Negative Power Factor

[topcat72]

During the commissioning process of a newly installed EDMI, CT AMR or smart meter, the meter was showing a negative or lagging power factor of -0.87.

I understand the relationship between reactive and true/apparent power and the theory of how the power factor is calculated and used for billing in respect of a customer having a lagging power factor and using more reactive power (kvar) in a commercial premises, however..

When commissioning the 3 phase EDMI meter, my Nanovip tester showed a positive power factor on each phase L1 = 0.89 L2 = 0.87 L3 = 0.91, so what i am failing to understand at this point is why the meter shows a negative power factor of -0.87,
is this because overall the meter can only display the power factor as an average and sees it as a lagging power factor, i.e less than the industry standard of 95% or 0.95 (as the customer will be charged for having a power factor below this) or is it because the customer is using alot of reactive power, as there is no power factor correction installed.

any comments would be appreciated

topcat72

 

[Marvo]

Leading PF is fairly unusual, most commercial and industrial loads especially will be overall inductive giving a lagging PF. On the odd occasion it does happen is usually caused by over eager correction.

L1 = 0.89 L2 = 0.87 L3 = 0.91 shows a lagging PF on all 3 phases, a PF of 1 is linear, anything less is lagging due to inductive loading.

 

[Knobhead]

Check if there is static PF correction fitted. Over correction is just as expensive as under. More expensive if you consider capital expenditure.

 

[topcat72]

no PFC fitted ( which i have mentioned to customer ) but it is quite a balanced load across the 3 phases, this is a sports and conference centre so quite a heavy inductive load.

metering has also just changed measurement class from non half hourly to half hourly.

customer has queried his billing and have explained the theory of the lagging pf, i think its a cost issue in terms of fitting pfc, something which he will have to take up with his supplier and electrical contractor.

topcat

 

[Marvo]

For a conference center it's possible they have a large IT load with servers PC's routers and switches permanently running with lots of switch mode supplies. If that is the case you could suggest they install a small local fixed pf correction unit which is pretty cheap because there's no switching or monitoring involved.

 

[Knobhead]

The meter gives a reading which should be compensated for current draw. 0.87 0.89 0.91 if on absolutely perfectly balanced loads would be 0.89. If however the load on the 0.87 line is greater it biases the reading against the other two.
Can you tabulate the PF and current for each phase?

If the problem is arising from IT equipment you’ll need something a little more sophisticated than a couple of static PF units.

 

[Bobster]

Check that the CT's are wired the right way round! I highly doubt it will be anything else.

 

[Bobster]

Any update?

 

[Darkwood]

In addition to CT polarity also need to check the phase sequence of the 3ph supply to the meter is the same as the sequence of which the CT's are ordered, this can give a low PF display.