I want to design a circuit for Three Phase Power fault monitoring with arduino. I have 3 live phases and no neutral, my objective is to detect the fault , it can be single phase out or all the 3 phase are out and give that input to arduino? How to do this.

 

What is the 3ph voltage?
A small 3ph transformer could be rare, so one way is with three small transformers, one such as shown could be with the secondary removed and a small few turn overwind placed on .
Each wired phase to phase.

 

I see they also have a low voltage sec version.
https://tanooga.com/

 

Welcome to AAC.

I would use three optocouplers fed by voltage dividers, one for each phase. Depending on the voltage involved I would provide isolation proportionally.

 

I want to design a circuit for Three Phase Power fault monitoring with arduino. I have 3 live phases and no neutral, my objective is to detect the fault , it can be single phase out or all the 3 phase are out and give that input to arduino? How to do this.

Use three of these
https://www.micro-transformer.com/2ma-2ma-voltage-transformer-ZMPT101B.html
with 400k resistors to limit the current to 1mA
then the op-amp circuit in the datasheet.

 

I would be a bit wary about Opto couplers on 440v , assuming that is the voltage being monitored, the transformer seems a little more rugged for this.
Either way, I would recommend referencing the Arduino side to earth GND.

 

I would be a bit wary about Opto couplers on 440v , assuming that is the voltage being monitored, the transformer seems a little more rugged for this.
Either way, I would recommend referencing the Arduino side to earth GND.

It's a good point, but I would probably do what I have done in other cases like this: make my own optocoupler with an LED, a fiber optic light pipe, and a phototransistor. The LED is located in proximity to the actual high voltage source and optically connected to the light pipe, then the light pipe is routed away a safe distance where it is connected to the phototransistor, which provides the digital signal to the Arduino.

 

Use three of these

They also offer 3ph current transformers, most likely would require a burden resistor to monitor voltage.
https://www.micro-transformer.com/Three-Phase-Current-Transformer-pl6873226.html

 

For the record, I don't think there is anything wrong with the transformer solution, and a good transformer should provide sufficient galvanic isolation, but I had a not good transformer decide that galvanic isolation was optional and while the result wasn't fatal to any people or pets, my wallet did spend a long time in recovery.

 

I would be a bit wary about Opto couplers on 440v , assuming that is the voltage being monitored, the transformer seems a little more rugged for this.
Either way, I would recommend referencing the Arduino side to earth GND.

It's the series resistor that needs careful choice. Most surface mount resistors will only stand 200V.
230V phase to neutral is 565V peak delta, add 10% tolerance makes 621V, so three in series isn't enough.
As the phase to neutral voltage is still 230V, the opto doesn't require any higher spec than normal.

 

3 of this simple circuit, driving interrupts.

 

Transformer vs. opto isolator depends on whether it is necessary to know that the voltage is within spec, or simply whether all three phases are present.

 

Transformer vs. opto isolator depends on whether it is necessary to know that the voltage is within spec, or simply whether all three phases are present.

The TS post suggests it is a go-no go test but it is very possible he wants an analog threshold test and the language is imprecise. Re-reading, though, if he means what he says it is just presence or absence he’s after.

 

Will this work if i used optocoupler, 817 optocoupler has forward voltage of 1.2v and current 0.15mA.
There is no newtral present, can i connect RYB phase as shown in photo, and the question mark to GND of arduno. Will this work. Or any other suggestion please.

 

Will this work if i used optocoupler, 817 optocoupler has forward voltage of 1.2v and current 0.15mA.
There is no newtral present, can i connect RYB phase as shown in photo, and the question mark to GND of arduno. Will this work. Or any other suggestion please.

Use an 814 not an 817 (because it is AC input) and watch the voltage rating of the resistors.
It might be an idea to put a transzorb (or back to back Zeners) in series (say 100V bidirectional) so the at optos are not switched on by small voltages remaining on the line even after a phase has failed.

 

Hello there,

I was going to mention opto couplers but @Ya'akov beat me to it.

If the voltage detection requirements are not too strict then a simple circuit like that already mentioned could work. You do have to be a little careful though as opto couplers can start to degrade over time due to the internal LED becoming less and less efficient over time. With low forward current through they should last a long time.

If you want to get more precise there is one sure way to do it. Use a separate low-cost microcontroller for each phase, and run the voltage for each one from the same phase they are measuring. Along with that, use optocouplers to transmit the state of each phase to a master microcontroller, which then can do the shut off control or measurement indication as needed. Doing it this way also allows you to transmit the voltage measurement of each phase to the master, which can then indicate the actual voltage to an LCD display.
The master can decide if the voltage is too low or too high or whatever, and if it stops receiving a signal from any of the uC on each phase, it can take that as a loss of a phase.

This requires three uC chips plus a master uC chip, but they can be low cost options, and the master can even be the Arduino.
This also requires three power supplies, one for each uC chip, but they can be offline type supplies because they will be galvanically isolated from the master anyway. You may even be able to get away with one power supply for all three with a little more thought.

I thought of this because I considered doing this for battery cells being charged in series, which each uC could monitor it's own cell, and also for a multiple battery installation where all the batteries were galvanically isolated and had to remain that way.

 

Welcome to AAC.

I would use three optocouplers fed by voltage dividers, one for each phase. Depending on the voltage involved I would provide isolation proportionally.

Hi Ya'akov,

You beat me to it I was going to mention that first.

One unusual thing came up though when I tried to mention you in my other post.
When you type the ampersand @ followed by a letter, you get a list of member names so you can choose the member you want to mention.
What happens when I type @ followed by 'Y' and even "Ya" your name never comes up so it looks like you cannot be mentioned in a post using the ampersand method. Is this a forum problem or something else. Maybe you are using a special character or something in your screen name.
I'll try it here again:
@Ya'
The list comes up after the 'a' but then goes away when I type the apostrophe.

 

If you put Zeners in series with each opto, then the pulse width on the output would be proportional to the time each phase was above the zener voltage. A look-up table could translate that into voltage.

 

I want to design a circuit for Three Phase Power fault monitoring with arduino. I have 3 live phases and no neutral, my objective is to detect the fault , it can be single phase out or all the 3 phase are out and give that input to arduino? How to do this.

If all three phases are imortant, then is phase sequence also important? It may be, as it controls the direction of rotation of 3-phase motors.
The opto-isolator scheme should be a best choice, but split the dropping resistance and put half of it in each leg for each optoisolator.. Then add 2 shunt diodes across each LED side to avoid over voltage damage. then the three outputs can go to three inputs and both phase presence and phase rotation can be monitored easily. This can be in a small package and battery powered. Do not use surface mount resistors or diodes on the 3-phase side of the isolators.

 

but split the dropping resistance and put half of it in each leg for each optoisolator..

A typical quarter-watt resistor has a maximum voltage rating of 250V, but the peak phase-to-phase voltage of a three-phase 230V supply is √2.√3.230V, and with a ±10% tolerance is 619V, so two in series may not survive. Three in series will be required. For surface mount resistors they tend to be 200V, in which case four would be required.