# Do transformers use up watts when on but not powering anything?



## kaboler

Okay, at that job today, I was showing the bosses the new lights that I put in. Finished up!!! And I asked them about why they have 2 transformers. They said that they bought the place as 2 bays and merged them into one.

Basically I want to know (rough rough estimate) how much electricity this was using, if at all.

347v feed -> 17kva trasnsformer -> 120v panel.

Inexplicably, the panel was wired to the 2 panel plugs, UNUSED, and THAT"S IT!!

Any watts? And it's not a bad idea to turn off a dry transformer is it?

Gonna see if I can talk to the boss and see if we can buy the transformer and panel at a discount. They're mint, and maybe we can get them for cheap, and REUSE!!!!


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## goose134

An unused transformer won't consume electricity as much as it will simply lose it through heat. I believe that most modern transformers run as much as 97% efficient. I'm sure someone more familiar with these things will chime in as the value of reclaimed transformers. Not sure myself.


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## guest

goose134 said:


> An unused transformer won't consume electricity as much as it will simply lose it through heat. I believe that most modern transformers run as much as 97% efficient. I'm sure someone more familiar with these things will chime in as the value of reclaimed transformers. Not sure myself.


Dude, what are you smoking?  Electricity isn't "lost" it is indeed consumed in the form of the magnetizing current of the idle transformer. (Actually it is both in this case. ) Most manufacturers can provide you with the no-load current of their transformers, or use a clamp-on ammeter to measure the current. 

I seem to recall that a typical figure for no-load consumption was around 5-7% of full load rated current.


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## micromind

I was curious about this too; several years ago, I built the following set-up.

1) 200 amp 277/480 meter/main.

2) 225 amp 277/480 panel; MLO.

3) 45KVA transformer; 480∆ to 120/208Y

4) 120/208 panel.

When the POCO set the meter, it read 0. I hotted up the 480 panel, and the transformer, but no other loads. 

The next day, at about the same time, the meter read 33KWhr.


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## kaboler

Wow craziness!!! Poor guy has been running this transformer since he moved in. Hahahaha, oh man.

I don't have a multimeter yet with a clamp-on, otherwise I could have mesured it. Plus, it's TEK cable to the transformer so I don't know if that clamp on could give me an accurate reading.

But micromind's post is pretty accurate.


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## Zog

There are 3 types of losses in transformers. 

Copper loss - dependant on loading, I2R losses from copper
Hysterisis losses - Energy required to align the domains in the core (What makes the transfoemr hum) - independant of loading
Edddy current losses - cirulating currents in the core - independenat of loading


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## goose134

I stand corrected.


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## BuzzKill

Zog said:


> There are 3 types of losses in transformers.
> 
> Copper loss - dependant on loading, I2R losses from copper
> Hysterisis losses - Energy required to align the domains in the core (What makes the transfoemr hum) - independant of loading
> Edddy current losses - cirulating currents in the core - independenat of loading


didn't know about the I2R losses.


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## kaboler

Time to look up some of these big words!


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## Zog

BuzzKill said:


> didn't know about the I2R losses.


Anything with current flowing in it will have I2R losses. :blink:


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## Zog

goose134 said:


> I stand corrected.


 97% is about right for a fully loaded transformer, but under low loading it is much less, at no load obviously it is 0%.


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## Zog

kaboler said:


> Time to look up some of these big words!


OK, let me expand on that

A perfect transformer would be 100% efficient and produce no heat. Unfortunately, this is not a perfect world and there is no such thing as a perfect transformer. Losses in a transformer include copper loss and core losses.

Copper losses

When a load is connected to the secondary, current will flow in the secondary windings. The magnetic flux in the core and the current flowing in the windings generate heat, which is called copper loss, and is equal to the square of the current times the resistance of the windings. Copper loss increases with load. 

Because transformers require such long lengths of wire, increasing the gauge of the winding wire is one way to minimize this loss, but only with substantial increases in cost, size, and weight. Typically the energy lost as heat is less than 1% of the total energy transformed

Core Losses

Resistive losses aside, the bulk of transformer power loss is due to magnetic effects in the core. Perhaps the most significant of these "core losses" is eddy-current loss, which is resistive power dissipation due to the passage of induced currents through the iron of the core. 

Because iron is a conductor of electricity as well as being an excellent "conductor" of magnetic flux, there will be currents induced in the iron just as there are currents induced in the secondary windings from the alternating magnetic field. These induced currents tend to circulate through the cross-section of the core perpendicularly to the primary winding turns (See 1st attachment). Their circular motion gives them their unusual name: like eddies in a stream of water that circulates rather than move in straight lines. 

Iron is a fair conductor of electricity, but not as good as the copper or aluminum from which wire windings are typically made. Consequently, these "eddy currents" must overcome significant electrical resistance as they circulate through the core. In overcoming the resistance offered by the iron, they dissipate power in the form of heat. Hence, we have a source of inefficiency in the transformer that is difficult to eliminate. 

The main strategy in mitigating these wasteful eddy currents in transformer cores is to form the iron core in sheets, each sheet covered with an insulating varnish so that the core is divided up into thin slices. The result is very little width in the core for eddy currents to circulate in.

Another "core loss" is that of magnetic _hysteresis_. All ferromagnetic materials tend to retain some degree of magnetization on a molecular level after exposure to an external magnetic field. This tendency to stay magnetized is called "hysteresis," and it takes a certain investment in energy to overcome this opposition to change every time the magnetic field produced by the primary winding changes polarity (twice per AC cycle). 

