transformer - Page 1
Forum section: electronics / projects

author: max2
author_rank: Newbie
timestamp: June 12, 2014, 01:18:57 am
content: I am trying to figure out what how the secondary on this transformer is wound and connected. Even if someone can point me to the right section in a book that is ok. Maybe even how to run the calculations on it. Thanks, Max2

author: jamesglanville
author_rank: Contributor
timestamp: June 12, 2014, 01:21:52 am
content: Is it not just a standard toroidal transformer, squished to save space and fit in the box? Looks like it's just a high current low voltage coil and a high voltage low current coil.

author: max2
author_rank: Newbie
timestamp: June 12, 2014, 01:32:44 am
content: no, it hasn't been squished. It is a coil out of a pole transformer. What I am not sure about is how the secondary ( small ) winding is wrapped and lugged into the primaries.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 12, 2014, 01:55:24 am
content: I don't see ANY connection to the "secondary" (if that is even what it is?)That may be a mains-service-input grade noise choke or something. as both "hot" wires go through it.If that is a secondary winding (?), then where are the connection leads? And what is it for?Is there a big condenser in there somewhere? Is it possibly a "constant voltage" transformer?

author: IanB
author_rank: Super Contributor
timestamp: June 12, 2014, 03:52:47 am
content: As Richard said. From where it's sitting and how it's wired, it looks like some kind of power conditioner?

author: Richard Head
author_rank: Frequent Contributor
timestamp: June 12, 2014, 05:47:26 am
content: The base support also doesn't look UL94-V0 compliant either!

author: gardner
author_rank: Regular Contributor
timestamp: June 12, 2014, 04:28:01 pm
content: Might help to know what country this is in, even. In NA, this would be a split-phase 240/120V system. The transformer could be some kind of phase balancer that evens out a load imbalance between the two halves of the split phase. I think in NA though, there would have to be a neutral conductor visible in that box, bring neutral from the service entrance to the main load centre.If it's a single-phase 240+N we're looking at, then I guess it's some sort of humungous common mode choke. Maybe a whole-house RCD/GFI?

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 12, 2014, 04:32:59 pm
content: The hardware looks very NA. Especially the meter and the outdoor switches.It is hidden in the shadows, but there may be another big conduit stub between the meter box and the breaker panel.Perhaps that is where the white neutral wire is hiding. Since this thing (whatever it is?) apparently doesn't need neutral.

author: calexanian
author_rank: Super Contributor
timestamp: June 12, 2014, 04:46:23 pm
content: I agree. It looks to be wired as a giant common mode choke/load balancer it even a voltage corrector. The neutral most likley passes through the conduit straight from the meter box to the breaker box.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 12, 2014, 04:57:20 pm
content: Quote from: max2 on June 12, 2014, 01:32:44 amThat seems extraordinarily unlikely. No distribution step-down transformer would have windings like that.The more I ponder it, the more likely it seems to be a "load-balancing" gadget to equalize the two sides of the service.

author: johansen
author_rank: Super Contributor
timestamp: June 12, 2014, 05:28:18 pm
content: That core isn't big enough for 10 volts per turn, so its not out of a pole transformer.furthermore the secondary wires are big enough for 100 amps.the largest core i have measures a cross section of 2 inches by 4.5, and that's big enough for about 2.2 volts per turn.

author: SeanB
author_rank: Super Contributor
timestamp: June 12, 2014, 06:03:59 pm
content: Probably a buck or boost transformer, to compensate for having either a long power line ( boost converter) or being on the transformer side of a long run where you need to drop 15V as the pole transformer is adjusted to still be in spec at the far end, so it high locally. Not common in residential areas, but in rural areas still likely to be used instead of running a long high voltage line and separate pole transformer or to upgrade an existing service that has drooped due to load below the tapping range on the pole transformer.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 12, 2014, 06:55:30 pm
content: But if it were a buck or boost compensation transformer (or "auto-former") there would NOT be such a HUGE disparity between the gauge of the windings.

