Energy Efficient Transformer Sepcifications

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Phil Devine

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My name is Phil Devine and I have an electrical construction background from trade school and almost 28 years in the U. S. Navy Seabees. I am now an assistant maintenance director for a county school system. I have been asked by our new construction director to give him some feedback on guidance he is being given on specifications for energy efficient transformers for our new schools being built. I have been out of this design area for many years and ask for help in determining if the juice is worth the squeeze on these transformers. I have a few initial questions:

Are they truely required? What are the benefits and energy savings verses life cycle costs? Are these type of transformers commonly specified for new school constuction now?

I have attached the correspondence between our Architect and design engineer. I have also included the attachments referenced in the e-mail dialog.

I tried my best to "sanitize" the documents so they can be posted and commented on in this forum. If I did not do a good job of that, please let me know what I need to delete so I can ask my questions.

Thanks in advance for your help.
 
It really depends on the total KVA we are talking about, has anyone done a feasability study?

Also keep in mind that you will have higher fault currents, your arc flash hazards may increase and/or you may exceed the AIC ratings of your equipment.
 
zog said:
It really depends on the total KVA we are talking about, has anyone done a feasability study?

Also keep in mind that you will have higher fault currents, your arc flash hazards may increase and/or you may exceed the AIC ratings of your equipment.
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An energy efficient transformer is different from a regular transformer in that it reduces internal core losses, correct? Does this really influence the short circuit current available at the transformer secondary? In looking through the specification documents in Section 2.2, the impedance of the transformer is between 3.5% and 5.8%, which to me, seems much like a regular transformer. Or do other similar transformers have a higher impedance? I suppose like you said it depends on the KVA rating.:)

To the original poster, I agree with zog that a feasibility study needs to be done or at least look at the savings realized vs. the extra cost and calculate a simple payback. Is this school going to be a LEED school, and the energy efficient transformer will get you points to attain that certification? If so, then that also influences your economic decision when comparing against other costs to get the LEED certification.
 
Good point, I didnt even thik about LEED certification.

Seems like 3.5% is pretty low Z, depends on the transformer you have now, either way the effect on available fault current needs to at least be considered.
 
Leadership in Eneregy Environment Design or something like that. It is really a "Green Building" certification and you get incentives from the Fed Gov I think.
 
From the Square D catalog (which I don't think even lists standard transformers anymore):

"Public Law 109-58 of the Energy Policy Act of 2005 requires the manufacturing of Energy Efficient Transformers after Jan. 1, 2007 for all General Puropose distribution applications."

Incandescent lamps are probably next :(

Besides, I think the payback is usually within a few years. Why would you need a study to decide if you want to start saving money after 3-7 years?

On another issuel, that spec looks like it has a lot of fluf in it. It might be written in a way that requires a certain brand of transformer. Lots of companies make EE transformers, so they should be competitavely priced. The difference in price between a standard model, and a EE shouldn't be huge.

Steve
 
steve66 said:
Besides, I think the payback is usually within a few years. Why would you need a study to decide if you want to start saving money after 3-7 years?

Steve
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You wouldnt need a study if that is true, not sure how you determined the payback time. It is not just the cost of the transformers, it is the labor of replacing them, the downtime, disposal, etc. If this is a new building (If it is I misunderstood the OP) then EE transformers are a no brainer, but to justify replacing existing ones with slightly more efficient ones shoud be a well thought out decision.
 
As was mentioned above all transformer built after 2007 must be energy efficient per TP-1.

This requirement forced manufacturers to re-design their transformers to be most efficient at 35% loading. If your loading profile differs from this your installation may be more or less efficient.

In general, transformer impedance is changed primarily through the inductive reactance component rather than via resistance. The transformer inductance has no effect on losses. So changing the efficiency of the transformer does not often impact its %Z.
 
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