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#41
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Isolation transformer draws excessive current under no load condition
On Feb 14, 7:07*pm, "Phil Allison" wrote:
"Robert Macy" *** Is there any way to shut fools like you up ?? *---------------------------------------------------- Shame you cannot supply one that backs up your idiotic comments about unloaded transformers. Listen PAL *!!!!!!!! YOU *are nothing but a lying, bull****ting *NUT CASE !! Clueless to the core *- * pun intended. FOAD. ... *Phil Although you are wrong, you say with such conviction that people believe. I would not have bothered replying and supplying references supporting my statements, except your claims/comments are proving a disservice to people seeking information. As an example of the effects of your incorrect statements, see reply posted by spamtrap1888, whose question appears to be based upon having accepted your erroneous claim that as a transformer is loaded, the inductive core current decreases. Not true. As an isolation transformer is loaded, the inductive core current DOES NOT decrease. rather stays fairly constant. Stop misleading people. You do NOT contribute, rather distract/ distort. Stop it. To prevent/undo the damage you cause, I post the following references: using advanced google search with the following words "magnetizing current" transformer distortion yields 38,200 results, starting at the first, they are worthwhile reading, such as... this shows how saturation causes a spike in current as the voltage waveform crosses zero: http://www.allaboutcircuits.com/vol_2/chpt_9/1.html section "Transformer Principles" describes constant voltage across the core, thereby constant inductive current, etc. http://lehmanengineering.com/quiz/quiz6sol.html also, these two pdf files are a decent background reference: http://classicaudio.ru/articles/Output_Transformer_a57.pdf http://www.classicaudio.ru/articles/ot_distortion_p2_a57.pdf etc, etc, etc. These references supported my statements. .. .. .. However, you did not supply any reference refuting my statements. |
#42
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Isolation transformer draws excessive current under no load condition
On Feb 15, 1:52*am, Sylvia Else wrote:
On 14/02/2012 12:52 AM, Robert Macy wrote: On Feb 13, 5:45 am, *wrote: ...snip... Adding capacitance in parallel has no effect on the tranny whatsoever *- and it will make the PF worse. Noted, and thanks. ...snip... Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, which means the amount of power you drop in your wiring [and pay for] will be less. Adding caps is a STANDARD way to adjust power factor to 1. Used by the industrial power consumers that are heavily penalized for lagging power factor. It is cheaper for them to add a building full of caps, just to shift their PF and pay less for power. If you do the analysis of power consumption throughout a standard AC mains power distribution, you will find that a lagging power factor [caused by motors, etc] INCREASES the power required to simply get billable wattage to you. And, it's surprisingly large. But, except for the extra power dissipated in the household wiring, is not measured by the meter, and not included in the billed energy units. Sylvia. True! Today, the only way that utilities companies can bill for this lost energy is by assigning a 'penalty' for bad PF. I'll bet with today's smarter metering, they'll figure a way to measure it real-time and bill for it. |
#43
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Isolation transformer draws excessive current under no load condition
On 16/02/2012 9:31 AM, Robert Macy wrote:
On Feb 15, 1:52 am, Sylvia wrote: On 14/02/2012 12:52 AM, Robert Macy wrote: On Feb 13, 5:45 am, wrote: ...snip... Adding capacitance in parallel has no effect on the tranny whatsoever - and it will make the PF worse. Noted, and thanks. ...snip... Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, which means the amount of power you drop in your wiring [and pay for] will be less. Adding caps is a STANDARD way to adjust power factor to 1. Used by the industrial power consumers that are heavily penalized for lagging power factor. It is cheaper for them to add a building full of caps, just to shift their PF and pay less for power. If you do the analysis of power consumption throughout a standard AC mains power distribution, you will find that a lagging power factor [caused by motors, etc] INCREASES the power required to simply get billable wattage to you. And, it's surprisingly large. But, except for the extra power dissipated in the household wiring, is not measured by the meter, and not included in the billed energy units. Sylvia. True! Today, the only way that utilities companies can bill for this lost energy is by assigning a 'penalty' for bad PF. I'll bet with today's smarter metering, they'll figure a way to measure it real-time and bill for it. And if we correct our power factor, our bills will be lower than they are now. Oh, wait a minute, what was I thinking? Sylvia. |
#44
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Isolation transformer draws excessive current under no load condition
On Feb 13, 4:42*pm, "Phil Allison" wrote:
...snip... ** *That is pretty high actually - *a typical 1KVA tranny has about 6 to 8 % power loss at full load. ...snip... Agree with that range. Assume for this transformer the power loss is 8%, 80W. Further assume this is a 'well designed' transformer where the designer allowed half the dissipation in the windings and half in the core. That means 40W in the core and 40W in the windings, at full load. Four windings with each carrying half the full load current, 4.167A, implies 0.576 ohms/winding two in series would be 1.15 ohm and since most pri/sec are 45%/55% that would mean each pri winding 0.52 ohm each sec winding 0.63 ohm Now unloaded the two pri windings are passing 1.27A each, dissipating almost 2 W and the core is dissipating around 40W, so JW would have measured power for the unloaded transformer at around 42W, which he said he measured. JW, Did you ever measure the winding impedance? It would be interesting to compare prediction to actual values. [of course, preaching to the choir, for better accuracy put the two pri in series and the two sec in series] |
