Advice before hardware purchase - 3 phase industrial unit

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Hello, thank you for reading my post.

I lease an industrial unit supplied with 3 phase electricity. It is important for me to track Power Factor due to additional charges if this is out of limits.

First question: Does emonCMS log/record PF over time, like energy usage?

Second question: I would like to achieve the most accurate recordings possible on all three phases. I understand I would want to use voltage etc. measurements on all three phases for this to happen.I therefore think I would need to order the following:

1 x emonTX with 3 CT clamps, Optical sensor (meter has pulse output) and UK plug power supply (for voltage etc readings on one phase)
1 x emonPi with both DC and AC power connected to record the voltage etc of a second phase and for hosting emonCMS
1 x emonTX with just the AC power connected to record voltage etc readings of the third phase.

Are they any other hardware suggestions or a better way of doing the above with less hardware/cost?

Thank you.

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Power factor isn’t normally sent to emonCMS by default, but there’s absolutely no reason why it cannot be treated in exactly the same way as any other variable. But you can’t quite compare it with an accumulated value like energy. You’d be able to watch it, but emonCMS doesn’t have alarms or anything like that. That would need to be done outside of emonCMS, and others here are better placed to tell you about that.

You’ll have the items you need, but if I understand you correctly (and I’m only trying to infer what you’re connecting where from what’s written), that won’t give you real power or p.f. if you attach the 3 c.t’s to the one emonTx.

I think your set-up will be:
1-off emonPi with 5 V USB power and one c.t. and a.c. adapter to measure real power on phase 1, and the optical sensor for your meter pulses.
2-off emonTx’s, each with one c.t. and a.c. adapter to measure real power on phases 2 & 3.

(But you can put the optical sensor on whichever you like.)

You’ll need to edit the software in the emonTx’s and in the front end (the “emon” part) of the emonPi to report the power factor. And you’ll need a programmer and leads to do that.

The question that drives that is, how accurate is the balance of your phase voltages? If it’s “good enough”, you could get away with a Raspberry Pi, and emonTx and connect the two by wires. The 3-phase sketch phase shifts the phase 1 voltage in software to provide a phase reference to the other two phase currents, but it can’t know the amplitude difference, which is where the error comes in.

Also, the two emonTx’s monitor continuously and report every 10 s (approx), the present emonPi front end software is still the ‘discrete sample’ version, though I’ve had a continuous monitoring version working for many months now, it’s yet to be released because it requires major changes everywhere. I’m still writing documentation.

If the emonPi sampling for 200-300 ms every 5 or 10 s is a problem (and if you have rapidly fluctuating loads, it could well be), and you can’t wait for the emonPiCM, then replace the emonPi with a third emonTx and an emonBase (essentially a Raspberry Pi with a radio receiver, or an emonPi minus the ‘emon’ part).

Alternatively, if you’ve got the expertise in-house, what about a stand-alone 3-phase meter with a Modbus output, which with the addition of a Modbus-Ethernet converter, will feed into your LAN and you can have a RPi or any server running emonCMS where you like.

One immediate advantage I can see for this is the meter will most likely give you vars and kvarh, which the emonTx/emonPi can’t calculate.

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Thank you Robert for such a comprehensive reply. I will investigate the additional meter and MODBUS option.