Comparing Transformers

[fifty60]

I typicaly use these general purpose enclosed transformers:http://dongan.com/Products/SinglePhaseTransformers.aspx Have never had any problems with them, they are solid and dependable. These transformers are fine until i have to purchase one that is CE marked. From this company the CE marked transformers are very big and more expensive.

I've found another company that sells what appears to be similar transformers: http://www.acmepowerdist.com/energy-efficient-transformers-single-phase.htm They seem similar, but their CE versions are smaller and less expensive.

Has anyone had any experience with the Acme transformers? Are they good quality? Any thoughts on what I should look at to compare the two? Any idea why one company can make the CE marked version smaller and less expensively?

 

[Smart $]

IMO, Acme is one of the better known by name transformer manufacturers of those that specialize solely in transformers.

That said, I don't know enough about Acme's product performance or CE conformance to advise further.

 

[fifty60]

Thanks again Smart$. Putting the CE mark aside, what parameters should I be most concerned with when comparing 2 general purpose transformers?
They are both in Nema 3R enclosures. The Acme has many more Taps than the Dongan, the Acme is also lighter, smaller, and less expensive.

I just feel like there is something I am missing here that is allowing the Acme to have all of the improved characteristics. Any help on this is greatly appreciated.

One thing about the ACME transformer is that its mounting brackets are not very rugged. It looks like it is more suited for vertical wall mounting. I want to mount the transformer horizontally underneath my equipment. Is there any reason why I would not be able to mount the transformer upside down or sideways? If I do end up using the transformer I will probably have to install a better mounting bracket. I do not think that spatial orientation would affect heat dissipation...

 

[GoldDigger]

I do not think that spatial orientation would affect heat dissipation...

If the transformer's enclosure is not ventilated, then the orientation will not have an enormous effect, although convection past the outer surfaces of the transformer will be better with the long dimension of that side vertical.
And if you are going to mount the transformer against a surface that blocks air flow the convection cooling will be a lot less effective than in vertical wall mount.
And finally the wiring compartment of the transformer may be designed so that the wires and terminals are in a cool area when the unit is mounted normally. Changing that may cause localized heating issues at the terminations and wire entries.

 

[fifty60]

The same surface will be against the Equipment enclosure whether it is mounted vertically on a wall or horizontally underneath my equipment. So the heat conducted away will be the same. As far as convection goes, the transformer is located inside the equipment enclosure in an area that we call the "powerpack". There are refrigeration compressors, piping, solenoids, condenser and condenser fan in this power pack area.

Sometimes it gets crowded in the powerpack area, but the Dongan's have never had any trouble. The larger size probably helps with the heat dissipation, so perhaps the smaller size would need more convection.

The ACME has UL? E79947 and CSA-7357 file #s.

The ACME also has an insulation temperature rating of 180 C vs the Dongans insulation rating of 200 C. What exactly is this insulation temperature rise rating? The ACME also has winding rise of 115 C.

 

[Smart $]

In making a comparison, a model or PN for each manufacturer would help... hmy:

In general, orientation can affect heat dissipation. Even if it doesn't affect the winding and core temp, it may affect the temp of the wiring compartment. Mounting beneath or on the underside of something can hinder dissipation if what's above blocks vertical air flow.

JMO but I feel you are already looking at the most pertinent parameters. The only other might be efficiency, if that even matters.

 

[fifty60]

Here are the 2 transformers....


http://dongan.com/Portals/0/Catalogs/ES-11%20Series%20Enclosed%20transformers.pdf

http://www.acmepowerdist.com/datasheets/Section 1/1-phase/TF-2-79262-S.pdf


The Dongan transformer above is their CE marked transformer which we also use but not nearly as much as the non CE marked version which is found on the bottom of page 6 of this document:
http://dongan.com/Portals/0/Catalogs/SINGLEPHASE.pdf

We can only use the Dongan ES-11 series up up to a 1KVA. Anything above that, even 1.5KVA is huge, and we have to get a custom Dongan which smaller than the ES-11 but expensive.

It looks like the standard Dongan we use (85 series) has 180 C insulation with 115 C temperature rise at 40 C. What exactly does this rating mean? It appears to me to be the same as the ACME shown in the link above.

 

[Jraef]

The main difference, which explains the difference in weight as well, is that the Acme uses aluminum coils, as opposed to the Dongan being copper wound. As a gross general rule, copper is "better" in terms of voltage stability and resistance to thermal expansion causing long term issues with connections, but copper transformers are also heavier and tend to cost a lot more. I couldn't quite follow what you say you are doing with this; it's a NEMA 3R transformer but mounted INSIDE of a cabinet? If so, I would be concerned for thermal issues and look for copper were it me. Why are you doing that though, as opposed to using an open style control power transformer?

 

[Smart $]

Just going by the manufacturer provided information, there is not enough difference to sway which I would choose. That is leaving size, weight, brackets, cost out of the picture.

The insulation temperature rating should go without explanation. As I understand the other, at continuous full load the core and winding temperature will reach the value specified operating in a 40?C ambient... with optimal air flow... thus 155?. This provides a 25? "cushion" for operating at slightly elevated operating ambient temperature or temporary overloading... either or a combination of both diminishing the MTBF. Someone will correct me if I am in error...

