Community
OpenEnergyMonitor

Community

Measuring 3 phase voltage, current and cos Phi in a 800 Ampere 400 V system

3-phase
raspberrypi3
Tags: #<Tag:0x00007f880e723538> #<Tag:0x00007f880e723100>
(Henk Schuurman) #1

In the first phase I need to measure the current and voltage and cos phi in a factory. The used current now is between 500 and 800 Amps. I need that data in a Siemens scada system. Next phase is programming in Python a Raspberry Pi to send CANbus codes to equipment for controling some processes. So I need 3 phase Voltage and current measurements.and minimum 100msec sampling. What would be the best solution for the hardware? Can I work with 3x emonTX and combine the results on the emonPi? What is the reason the EmonTx only measures 1 AC Voltage?

(Robert Wall) #2

Welcome to the community, Henk.

Starting with the easy question first: OEM is based in the UK and the emonTx and emonPi were designed for the UK domestic market, which is almost exclusively single phase, TN-C-S at 240 V. So there is no need for more than one voltage measurement. I have been recommending the development of a 3-phase version for a number of years, but it has not happened.

You can certainly use 3 × emonTx and combine the results later, and that is probably the most accurate way to do it. If you use the standard default sketch in the emonTx, that measures for 200 ms every 10 s - but it is not easy to synchronise all three emonTx’s so that they all read at the same instant.

The new emonTxCM samples continuously and can report the data at much more frequent intervals, but I think you would have a problem with 3 sending a report every 100 ms by radio, as there is nothing to stop two transmitting at once and jamming each other.

The other problem I see is both emonLibs don’t measure cos Φ, but the ratio of real power to apparent power - which is not the same thing, and so we cannot tell whether the power factor is leading or lagging.

If you look at our “Use in North America” page, there are several C.T’s listed there that will be suitable for 800 A.

As an alternative, if you have someone who is able to do so, I suggest you look at one of the higher powered Arduino units and build an analogue input front end, based on our emonTx design. That could give you the necessary 3 voltage inputs and at least 3 (maybe 6) current inputs, and because everything would be in one processor, you would be able to customise the software to synchronise the readings and use a wired connection to the emonPi; and I think that would be preferable in a factory environment.
This https://boredomprojects.net/index.php/projects/home-energy-monitor is a practical implementation of that, it could very easily be built as 3 voltage and 9 current inputs, though I cannot say whether you would be able to have true continuous monitoring with that many inputs.

Yet another possibility that you might not have considered: there are 3-phase DIN-rail energy meters available that can be connected via MODBUS. I do not know the details, but it is something to look at.