[AMPS] HT supplies for 3 phase?

[Barry Kirkwood]

FWIW : I once bought a British Admiralty Marconi HF broadband TX (used rows
of 4x250s feeding ?delay lines). It had three phase transformers in the HT
supply. Only about 1.1 kV secondary as I recall, but husky. Gs reading this
may be able to find them, cheap.

>From what I have been reading, my dream shack will have three phase power.
The single phase I have at the moment is a bit  vague, thinking of getting a
stabilised supply for the lights, hi! At least the power stays on almost all
the time nowadays.
73
end
Barry Kirkwood PhD ZL1DD
Signal Hill
66 Cory Road
Palm Beach
Waiheke Island 1240
NEW ZEALAND
www.waiheke.co.nz/signal.htm
----- Original Message -----
From: John Lyles <jtml@lanl.gov>
To: <amps@contesting.com>
Sent: Monday, 08 January, 2001 10:38 AM
Subject: [AMPS] HT supplies for 3 phase?


>
> Dave, G8WRB, inquired about 3 phase HT supplies:
>
> > I'm looking to design an HT power supply for a YC156 (3CPX5000A7)
> >triode. One approach is the common single phase input, single phase
> >transformer, lots of expensive high voltage capacitors.
> > I've been considering another approach, which seems to me to be much
> >simpler:- use a 3-phase supply, 3-phase transformer, and a bridge with 6
> >diodes. This gives 4.2% RMS ripple, without any storage capacitors,
> >compared with a totally unacceptable 48.2% for single phase bridge
> >without any storage capacitor or choke.
>
> Absolutely correct. Much lower ripple, and needs 6 instead of 4
> diodes for a full wave bridge rectifier.
>
> >I suspect the 3-phase transformer will cost more than a single phase
> >one, as there are more windings, but this cost is probably more than
> >offset by the cost savings in not having any electrolytic capacitors.
> >The other potential advantage, is that in the event of an arc in the
> >tube, there is far less stored enegy, so protection systems don't need
> >to be as rugged. Assuming you have a 3 phase supply (which I do) it
> >seems the obvious way to go.
>
> Yes, 3 phase system is so much better if you have the AC feed for it.
> You still need some capacitance to reduce that 4.2% ripple to a more
> insignificant amount. But you can go from say, 20 uF to 4 uF with
> similar residual ripple, for a choke input filter, and much smaller
> choke to meet the critical inductance criterion for best regulation.
>
> >However, somone once told me that such a system with no storage
> >capacitance would destroy a transformer. Does anyone know if this is
> >true ? What approaches are taken on large HT supplies for amplifers much
> >bigger than amatuer ones? 3-phase would obviously be used, but do they
> >use storage capacitors ??? Perhaps just a small amount would be enough,
> >but I'm not sure why any would be needed.
>
> Not a problem. I haven't heard that one!
> I helped develop 3 and 5 kW Fm transmitters which were marketed, and
> they used the same final, and the same PA cavity. The high power rig
> had higher plate voltage. Other difference was single versus 3 phase
> iron. The 3 phase was cheaper to built if I remember correctly. The
> cost of the iron was offset by the cost of the bigger LC filter
> needed for 1 phase HT supply. Also the inrush to the diodes and the
> peak charging current through them is reduced if you have lower
> capacitance filters - Another advantage that allows derating the
> rectifier diodes.
>
> If you really want to run it with low stored energy, get a second 3
> phase transformer, and run one in Delta and one in Wye. Series of the
> two secondaries (after each is rectified with diodes) of them results
> in a 12 pulse ripple, with extremely low ripple as is.
>
> >I once played around with the concept of using three single phase
> >transformers on a 3-phase supply. This works fine, which does mean it
> >would be possible to design an HT supply that worked with a 3-phase
> >supply, or used the three tranformers in parallel to use it from a
> >single phase supply. It would only take an hour or so to reconfigure the
> >transformers to swap from single phase to 3-phase operation.
>
> Thats a lot of iron to be packaging! It should work though. However,
> the voltage may be different out of one versus the other. (phase to
> phase voltage of the 3 phase versus end to end voltage of the
> secondary winding of paralleled transformers).
>
> 73
> John
> K5PRO
>
>
>
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>


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