 

[Jraef]

Re: Temperature rating and rise. There used to be an older rating system using letters, which is still what Dongan is showing when they say Class H. The new version of that did away with the confusing letters and replaced them with confusing numbers... The Acme transformer is a Class 180 design, meaning it can allow a 115C rise over a 40C ambient (so 155C) and an allowable 25C "hot spot", for a maximum of 180C operating temperature of the windings themselves. On the Dongan, being a Class H, you have exactly the same thing technically, but Dongan goes on to say 200C as opposed to the 180C that was the requirement for Class H. Everyone has the right to exceed specifications..

 

[fifty60]

The main reason I cannot use an industrial control transformer is because the Power Pack area where the transformer is located also contains refrigeration equipment. This possibility of moisture necessitates the encapsulated transformer.

It certainly helps with temperature that I am only using 2KVA of the 3KVA transformer right? I've often wondered why my predecessors used a 3KVA when a 2 KVA would work, maybe it was because of the temperature rise.

It seems like the non CE marked Dongan and the CE marked Acme are very similar general purpose transformers. Dongan makes a larger CE marked transformer with a higher insulation temperature, but at a higher cost. I am not sure how you can tell that the transformer is aluminum rather than copper, but if that is the case it would appear that the Dongan is the overall higher quality transformer especially in the CE version.

We have not had any trouble with Dongan other than the size and price of the CE marked transformers. I don't like the mounting brackets on the Acme, but it is not much trouble for us to add a bracket to better secure the transformer.

What types of tests should I run to make sure that the transformer stays within its temperature ratings? The outside enclosure, the terminal area...under normal and single fault (blocked vent) conditions?

With the Acme's 180 C insulation rating, 115 C coil temp at 40 C, does that mean I can operate the transformer under full load in ambient conditions of up to 65 C and be right at the the insulation rating of 180 C?

 

[fifty60]

I understand now. 180 C insulation with 115 C rise at 40 C ambient means that I do not have any room to overload the transformer. At 40 C, at full load, the transformer windings will have an average temp of 155 C. I have to leave the remainder 180 C - 155 C = 25 C as room for hot spots in the transformer so as not to destroy the insulation. I cannot overload the transformer or operate at an ambient above 40 C or the hotspots will overtake the insulation rating.

So if my ambient temperature is 40 C or below, and I am not running at full load, then I should expect a long life (20 years?) out of my transformer.

The Dongan CE marked transformer has a 200 C insulation rating, but it does not give the winging temperature rise over ambient. Should I assume that the 200 C insulation allows for 20 C of overload, or a 20 C rise in ambient temperature?

Should the 40 C be measured a few cm's away from the enclosure?

 

[GoldDigger]

Should the 40 C be measured a few cm's away from the enclosure?

It should be the temperature of the free air which is available to circulate past the transformer.
If the transformer is attached to a metal plate which is also heated from the other side, then the effective ambient temperature for that side of the transformer would be more or less than the temperature of the plate depending on the exact heat conduction paths.
If the transformer is surrounded by other hot components, the ambient will be hotter than the air temperature surrounding the whole unit.

 

[fifty60]

For the side of the transformer that is touching the equipment enclosure, how should I factor that into my ambient calculations? For example, the equipment enclosure reaches 60 C, but the ambient air around the transformer is 30 C?

Also, is there any way to extrapolate what my winding temeperatures are at less than full load? Does operating at less than full load mean that I have a room to operate at above 40 C, hypothetical?

 

[GoldDigger]

For the side of the transformer that is touching the equipment enclosure, how should I factor that into my ambient calculations? For example, the equipment enclosure reaches 60 C, but the ambient air around the transformer is 30 C?

You do some complex heat flow calculations, if you have a suitable computer program and more data from the manufacturer than they normally provide.
My initial take would be that a conservative analysis would have to use a 60C ambient.

Does operating at less than full load mean that I have a room to operate at above 40 C, hypothetical?

Absolutely. But again the exact calculation will be complex. I do not have a quick and dirty rule of thumb for you, except that the temperature rise may be roughly proportional to the load factor as long as the load is high enough that you can still ignore magnetization related losses. That is if you are loading the transformer at 50% of its rating, the temperature rise may be not much more than half of the rated temperature rise.

You may get better results by talking to an application engineer at the manufacturer, or they may not want to commit themselves to anything except what they have directly tested.

 

[fifty60]

So if I took 60 C then I would not be able to operate the transformer at full load right? There is no way to actually (and easily/ non destructive) to measure the actual winding temperature, and even if you could you would have to take multiple readings to get an average....

the Acme transformer bracket does not place the transformer flush against the wall/enclosure, it does allow for air flow. That would probably be my worst case temperature...so i would probably need the temperature between the transformer and the equipment enclosure...

 

[GoldDigger]

So if I took 60 C then I would not be able to operate the transformer at full load right? There is no way to actually (and easily/ non destructive) to measure the actual winding temperature, and even if you could you would have to take multiple readings to get an average....

the Acme transformer bracket does not place the transformer flush against the wall/enclosure, it does allow for air flow. That would probably be my worst case temperature...so i would probably need the temperature between the transformer and the equipment enclosure...

Yes on all accounts, except to add that the actual air temperature between transformer and enclosure will be a worst case. The effect could be a lot less than that, especially if the ambient air around the rest of the transformer is cooler.