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3 phase to single phase larger transmitters




 
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Author Topic: 3 phase to single phase larger transmitters  (Read 2713 times)
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KL7OF
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« on: January 08, 2019, 07:02:48 PM »

There are several ways to run a 3 phase transformer on single phase.....Most are a compromise of some sort...The conversion linked to here is for a welding machine but the result should be the same for a transmitter plate transformer.   http://pounceatron.dreamhosters.com/docs/misc/CP-200_Single-Phase_Step-By-Step.pdf    Using motor run capacitors to achieve the proper circulation of currents in the iron core seems like it should be effective for a transmitter.  I'm not just sure how the capacitors "delay" the current to achieve proper phasing.. They don't say how the capacitance value was calculated but I presume it depends on the total current drawn.  Any comments about the "Haas-Kamp" method would be appreciated....  Steve KL7OF


addition:  Found this capacitance formula..https://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/miller-cp-250ts-converted-single-phase-206509/
is this correct?
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SM6OID
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« Reply #1 on: January 09, 2019, 10:40:38 AM »

Hi!

Usually I keep my mouth shout if I'm not sure of what I'm saying...
But, I curious about this, so let me share my thoughts.

The main problem I see is the (usually) varying load that the transformer will see.
As a result of this, the phase shift will vary.
I suspect that this will result in ripple in the DC voltage.

Remember that a 3-phase rectifier usually calls for a fairly small capacitor bank.
(Specially if the secondary is a combination of D/Y windings.)

IF the transformer is affected in any detrimental way, I do not know, have to ask my wife.
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KL7OF
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« Reply #2 on: January 09, 2019, 01:01:19 PM »

Here is another approach...https://www.qsl.net/kf8od/transformer.html   I may try this one.  I am wondering about how much the current ratings will change.
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W1ITT
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« Reply #3 on: January 09, 2019, 02:17:09 PM »

I looked at the band saw conversion of 3-phase to single-phase transformers.  I have a big honking one out in the garage that would be a nice candidate.  My concern is the the band saw would leave burrs that would short circuit most of the laminations to each other.  Perhaps a belt sander with progressively finer grit would solve this, followed by a varnish treatment.

By the way, that same KF8OD site has a good article on winding your own plate transformer on C-cores.  Now that Peter W. Dahl company is out of business, you have to do your own if you want good transformers. 
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WZ1M
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« Reply #4 on: January 10, 2019, 03:02:58 AM »

Burrs, shorted laminations, wont make a difference. Laminations should all be "shorted" anyway. I have done this trick with a few 3 phase beautys and found out that you have to experiment with the connections to make sure they are not out of phase. Just use a variable supply at 20vac, monitor the current draw which should be pretty close to nothing at 20 vac, on the primary. If its drawing a fair amount of current then try another connection. While your doing this to the primary, be sure that all the secondary windings are not connected. If they are, your just chasing your tail.
Regards,
Gary
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« Reply #5 on: January 10, 2019, 11:19:07 AM »

I've successfully disassembled several of them and set them up as single-phase jobs for clients. 

So far, the alternating nature of the lams allowed it to go together fine without any cutting. 

Look to get a little less than 2/3 the power out of it, or basically the difference between CCS and ICAS service.

73DG
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« Reply #6 on: January 10, 2019, 10:55:04 PM »

I vouch for the high quality of the above work.
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KL7OF
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« Reply #7 on: January 11, 2019, 09:54:30 AM »

The plate iron from TMC GPT 10-K.  Spec book says 1.6 Amp.   Has 3 ea. multi-tap primaries and 3 ea. 3400V secondaries. It is set up as Delta primary, Wye secondary. weighs over 200 lbs.  I'm going to town to buy some new band saw blades...


* tmc plate txfmr1.jpg (118.02 KB, 720x1280 - viewed 128 times.)

* tmc plate txfmr2.jpg (142.2 KB, 720x1280 - viewed 107 times.)