#45
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Isolation transformer draws excessive current under no load condition
On Feb 13, 5:45*am, JW wrote:
On Sun, 12 Feb 2012 01:05:04 +1100 "Phil Allison" wrote in Message id: : ...snip... Adding capacitance in parallel has no effect on the tranny whatsoever *- and it will make the PF worse. Noted, and thanks. A cap does improve PF... To answer the question whether an external capacitor placed in parallel with the input of a transformer improves power factor or not, for both loaded and unloaded conditions; I started the following analyses and share with others who may be interested. First, use a Linear Model to represent the isolation transformer. Simulate the iso transformer and circuitry by using LINEAR SIMULATION, that is, only using linear components to represent observed data. Second, simulate using nonlinear components, specifically the chan model, which simulates BOTH hysteresis (coercivity) and saturation. TO BE DONE LATER. (Model of the 1kVA ISO-Transformer wound for 120/120 operation) LINEAR SIMULATION The following transformer model is accepted for low frequency operation. The transformer is approximated by representing the transformer as primary and secondary winding resistances connected to a core which has a parallel resistance to represent the core losses. The transformer's coupling coefficient was arbitrarily set to one, more likely to be as low as 0.98. But modifying coupling coefficient does not appreciably change results. Values for core inductance and parallel resistor were determined from data provided by JW and winding resistance values were estimated based upon experience: Core Inductance: Lcore = 0.128 H, based upon JW's measurement of current with NO LOAD Core Losses: Rcore = 360 ohms, based upon JW's measurement using Watts Up meter with NO LOAD Winding Resistances: Rpri = 0.26 ohms, Rsec = 0.315 ohms estimated from experience The measurements that one would obtain with this linear model are Current NO LOAD = 2.54 Arms Power NO LOAD = 41.7 W PF = 0.137 All fairly close. As a sanity check, what happens at FULL load with 14.4 ohms? Vout = 115V, Power = 922W, PF = 0.960, which is reasonable. Load regulation is not that good in this model. The output voltage with NO LOAD is 120V, but when loaded with 14.4 ohms to get the expected 1kW output, the output voltage drops to 115V. This manufacturer probably did what everyone else does and not wind the transformer EXACTLY 1:1, but add a few extra turns on the secondary to compensate for this expected drop, more like 100:105 or such. JW could verify the winding ratio by running the transformer 'backwards'. He would then see he'd probably only get 110 out the pri with 120 into the sec. Anybody who has used two doorbell transformers, one down and one back up just to make an isolation transformer has discovered this 'feature'. For simplicity, I leave the winding ratio as 1:1, which will not appreciably change results. In a previous post I said add a parallel capacitor, 55uF, to adjust the PF closer to 1. When 55uF cap is added in parallel to the input of the transformer, the PF does indeed change. NO LOAD: PF = 0.997 FULL LOAD: PF = 1.00 And, as I claimed adding a cap improved for both NO Load and FULL Load. I've included a copy of the simulation model below, watch out for word wrap, but feel free to try it in FREE LTspice and see for yourself. CONCLUSION: Adding a parallel capacitor to the input of a transformer does help power factor both loaded and unloaded. Now, this was LINEAR simulation. I will now more accurately model the non-linear characteristics of a real transformer and compare to see if my assertion is still true. LINEAR SIMULATION: Version 4 SHEET 1 3060 1012 WIRE 1216 752 1184 752 WIRE 1344 752 1296 752 WIRE 1456 752 1344 752 WIRE 1584 752 1456 752 WIRE 1728 752 1664 752 WIRE 1808 752 1728 752 WIRE 1904 752 1808 752 WIRE 2080 752 1984 752 WIRE 2384 752 2160 752 WIRE 2432 752 2384 752 WIRE 1728 768 1728 752 WIRE 1808 768 1808 752 WIRE 1904 768 1904 752 WIRE 1984 768 1984 752 WIRE 2432 768 2432 752 WIRE 1456 784 1456 752 WIRE 1184 800 1184 752 WIRE 1728 880 1728 848 WIRE 1808 880 1808 848 WIRE 1904 880 1904 848 WIRE 1984 880 1984 848 WIRE 2432 880 2432 848 WIRE 1184 896 1184 880 WIRE 1456 896 1456 848 FLAG 1184 896 0 FLAG 1808 880 0 FLAG 1904 880 0 FLAG 1984 880 0 FLAG 2432 880 0 FLAG 2384 752 OUT FLAG 1344 752 IN FLAG 1728 880 0 FLAG 1456 896 0 SYMBOL voltage 1184 784 R0 WINDOW 0 48 52 Left 0 WINDOW 3 47 113 Left 0 WINDOW 123 49 82 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName Vac SYMATTR Value SINE(0 170 60) SYMATTR Value2 AC 120 SYMBOL res 1200 768 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName Racmains SYMATTR Value 0.01 SYMBOL ind 1792 752 R0 SYMATTR InstName Lcore SYMATTR Value 0.128 SYMBOL ind2 1888 752 R0 SYMATTR InstName Lpri SYMATTR Value 10 SYMATTR Type ind SYMBOL ind2 1968 752 R0 SYMATTR InstName Lsec SYMATTR Value 10 SYMATTR Type ind SYMBOL res 1568 768 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName Rpri SYMATTR Value 0.26 SYMBOL res 2064 768 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName Rsec SYMATTR Value 0.315 SYMBOL res 2416 752 R0 SYMATTR InstName Rload SYMATTR Value 10MEG SYMBOL res 1712 752 R0 SYMATTR InstName Rcore SYMATTR Value 360 SYMBOL cap 1440 784 R0 SYMATTR InstName Cc SYMATTR Value 55µF TEXT 1808 936 Left 0 !K1 Lpri Lsec 1 TEXT 1152 624 Left 0 !.ac LIN 201 50 70 TEXT 1152 552 Left 0 ;.ac LIN 201 50 70 TEXT 2672 800 Left 0 ;NO Load Rload = 10MEG\nFULL Load Rload = 14.4 ohms TEXT 1648 624 Left 0 ;PF = RE(V(in)*I(Racmains))/(V(in)*I(Racmains)) TEXT 1400 936 Left 0 ;NO PF Correction Cc = 55pF\nWITH PF Correction Cc = 55uF |
