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Pls tell method for Power Factor Measurement

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svaidy

Newbie level 5
power factor measurement

Hello,

I wish to know the how to find Power Factor for 1-phase voltage and current wave forms with different loads,

Thank you,

power factor measurement ic

Hai,
Put the zero cross detector for current and voltage.Connect these zero cross detector outputs in XOR gate.The On time width of the xor gate out put says power factor.
The time can be measured by simple 555 IC or by microcontroller.

svaidy

Points: 2
power factor measurement

svaidy,
The method proposed by harii74 will work for sinusoidal load currents. However, for non-sinusoidal currents, the problem is more complex. By definition, power factor is equal to real power divided by apparent power. Apparent power can be obtained by measuring the True RMS current, and the true RMS voltage. Apparent power is the product of the two. Real power is most easily measured by using a power meter whose frequency range encompasses the frequency spectrum of the harmonic currents.
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If you don't have access to a power meter, you can remove the current harmonics using a filter, being careful that the filter has zero phase shift at the fundamental frequency. Once you have a pure sinusoidal current waveform, you can calculate the real power as P = VIcos(Theta), where I is the filtered current. Theta can be measured by a zero-crossing method as suggested by harii74. Theta = ArcCos[(Delta t)/T], where Delta t is the time difference between zero crossings, and T is the period of the waveform.
Regards,
Kral

tell method

Hello,

I have the following values : V=210volts, I=1.3 Amps, time=20ms

Please tell how to calculate the power factor. please tell the procedures.

Thanking you,

with regards,
S.Vaidyanathan,

how to calculate power factor for a filter

Hello.

If you don't have access to a power meter, you can remove the current harmonics using a filter, being careful that the filter has zero phase shift at the fundamental frequency. Once you have a pure sinusoidal current waveform, you can calculate the real power as P = VIcos(Theta), where I is the filtered current. Theta can be measured by a zero-crossing method as suggested by harii74. Theta = ArcCos[(Delta t)/T], where Delta t is the time difference between zero crossings, and T is the period of the waveform.

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how to find real power when power factor is given

svaidy,
Regarding your 02 Sep 2009 8:36 post: I'm assuming that t = 20mS is the period of the waveform. If this is the case, you haven't given enough information. In the case of a purely sinusoidal voltage and current, the amplitudes of the voltage and current are irrelevant. You must know the phase shift of the current with respect to the voltage. This can be measured directly on a dual trace oscilloscope, or by otherwise measuring the time delay between the zero crossings of the current and voltage. If you choose to measure the time delay, then the phase shift (theta) is equal to 360(t/T), where t is the time delay, and T is the period. Once you know the phase shift, then pf = Cos(Theta). It is independent of the vaues of the voltage and current.
Regards,
Kral

svaidy

Points: 2
Re: power factor measurement

If you don't have access to a power meter, you can remove the current harmonics using a filter, being careful that the filter has zero phase shift at the fundamental frequency.
Kral

Do you suggest any idea how to design that filter for removing harmonics to calcultate power factor easily...?
Regards..
Waqas

To design a filter, you must calculate or estimate the expected the frequency and amplitude of the harmonics. This will depend on the application. For example, a rectifier with a capacitor filter will have even harmonic currents of high amplitude. The next step is to determine the attenuation required. This will be determined by the accuracy requirements of the power factor calculations. If you design a filter with a small safety margin for attenuation of the lowest frequency harmonic, the higher order harmonic attenuation will usually be adequate. Finally, you must determine the type and order of the required filter required to get the attenuation you need. One way to approach this is to cascade several bandpass filters. See the URL below for a design procedure for a multiple feedback active bandpass filter.
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After the filter is built, you can "tweek" one or more components to get exactly zero phase shift at the fundamental (mains) frequency. Or, you can cascade an allpass filter, which provides phase adjustment with no gain change using one variable resistor. See the URL below for an active all-pass filter design.
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All-pass filter - Wikipedia, the free encyclopedia
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If you can provide information on the harmonic content, I can provide more specific design guidance.

Waqas_MicroSolutions

Points: 2
I have to measure, graph and display parameters of 3φ Induction Motor on a Graphic LCD at about 30 feet form the motor and transmit to a computer at about 60 feet from the motor to display it on VB application... The VB application should also be able to save one week record of the data sampled each hour, and display their graph at the end of week....
The parameters are....
1-Power factor
2-kW
3-kWh
4-kVA
5-Voltage
6-Current
7-rpm
8- Temperature

I hope I'll use PIC18F452...

->5 & 6 can be measured with PT and CT respectively--> Precision rectifiers---> 2 ADC channels
-->4th can be calculated with the help of above (VxI)
-> rpm with hall effect sensor or an optical one..
-> Temperature with DS1820 or LM35/34-->3rd ADC channel
-> 2 and 3 can be easily calculated if 1 is known(The only Problem I'm having)

We use 50Hz ac 440V 3φ supply in our country...
I really do not have any information on its harmonic content( Probably 3rd is more common here...) The motor is somewhere in steel mill.. with a heavy flywheel on its shaft..

Before final implementation I think I should make a test circuit for above specs with a single phase 220V,1KVA,50Hz Induction Motor.. and I will...
If you can provide information on the harmonic content, I can provide more specific design guidance.

I hope above info is sufficient for you to guide me....

Regards
Waqas Rafiq

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