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Background Power companies, including our local Florida Power and Light (FPL), use transformers to bring voltage down from a high dangerous voltage the voltages we use inside our homes and businesses. These transformers usually drop 7500 volts down to a more manageable 120 or 240 volts. The problem is that they're not perfectly efficient. Have you ever pulled the charger for your cell phone out of the wall and noticed it was slightly warm? That's power being converted into heat. Even when you're phone isn't connected to it, the transformer uses a certain amount of power to generate heat. That's not a failure of the transformer, it's just proof that we can't make perfectly efficient transformers. When a customer is disconnected from their power feed, the power company should either remove the old transformers, or at least disconnect them at the input. All around Miami I see lots where buildings once stood. The power lines have been cut, but the fuse feeding the transformer is still on. So the transformer is only making heat. Something we have more than enough of in Miami. Another common situation is a transformer installed for the construction of a building but never removed when the work is done. The fuses for transformers on poles are very easy for me to see. We'll never know about the underground transformers that are wasting power. Since all the wiring is underground, there's no way for me to follow it to see if the load is gone. I'll document, with pictures when I can, transformers around Miami that need to be removed or disconnected or both. My hope is that someone from FPL will check this page from time to time and take some action. As I find the data, I'll document here the published specs for the power wasted by a transformer. Then I'll be able to calculate the money lost by us rate payers every month. Will disconnecting an unused transformer stop the energy crisis? No. Will removing one no-load transformer save more power than all the compact florescent lights in my house? Maybe. And another thing... How about the wasted equipment? Even the ones installed on poles with the fuses disconnected. What about all that capital equipment depreciating without any revenue through it? These transformers, powered up or cold, could be in storage for the next major wind storm. On the poles, they're just susceptible to damage. Since they add wind load to the poles, they could even increase odds that the poles will fail. In other words, if they don't need to be there, remove them and put them somewhere that they can do more good than bad. In the examples I show below, I'm estimating the wasted power based on this table which is based on data cited below: Size Power kVA Eff % Waste kWh/day kWh/yr 10 98.3% 170 4.08 1490.22 15 98.5% 225 5.40 1972.35 25 98.7% 325 7.80 2848.95 37.5 98.8% 450 10.80 3944.70 50 98.9% 550 13.20 4821.30 75 99.0% 750 18.00 6574.50 A From Transformer Marking B Table 3.7.1 NEMA Efficiency Levels for Liquid-Immersed Distribution Transformers C Power wasted to heat D Power converted to 1000's of Watt Hours E kWh wasted per year
Cases
These are special cases I found. Not a true no-load situation, but close.
Research I've been trying to find the no-load specs for the transformers used by FPL. So far, not much luck. I found the literature, but not detailed specs on the transformers I've seen around Miami. One vendor won't allow access to the specs without signing up with their web site. It appears I might not be the only one interested in the efficiency of transformers. On this page, a manufacturer explains the higher costs to expect when new rules about transformer efficiency go into effect in 2010. Are they trying to justify their low performance? And here is the Department of Energy's Notice of Proposed Rule Making about Distribution Transformers. Lots of good data here for me to digest. Here's a starting point: Table 3.7.1 NEMA Efficiency Levels for Liquid-Immersed Distribution Transformers Liquid-Immersed, Single-Phase Liquid-Immersed, Three-Phase kVA Min Efficiency (%) kVA Min Efficiency (%) 10 98.3 15 98.0 15 98.5 30 98.3 25 98.7 45 98.5 37.5 98.8 75 98.7 50 98.9 112.5 98.8 75 99.0 150 98.9 100 99.0 225 99.0 167 99.1 300 99.0 250 99.2 500 99.1 333 99.2 750 99.2 500 99.3 1000 99.2 667 99.4 1500 99.3 833 99.4 2000 99.4 - - 2500 99.4 Notes: Temperature: load-loss 85ºC, no-load loss 20ºC Efficiency levels at 50 percent of unit nameplate load I bolded the types of transformers I have discovered. You can see the efficiency gets worse as the transformers get smaller. Most of the ones I've seen so far are the smaller sizes. DOE is working to make the whole system more efficient by requiring more efficient transformers. My goal is even simpler... get rid of transformers that are doing nothing but heating air. Another subject is over-sized transformers. I've seen cases where a building has been disconnected from a 50 kVA transformer, but a single 100 watt street light remains. So this 100 watt street light is actually lighting with 100 watts at night and heating another 550 watts 24/7. Is the distribution system ever audited to make sure that waste is minimized? I'm all in favor with leaving larger transformers when there is a chance growth will result in more load. But in some cases, the growth, like a new building with it's own transformer vault, orphaned the pole mounted transformer. There are much smaller, more efficient transformers available for very small loads such as street lights, traffic lights and so on. But so far, I haven't seen them in use in FPL's service area.
Let's do a sample of each size: Size Power kVA Eff % Waste kWh/day kWh/yr 10 98.3% 170 4.08 1490.22 15 98.5% 225 5.40 1972.35 25 98.7% 325 7.80 2848.95 37.5 98.8% 450 10.80 3944.70 50 98.9% 550 13.20 4821.30 75 99.0% 750 18.00 6574.50 A From Transformer Marking B Table 3.7.1 NEMA Efficiency Levels for Liquid-Immersed Distribution Transformers C Power wasted to heat D Power converted to 1000's of Watt Hours E kWh wasted per year
Here is a paper from Japan about the losses in distribution transformers
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