measurement of power factor

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Hello.

Could anybody tell me how to measure the power factor without the power factor meter?I mean I want to make a circuit that can measure the power factor.

Thanks ;q

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Hello Lewis

Assuming that you are measuring the powerfactor of a circuit that is drawing a sinusoidal current, you can measure the power factor by measuring the angle between the voltage and the current. This is easily done using two comparators and an XOR gate. Use one comparator to monitor the voltage, giving you an output indicating the polarity of the voltage, and a second comparator indicating the polarity of the current. (the current can be monitored by the use of a CT) take these two square wave outputs and feed them into a XOR gate. The output of the gate will be a pulse stream with the mark space ratio indicating the phase angle, so you can filter this and measure the average level.

If the current is not sinusoidal, than you need to measure the rms current and the rms power. Power factor = KVA / KW

Best regards,

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Hello Marke

The waveforms acquired from CT is analogue signal, how to convert it to digital signal (square wave)?

Could you explain more about the comparators?

Besides, have any other methods to measure the p.f. ? Do you know the "C/k value"?

Thank you

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Hello Lewis

Yes the output of a CT is analogue.

A comparator is an electronic component, similar to an opamp that has an inverting input and a non inverting input and a digital output. If the inverting input is lower than the non inverting, the ouput is high. If the inverting input is higher than the non inverting input, the output is low. Have a look at the data for an LM339 and you will see more.

Best regards,

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• 3 weeks later...

In another message I had seen......

Power factor=kVA/kW but it should be

Power factor=kW/kVA.

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• 1 year later...
is there any single ic chip to measure power factor
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• 2 months later...

;f;

so, setting up a clock and a counter, counting when both U & I is positive, I can measure the p.f.? This means it is quikly to measure p.f. using soc, e.g. 8051. Why there is so many algorithm based on DFT to measure p.f.?

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• 1 month later...

Power factor comprises two components, displacement power factor and distortion power factor.

In the case of a motor load, the power factor is essentially displacement power factor.

Displacement power factor could be measured by using an 8051 to measure the percnetage of each cycle that the U & I are both positive. Distortion power factor would ned to have an analysis of the harmonic currents flowing.

Best regards,

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Try this circuit it is made for singal phase the components are not hard to find,the more current you draw the bigger the wire.15a=14G wire.

this is the site

http://www.designnotes.com/CIRCUITS/pwrfact.htm

Will

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can i use 89c51 for power factor measurement...i am developing a circuit for power factor correction..can u suggest techniques for pf measurement using 89c51?
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Anybody knows a circuit to measure power factor on 3phase motor?

The circuit in the link http://www.designnotes.com/CIRCUITS/pwrfact.htm

is just for one phase!

Instead of current transformer can I use hcpl-788j?

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Use the same circuit for each phase, (three circuits) and combine the outputs.

You need a Current transformer to mearsure the current. An opto isolator will not carry the current.

Best regards,

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What current transformer should I choose to support a current of 15.9A at 400VAC (3phase - I leave in Portugal and F-N it´s 230VAC). The current transformer with ratio 1:1000 that´s oK? You said that I had to do the same circuit in each phase (I supposed that) but I only need one current transformer, that´s right?!

In each comparator I have to supply them with current and voltage... The current we use current transformer and the voltage we supply directly,passing by resistances, the Amp-Ops?

Just one more question... and if we haven´t Neutro (just 3phase) how we connect the circuit?

Thank´s!

Regards

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• 4 weeks later...

yea hi just been thinking abut it and i dont axually know why i can never get my power factor to 1. it sits at the mo @ 0.96 but i can get it no closer.

out of intrest any one know why that is or wat i can do to get it higher

cheers willie

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Hello willie

If the power factor is purely displacement power factor, then you can in theory correct it to 1 provided that you have small enough steps in your capacitor bank.

Three possible reasons for not getting to 1.0 are:

1. Poor power factor less than 1 due to presence of distortion (or harmonic) power factor.

2. Meter not accurate around 1.0

3. Capacitor steps not small enough. If you add too much cpacitance, you will go from a lagging power factor less than 1, to a leading power factor less than 1.

Best regards,

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yea i think that the meatre is slightly off...

however was chating with a mate in the electricty board he came to a conclusion that for some strange reason (in real life senairos) that it is imposable to get 1...

any thoughts

cheers

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i am studying PFC as part of an engineering services surveying degree.

can anyone spare me 10 minutes to review a question that i am completely stuck on.

my email address is lionel.hives at cyrilsweett.com

cheers

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Hello chives

Post your question in the student section and we will look at it. - we do not do your homework for you, but will offer some guidence as to how to solve the problem.

Best regards,

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hi,

I am also studying/making energy power saving device for single phase.is it possible to use capacitor to 200W heater coil that is use in my incubator.I have 9 doors of incubator having 400W heaters each doors.or can i used thyristor unit to breakdown my electric bills?pls help, any suggestion pls.....

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by the way i am junior, tnx.....

regards....;p;

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• 1 month later...

I would ask how far is purely transmition line can affect of the cost of power factor in an industrial firm?

i mean if i received 0.95 from transmition line is the same cost for correction capacitor bank if i received poor 0.6 pf?

best regards;)

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The power factor of the transmission lines has no effect on your load. When you measure the power factor at your point of supply, you are only seeing the power factor of your plant. You can not see the power factor of the transmission lines.

A poor power factor on the transmission system will not affect your firm.

Best regards,

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thank you mark for yr quick reply, i am greatly appreciated your heigh quality of great experience you got on the long past years.

best wishes

abbas:D

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Hi

can u tell me how can i use 89c51 for my power factor measurement and control?

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