty if the PF is lower than 0.9.

If you say for one year they were charging as per meter and suddenly they have demanded then for one year PF should have been normal and they have not penalysed.

Where is the PF measured?

We can study your billing, Log details, distribution arrangement, type and make of instrument and CTs and give appropriate solution provided you share all the information.

Your Capacitors are connected to system manually or through APFC relay.

Have you taken PF readings without Capacitors connected?

Dear Mr. nvrsrinivas,

The capacitor should be as close as possible to the connectedload. Pl. try this and post the information.

DHAYANANDHAN.S