Transformers
Home Up

 

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

1450 NW 87 Ave, Miami

10/02/2007

Active 25kVA Transformer, no load connected

2849 kWh of power wasted per year.

 

SW 87 Ave, Just North of Coral Way, Miami

10/19/2007

Active 10kVA Transformer, no load connected.

1490 kWh of power wasted per year.  I believe this used to feed a lighted bus shelter.  Most were disconnected years ago after an electrocution.  I have to wonder how many of the transformers remain to this day.

 

These are special cases I found.  Not a true no-load situation, but close. 

NW 87 Ave just north of 13th Terr.

10/19/2007

Active 25kVA (est.) Transformer, minimal load connected

This is one busy pole.  I know the white boxes are radios for telemetry.  That may be the only load still on this transformer.   The drop cable going north is disconnected.  This pole could be cleaned up a lot by removing the transformer and moving the radios a pole or two to a pole that has a transformer for other loads.

1650 NW 87 Ave, Miami

10/19/2007

Active 25kVA Transformer, minimal load connected

At first look, I thought this was a no-load.  The cut off cables were the major load at one time in history. But you can see the lighter gauge drop cables going north and south are still connected.  The one going north does have some load... an older style capacitor bank that needs an external power source.  The modern ones have their own step down transformer.   The the drop cable going south is disconnected at the pole.  Again, this is not a no-load situation, but with a modern capacitor bank, this transformer and two drop cables could be eliminated.

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

 

Except for portions owned by others, Copyright: Ray Vaughan, 2008

Comments/Questions