#46
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Isolation transformer draws excessive current under no load condition
"Robert Macy" = one stubborn ****er A cap does improve PF... ** But only with theoretical transformers - NOT real ones. First, use a Linear Model to represent the isolation transformer. ** Waste of ****ing time and effort - as it only repeats the same ****WIT error you have been sprouting here all along. The primaries of REAL commercially made E-core transformers are NOT linear inductors !!!!!!!!!!! The off load primary current at rated voltage is *dominated by the third harmonic * of the AC supply frequency. The laminated iron core is then saturating, quite heavily. JW's 1kVA iso tranny is a very typical example of this fact. You will NOT find this information on webs sites that merely discuss transformer basics. You WILL find this if you test a cross section of commercial E-core transformers with the aid of a variac, RMS current meter and a scope monitoring the current waveform. This has NOTHING do with badly or well made transformers - all makers do it to save weight and cost. BTW: I happen to own a 1kVA transformer very similar to that described by the OP. Tested as above, these are the figures: VAC A rms I peak 30 0.08 0.11 50 0.11 0.14 70 0.20 0.35 90 0.45 1.0 110 1.0 2.0 120 1.4 2.9 130 2.2 4.6 Up to 70 volts AC, the tranny is approximately linear with an effective inductance of about 1.1 H. At and above 90 volts AC it suddenly changes - current starts to increase exponentially and the wave becomes very peaky with a 1:2 ratio between rms and peak values. At 130 VAC input, effective primary inductance ( based on simplistic calculations) has dropped to less than 0.2H due to core saturation. I must have tested hundreds of E-core trannys this way in the last 20 years or so and ALL do much the same thing. Toroidal and C- core types are different. ..... Phil |
#47
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Isolation transformer draws excessive current under no load condition
On Feb 17, 6:25*pm, "Phil Allison" wrote:
"Robert Macy" = *one stubborn ****er A cap does improve PF... ** But only with theoretical transformers - *NOT real ones. First, use a Linear Model to represent the isolation transformer. ** Waste of ****ing time and effort *- *as it only repeats the same ****WIT error you have been sprouting here all along. The primaries of *REAL *commercially made E-core transformers are *NOT linear inductors !!!!!!!!!!! The off load primary current at rated voltage is *dominated by the third harmonic * of the AC supply frequency. The laminated iron core is then saturating, quite heavily. JW's 1kVA iso tranny is a very typical example of this fact. You will *NOT *find this information on webs sites that merely discuss transformer basics. You WILL *find this if you test a cross section of commercial E-core transformers with the aid of a variac, RMS current meter and a scope monitoring the current waveform. This has NOTHING do with badly or well made transformers - *all makers do it to save weight and cost. BTW: I happen to own a 1kVA transformer very similar to that described by the OP. Tested as above, these are the figures: VAC * A rms * *I peak 30 * * * 0.08 * * * 0.11 50 * * * 0.11 * * * 0.14 70 * * * 0.20 * * * 0.35 90 * * * 0.45 * * * 1.0 110 * * 1.0 * * * * 2.0 120 * * 1.4 * * * * 2.9 130 * * 2.2 * * * * 4.6 Up to 70 volts AC, the tranny is approximately linear with an effective inductance of about 1.1 H. At and above 90 volts AC it suddenly changes - *current starts to increase exponentially and the wave becomes very peaky with a 1:2 ratio between rms and peak values. At 130 VAC input, effective primary inductance ( based on simplistic calculations) *has dropped to less than 0.2H due to core saturation. I must have tested hundreds of E-core trannys this way in the last 20 years or so and ALL do much the same thing. Toroidal and C- core types are different. .... *Phil Thank you for the explanation and the data. I did see that in my non-linear models the third harmonic peaks started 'popping' up as the voltage increased. Obviously, the concept of inductance loses something with that much distortion. Will try to curve fit that data to the chan model and see if the simulations match your measurements. It would be great to have a model one can trust to at least somewhat 'look' like reality. |
#48
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Isolation transformer draws excessive current under no load condition
Sylvia Else wrote:
On 14/02/2012 12:52 AM, Robert Macy wrote: On Feb 13, 5:45 am, wrote: ...snip... Adding capacitance in parallel has no effect on the tranny whatsoever - and it will make the PF worse. Noted, and thanks. ...snip... Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, which means the amount of power you drop in your wiring [and pay for] will be less. Adding caps is a STANDARD way to adjust power factor to 1. Used by the industrial power consumers that are heavily penalized for lagging power factor. It is cheaper for them to add a building full of caps, just to shift their PF and pay less for power. If you do the analysis of power consumption throughout a standard AC mains power distribution, you will find that a lagging power factor [caused by motors, etc] INCREASES the power required to simply get billable wattage to you. And, it's surprisingly large. But, except for the extra power dissipated in the household wiring, is not measured by the meter, and not included in the billed energy units. Sylvia. yes it is. the problem with low power factors is the power loss before the meter, which isn't measured and can be huge for large customers. If at home, I toss a giant capacitor or huge inductor across the line, my meter will pick up all the wiring and heating losses from the capacitors or inductor. It will not measure the losses to the power company for me circulating 100 amps to and from the power grid. the power companies losses on that will be larger than mine, plus it wastes capacity of the grid itself. For residential customers in the US, it's just assumed we're not idling huge motors or testing capacitor banks in the dining room, so the utilities don't pay attention to us. |