author: SeanB
author_rank: Super Contributor
timestamp: June 12, 2014, 07:10:43 pm
content: All it needs is to either boost 5v to bring the voltage into the bottom of spec, while not going over max at low load periods. In buck it also only has to shave a small amount off as well, so the wire thickness and turns ratios look fine.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 12, 2014, 07:21:30 pm
content: Quote from: SeanB on June 12, 2014, 07:10:43 pmI disagree on both details. In general, a buck or boost transformer needs the "secondary" windings to be of EQUAL GAGE to the primary in order to preserve the current capacity of the feed. Else, the current capacity is limited by the "weakest link" the secondary winding gauge (which in this example is minuscule by comparison).And I agree with johansen that the turns, the turns-ratio, and the cross-section area of the core just seem way off.It seems to me like more of a current "averaging" device to equalize the current in the two mains leads. And if that "secondary" winding is even used at all, it may be a monitoring device to detect how much imbalance there is.

author: retrolefty
author_rank: Super Contributor
timestamp: June 12, 2014, 08:19:39 pm
content: My guess it"s what the electricians at my refinery called a line reactor. Used to improve 'power factor' (and I think also helped suppress harmonics) for a specific load.

author: johansen
author_rank: Super Contributor
timestamp: June 12, 2014, 08:40:13 pm
content: Quote from: Richard Crowley on June 12, 2014, 07:21:30 pmno, a buck or boost transformer is just wired as an auto transformer, and that transformer shows approximatly 10:1 ratio in size of those wires, so that fits the bill for a 4 kva transformer with 2x 20vac secondaries. and its about the right size.i'm guessing 8 awg wire on the high voltage.so, its possible it was intended for buck/boost operation, but it appears to be configured as a common mode choke.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 12, 2014, 08:57:15 pm
content: Quote from: retrolefty on June 12, 2014, 08:19:39 pmI have seen many instances of large banks of capacitors they use for power-factor correction.But I suppose that conversely, capacitive loads would require inductance for PF correction.Presumably, inductive PF correction is much less common, or else correction inductors are cleverly disguised as transformers so they aren't as easy to spot.PF correction capacitors....

author: retrolefty
author_rank: Super Contributor
timestamp: June 12, 2014, 09:05:49 pm
content: Doing a little goggling I found another use for line reactors:Quote

author: calexanian
author_rank: Super Contributor
timestamp: June 13, 2014, 03:27:29 am
content: That is looking to be the case.. The inner winding may be for connecting capacitors for filtering. There does not appear to be any here, but my guess is the unit can be used either way. Sola voltage correcting transformers have that sort of construction.

author: SeanB
author_rank: Super Contributor
timestamp: June 13, 2014, 04:20:04 am
content: Line reactors are used on larger VFD drives to increase conduction angle through the input rectifiers to reduce peak current when supply impedance is low. If you have a 2kVA inverter and it sits with 5m of cable total including panels and breakers between it and a 1MVA transformer driving the whole plant it is needed. If it has 30m of 2.5mm cable then it is not required, but recommended. It increases line reactance so the diodes will have lower current, and as the voltage drops per cycle the stored energy in the inductor is partially transferred to the inverter to charge the input capacitors.Power factor correction is mostly done with capacitors as most loads are inductive motor loads, or bridge rectifiers or plain resistive. There you find the current lags, so the capacitance is added to bring power factor closer to unity. If you have a very big constant draw load driven by a set of motors often they are specified to be synchronous motors, and the field current is increased such that the motor power factor becomes leading so compensating for the lagging power factor in the rest of the plant. This is only done by companies that get a reduced rate power on the proviso that they have both maximum demand limiting and power factor billing, often it is a company where they have their own grid substation and internal medium voltage distribution and switchgear.

author: RazSlack
author_rank: Contributor
timestamp: June 14, 2014, 11:46:00 am
content: It looks like an isolation transformer to me, but i might be wrong. The thick wires appear to be the same amount on both (front and back on the picture) sides of it, with the thin lines being the shield winding. It's a standard 1 to 1 safety transformer by the looks of it.

author: madires
author_rank: Super Contributor
timestamp: June 14, 2014, 12:24:29 pm
content: I'd say it's a common mode choke, but I have no idea about the low current windings.

