Harvesting energy from 3-phase

Clive Arthur · 2019-08-08T08:55:47+00:00

A customer has a three-phase supply drawing from 50A to 100A at nominally 60Hz. He wants to tap some power from this without any electrical contact, so probably using say three current transformers with each phase going through one toroid. Probably the wire is too thick to make multiple turns. The power needed will have to end up as a 30V 300mA supply, so 10 watts or so which is a lot for a normal CT. This is not something I've looked at before and sounds quite difficult - a quick Google shows that this can be done for very low power devices. Any ideas? Multiple toroids with secondaries in parallel? Long sausage toroid? The energy has to come from the wire, obviously, so the impedance of the wire will have to increase a little which implies that some length will be needed, but now I'm rambling. Is the following even in the same county as the ballpark?.. 30V @ 300mA is 100R 50A -> 300mA is a turns ratio of 1:167. Inductance goes with the square of the turns, so the wire must see 3.6mR 3.6mR at 60Hz is 10uH 10uH/N^2 cores are doable, maybe multiple 3 watts per core isn't too big Cheers -- Clive

Aug 08, 2019 20 Replies

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Massoud 7 years ago

snipped-for-privacy@downunder.com wrote in news: snipped-for-privacy@4ax.com:

Current transformer's secondary should never be open. Zs=N^2*Zp so if Zs is infinite, current line becomes hi impedance and destroys the transformer. Consider off mode of you gadget.

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Harvesting energy from 3-phase

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