#49
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Isolation transformer draws excessive current under no load condition
JW wrote:
Hi all, Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference: http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet: http://attachments.temcoindustrialpo...120x240Pri.pdf I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. I just ran a test I have on a similar transformer. Mine is a cutler hammer 1.5kVA unit in the same type of metal box and potted in expoxy and sand - nothing special. it's actually a 240/480 to 240/120 unit, but you can switch the H and X leads with no no big deal. Anyways, running 125 VAC (line voltage is high around here) across "half" the secondary (X1 and X2 instead of X1+x3 and X2+x4) resulted in 24 watts of loss and a current of 0.5A according to the kilowatt meter. The thing even buzzes somehow. I'd say your transformer is bad or somehow connected wrong. My transformer is rated 115C rise, so it's probably no winner when it comes to energy efficiency. %Z isn't even listed on the nameplate. |
#50
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Isolation transformer draws excessive current under no load condition
"Cydrome Leader" I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. ..... Phil |
#51
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Isolation transformer draws excessive current under no load condition
Phil Allison wrote:
"Cydrome Leader" I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. .... Phil that's a pretty horrible transformer if those parameters are A-OK. |
#52
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Isolation transformer draws excessive current under no load condition
"Cydrome Lunatic"
I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. that's a pretty horrible transformer if those parameters are A-OK. ** ROTFL - you are one colossal, know nothing bloody fool. ..... Phil |
#53
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Isolation transformer draws excessive current under no load condition
On Feb 18, 4:22*pm, "Phil Allison" wrote:
"Cydrome Leader" I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. .... *Phil Why doesn't the transformer data sheet include idle current, power factor, etc.? Or is it embedded in some transformer standard I have to spend 2000 swiss francs to get? |
#54
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Isolation transformer draws excessive current under no load condition
"spamtrap1888" "Phil Allison" I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. Why doesn't the transformer data sheet include idle current, power factor, etc.? ** Why should it ? They are easily measured parameters and of little interest to most users. If the safety ratings, VA rating, temp rise, dimensions, weight and mounting details are all described - that is enough. .... Phil |
#55
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Isolation transformer draws excessive current under no load condition
"Phil Allison" wrote in message
... "Cydrome Lunatic" I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. That's a pretty horrible transformer if those parameters are A-OK. ** ROTFL -- you are one colossal, know[-]nothing bloody fool. Phil, do you know the word "empirical"? If not, you should learn it. Empirical data are knowledge, as assuredly as theoretical considerations. Last week I measured the no-load drain of a 1.5A isolation transformer. * My Kill A Watt read 0.06 amperes, which could be anywhere between 0.055 and 0.065 amps. (The display doesn't have enough resolution.) That's 4% of the rated load. Not bad. The OP's transformer seems way out of line. It should definitely be placed off-line. (Ar, ar.) * I was about to specify 125V, when I realized that, in theory, an isolation transformer should "work" at any voltage -- short (joke intended) of a voltage high enough to break down the insulation, etc, etc, etc. |
#56
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Isolation transformer draws excessive current under no load condition
spamtrap1888 wrote:
On Feb 18, 4:22?pm, "Phil Allison" wrote: "Cydrome Leader" I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. .... ?Phil Why doesn't the transformer data sheet include idle current, power factor, etc.? Or is it embedded in some transformer standard I have to spend 2000 swiss francs to get? The only transformers I've seen specs for idle power consumption listed (but not on the nameplate) are for distribution transformers the power company would own. They seem to care about how much money it costs to keep a transformer running for 30 years or until it finally explodes, so every watt counts. For loose reference, I recall some 1kVA oil filled poole mount distribution tranformers with the real step-lap core idling at 14 watts, or something close to that. They really make 1kVA units for stuff like streetlights and running switchgear. At the 10kVA oil filled ones with the typical step-lap cores, something like 45 watts is normal for some brands. These monsters aren't really rated the same as smaller EI core potted unit which are only meant to be cheap to produce in mexico or china or wherever they come from these days. |