* tmc plate txfmr3.jpg (115.46 KB, 720x1280 - viewed 102 times.)
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« Reply #8 on: January 11, 2019, 06:39:01 PM »

I find it easier (and cheaper) to restack them.

73DG
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KL7OF
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« Reply #9 on: January 11, 2019, 07:05:55 PM »

I find it easier (and cheaper) to restack them.

73DG
Dennis...Thanks for the information..Especially useful is your comment from your personal experience that one can expect a little less than 2/3 power out...I have been looking at the interleave pattern on the transformer I want to modify and it looks like I would have to take all the coils off and disassemble the entire 3 pillar core in order to restack them as a 2 pillar core....Is that how it works for you?  How long does it take to restack one of these things?  Any tricks for keeping the leaves aligned as you do it....?  I have several 3 phase transformers...I am going to try the Haas-Kamp method at some point as well....
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« Reply #10 on: January 11, 2019, 07:13:55 PM »

I have been separating the horizontal lams from those vertical thru the core, leaving them in the core(s).

Then I sort out those that will bridge the two cores with necessary clearance, and reinsert them.

Cut and redrill the angle irons and terminal plate, done.

This leaves a lot of silicon steel left over.  You can, if you have enuf steel from several rebuilds, make an "O" core with the single leftover core for a decent HV trans as well.

Around here, I'm lucky enuf to have real 3-phase power: 277/480 200A.

73DG
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KL7OF
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« Reply #11 on: March 07, 2019, 03:04:12 PM »

I sawed one core off my 3 phase transformer and hooked it up to the transmitter and it is working very well ...No hum....no buzz... no sparks...I did have to swap the leads around on the 240V primary to get everything in phase as recommended by Gary.  It  did nothing with the phase incorrect...This transmitter idles at 1/2 amp and that is all the load I've put on it so far..It was quick and easy to cut the core off and trim the mounting hardware down to fit..Im going to put some load on it this afternoon on 40 metros....I'll post the results....Thanks...Steve

UPDATE:   7290 khz... I ran the transmitter into the dummy at 2.5 KW carrier level ....yallos etc got all tuned up.. Transformer cool to the touch..No Buzzing, or flamage...got on the antenna..retuned...worked Calif on AM got a good report from Tom...then I .got an unsolicited report from an unidentified station that I was 10 kcs wide and had a hum..  So the transformer is working well...but I need more filtering ...the filter section is designed for 3 phase and comes up lacking on single phase...I'm happy...


* Look at those hams.jpg (85.07 KB, 564x624 - viewed 159 times.)
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W2PFY
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« Reply #12 on: March 22, 2019, 04:34:09 PM »

Very interesting! I wuz talking with Tim of HLR fame and he was explaining to me a way to hook up 3 phase to single without tearing it apart to do so. He also stated that the output in current would be about 2/3 of original. On my big Westinghouse MW-2, I had been using a 17 KVA  3 phase BC pull plate transformer. It can be wired wye or delta. I think it may have to be wired delta for it to work on 1 phase? At my camp where the big Westinghouse is located, I had to generate my own power to power it but the big 3 phase gen set has been broken for about 8 years now and I want to get the transmitter back on the air. My working gen set is a Generac at a rated power of seven KW. I need to get a real wiring diagram on how to change the connections on the transformer for it to operate on 240 volts AC. Can anyone on here draw up a diagram that I could use?

Thanks Terry
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KL7OF
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« Reply #13 on: March 22, 2019, 07:41:00 PM »

Terry ..there are a couple ways to run that big transmitter on single phase....see the link in the first entry in this thread  for the cap method and there is an article in electric radio on how to do it by wiring the single phase into the transformer to get the best flux patterns...I will look for a link to the ER article...neither method requires cutting....I have used the ER method...It gives full voltage at reduced amperage..
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« Reply #14 on: March 23, 2019, 01:43:34 AM »

Running it on single phase is pretty simple, pick two legs and fire in.  Your problem will be the rest of the PSU...it used to look for 360Hz ripple, now will be seeing 120Hz.  More cap necessary, and most 3PH supplies don't need a swinging choke as the source impedance is so low.  Get ready to add more iron, too.

