Lead power factor PF by software only?

pad · Joined: 29 Nov 2007 Posts: 15

Hi all.
I am working on a project where I have to display electrical parameters like KW,KVA,KVAr & PF Power Factor. I can measure instantaneous Power KW and Apparent rms KVA & Derive reactive power KVAr from them.

Now I want to display Lead PF but I have not included any hardware pin for detecting it.

So my question is, is there any software method for it?

Power quadrant might be useful but KVAr is derived and it always positive.
voltage Zero crossing is also not there.

regards,
PAD

Ttelmah · Joined: 11 Mar 2010 Posts: 19520

If you have kVA, and kW, you have all you need.
kW = kVA * power factor

pad · Joined: 29 Nov 2007 Posts: 15

thanks.
I have value of cos(phi). Issue is its sign - inductive(Lag PF) or capacitive(Lead PF). I don't know how to get it as my KVAr is always +ve as it is derived quantity(square, subtact then sqrt).

PAD

Ttelmah · Joined: 11 Mar 2010 Posts: 19520

OK. You want the load angle.

Now I don't know whether you have the data needed to derive this, without knowing exactly how your measurements are made. You only need to be able to tell if the current leads or lags the voltage, depending on how your measurements are actually made you may be able to 'see' this by looking at where the peaks occur in the data from your existing sensors. If you can access this, then you are 'laughing'. Otherwise if everything is 'timeless', you do not have the data to derive this.

If current leads the voltage, you have a capacitive load (leading power factor).

temtronic · Posted: Sat Aug 02, 2014 5:25 am

Presuming you have zero cross detection on the voltage and current sensors, I'd think measuring the time they happen will tell you which is leading.Math will be similar for 50Hz or 60Hz sides of th epond.

hth
jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19520

He says:

"voltage Zero crossing is also not there."

Sad

pad · Joined: 29 Nov 2007 Posts: 15

thanks all.
I somehow managed it.
I check ADC samples of voltage. If they are at zero cross point (+- 10 of 512 count DC Ref),I store current I adc samples count.
If voltage sample counts (5 conse. counts) are increasing ie +ve going V, check current samples. If Current samples are greater than center Ref. i assume Lead pf (current count is more than voltage count) and if current sample count is less than DC ref PF is Lag.
Its seems working,but dont know what if harmonic in current.

PAD

temtronic · Posted: Sat Aug 02, 2014 8:37 am

Without proper zero cross detection the 'math' must be 'fun' !
However as long as you get good,consistent , reliable numbers if it works that's great.

jay

Mike Walne · Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK