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Triphase without neutral

(Roland) #1

Hello, We are looking for a solution to mesure the power of our electrical installation. For the moment no commercial solution exist for our configuration.

We are living in Belgium and the electrical are 3X240V without neutral. So it’s a three wires system.
Is this system capable to make good mesure of power?

Regard’s
Roland

(Robert Wall) #2

Welcome to the forum, Roland.

You can indeed use the 3-phase sketch to measure a 3-wire system, and the result will be a good approximation. It will not be an exact measure, because only one voltage is measured, the second voltage (because the sketch uses the 3rd phase as the “neutral” and treats the other two as a 2-phase system) is assumed to be equal in magnitude to the first.

What you will need is an emonTx, two c.t’s and a 230 V (Are you sure your voltage is 240 V, not 230 or even 220?) a.c. adapter, and a programmer to upload the sketch.

The sketch will not run on the emonPi, therefore if you want to have emonCMS to record and display the data you need either the ESP8266 WiFi module (plus a 5 V d.c. USB power pack) and a Raspberry Pi for emonCMS to run on as a web server, or you need an emonBase, or you can use the ESP8266 and the on-line service emoncms.org.

If you really need accurate measurements, then I would suggest the same strategy, i.e. treat one wire as the neutral, and have an emonPi (with 1 c.t. and a.c. adapter) measuring one voltage and one phase current, and an emonTx (again with 1 c.t. and a.c. adapter) measuring the second voltage and phase current.

One final note: whichever way you measure, the two “powers” you will read are meaningless, but the sum of the two will be correct (within the accuracy of the measurement, of course).

(dBC) #3

So do countries that use 3-wire for the final distribution leg still have the concept of safety earth? I assume there’s no such thing as an earth leakage fault when all 3 phases are just floating?

(Robert Wall) #4

That’s a good question. It’s quite possible that the final distribution transformer has its secondaries in star, which could (and almost certainly would) have the star point earthed. And in that case, you would of course be able to detect earth leakage.

But a safety earth is still necessary because there is still danger, both from capacitance to earth which will give a (low-ish) fault current in the first earth fault, but more particularly from the second earth fault which could result in a full fault level current flowing.

I believe the system is obsolescent, and exists only in parts of Belgium and Norway.

(And of course if there was a neutral, 132 V L – N isn’t exactly standard.)

(Roland) #5

We have naturally a earth, but it’s not a neutral. Between wires we have 240 v. It’s a triangle without neutral.

(Roland) #6

The figure 4 is our configuration

https://www.google.be/search?source=hp&ei=JMXTXPKuLcHewQKWw4KwCg&q=chema+triphasés+Belgique&oq=chema+triphasés+Belgique&gs_l=mobile-gws-wiz-hp.12..30i10.3550.22073..24296...2.0..0.3564.10572.0j12j2j5-1j1j1j0j2…0…1…8…35i39j0j46i131j0i131j46j46i275j0i10j0i203j0i22i10i30j0i22i30j0i13j0i13i30j33i160.0myelarTFDM#imgrc=4iZexSgUlqYDUM: