Possibly a third harmonic problem? Phase angle dimmers are notoriously hard on the neutral at some settings (30% gives more total RMS neutral current then the RMS current in any individual phase!). I have seen some *REALLY* wird shit when running these loads on gen sets.....
Regards, Dan.
I was reading some literature on light dimmers, the kind that "chop" the AC wave cycles, which said that when the dimmers are installed on 3-phase power service, it can sometimes result in the lights flickering.
Has anyone heard of this, or know why/how it happens? What kind of flicker would this be referring to? Fast as in 50/60 cycle? Or slower?
in article snipped-for-privacy@news2.newsguy.com, snipped-for-privacy@ipal.net at snipped-for-privacy@ipal.net wrote on 4/3/04 11:23 PM:
The dimmers referred to here are based upon thyristors and phase control. That is an electronic method using semiconductor properties.
Three phase dimming is possible without phase control. I have used three phase gangs of variable auto-transformers (Powerstats, Variacs).
It is also possible to use an induction regulator. That is a wound three phase motor that cannot have continuous rotation. The rotor position is fixed by a worm gear that sets the coupling between primary and secondary (the wound rotor). I do not personally know how prevalent induction regulators were for applications such as stage lighting.
Bill
On Sun, 04 Apr 2004 16:21:49 GMT Repeating Rifle wrote: | in article snipped-for-privacy@news2.newsguy.com, snipped-for-privacy@ipal.net at | snipped-for-privacy@ipal.net wrote on 4/3/04 11:23 PM: | |> I was reading some literature on light dimmers, the kind that "chop" the |> AC wave cycles, which said that when the dimmers are installed on 3-phase |> power service, it can sometimes result in the lights flickering. |> |> Has anyone heard of this, or know why/how it happens? What kind of flicker |> would this be referring to? Fast as in 50/60 cycle? Or slower? | | The dimmers referred to here are based upon thyristors and phase control. | That is an electronic method using semiconductor properties. | | Three phase dimming is possible without phase control. I have used three | phase gangs of variable auto-transformers (Powerstats, Variacs). | | It is also possible to use an induction regulator. That is a wound three | phase motor that cannot have continuous rotation. The rotor position is | fixed by a worm gear that sets the coupling between primary and secondary | (the wound rotor). I do not personally know how prevalent induction | regulators were for applications such as stage lighting.
But do you know why it is that the electronic controls have this flicker problem with what changes is that some other controls elsewhere happen to be getting their power 120 degrees out of phase instead of 180 degrees?
in article snipped-for-privacy@news4.newsguy.com, snipped-for-privacy@ipal.net at snipped-for-privacy@ipal.net wrote on 4/4/04 9:55 AM:
I have had some serious problems using electronics in the old days. The simple circuitry depended upon the behavior of unijunction transistors. Conducted spikes could and did trigger the unijunction transistor at inopportune phases. Onced that happened, my circuitry tried to recover but did not do so gracefully. There are ways to get around that, but then the circuitry became much more complex. A brute force approach is to put low pass filters in the lines.
Bill
| in article snipped-for-privacy@news4.newsguy.com, snipped-for-privacy@ipal.net at | snipped-for-privacy@ipal.net wrote on 4/4/04 9:55 AM: | |> But do you know why it is that the electronic controls have this flicker |> problem with what changes is that some other controls elsewhere happen to |> be getting their power 120 degrees out of phase instead of 180 degrees? | | I have had some serious problems using electronics in the old days. The | simple circuitry depended upon the behavior of unijunction transistors. | Conducted spikes could and did trigger the unijunction transistor at | inopportune phases. Onced that happened, my circuitry tried to recover but | did not do so gracefully. There are ways to get around that, but then the | circuitry became much more complex. A brute force approach is to put low | pass filters in the lines.
So a spike introduced in the line (common neutral) by one dimmer switching would cause another dimmer to "decide" it had reached the point in the AC cycle where it should come on (because the variable sampled voltage that is used to gate the switching triac reached threshhold on the spike).
I guess a shared neutral can cause more of a problem with this than a neutral that has to go all the way back to the breaker panel before the common point of connection.
Would that not also cause some dimmers to trigger other dimmers to activate sooner in a 1 phase system (the one with a brighter setting gates on first, causing an earlier spike that gates on the others too soon)?
in article snipped-for-privacy@news1.newsguy.com, snipped-for-privacy@ipal.net at snipped-for-privacy@ipal.net wrote on 4/5/04 9:41 AM:
That is pretty much what hapened. One help was to make sure the timing capacitor was clamped to zero voltage at the start of the timing irrespective of how there may have been a previous trigger.
Bill
On Mon, 05 Apr 2004 18:01:33 GMT Repeating Rifle wrote: | in article snipped-for-privacy@news1.newsguy.com, snipped-for-privacy@ipal.net at | snipped-for-privacy@ipal.net wrote on 4/5/04 9:41 AM: | |> So a spike introduced in the line (common neutral) by one dimmer switching |> would cause another dimmer to "decide" it had reached the point in the AC |> cycle where it should come on (because the variable sampled voltage that is |> used to gate the switching triac reached threshhold on the spike). | | That is pretty much what hapened. One help was to make sure the timing | capacitor was clamped to zero voltage at the start of the timing | irrespective of how there may have been a previous trigger.
I've heard that some dimmers chop the power at an unsyncronized rate and only depend on their own timing, and not on the supply voltage. These would be the "expensive" ones referred to earlier? I can see where they would also be more likely to cause RFI since the chopping rate would have to be fairly high, and possibly have to be above human hearing threshhold to avoid audible issues.
Indeed, 3-phase Variacs are the only method (of which I am aware) to accomplish this function adequately. It's hard for me to imagine the use of "chopper dimmers" for the purpose, at least without employing a horrible level of synchronization complexity. Harry C.
An electronic dimmer design that chops the power at a very high frequency, and has separate triacs for each phase, could do this for 3 phase power where compatible with the load (incandescent lighting). You'd only need one pulse timing circuit and one control device. But then, anyone who has so much lighting to control that they need to run it balanced on 3 phases probably isn't using some cheap wall and switch plate mounted dimmer.
in article snipped-for-privacy@posting.google.com, Harry Conover at snipped-for-privacy@yahoo.com wrote on 4/6/04 2:43 AM:
I did mention induction regulators. These do not use brushes like Variacs do. They, in principle, have infinite resolution because the contact does not jump a turn at a time. I just do not know what their availability is.
Bill
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