[Amps] HV transformer test tspa
John T. M. Lyles
jtml at lanl.gov
Wed Jun 15 11:03:54 EDT 2005
I agree with Harold about it being coated. Although I have bought
plenty of HV transformers (single and three phase) which had only a
sinple varnish overcoat that are in commercial transmitters
(numbering in the hundreds of units in field since 1982). I say
simple, well, probably they had numerous coats, but they were not
potted solid like would be if they were done in a tank under vacuum.
Another trick would be to just place the iron into a large polymer or
steel tank, full of good oil.
I remember a trick from a now retired transformer designer from SNC
(Oshkosh, WI), which was to measure the copper primary resistance
cold (use a four wire milliohmeter) then power test it and measure it
hot. You should be able to calculate the average temperature rise in
the winding from the delta R of the copper.
The most potted HV transformer I have seen is the plate tranny from a
Harris RF102 that I got. It looks like a blob of epoxy, with the
edges of the lams exposed and flying leads coming out of the gunk.
Depending on the insulation, class B, class F, class H, etc, the
transformer can run very hot without damage. If it is only class B
for instance, it must be wound with heavier guage wire and use more
iron to keep the temp rise down. You can read about these ratings in
any of the big thick Electronics Handbooks, like the one by IEEE.
73
John
K5PRO
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>Today's Topics:
>
> 1. SBE SB1-LA Power out meter (Randy K4QO)
> 2. questions on my tranformer test (kenw2dtc)
> 3. Re: questions on my tranformer test (Dr. William J. Schmidt, II)
> 4. Fw: TRANSFORMER-TEST (Harold B. Mandel)
> 5. Re: TRANSFORMER-TEST-webpage (kenw2dtc)
> 6. Re: questions on my tranformer test (kenw2dtc)
> 7. GS35 QUESTION (ON4IQ)
> 8. Re: questions on my tranformer test (Steve Thompson)
> 9. Re: GS35 QUESTION (Ian White GM3SEK)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Sun, 12 Jun 2005 12:29:41 -0400
>From: "Randy K4QO" <k4qo at earthlink.net>
>Subject: [Amps] SBE SB1-LA Power out meter
>To: <Amps at contesting.com>
>Message-ID: <018201c56f6b$ef492820$6401a8c0 at randyyf6hns82y>
>Content-Type: text/plain; charset="iso-8859-1"
>
>Anyone out there in Amps-land know of a defunct SBE (SideBand Engineers)
>model SB1LA linear that might have a working RF Output meter I can obtain
>from it? (or perhaps the whole thing...)
>
>I have a restored SB1-LA in need of the stock meter. I have a generic meter
>in there now and while its not totally ugly (and it works) it would be nice
>to put the stock meter in there.
>
>Thanks and 73,
>Randy
>K4QO
>
>
>
>
>------------------------------
>
>Message: 2
>Date: Sun, 12 Jun 2005 14:39:52 -0400
>From: "kenw2dtc" <kenw2dtc at comcast.net>
>Subject: [Amps] questions on my tranformer test
>To: <amps at contesting.com>
>Message-ID: <000301c56f7e$1f12dee0$67612744 at ken>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
>Hi,
>I'm trying to figure out the current rating of a plate transformer. This is
>my test setup:
>
>http://w2dtc.com/2005-0610-transformer-test-page.htm
>
>Questions:
>1. Is this a valid way to find the secondary current capability?
>2. Is the internal temperature of 180 degrees F too high for a transformer
>under load for 5 hours?
>3. Is there a problem running this center tapped beast in a full wave
>capacitive input configuration?
>
>Thanks and 73,
>Ken W2DTC
>
>
>
>
>
>
>------------------------------
>
>Message: 3
>Date: Sun, 12 Jun 2005 14:11:50 -0500
>From: "Dr. William J. Schmidt, II" <bill at wjschmidt.com>
>Subject: Re: [Amps] questions on my tranformer test
>To: "kenw2dtc" <kenw2dtc at comcast.net>, <amps at contesting.com>
>Message-ID: <00dd01c56f82$a7209850$1600000a at SchmidtNet.local>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
>I would think that the best way to tell is measure the wire size of the
>secondary winding. The second best way is measure he cross-sectional area
>of the transformer, as theoretically it is related to the power capabilities
>of the steel.... which you can back into current (after accounting for
>reasonable efficiencies). 180F seems a little warm for a CCS transformer...
>maybe Will can weigh in here...
