Re: Core imbalance in RCDs

Roger Johansson wrote: 
Tony Williams wrote:


Nice pictures. 

....but very wrong (electrically speaking).


The first picture shows a 1/3 turn, as the wire goes straight
tangentially on the outside, result 35mV.

There's no such thing as a partial turn. Think about it. If you have current flow, you have a circuit, which means you have a complete loop (i. e., turn). It doesn't matter much whether the return path is 1/16" away, or 12" away, or 100ft away. It's still a complete loop.

The larger the loop is, the more opportunity there is for parasitics to siphon off some of the field; but the core is generally very high mu, and offsets the parasitics almost completely.

That's why standard current transformers (remember the discussion of a few days ago?) work quite well with just a single cable threaded through the core.

Picture 1 gave a tiny voltage because a tiny fraction of the field passed through the core hole, inducing voltages into the near wires without being cancelled by corresponding induction into the opposite wires on the core.

Picture 2 had roughly equal and cancelling fields inside the hole.

Picture 3 had a slightly higher voltage than 1, probably because the wires were not bent exactly at the same angles, so got a trifle more of the uncancelled field in the hole.

Picture 4 is picture 1 plus 2 copies of picture 2.  Same voltage out as 1.

I don't know how many turns you had on the secondary, butput the primary wire inside the hole and the output voltage will be very high if you've wound it at all like a CT (which is what a GFCI or RCD is, after all).

Put the primary inside the hole, loop it back inside again without going around the core, and you'll have zero out. That's a GFCI/RCD.

jp
.

Relevant Pages

  • Re: Receiving Loop Antenna Question
    ... (something like 25 wires - the sort used in PCs to connect hard ... and the like) put away for a rainy-day loop antenna project. ... that has distributed loads and ZERO lumped loads, ...
    (rec.radio.amateur.antenna)
  • Re: Receiving Loop Antenna Question
    ... (something like 25 wires - the sort used in PCs to connect hard drives ... and the like) put away for a rainy-day loop antenna project. ... Both are using basically the same cap values. ... capacitance build up but also the inductance build up. ...
    (rec.radio.amateur.antenna)
  • Re: Receiving Loop Antenna Question
    ... (something like 25 wires - the sort used in PCs to connect hard drives ... and the like) put away for a rainy-day loop antenna project. ... I did wonder about the effects of distributed capacity between the windings. ...
    (rec.radio.amateur.antenna)
  • Re: Snow and traffic light pavement sensors
    ... established in the wires buried in the pavement, also caused by vehicles which disturb the field. ... piece of aluminum foil over the loop would trigger it. ... Loop detectors detect a change in phase of the electic currentwhich is ... vehicle disrupts the field. ...
    (misc.transport.road)
  • Re: 1975 Wizard EM repair
    ... detailed picture and saw where the red wire is and put one in. ... Now the game when powered on blows the 50 volt 15 amp fuse when I open ... I'm not sure we're talking about the same wires here, ...  The switch wires are the ones off to the right connected to ...
    (rec.games.pinball)
Quantcast