author: rexxar
author_rank: Frequent Contributor
timestamp: June 14, 2014, 05:40:58 pm
content: It looks to me like the low current windings are actually connected in parallel to the high current ones?

author: madires
author_rank: Super Contributor
timestamp: June 14, 2014, 06:48:33 pm
content: Quote from: rexxar on June 14, 2014, 05:40:58 pmThe choke/transformer is outside, maybe the low current windings are used as a heater.

author: chrisbrown
author_rank: Contributor
timestamp: June 14, 2014, 07:17:40 pm
content: If it is a choke, could they be using electrical coupling as well as magnetic to increase the high-frequency attenuation? A chunk of iron that heavy probably has a fairly low permeability to keep costs down.Something like this maybe:

author: rexxar
author_rank: Frequent Contributor
timestamp: June 14, 2014, 08:33:27 pm
content: Quote from: madires on June 14, 2014, 06:48:33 pmTransformers need heaters?

author: madires
author_rank: Super Contributor
timestamp: June 14, 2014, 08:50:05 pm
content: Quote from: rexxar on June 14, 2014, 08:33:27 pmThat's my wild guess in this caseA cold choke (no or low load) with a nice metal core would attract condensation.

author: johansen
author_rank: Super Contributor
timestamp: June 14, 2014, 09:26:31 pm
content: Quote from: madires on June 14, 2014, 08:50:05 pm...

author: G7PSK
author_rank: Super Contributor
timestamp: June 15, 2014, 08:25:37 am
content: I don,t have any idea as to what the devise is but looking at the last photo carefully I can only see the smaller wire winding connected to the output side of the device, the smaller winding dose not appear to connect to the meter side of the heavy winding. You can see the insulated end of the fine winding coming over and bonding on the output tails of the heavy windings, a greenish yellow colour.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: June 16, 2014, 12:39:11 am
content: I also think it is a choke. These do come in large sizeshttp://dir.indiamart.com/impcat/high-current-choke.html

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 16, 2014, 03:25:51 am
content: Hi,My vote is for it being a Buck/Boost transformer. The wire gauges and turns ratio look to be right for that application.If you consider the transformer to be 100% efficient, (and it will be close to 98%) Input power = output power.Input Current = 110V x 100A / 100V = 110AThe current in the heavy winding is the output current = 100ATherefore the current in the low current winding is 10AThe VA rating is equal to the boost (or buck) voltage x output current.In this case for a 10v x 100A = 1 kVAThe size seem reasonable for that.There are probably two secondary windings and a single 220V primary for North American split-phase applications.Regards,Jay_Diddy_B

author: TerminalJack505
author_rank: Super Contributor
timestamp: June 16, 2014, 03:41:46 am
content: Apparently there's more than meets the eye for this transformer.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 16, 2014, 04:31:52 am
content: So do you see a connection to "neutral" (white insulated wire) there in those photos anywhere? I don't.'That rather puts a crimp in Jay_Diddy_B's diagram.I see a common-mode choke with only the two main (black) "phase" conductors.I think what appears to be a secondary winding is a red herring and is not even connected.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 16, 2014, 11:14:18 am
content: Quote from: Richard Crowley on June 16, 2014, 04:31:52 amThere is no need for a neutral connection. Here are the two configuration that are possible with this transformer:This fits the picture, four heavy wires entering the box, two heavy windings and one light winding. The transformer can be used to raise or lower the voltage by a small percentage.Regards,Jay_Diddy_B

author: gardner
author_rank: Regular Contributor
timestamp: June 16, 2014, 02:21:00 pm
content: Quote from: Richard Crowley on June 16, 2014, 04:31:52 amGiven the turns ratio (I make 8:1) and the primary voltages involved, the secondary could be carrying 900V to 1,800V. That's a lot of voltage to just leave hanging in mid air.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 16, 2014, 06:21:18 pm
content: Quote from: Jay_Diddy_B on June 16, 2014, 11:14:18 amYes, you have convinced me. I believe you are correct.However, gardner brings up an interesting point regarding the turns ratio.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: June 16, 2014, 08:45:37 pm
content: Unless thin winding is bifilar or quad-filar?