#57
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Isolation transformer draws excessive current under no load condition
On Feb 10, 4:42*pm, Ian Jackson
wrote: In message , Robert Macy writes On Feb 10, 1:36*pm, Robert Macy wrote: On Feb 10, 9:40*am, nesesu wrote: On Feb 10, 8:17*am, JW wrote: Hi all, Is there any reason that a 120VAC to 120VAC *isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference:http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet:http://attachments.temcoindustrialpo...o/Federal_FB_1... I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. As a quick test, disconnect all the windings from each other and then power up any ONE winding and see what the current draw is. I see that it is a 15kVA rated, so it is not unreasonable that the magnetizing curent is that high, but the actual power dissipation would be much less than that current suggests. It is probably working correctly, but a bit of an overkill for the average workbench. Neil S. Sounds VERY reasonable for a 15kVA transformer. 2.5 A suggests coupling ratio on the order of 0.982, not bad for an AC mains transformer that weighs that much. If it bothers you, you can add *a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. Or, ignore it and let your house wiring dissipate a bit of power less than 1W ? ARRRGGG! *That'll teach me NOT to do my own research. *Now, I have to reply to my OWN posting! ok your transformer is the *1kVA version of that series, the smallest transformer. current of max load is 1kVA/120 or 8.3A. reactive current is 2.5 A that implies the core reactive impedance from its inductance is around 3.3 to 1 *Seems a little low, but in range for a super cheap transformer that will get hot while running. I would have expected more like around 1A, or less. Here are some 'good' rules of thumb: The core inductance reactance is probably 5 to 10 times the load impedance, I've seen as low as 3 times. The winding resistance is usually split half in pri and half in sec. actually more like 45% in primary and 55% in sec.and the total is less than 1/10 of load impedance. So the transformer is in 'range' but that current does seem pretty high for what should be a high quality transfomer. *Could be a short somewhere. Depending on how the transformer is wound, you may or may not learn much from measuring the DC resistance of each winding. *You could power each winding with 120Vac and measure the current of each winding, but then again. If you don't need much power through this thing, like less than 500W, wire it for 240/240 and that'll lower the core current for you. The symptoms described sound very similar to using a 60Hz transformer on a 50Hz supply (as might happen if you are using American equipment in Europe), and the transformer hasn't got enough iron in it - so it's saturating. However, that's not what you are doing. If saturation IS the problem, you can usually confirm it (under no-load conditions) by winding the supply voltage up on a variac, and measuring the current the transformer draws. It will rise suddenly when the core starts to saturate. Although the problem is much more likely to be shorted turns, a quick test for saturation might be interesting. -- Ian When I buy transformers I always buy ones rated for 50 Hz, that way on 60 Hz they run cooler. That does not apply to ferroresonant transformers of course, but I have never bought one so it doesn't matter. |
#58
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Isolation transformer draws excessive current under no load condition
On Feb 13, 10:15*pm, "Phil Allison" wrote:
"Robert Macy" ** Is there any way to shut fools like you up ?? * *---------------------------------------------------- Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, ** Absolute BULL**** !!!!!!!!! which means the amount of power you drop in your wiring [and pay for] will be less. ** Absolute IDIOCY !!!!!!! Adding caps is a STANDARD way to adjust power factor to 1. ** But never used with an off load transformer - because that idea is 100% STUPID. YOU are an obsessed IDIOT with a one track mind. **** off. I stand by what I said as technically correct. ** LOL - *that only makes you a BIGGER ****ing idiot. Many, many technical journals, text books, and supporting calculations based upon terms of definition confirm what I said. ** Shame you cannot supply one that backs up your idiotic comments about unloaded transformers. Listen PAL *!!!!!!!! YOU *are nothing but a lying, bull****ting *NUT CASE !! Clueless to the core. FOAD. ... *Phil Phil is mentally disturbed, probably autistic, although he is technically knowledgeable. He'd be okay but for his illness. |
#60
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Isolation transformer draws excessive current under no load condition
"William Sommer****** TROLL" ** Big shame narcissistic ****ing idiots like you still roam the earth. FOAD now !! |
#61
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Isolation transformer draws excessive current under no load condition
"Phil Allison" wrote in message
... "William Sommer****** TROLL" ** Big shame narcissistic ****ing idiots like you still roam the earth. FOAD now !! ROAR! I am a tyrannosaur! I will rip off your limbs with my silly two-fingered arms, and greedily scarf them down. If you are still alive after all your limbs have been consumed, I will bite through your skull and savor the crunching sound. ROAR! |
#62
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Isolation transformer draws excessive current under no load condition
It should have read...
