3 Phase Motor Control ?

[Craig]

Hello

I am busy with a project where I need to Monitor a 3 Phase 7.5HP (5.6Kw) Motor on a pump [230Vac Single Phase & 400Vac 3 Phase All @ 50Hz].
What I need to monitor on Each Phase is Over Voltage, Under Voltage and then Over Current and Under Current and possibly Phase Rotation.
This is part of a much bigger project where a lot of other apparatus is being sensed and monitored and I need to look at integrating this
into the initial design which affords me better control over everything.

I have been looking at various ideas like CT'S and maybe using a Chip Which is used in the Electrical Prepaid meters etc.

What I would like to ask is the advice of other forum users which might have previous experience with this type of equipment, which would be the right way to tackle something like this?
I need to look at the most Cost effective but, yet Practical approach to this taking Power Surges and Lightning Problems into consideration.
I will be very grateful and thankful for your help in choosing the right approach!

Regards

Craig 

[shantanu@india]

The ACS712 30A Hall sensors are good for current measurement for your application.
Phase rotation can easily sensed by 3 optocouplers.
Voltage sensing is straightforward... 3 PCB mounted transformers protected by glass fuses on the primary side.
All can be placed on a single PCB with the PIC
Alternatively you can go for ADE7754 that I had used for one of my projects... but that would be an overkill.

[Sommi]

If you want it cheap you reference your circuit to neutral connector, 5V negative to neutral and have a pic there. Measure each phase voltage with 8 series resistors 0805 or 1206 in series as the high side of a voltage divider, have the root of the voltage divider referenced to 2.5V, adjust the voltage divider so each phase results in a sinewave approx. 1.5V (negative peak) to 3.5V (positive peak). All necessaty stuff then can be done in SW. For current measurement use the recommendation of Shantanu or use cheap 1:1000 corrent transformers.

Regards Sommi

[Craig]

Thanks Shantanu and Sommi for you very valuable input, I really appreciate your feedback.
I did think of using the ADE7754 but, do agree that it will be overkill and add unnecessary costs to the project.

I think as suggested that a mixture of Ideas will work well for the various measurements.

Thanks again for your help

Kind Regards

Craig

[steyn]

Hi Craig...nice project I did something similar when i lived in South Africa due to the energy supply issues. I guess first question would be the legal requirements regarding making this. I experimented with a few things, for current i used ct's...Lem current transducers and ACS current sensors. My biggest problem was distorted current waveform in single phase inductive loads. Another hurdle and most likely the biggest was filtering the board/controller against electrical noise. My products worked well although in software i never really got the distorted current reading 100% sorted...good luck with your project

[Craig]

Thanks Steyn ,Ja we still have load Shedding and then the problem is when the power comes back you find that the Various Voltages on the Phase are low.
It is a headache as you know which we have to work around.
Regards
Craig

[steyn]

Wow, i thought that they would have sorted all this by now. Not good...Must be honest with most of my projects i have always been limited by my programming skills. Anyway if you want to "chat" feel free to pm me

[See_Mos]

Commonly referred to as protection relays.  An interesting project and one that I have considered a few times.  The basic idea is quite straightforward. All of the functions that you mentioned are already available in commercial units varying from simple function DIN rail modules right up to very complex microprocessor controlled units.

I have already done frequency protection using PIC and somewhere I have a very simple two transistor phase rotation indicator that could be modified to use opto isolators.

[Craig]

See_Mos that sounds like a very useful circuit, Hopefully you can dig it up.?
Kind Regards
Craig

[See_Mos]

Hi Craig,

The original article can be found here on PDF page 33. magazine page 548

https://worldradiohistory.com/UK/Wireless-World/00s/Electronics-World-2001-07.pdf

I just added opto couplers in series with the LED's

[Craig]

Thanks Bob
That Looks Excellent.
Regards
Craig