>
>Sincerely,
>
>Dr. William J. Schmidt, II K9HZ
>Trustee of the North American QRO - Central Division Club - K9ZC
>
>Email: bill at wjschmidt.com
>WebPage: www.wjschmidt.com
>
>"If computers get too powerful, we can organize them into a committee; that
>will do them in." -- Bradley's Bromide
>
>
>----- Original Message -----
>From: "kenw2dtc" <kenw2dtc at comcast.net>
>To: <amps at contesting.com>
>Sent: Sunday, June 12, 2005 1:39 PM
>Subject: [Amps] questions on my tranformer test
>
>
>> Hi,
>> I'm trying to figure out the current rating of a plate transformer. This
>> is
>> my test setup:
>>
>> http://w2dtc.com/2005-0610-transformer-test-page.htm
>>
>> Questions:
>> 1. Is this a valid way to find the secondary current capability?
>> 2. Is the internal temperature of 180 degrees F too high for a
>> transformer
>> under load for 5 hours?
>> 3. Is there a problem running this center tapped beast in a full wave
>> capacitive input configuration?
>>
>> Thanks and 73,
>> Ken W2DTC
>>
>>
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
>
>------------------------------
>
>Message: 4
>Date: Sun, 12 Jun 2005 15:23:23 -0400
>From: "Harold B. Mandel" <ka1xo at juno.com>
>Subject: [Amps] Fw: TRANSFORMER-TEST
>To: amps at contesting.com
>Message-ID: <20050612.152329.2444.4.ka1xo at juno.com>
>Content-Type: text/plain; charset=us-ascii
>
>
>Dear Ken,
>
>You did a great job in investigating the transformer!
>
>Let's see: My PWD monster that took three tries to get right
>from Peter is 12" high by 11" wide by 10 inches across, and weighs
>167 pounds. It is a "hypersil" object rated at 0 - 1800 - 3000 volts,
>at 3 amperes CCS.
>
>Peter had to do it over and over because he didn't wind a 3 ampere
>CCS piece and I caught it when it arrived.
>
>Since I build monster power supplies I have learned the hard way
>about component ratings, (almost electrocuting myself last Fall.)
>
>The one feature I see on your iron is that the windings are not
>potted. This means the unit, as it heats and cools, absorbs moisture
>from the air around it, said moisture settling in the paper laminations
>and
>in the wiring. To forestall disaster, I myself pot HV stuff, especially
>transformers, chokes and coils.
>
>I found that the best stuff isn't too expensive: Dolph's Synthite AC-41.
>
>It's about 25 dollars a gallon and is made for HV insulation potting, and
>has
>the consistency of plain old varnish, but with much better breakdown
>characteristics. There are several distributors and the stuff is made in
>Monmouth Junction, New Jersey (732) 329 - 2333. For my 10KV
>plants I use about 10 layers, either brushing or dipping.
>
>The test jig you set up is perfect for doing a preliminary examination.
>Once you place the transformer into service I would suggest using
>a mighty fan such as a Tarzan 320CFM, 230vac to move air around
>the structure.
>
>>From your temperature observations I would concur that this is a 2 ampere
>CCS
>transformer.
>
>However, the acid test will be to actually construct a load bank. Your
>calculation
>of 6719.33 vac, after filtering, would yield 6047.40 VDC. (Applying the
>0.9 factor).
>
>Since the power factor comes out to 12KW using around 3K of resistance, I
>don't
>know if you want to invest in a bunch o' resistors to do the test, but
>let's figure
>this transformer was made for broadcast use.
>
>Two 4-1000A's would need 2 amps at 6KV.
>
>You'll not probably melt the transformer down at 2 amps CCS, but if you
>jump to
>three amps and run AM 'Phone or RTTY it will get plenty hot.
>
>Just choose your rectifier bank carefully, Ken. Build it for 18KV,
>minimum, at four
>amps, minimum. Cool the diodes with that Tarzan fan, and then, let's
>talk about
>capacitors. Please don't tell me you're going to use photoflash
>oil-filled caps
>unless you see their voltage rating at 30% of what's written on the cans.
>One screw-up
>and the blown cap takes out your diode string and the transformer. I had
>a huge argument
>with my capacitor supplier about this and ended up backing up my argument
>with
>written evidence. The end result was that for the same money I was
>shipped three times
>the actual units to make up a 100 percent Working Voltage Direct Current
>filter
>instead of a Peak Voltage Direct Current filter. Your filter better be
>rated at 12KV
>also.
>
>Work Safely!