73DG
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« Reply #15 on: March 23, 2019, 09:47:23 AM »

First, get a Variac for 240 volts.
Then find the primaries for each winding. Get out the clip leads, at reduced voltage, experiment to find out how to get the two primaries in phase to generate a secondary voltage. Then figure out the phase of the secondary to series the windings to generate the most voltage. Just ignore the third phase, it will not be used. Once you have everything in phase at low voltage you can crank up the primary voltage and adjust the taps on the primary and secondary to get the voltage you are looking for. All the transformers are a little different buy experimenting with a lower voltage and getting the phase figured out of the windings will get you there safely. This gets you 4000 Volts at a few amps easy with surplus 5K FM transformers. Just be careful. This stuff is lethal.
Keith
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« Reply #16 on: March 23, 2019, 10:15:40 AM »

Running it on single phase is pretty simple, pick two legs and fire in.  Your problem will be the rest of the PSU...it used to look for 360Hz ripple, now will be seeing 120Hz.  More cap necessary, and most 3PH supplies don't neede a swinging choke as the source impedance is so low.  Get ready to add more iron, too.

73DG

The ones with a choke will use a small one. I saved a 2.3H choke from a 5-7KVA 3-phase klystron power supply. I want to use that or a similar choke for use as a resonant filter. I'm not sure about voltage ratings needed. There is a difference between volts-to-GND and volts-across-winding.

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KL7OF
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« Reply #17 on: March 23, 2019, 10:42:23 AM »

The original 3 phase setup had a 5 H choke input and a 5 uFcap...after converting the transformer to single phase, I paralleled in  another 5uF.  Ripple looks much better on the scope...no more reports of hum... I would like to have about 20H and 50 uF...  I'm having a difficult time finding components rated for 10KV+ locally
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« Reply #18 on: March 23, 2019, 11:06:48 PM »

You know where to go for that sort of stuff, Steve...:-).

73DG
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« Reply #19 on: March 24, 2019, 10:44:34 PM »

Thanks Guys, I wuz at the camp on Thursday up in the Adirondacks and there was still three feet of snow in my driveway! Looks like I'll try again in about 3 weeks  when the snow melts and then start experimenting with single phase on the plate transformer. I'll need to use a four tube bridge circuit from the original six and see how that wiring is going to go? I'll have 8 henrys of inductance and the original 15 uf 5000 volts cap to work from. The rectifier in this thing was rated at 4 KV at 4 amps. It was a multi channel system.

Wish me luck!

Terry

Here's a link to the Big W that some of you may not have seen?


https://get.google.com/albumarchive/110796788101790984942/album/AF1QipOu4bOtdDCyzFHlRd2Ors87hVgRkIdLFTdOcIdE?source=pwa
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« Reply #20 on: March 25, 2019, 08:23:47 AM »

Hello
i've a three phase power transformers 3 primary with 240v and 3 secondary 2400v, i have an access to the wiring, i wonder if i could disconnect one column and leave it with out any change on the iron.
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« Reply #21 on: March 25, 2019, 08:57:30 AM »


"
Looks like I'll try again in about 3 weeks  when the snow melts.     "

Hope springs eternal.


KLC
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W2PFY
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« Reply #22 on: March 25, 2019, 05:16:16 PM »

Quote
Any comments about the "Haas-Kamp" method would be appreciated....  Steve KL7OF

I like the idea of putting a cap in there or caps. I wuz a bit worried that the value needed might change with varying load under modulation,but welders at least the stick type, can be all over the place depending on the arc, metals used and amp settings. Welding may be may be more extreme than a class C transmitter with a class AB or B modulator with varying loads?