ROAR! I am a tyrannosaur! I will rip off your limbs with my silly two-fingered arms, and greedily scarf them down. If you remain alive after all your limbs have been consumed, I will bite through your skull and savor your agonized screams of fear and excruciating pain, before you pass forever from this world. ROAR! |
#63
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William Sommer******= TROLL
"William Sommer****** TROLL" ** Big shame narcissistic ****ing idiots like you still roam the earth. FOAD now !! |
#64
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Isolation transformer draws excessive current under no load condition
On Sat, 18 Feb 2012 21:31:17 -0800 (PST), spamtrap1888
wrote: On Feb 18, 4:22*pm, "Phil Allison" wrote: "Cydrome Leader" I'd say your transformer is bad or somehow connected wrong. ** No way. The OP's data shows it is operating normally and correctly. 10 degrees temp rise and a PF of 0.15 is A-OK. .... *Phil Why doesn't the transformer data sheet include idle current, power factor, etc.? Or is it embedded in some transformer standard I have to spend 2000 swiss francs to get? If it is covered under a IEEE standard it would be about uS$100 to $200. I have several of them already, but maybe not the one for your transformer. Nor is the IEEE standard a mandatory one, check local regulation for what is mandatory. Speaking of, i need to go buy some more standards right now. ?-) |
#65
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Isolation transformer draws excessive current under no load condition
On Feb 17, 6:25*pm, "Phil Allison" wrote:
"Robert Macy" = *one stubborn ****er A cap does improve PF... ** But only with theoretical transformers - *NOT real ones. First, use a Linear Model to represent the isolation transformer. ** Waste of ****ing time and effort *- *as it only repeats the same ****WIT error you have been sprouting here all along. The primaries of *REAL *commercially made E-core transformers are *NOT linear inductors !!!!!!!!!!! The off load primary current at rated voltage is *dominated by the third harmonic * of the AC supply frequency. The laminated iron core is then saturating, quite heavily. JW's 1kVA iso tranny is a very typical example of this fact. You will *NOT *find this information on webs sites that merely discuss transformer basics. You WILL *find this if you test a cross section of commercial E-core transformers with the aid of a variac, RMS current meter and a scope monitoring the current waveform. This has NOTHING do with badly or well made transformers - *all makers do it to save weight and cost. BTW: I happen to own a 1kVA transformer very similar to that described by the OP. Tested as above, these are the figures: VAC * A rms * *I peak 30 * * * 0.08 * * * 0.11 50 * * * 0.11 * * * 0.14 70 * * * 0.20 * * * 0.35 90 * * * 0.45 * * * 1.0 110 * * 1.0 * * * * 2.0 120 * * 1.4 * * * * 2.9 130 * * 2.2 * * * * 4.6 Up to 70 volts AC, the tranny is approximately linear with an effective inductance of about 1.1 H. At and above 90 volts AC it suddenly changes - *current starts to increase exponentially and the wave becomes very peaky with a 1:2 ratio between rms and peak values. At 130 VAC input, effective primary inductance ( based on simplistic calculations) *has dropped to less than 0.2H due to core saturation. I must have tested hundreds of E-core trannys this way in the last 20 years or so and ALL do much the same thing. Toroidal and C- core types are different. .... *Phil For various reasons, it took MUCH longer than I anticipated to post back here! After more accurately modeling a REAL transformer based upon PA's data, I am convinced that adding a cap in parallel will NOT improve the PF. The best intuitive way to explain is to simply say: in order to reduce PF, a resonating cap is added in parallel to cancel the effect of the inductance. The effect relies upon the inductance to be a CONSTANT value, the core of a typical isolation transfomer during its operation is NOT constant {reducing dramatically as the peak current flows. With this changing value of inductance all the 'goodness' of adding the cap completely disappears. Using the following simple model, I could not even change the cap to some 'optimum' value. PF just stayed bad, did not get worse, just stayed bad, and the cost of adding any cap was wasted. . Small discussion about the dataset. The slight increase in apparent inductance going from 30 to 50 can be explained as being due to the coercivity of the core material. At low currents, the BH curve loop being followed is more horizontal than the BH curve being followed as the voltage increases and current increases, the inductance then starts dropping due to the saturation of the core. If you plot the data set as Apk/(sqrt(2)*Arms) vs Vac, you'll