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Power Factor confustion

Johno12345
Hi,


I have a new metering system installed  which uses CTs at the main distribution. One on the main supply 1,600a, then meters on the first level of breakers, between 125a and 630a. 


Because of how we operate, sometimes the load is a couple of amps, and other times its banging it out at close to the capacity of the breaker. 


The load is machine tools, mix of inverters and direct, the lighting and general industrial uses



one area seems to have a really bad power factor, around 0.5, but depending on the loading, it can be as good as 0.8 


another area is very lightly loaded, and that has a power factor that swings from -0.8 to 0.9, that's got office equipment on it, heat pump some lights


I have 600kVAR or power factor correction at the main breaker, no meters on that.



The meters look like they are all connected fine, and the other readings are sensible and accurate, kW all positive readings so I don't think there is an error with the installtion.



I guess the question really is, should I be getting hung up on the power factor, or focus on the kWh to target energy savings? Has anyone had experience of it varying like this?
  • 0
    The only reason to worry is what your metering for the overall supply sees, this presumably being KVAh not kWh, which is normal for industrial supplies. The PFC unit will get your overall PF as good as it can to minimise your costs, the rest doesn't matter to you very much.
  • 0
    my PF at the incomer is .99 , and the bill shows the average as 0.98 


    the PFC equipment is lovingly maintained 



    Ill ignore the PFC at the distribution level then and focus on kW
  • 0
    I am not an expert on this but my understanding is that inverters have very poor power factor at light load with the pf improving to close to unity at full load. As you don't say what the loading is at the different power factors (or vice versa) I don't think I can add much more at this point.


    Alasdair
  • 0
    the loading on the inverter driven motors could easily be slight, depending on the job in the machine, it could be a few hundred kilos, or 10 tonnes so that probably explains the massive range of PF


    many run at 5% speed, but could be up at 100% depending on the material being cut, its why we have inverters rather than the old DC resistor banks
  • 0
    If your power factor correction is achieving 0.98 in total at the intake, then there is almost certainly nothing to be worried about.


    A poor power factor on one submain that is corrected at the intake will lead to extra losses in that submain for which you will be paying. These losses are unlikely to be significant except in the case of a long and heavily loaded submain. In such a case it MIGHT be worth adding automatic power factor correction equipment at the distant or load end of the submain.

    Even under worst case conditions, the savings will be marginal.
  • 0
    Ill not worry, i doubt the losses will be significant, although we like to think we are huge, we arent really and the supplies are only heavily loaded for shortish periods


    its time I got down to working out where to concentrate for potential savings now, have data coming out of my ears!

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