I am surprised that we haven't dredged up at least one electrical engineer who might say this is a bad idea Grin Grin

Quote
Hello
I've have three phase power transformers 3 primary with 240v and 3 secondary 2400v, i have an access to the wiring, i wonder if i could disconnect one column and leave it with out any change on the iron.

That's what this thread is all about. Why not try it on your transformer and let us know? I have also wondered that if you leave one winding isolated, could it have a useful output on its primary or secondary? Could you use it like a magnetic amplifier by placing DC to magnetize the core to vary the output voltage etc?? I don't have a clue but it would be fun to play with! Perhaps with a stick and rubber gloves Cheesy Cheesy Cheesy

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« Reply #23 on: March 25, 2019, 08:31:10 PM »

FG5FC:
"Hello i've a three phase power transformers 3 primary with 240v and 3 secondary 2400v, i have an access to the wiring, i wonder if i could disconnect one column and leave it with out any change on the iron."

Yes. Only 1/2 to less than 2/3 the power will be had at the same duty cycle and some power is wasted in the unused iron leg so it's inefficient and overly large.

W2PFY:
"Could you use it like a magnetic amplifier by placing DC to magnetize the core to vary the output voltage etc??"

I asked a similar question about the magnetic amplifier experiment but there were no useful responses. There may be some old examples of these uses on the internet.

To use the spare winding on the actual plate transformer itself will not work because as you saturate the core this looks like a short circuit as far as the primary input windings are concerned. It is, however, done in quite low-power circuits as sensing or control function where the power lost does not matter and the transformer is not going to be damaged by looking at a short, usually because the circuit energizing it can't blow it. That hookup just about always uses a transformer specifically designed for the purpose. Hobby use of common transformers works to some degree, when the power limitation caveat is considered.

My similar question was about using the two outer primaries of a separate 3 phase power transformer as the element in series with the plate transformer primary, and a middle leg winding, either pri or sec as the control element. I believe that is the right way to do the experiment.

In the past I had a Nobatron power supply with a 3-winding saturable reactor. A 6L6 on 300VDC fed into a high-turns winding on the middle leg regulated 28VDC/50A output. The two other windings, on the outer legs, were connected to oppose AC current. As the 6L6 magnetized the core in response to the output going lower under load, more AC mains juice was allowed through this reactor into the power transformer to bring it back up to 28VDC. The range of adjustment was smallish. There was a mains input transformer ahead of all of this, that gave about 160VAC. This is because otherwise the normal loss in the saturable reactor's series inductance would not have given the desired output voltage. I believe it was also because the saturation did not proceed linearly over the regulating range.

Trying different things out with the Nobatron's circuit is part of my education on this subject. Unfortunately I was too young at 14 to understand the beauty of that power supply and ended up parting the thing out. Still have the rectifier transformer, choke or input voltage booster, and nasty old selenium rectifier redone into a battery charger.

Also, one of the major transformer manufacturers sold a 'companion' saturable reactor type unit to go with their plate iron. In the AM transmitters they shewed, it served as a form of syllabic carrier control.

I do not have an electrical engineering degree. If I'm wrong on this then someone should point it out for everyone's benefit!
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« Reply #24 on: March 26, 2019, 12:36:02 AM »

On Hass-Kamp, I opine that the 'created' phase's voltage will change with the amp load, and phase will change with inductor and or transformer tap changes. It might not be too critical for welding because they use a narrowly selected current range and can adjust the current with the control to get it there. After reading all of the articles it looks like they might be better served by adding a switch to cut in or out banks of capacitors and adding some kind of 'phase-o-meter' to see when the created phase is 'closest to the middle' once the arc is struck.

It would be a wild experiment to try it on an AM transmitter. Whatever effect it may have would probably not improve the modulation quality. For once I am glad to have a valid excuse not to try a wild experiment. spitzensparken und poppencorken.
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