Each molecule of the ferromagnetic material (commonly referred to as “domains”), must physically line up with the magnetic field, this cases friction to produce heating in the core and the familiar “B flat” hum that transformers produce.

This type of loss can be mitigated through good core material selection (choosing a core alloy with low hysteresis, as evidenced by a "thin" B/H hysteresis curve, see 2nd attachment), and designing the core for minimum flux density (large cross-sectional area).


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## kaboler

Yeah I wikipedia'd it all, but thanks!


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## bobelectric

micromind said:


> I was curious about this too; several years ago, I built the following set-up.
> 
> 1) 200 amp 277/480 meter/main.
> 
> 2) 225 amp 277/480 panel; MLO.
> 
> 3) 45KVA transformer; 480∆ to 120/208Y
> 
> 4) 120/208 panel.
> 
> When the POCO set the meter, it read 0. I hotted up the 480 panel, and the transformer, but no other loads.
> 
> The next day, at about the same time, the meter read 33KWhr.


 33000 watts, 24 hours, no load, Idleing? I object!


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## Zog

bobelectric said:


> 33000 watts, 24 hours, no load, Idleing? I object!


No 33kWH over a 24 hour period. The transformer was losing 1375W to core losses, for a 45kVA transformer (assuming PF=1) that is only about 3% losses (Or 97% efficienct) which is very reasonable for an unloaded transformer. 

Your 33000W for 24 hours would be 792kWH, which would be unreasonable.


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## Ghandiswrath

So is it a bad idea to shut the XFMR off to save electricity?


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## guest

Ghandiswrath said:


> So is it a bad idea to shut the XFMR off to save electricity?


For dry-type transformers:

If indoors, in a reasonably climate-controlled area, no problem in shutting it off. If the area is damp/wet or subject to extremes of temperature/humidity, would be better to leave it on to keep the windings dry. 

For liquid-filled transformers, in 99.99% of the cases, if it is new or if the fluid was recently tested and free of excess moisture/contamination, safe to turn it off. Beware that an old trans, one that has been under water or exposed to the elements may have enough contamination in the fluid that it may fail upon re-energization. If an older transformer is to be shut down, the fluid should be tested both before shutdown and after it has completely cooled to ambient temperature. 

All above is my opinion, based on research, personal experience and advice/conversations with POCO workers.


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## sparky.jp

mxslick,

Thanks for pointing out the potential issues with transformers. In utility systems, failure to understand and follow these recommendations can lead to some spectacular (and quite dangerous if you are in the vicinity) failures.

Just this morning in Chehalis, WA at a natural-gas-fired power plant, one of the three main facility transformers (or possibly one of its bushings), not under load at the time since the plant was not operational, exploded and the fire could be seen from miles away. The first thing that I thought of was moisture contamination of the cooling oil.


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## kaboler

I value opinions. I mean, you risk getting your head cut off here if you're wrong, but I like opinions. Interesting about the humidity and such. The one I shut off is dry and in a really safe spot (hanging above a door kinda, protected from mechanical damage, on a really nice shelf)


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## kaboler

Oh, and Today, the customer from that job said that I was "one of the best tradespeople that ever did work for him". I don't have the heart to tell him I'm a first year hahahaha.


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## bobelectric

Reminds me of a job I was on when times were good and the local would hide men to keep them working. One day I stumbled across an older electrician in a back room at a desk watching an xfmr. Whatup,I asked. He replied,"Testing all the transfomers that come in,to make sure they are dry.


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## guest

sparky.jp said:


> mxslick,
> 
> Thanks for pointing out the potential issues with transformers. In utility systems, failure to understand and follow these recommendations can lead to some spectacular (and quite dangerous if you are in the vicinity) failures.
> 
> Just this morning in Chehalis, WA at a natural-gas-fired power plant, one of the three main facility transformers (or possibly one of its bushings), not under load at the time since the plant was not operational, exploded and the fire could be seen from miles away. The first thing that I thought of was moisture contamination of the cooling oil.


You're welcome. :thumbup:

In the electrical engineering handbook I have, there is a good section on transformers, and they explained that one of the most common causes of failures of oil-cooled transformers is from contamination. They explained that in normal operation, the heat and movement in the oil during operation traps contaminants in suspension in the oil. When the transformer cools down, the contaminants migrate to the insulation and coils, which results in breakdowns when the transformer is energized. 

Some time ago in my neighborhood, a small plane crashed and took out a padmount transformer. After the repairs (a 16 hour outage) when the POCO re-energized the feeder, an underground transformer serving several apartments failed and sent 12kV into the services. Several panels exploded and many risers burned up. It was later determined that the transformer that failed had contaminated oil.


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## BBQ

Yeah .... you just can't let transformers hang around and expect them to work in the future.





Oh wait, that is exactly what we do without any trouble at all. :laughing:


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## Jlarson

Ah BBQ, I don't think that's a climate controlled environment. :laughing:


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## HARRY304E

Jlarson said:


> Ah BBQ, I don't think that's a climate controlled environment. :laughing:


Oh thats normal around here..:laughing::laughing:


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## guest

BBQ said:


> Yeah .... you just can't let transformers hang around and expect them to work in the future.
> 
> 
> 
> 
> 
> Oh wait, that is exactly what we do without any trouble at all. :laughing:



Hey guys, BBQ finally posted pics of the service to his house!!:laughing:


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## BBQ

Jlarson said:


> Ah BBQ, I don't think that's a climate controlled environment. :laughing:



Oh it is very controlled, mother nature controls it continuously.:thumbsup:



mxslick said:


> Hey guys, BBQ finally posted pics of the service to his house!!:laughing:


If only it looked that good!


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