Zero crossing detecting formula 3 phase network

[nayakajit87]

Dear all.

I am looking for the simple 3 phase zero crossing ckt and its formula to calculating it. I am trying with arduino uno board. Kindly suggest any recommended CKt

 

[c_mitra]

I am looking for the simple 3 phase zero crossing ckt...

I do not believe there is anything special for a 3-phase zero crossing detector. You treat each phase individually and use the output from each phase as needed. If you desire, you can OR the three outputs to get one single result.

For simplicity, you can use simple diode logic AND /OR gates. You should also limit the final pulses with a voltage limiter (say with a zener diode).

 

[Easy peasy]

You need to identify whether you need to detect the zero crossing relative to neutral point - or between each pair of two phases - these are different points and phase shifted in time.

 

[nayakajit87]

i wanted to measure degree phase shift. I wanted calculation for my application like this
i have 3 phase 4 wire system. looking for equations
Line to Line and Line to Neutral voltage.when R,Y,B are independently connected.

Now assume that i have tapped R to common point Y-phase and B-phase. During this condition there will be no phase shift since i have used single phase line. Then how calculations are taken into consideration.

Line to line and line to neutral .

i thought zero crossing ckt and equation might solve this. Is there any example ckts and equation that i can tested out with MCU.

 

[KlausST]

Hi,

To be able to calculate the phase shift you need the zero cross of voltage as well as zero cross of current.

Please consider:
If you have symmetric load you need just one pair. Otherwise you need a pair for each phase.

Please know that: cos(phi) = power_factor is only true for purly sinusoidal waveforms.

For varying currents (sometimes small, sometimes high) it's very difficult to get a precise zero cross signal.
Also note that overtones or other noise in voltage and current will cause the phase shift to jitter causing faulty results.

Thus: if you have varying currents and/or overtones in current, then I recommend to use 4 (1 x V, 3 x I) ADC channels to measure and calculate V_RMS, I_RMS, phase shift, true_power, power_factor .... precisely.

If done precisiin measurements many times. If you want precision your task becomes really difficult.

Klaus

 

[betwixt]

Also be aware that simply using a voltage divider to drop the phase voltages will not in itself make it measurable or even zero crossing detectable if fed to an MCU. You at the very least need to cater for the reversal of polarity and some over voltage protection would be a worthwhile addition.

There is no definitive reference to the phase timings, you have to measure one relative to the other two. As Klaus stated, ideally you need three voltage detectors and three current detectors. The voltage zero crossings will tell you the angle between the phase wires and the current zero crossing relative to those will give you the load phase shift.

Brian.

 

[schmitt trigger]

Lastly....
Those capacitors, C1, C2, C3 will generate a phase shift on the voltage samples.

As shown in the simulation, it will be about 7.5 degrees at 60 Hz. This can be significant, depending on what you want to measure.

 

[BradtheRad]

A pair of anti-parallel led's makes a handy method to indicate volt level and polarity. Or optoisolators.

Another pair of led's (optoisolators) can indicate current, if it's low enough to be safe for led's. Or else to indicate high current, place a shunt in parallel with the pair, but then it has to develop sufficient voltage so that led's turn on.

All photodetectors are in a separate circuit together with a low voltage power supply and your Arduino. It's isolated from high voltage, and it easily reads 3-phase behavior, positive and negative polarities, star and delta. It allows easy interpretation of phase differences between voltage and current waveforms.