see a strange shape to the curve. plot as 20*log10(Apk/Apkcalc) vs Vac and it is VERY interesting to notice a 'step' and then constant value. see the undershoot, overshoot, and ringing of the data as Vac increases. Note: The following model does NOT display this type of performance. I wonder if it was caused by a 'two-step' saturation? In other words, material saturated leaving another material that saturates at a higher current value, like regions in the core?. I'm going to go back and try 3 inductors in series, to see if I can get a 'better' fit - air core inductor, inductor 1 saturating first, inductor 2 saturating 2nd. Only mentioned as interesting, do not think a finer model will result in a different conclusion, though.] LTspice has a simple nonlinear model, called "Behavioural Model", for an inductor. The inductor's flux is: Flux = tanh(x), where x is the current through the inductor. The model is supposed to follow the saturation curve fairly well, but assumes ZERO coercivity, in other words, zero hysteresis. The model is like following the 'centerline' of the hysteresis curve. Several observations, I could NEVER get the model to fit the data provided by Phil Allison, [which translates to still don't have a good model]. However, after some 'adjustments'. the characteristics of the model did fit the characteristics of the data [No time to EXACTLY create/present the tables of comparison, will do later] Suffice to say, as the input voltage increased; the rms current went up faster than if the transformer's core were a constant inductor, the peak current for the rms current went up at about the same ratio as PA's data. At higher voltage, the peak current noticeably distorted the current waveform into appearing to have severe 3rd harmonic distortion. Actually, instead of sinusoidal, looks triangular. Using this model, I calculated an appropriate cap, added it to the circuit, and found NO EFFECT on PF !!! I then started changing the cap's value, looking for some optimum, and found none. CONCLUSION: For "real" isolation transformers, it is NOT POSSIBLE to add a cap to 'adjust' the PF for the load. I defer to PA's experience with a multitude of manufactured transformers, in defense of my comments, my experience was limited to custom transformers [whose performance was always better than commercially available] and my own transformers, which perform a bit better. Example, 100 turns to get 1 Henry. No DC current is allowed, but you do measure 1H inductance with only 100 turns. Coercivity is about 1/100th silicon steel, which my understanding is usually used in commercial transformers. So what I'm used to working with does approach 'ideal' inductance. The simple model is here for any interested: name the file something ending with .cir LTspice will run the simulation. You're on your own for changing values. Note the Rcore value was added to represent the unloaded 40+W dissipation, you will find its absence/presence does not affect the conclusions. TEST_ModelBehaviour - nonlinear inductor using behavioural Model * for use on LTspice * ..tran .1 20 19.95 .1m ..param k0=sqrt(2) ..param k1=120 Vac 1 0 AC={k1} SIN(0 {k0*k1} 60) Racmains 1 IN 0.01 *Cc IN 0 30uF Rpri IN 3 0.26 ..param kk0=1 ..param kk1=1.2/{kk0} ..param kk2=0.412 Lcore 3 0 Flux={kk2*kk1}*tanh(x/{kk2}) Rcore 3 0 350 ..end |
#66
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Isolation transformer draws excessive current under no load condition
On Feb 21, 10:18*am, Robert Macy wrote:
On Feb 17, 6:25*pm, "Phil Allison" wrote: "Robert Macy" = *one stubborn ****er A cap does improve PF... ** But only with theoretical transformers - *NOT real ones. First, use a Linear Model to represent the isolation transformer. ** Waste of ****ing time and effort *- *as it only repeats the same ****WIT error you have been sprouting here all along. The primaries of *REAL *commercially made E-core transformers are *NOT linear inductors !!!!!!!!!!! The off load primary current at rated voltage is *dominated by the third harmonic * of the AC supply frequency. The laminated iron core is then saturating, quite heavily. JW's 1kVA iso tranny is a very typical example of this fact. You will *NOT *find this information on webs sites that merely discuss transformer basics. You WILL *find this if you test a cross section of commercial E-core transformers with the aid of a variac, RMS current meter and a scope monitoring the current waveform. This has NOTHING do with badly or well made transformers - *all makers do it to save weight and cost. BTW: I happen to own a 1kVA transformer very similar to that described by the OP. Tested as above, these are the figures: VAC * A rms * *I peak 30 * * * 0.08 * * * 0.11 50 * * * 0.11 * * * 0.14 70 * * * 0.20 * * * 0.35 90 * * * 0.45 * * * 