>
>Regards,
>
>Hal Mandel
>W4HBM
>
>
>------------------------------
>
>Message: 5
>Date: Sun, 12 Jun 2005 15:53:03 -0400
>From: "kenw2dtc" <kenw2dtc at comcast.net>
>Subject: Re: [Amps] TRANSFORMER-TEST-webpage
>To: "Harold B. Mandel" <ka1xo at juno.com>
>Cc: amps at contesting.com
>Message-ID: <002a01c56f88$58515dd0$67612744 at ken>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
>Hal said:
>
>"The one feature I see on your iron is that the windings are not potted.
>This means the unit, as it heats and cools, absorbs moisture from the air
>around it, said moisture settling in the paper laminations and in the
>wiring. To forestall disaster, I myself pot HV stuff, especially
>transformers, chokes and coils. I found that the best stuff isn't too
>expensive: Dolph's Synthite AC-41. It's about 25 dollars a gallon and is
>made for HV insulation potting, and has the consistency of plain old
>varnish, but with much better breakdown characteristics"
>
>Sounds good Hal. I can't lift this transformer so painting would be best.
>I guess I would apply a gererous amount on the top and let it drain into the
>windings and paint the bottom and sides. You mentioned 10 layers. Does
>this mean you paint it, let it dry and paint it again etc., if so how long
>is the drying period between applications?
>
>73,
>Ken W2DTC
>
>
>
>------------------------------
>
>Message: 6
>Date: Sun, 12 Jun 2005 16:07:20 -0400
>From: "kenw2dtc" <kenw2dtc at comcast.net>
>Subject: Re: [Amps] questions on my tranformer test
>To: "Dr. William J. Schmidt, II" <bill at wjschmidt.com>,
> <amps at contesting.com>
>Message-ID: <004101c56f8a$574ad860$67612744 at ken>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=response
>
>Dr,
>I agree with you on measuring the wire size; however, upon investigation the
>secondary terminals are fed with , thick flat copper bus which has much more
>area then the actual secondary wires, so I'm not going to tear open the
>beast to find the wires. A couple of other gentlemen suggested that maybe
>the transformer has a 2 amp rating, so for the heck of it I will run the
>test for another 5 or 6 hours at 2 amps and check the temperature again.
>
>73,
>Ken W2DTC
>
>------------------------
>
>----- Original Message -----
>From: "Dr. William J. Schmidt, II" <bill at wjschmidt.com>
>To: "kenw2dtc" <kenw2dtc at comcast.net>; <amps at contesting.com>
>Sent: Sunday, June 12, 2005 3:11 PM
>Subject: Re: [Amps] questions on my tranformer test
>
>
>>I would think that the best way to tell is measure the wire size of the
>>secondary winding. The second best way is measure he cross-sectional area
>>of the transformer, as theoretically it is related to the power
>>capabilities of the steel.... which you can back into current (after
>>accounting for reasonable efficiencies). 180F seems a little warm for a
>>CCS transformer... maybe Will can weigh in here...
>>
>> Sincerely,
>>
>> Dr. William J. Schmidt, II K9HZ
>> Trustee of the North American QRO - Central Division Club - K9ZC
>>
>> Email: bill at wjschmidt.com
>> WebPage: www.wjschmidt.com
>>
>> "If computers get too powerful, we can organize them into a committee;
>> that will do them in." -- Bradley's Bromide
>>
>>
>> ----- Original Message -----
>> From: "kenw2dtc" <kenw2dtc at comcast.net>
>> To: <amps at contesting.com>
> > Sent: Sunday, June 12, 2005 1:39 PM
>> Subject: [Amps] questions on my tranformer test
>>
>>
>>> Hi,
>>> I'm trying to figure out the current rating of a plate transformer. This
>>> is
>>> my test setup:
>>>
>>> http://w2dtc.com/2005-0610-transformer-test-page.htm
>>>
>>> Questions:
>>> 1. Is this a valid way to find the secondary current capability?
>>> 2. Is the internal temperature of 180 degrees F too high for a
>>> transformer
>>> under load for 5 hours?
>>> 3. Is there a problem running this center tapped beast in a full wave
>>> capacitive input configuration?
>>>
>>> Thanks and 73,
>>> Ken W2DTC
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>
>
>
>
>------------------------------
>
>Message: 7
>Date: Sun, 12 Jun 2005 22:09:00 +0200
>From: "ON4IQ" <on4iq at telenet.be>
>Subject: [Amps] GS35 QUESTION
>To: <amps at contesting.com>
>Message-ID: <001201c56f8a$9297a970$e8b9a451 at PIV3000>
>Content-Type: text/plain; charset="iso-8859-1"
>
>I have a 2m amp running a gs35 tube and a G3SEK triode board in it.
