No load losses - normal vs reverse fed

[Phil Corso]

Gar; Electric-Light

In general, two usual types of transformer design are dominant: a) one based on temperature-rise; b) the other based on minimum-regulation! For the latter, core and conductor elements are usually larger.

Gar has shown that his Xfmr has more iron, thus, corroborating it’s type b)! Electric-light comments list some characteristics detrimental to type b)!

When I was required to provide a quick evaluation comparing mfg’r proposals I used a Figure-Of-Merit, FoM = (wgt of Cu+Fe)/VA!

Gar, can you provide additional detail, such as: 1) primary and secondary wire-size(s); 2) whether both coils are concentrically-located on a center-limb of a 2-window, type E-core); or 3) whether both coils are separately-located on a 1-window, type C-core!

Regards, Phil Corso

 

[Electric-Light]

Gar has shown that his Xfmr has more iron

Regards, Phil Corso

His transformer is rated 50/60Hz and perhaps smaller they are, the more margin they have. would a 13,200v 60Hz transformer tolerate 50Hz application?

If you keep increasing the voltage or lowering the frequency, it will eventually become saturated and act as if you didn't have a core.
I checked a battery charger. It's rated for 6 seconds on, 5 minutes off in 50A boost mode. When you switch it to that mode, the no load power is 30W, 300VA at PF 0.1 it hums abnormally loud.

How close to saturation are transformers normally used at?

 

[Phil Corso]

His transformer is rated 50/60Hz and perhaps smaller they are, the more margin they have. would a 13,200v 60Hz transformer tolerate 50Hz application? If you keep increasing the voltage or lowering the frequency, it will eventually become saturated and act as if you didn't have a core.
I checked a battery charger. It's rated for 6 seconds on, 5 minutes off in 50A boost mode. When you switch it to that mode, the no load power is 30W, 300VA at PF 0.1 it hums abnormally loud. How close to saturation are transformers normally used at?

I said earlier in this thread my answers were not to be misconstrued as XFMRS-101. That said, I’ll have a go at the weight topic! If Gar's 80W and 175W xfmrs were similar in design, and the latter weighed ~10lbs, then using DOE's Weight Scale Factor, the 175W unit should weigh ~18lb! Instead, Gar said, the 80W unit is 50% heavier than 175W unit!

As for operation of a 13,2kV,60Hz xfmr operating at 50Hz... I suggest you post a new thread! Same for the Duty-Cycle topic!

Regards, Phil

 

[gar]

170120-2518 EST

Phil Corso:

Both transformers are identical EI cores and after a more close measurement the A41-175 has a stack of 1.5" and the 80 W unit about 1.38".

Can't measure wire on the 80 W because it is enclosed. Almost certainly it is wound with one winding on top of the other. Typical of low cost transformers of that time period. I believe the transformer iron of the 80 W unit is quite different than that of the A41-175.

The A41-175, as said, is also on an EI core with identical bobbins for the primary and secondary side by side on the center leg.

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[Phil Corso]

170120-2518 EST Phil Corso: Can't measure wire on the 80 W because it is enclosed. Almost certainly it is wound with one winding on top of the other. .

Gar...

1) Are not the wires accessible at their terminals? Or, can't you see them at all?

2) One winding on top of the other means "Concentric"!

Phil

 

[gar]

170121-1219 EST

Phil Corso:

Photos of the two transformers:

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.The 80 W isolation on the left ---------------------- and the 175 VA on the right.


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A closer view of the 175 VA.

These two coils share a common axis. Are they not concentric? Webster's definition includes a common axis, not just a common cemter.

This type of construction will provide essentially the same unloaded core and IR losses whether driven from primart or secondary.

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[Phil Corso]

Gar...

Concentric: Two winding disks on the same core-limb, with one (usually LV) inside the other (usually HV)!

Co-Planar: Two winding discs on the same core-limb, with one above (or below) other!

Regarding wire-size: for '80' the two pair of black wires coming out of the cover; for '175' the two sets of shellac coated-wires!

Unfortunately, all is for naught! The difference, then, must be related to core-material!

Phil

Ps: Next time send the pics first!

 

[gar]

170121-2149 EST

Phil Corso:

The 80 W isolation transformer I used in earlier tests is the only one i ran tests on to illustrate that transformer no-load losses were essentially the same whether the transformer was forward or reverse driven provided that one was comparing comparable flux operating levels.

This supported your statement of post #2 with experimental results.

By chance, but also since the transformer was old and of a low cost construction technique, this falls under your concentric ckassification.

I provided some data with the Signal A41 transformer that showed what appeared to be a different core alloy, and that its design resulted in less no-load power even though it had approximately twice the load capability.

I don't believe I ever implied these transformers were comparable or performed the same function.

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[Phil Corso]

Gar...

You misunderstood me! I was not being critical of your efforts. I just wished you had presented the pics, earlier. Paraphrasing a popular adage, "One picture is worth... lots of needless keystrokes on a very, very slow keyboard?"

Regards, Phil

Ps: However, I am disappointed that you failed to reply on my use of the word "shellac" as an age-indicator! No... not the hardware... mine!

 

[templdl]

The explanation I have heard is that the inrush (as a multiple of full load amps) will vary depending on whether the winding being energized is wound closest to or farthest from the core. I have not seen a good theoretical explanation for this though.

Yes, the common as trip down transformer is used to step up being that the taps are on the HV windings the LV windings are wound first closest to the core. One would expect that the inrush current would be proportional but they are greater when using the transformer as a stepup to some degree. In using that HV taps you have to think backwards as it plays with you brains somewhat when you attempt to adjust for either high or low supply voltages.
However, the question of losses, good question. I don't have access to he engineers that I once had and have no application notes to address that application. One would like to assume that out would be the same either way. But I wouldn't want to conclude that.

 

[gar]

170122-1007 EST

Phil Corso:
I ignored "shellac" because it did not apply to the A41 transformer which is only about 20 years old.

Besides a core material difference between the two transformers there is going to be a great difference in the wire insulation temperature capability. This would be a big factor in the VA rating for what otherwise might seem to be almost the same core physical size.

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[electrofelon]

I just did an experiment of my own. This is the system I mentioned earlier.

To Recap: Transformer A, 15 kva encapsulated, 240/480 to 2400. Transformer B, 2400 to 120/240 15 KVA single bushing/MGN padmount. Transformer A is on the utility end, windings connected in parallel for 240V. I dont have a PT to use on the 2400 side, so I can only measure the 240V side and add/subract to get power measurements. No load loss when feeding A 240V is 130 watts. With transformer B connected, 190 watts total. I reverse fed the setup with a generator and got the exact same losses. The padmount is clearly quite efficient, using only 60 watts. But the Encapsulated is still way more efficient than the first transformers I used which were only 10 KVA and used 300 watts each. They were super old. The Olsun encapsulated is newer than 1993, thats all I know. The padmount was manufactured in 2009, FWIW.

This works out to about $80 per year over if I used another padmount. I got this one for about $650 delivered, and that was the cheapest I have found them. I think Ill just plan on adding a few more panels to my PV system