power factor calculations in LV and HV metering 4

[galleon50]

What calculations do you use to check total PF useing L1,L2,L3 PF readings in LV supply's and L1 and L3 in HV supply's also KW,KVA and KVArh readings are available

 

[stevenal]

pf=kW/kVA

 

[wareagle]

You need to ensure you have the max readings for KW and KVA and that they occured at the same time. As Steven said
PF = KW/KVA.

 

[galleon50]

Thanks for your replies ,what would the calcs be to check the total PF using each individual PF reading.

 

[electricpete]

KWtotal = KW1 + KW2 + etc
KVARtotal = KVAR1 + KVAR2 + etc
PFcomposite = KWtotal/KVARtotal


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[PHovnanian]

galleon50, all of the above comments are valid. But before diving in, consider exactly what you need this p.f. figure for.

Are you being billed for low p.f. specifically or peak KVAR demand? The worst p.f. may not be occurring at peak demand times. The same logic applies to sizing p.f. correction equipment (capacitors). You'll want to know the peak KVAR.

 

[galleon50]

I am involved with CT meter testing,i am now required to prove total power factor using red phase PF and Blue phase individually to calculate the total ,

 

[stevenal]

"PFcomposite = KWtotal/KVARtotal"

No. See my post above. If quantities are mostly sinusoidal, you can approximate with PFcomposite = cos(atan(KWtotal/KVARtotal)).

 

[Wyeman]

stevenal,
I believe you mean sinusoidal PF = |cos(90-atan(kWtotal/kVARtotal))|

The 90-atan(kWtotal/kVARtotal) would be the actual phase angle. Use absolute value around the cosine because you cannot have a negative PF.

That PF formula works ok with wattless reactive power until you introduce harmonic distortions...

 

[galleon50]

Thanks for your input Wyeman , but you do get negetive PF registering in CT metering

 

[stevenal]

Wyeman,

Yes, you are correct. What I meant to say was cos(atan(kVARtotal/kWtotal)). Pete's formula threw me off I guess. No absolute value is needed because atan returns a value in the first or fourth quadrant (depending on the sign of the argument), and cos then always returns a positive value.

galleon,

Sometimes pos/neg in inserted in front of pf to indicate leading/lagging reactive current. It is not mathematically correct, though.

 

[galleon50]

Thank you for all your imput,this has been a great help.