[RE-wrenches] Efficient step up, down transformers

[William Miller]

Lars:

I have been dealing with the same issue for an on-grid scenario.  We were 
asked to bid a large installation to cover the idle losses of poorly 
selected transformers.  Before we bid the project, we first looked at why 
the client's electric bills were so high.  We found that changing out his 
transformers would save him considerable power.  We are waiting for that to 
be accomplished and then we will bid on a smaller system.  Here is the 
scenario:

The customer built a new straw bale home 2,000 feet from his meter.  The 
electrician ordered two large (75KVA), standard-wound transformers to step 
up to 600 VAC and then down to 120/240.  The customer's electric bill went 
from ~$50/month to ~$200/month and he has yet to move his laundry equipment 
into his new house.

Turns out the transformers had a large idle loss.   Using less electricity 
did not help this customer.  We had an electrical engineer do an analysis. 
Answer:  Changing the large  transformers to custom-wound 15KVA units would 
reduce the monthly bill enough to pay-off in 5.4 years.

Installing standard transformers in step-up / step-down configuration is a 
mistake.  Voltage drop and in-rush problems occur (I have experienced the 
in-rush problems and they can be difficult to resolve).  I have attached a 
white paper that explains.

Good luck,

William Miller


At 07:42 AM 7/25/2011, you wrote:

>Wrenches,
>                 I recently installed three "ultra -efficient" step 
> up-down transformers on an off grid micro grid project with a 1500' wire 
> run. The grid is powered by a an old SW4024(120v) output, stepped up to 
> 480v, and stepped down to 240v at two locations. I was told by the 
> manufacturer that they were "99% efficient under a full load", but upon 
> firing up the system, I found a NO LOAD AMPEREAGE OF 15.6 amps!!! 
> Needless to say, a completely unworkable situation for an off grid 
> scenario, as the 840ah battery would be drained in a couple of hours 
> before anything was turned on. I'm wondering if anyone out there has 
> either found off grid friendly step up-down transformers, or if I'm just 
> screwed and need to pull parallel 4/0 runs (probably the price of a new 
> car) to fix the problem. HELP!
>
>Lars Ortegren
>

William Miller
Miller Solar
Voice :805-438-5600
email: william at millersolar.com
http://millersolar.com
License No. C-10-773985
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110726/139d08d4/attachment-0004.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Backfeeding Transformers.pdf
Type: application/octet-stream
Size: 38283 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110726/139d08d4/attachment-0007.obj>