>While runnning the anode at 3.2kv , i get good bias control and all is well.
>
>Raising the voltage to 4.2kv off load gives met correct Ia when in
>ptt, but once
>the tube goes in cut off , the Ia drops to zero ( thats good) but
>grid current goes
>completely negative. After changing tubes with brand new one still
>have the same problem.
>
>
>I suspect there is something wrong in circuits or power supply.
>I've checked power supply and find no leakage to ground.
>
>Would you have any idea where this negative grid current comes from
>when tube is in cuttoff.
>
>Its abt 50ma.
>
>Best regards
>
>
>Johan
>
>------------------------------
>
>Message: 8
>Date: Sun, 12 Jun 2005 21:14:21 +0100
>From: Steve Thompson <g8gsq at ic24.net>
>Subject: Re: [Amps] questions on my tranformer test
>To: amps at contesting.com
>Message-ID: <42AC979D.1090406 at ic24.net>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>kenw2dtc wrote:
>> Hi,
>> I'm trying to figure out the current rating of a plate transformer. This is
>> my test setup:
>>
>> http://w2dtc.com/2005-0610-transformer-test-page.htm
>>
>> Questions:
>> 1. Is this a valid way to find the secondary current capability?
>I think so. Remember that what you have measured is the rms secondary
>current - which defines the heating effect. The dc current you can end
>up with depends on several factors but is likely to be 30-50% of the rms
>value. Best check is with the Duncan Amps PSU designer which will tell
>you the rms current in the winding for different configurations,
>capacitor values and load resistances, but you will have to edit the
>rectifiers file to create a diode with enough PIV.
>
>It's also worth checking how much it heats up with full primary volts
>and o/c secondary, and derate the secondary current if necessary. I have
>transformers that run cold like that, and others with noticeable iron loss.
>
>> 2. Is the internal temperature of 180 degrees F too high for a transformer
>> under load for 5 hours?
>
>I'll pass on that one - if you run it at 2.9A rms but, say, 50% duty
>cycle then the temperature rise will be much lower.
>> 3. Is there a problem running this center tapped beast in a full wave
>> capacitive input configuration?
>Depends on the insulation between the centre tap and the frame. If the
>designer assumed the ct was going to be ground, it might not be rated
>for it. I've lost a transformer that way.
>
>Steve
>
>
>------------------------------
>
>Message: 9
>Date: Sun, 12 Jun 2005 22:42:59 +0100
>From: Ian White GM3SEK <g3sek at ifwtech.co.uk>
>Subject: Re: [Amps] GS35 QUESTION
>To: amps at contesting.com
>Message-ID: <ffNtqvkjxKrCFAYo at ifwtech.co.uk>
>Content-Type: text/plain;charset=us-ascii;format=flowed
>
>ON4IQ wrote:
>>I have a 2m amp running a gs35 tube and a G3SEK triode board in it.
>>While runnning the anode at 3.2kv , i get good bias control and all is well.
>>
>>Raising the voltage to 4.2kv off load gives met correct Ia when in ptt,
>>but once
>>the tube goes in cut off , the Ia drops to zero ( thats good) but grid
>>current goes
>>completely negative. After changing tubes with brand new one still have
> >the same problem.
>>
>>
>>I suspect there is something wrong in circuits or power supply.
>>I've checked power supply and find no leakage to ground.
>>
>>Would you have any idea where this negative grid current comes from
>>when tube is in cuttoff.
>>
>>Its abt 50ma.
>
>
>What's happening is that with the higher B+, the tube needs a higher
>bias voltage to cut it off. This voltage may be greater than the turn-on
>voltage of the VDRs, so some current will flow through the VDRs.
>
>If you trace the current path back to B-minus, you will find that it
>flows in the reverse direction through the grid current monitoring
>resistor - that is why you see the apparent reverse grid current. You
>will also probably find that the VDRs get slightly warm on standby
>(careful!).
>
>If you know what is happening, this is actually not a big problem. I
>suggest that you do not increase the VDR voltage, because the VDRs are
>protecting the bias circuit from excess voltage.
>
>
>
>--
>73 from Ian GM3SEK
>
>
>------------------------------
>
>_______________________________________________
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>
>
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