1.0 110 * * 1.0 * * * * 2.0 120 * * 1.4 * * * * 2.9 130 * * 2.2 * * * * 4.6 Up to 70 volts AC, the tranny is approximately linear with an effective inductance of about 1.1 H. At and above 90 volts AC it suddenly changes - *current starts to increase exponentially and the wave becomes very peaky with a 1:2 ratio between rms and peak values. At 130 VAC input, effective primary inductance ( based on simplistic calculations) *has dropped to less than 0.2H due to core saturation. I must have tested hundreds of E-core trannys this way in the last 20 years or so and ALL do much the same thing. Toroidal and C- core types are different. .... *Phil For various reasons, it took MUCH longer than I anticipated to post back here! After more accurately modeling a REAL transformer based upon PA's data, I am convinced that adding a cap in parallel will NOT improve the PF. ,,,snip...!!! What a WRONG STATEMENT! Adding a cap in parallel to the isolation transformer 'should' improve PF, but not as much as one would like., but does improve it, without makinganything worse, except cost. The error was caused by monitoring the current through Rpri, not through Racmains, so OF COURSE PF never changed!!! Didn't discover the error until went to a three inductor model which matches the data fairly closely. Note: the behavioural model should be fairly accurate, because the transformer has a constant voltage across it, so it is possible to approximate the hysteresis loss with a fixed resistor. The transformer has enough voltage that each cycle the same amount of power is lost. I would NOT use this model tor represent an audio transformer, where the drive can vary a great deal. The 'three' inductor model starts very closely matching the data, results and data are at the end of this posting. Same conclusion, adding a cap helps PF. For the single inductor model, I added a residual amount of AIR inductance [about 30mH] and got the following: The model very closely models observation, at low voltages current is fairly sinusoidal, near 70+ Vac, the thrid harmonic starts to dominate the wave shape, DRAMATICALLY. We're talking major 'pointy' waveforms. I can't post the plot, but you can copy the model below and see for yourself. Checking the model's match to the data: LTspice PA's Data Vac Arms Apk Arms Apk 30 0.068 0.098 0.08 0.11 50 0.118 0.172 0.11 0.14 70 0.180 0.270 0.20 0.35 90 0.275 0.447 0.45 1.0 110 0.744 1.68 1.00 2.0 120 1.38 2.96 1.4 2.9 130 2.08 4.22 2.2 4.6 simulating the circuit with the model: NO LOAD [add Rcore = 350] 120Vac Arms Vinrms Pwr(Rcore) PF no cap 1.408 119.9 41.54 0.25 28uF 0.762 120 41.57 0.45 56uF 1.542 120 41.61 0.22 FULL LOAD 14.4 ohm [add Rcore = 350] 120Vac Arms Vinrms Pwr(Rcore) PF no cap 8.594 119.9 1,020 0.99 29uF 8.533 119.9 1,020 1.00 CONCLUSION: adding a cap in parallel to an isolation transformer, whether loaded or unloaded, is expected to improve PF copy and name something ending in .cir: TEST_ModelBehaviour - nonlinear inductor using behavioural Model * Voltage is V(in), current is I(Racmains) * Real power is average of V(in)*I(Racmains) * apparent power is V(in)rms times I(Racmains)rms * Plot these three: I(Racmains), V(in), V(in)*I(Racmains) ..tran .1 10 9.95 .1m ..param k0=sqrt(2) ..param k1=120 Vac 1 0 AC={k1} SIN(0 {k0*k1} 60) Racmains 1 IN 0.01 *Cpf IN 0 28uF Rpri IN 3 0.26 * ..param kAIR=.03 ;set to 'residual' inductance in Henries ..param kk0=1.2 ;set to 'initial' inductance very low current ..param A0=0.274 ;set to current where var. ind. drops to half ..param kk=1.13 ..param kk1={A0*kk} ;set to current for half saturation ..param kk2={kk0-kAIR} * Lcore 3 0 Flux={ {kk2*kk1}*tanh(x/{kk1})+{kAIR}*x } * *Rcore 3 0 350 *Rload 3 0 14.4 ..end = = = = The three inductor model: LTspice PA's Data Vac Arms Apk Arms Apk 30 0.071 0.114 0.08 0.11 50 0.130 0.210 0.11 0.14 70 0.231 0.383 0.20 0.35 90 0.464 0.830 0.45 1.0 110 0.922 1.74 1.00 2.0 120 1.40 2.83 1.4 2.9 130 2.21 4.58 2.2 4.6 NO LOAD 120Vac Arms Vinrms Pwr(Rcore) PF no cap 1.441 119.9 41.30 0.24 29uF 0.642 120 41.31 0.54 64uF 1.728 120 41.32 0.20 FULL LOAD 14.4 ohm 120Vac Arms Vinrms Pwr(Rcore) PF no cap 8.708 1,032 119.9 0.99 29uF 8.622 1,032 119.9 1.00 TEST_MB three - nonlinear inductors using behavioural Model * for use on LTspice * ..tran .1 20 19.95 .1m ..param k0=sqrt(2) ..param k1=120 Vac 1 0 AC={k1} SIN(0 {k0*k1} 60) Racmains 1 IN 0.01 Cpf IN 0 29uF * Rpri IN 3 0.1 * * first inductor ..param kk0=1.2 ..param kk1={kk0-mm0} ..param kk2=.2 Lcore01 3 4 Flux={kk2*kk1}*tanh(x/{kk2}) * second inductor ..param mm0=0.185 ..param mm1={mm0-nn0} ..param mm2=1.17 Lcore02 4 5 Flux={mm2*mm1}*tanh(x/{mm2}) * third inductor == air core ..param nn0=.02 Lcore03 5 0 {nn0} * Rcore 3 0 350 *Rload 3 0 14.4 ..end |
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