Faulty Transformer?
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  1. #1
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    Default Faulty Transformer?

    Hello All. We recently moved into a new commercial faculty. We are trying to figure out our high power consumption. Our first bill showed a use of 3400kWh while we were moving. During the move we did not use any equipment other than computers, lights and AC for a 1500SQFT office.

    We did some digging and found that our Delta-Delta 480V to 240V transformer was putting out a lot of heat. We shut off all the loads on the secondary and measured input current on the primary.

    Primary input current (No load)
    L1 = 8A
    L2 = 8.4A
    L3 = 11.5A

    Is this typical input current for a unloaded 150kVA transformer?

    I just did some more detailed measurements with equipment running and it appears the primary input current is unbalanced. However the voltages are close.

    Primary input current (Loaded)
    L1 = 29.2A
    L2 = 11.4A
    L3 = 34.5A

    Primary phase to phase voltages (Loaded)
    L1-L2 = 494V
    L2-L3 = 491V
    L1-L3 = 491V

    Primary phase to neutral voltages (Loaded)
    L1 = 284V
    L2 = 285V
    L3 = 283V

    Secondary phase to phase voltages (Loaded)
    L1-L2 = 247V
    L2-L3 = 244V
    L1-L3 = 243V


    Secondary phase to neutral voltages (Loaded)
    L1 = 122V
    L2 = 213V
    L3 = 122V

    I called the utility out and they claim the power outside of the building is fine. My electrician thinks the utility is sending us unbalanced power causing the transformer to heat up.

    Any ideas? Any help would be appreciated.


    trans.jpg

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    Quote Originally Posted by Richie V6 View Post
    My electrician thinks the utility is sending us unbalanced power causing the transformer to heat up.
    WHY does he think so? EG: On what line-side measurements as evidence?

    The/a utility is ordinarily obligated by regulations and also reasonably comfortable as standard practice to work with your own experts (amateurs, not so much..) to clarify such issues, either also resolve them or rule them out as the problem source.

    "New" installs or new occupancy, with new loads most of all. They usually need to do this very seldom over long years once use has gone routine.

    Premature to start guessing until that has been better documented. Their figures are not rocket-science.

    PS: New facility also means new metering and perhaps new type and "step" on billing plan. Rare that they are easily compared, directly, regardless. Keep that separate from the chasing of possible equipment issues.

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    Your numbers seem reasonable.

    The line currents on a lightly loaded transformer are mostly reactive (KVAR) or watt less power.


    Reality check time:

    $0.15/KWH is only an estimate, Be sure to figure in any demand charges on your electric bill.

    30 day month at 24/7 is 720 hours.

    3400 kWh / 720 = 4.722 KWH draw all the time (ignoring actual usage)

    3400 kwh x $0.15 / kwh = $510.00 per month X 12 = over $6100 per year JUST to keep the transformer warm.

    150 KVA transformers do run warm, even with no load!!

    150 KW transformer drawing a little over 3.1% of rated capacity to stay warm seems appropriate.

    If this transformer is in an air conditioned shop, and being cooled by the A/C the losses are even higher.
    Normally there is an equipment room with large transformers, air compressors etc. that is not air conditioned.

    Hope this helps,
    Bill

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    Quote Originally Posted by hitandmiss View Post
    Reality check time:
    Indeed.


    150 KVA transformers do run warm, even with no load!!

    150 KW transformer drawing a little over 3.1% of rated capacity to stay warm seems appropriate.
    Some are but 2%, but yes.

    Users of such critters should keep in mind "warm" cometh because each cyle, the Iron actually moves.

    Which we all "know" arredy.

    Lotta folk forget that so does the wire move. Within itself. Not just on the bobbin.

    R.E. Uptegraff's explanation of why they offered Elliptical coils, not just rectangular with rounded corners, they showed the math for copper wire being squeezed and released in diameter, lengthening and shortening accordingly. Elliptical was intended to spread the stress with gentler corners, last longer before there was a fail in the coating or fatigue of the wire.

    It ain't MUCH movement. But it goes-on for a loooooong time. "Many" cyles. Really many.

    A stout disconnect, line side of the transformer, and SOP to religiously open it when shift ends is recommended.

    Figure 10 hours by 6 days live vs 24 X7?

    Xfrmr lives longer. Power bill does the expected..

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    transformer sounds like it is just "being a big transformer". If you ae not going to use that much capacity, and it is "your" transformer, you could easily be money ahead to put in a different one and have that one disconnected.

    What makes it worse, is that the "magnetizing current" , which is what is being drawn, is at a horribly low power factor, and the powerco may be charging you extra for that, an adder or multiplier on your bill.

    If you do not need that much capacity, disconnect that, and get one put in that is sized for your needs. You may be able to pay for it with the savings in a fairly short time.

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    I would check your primary voltage tap adjustments. Your input and output line voltages are higher than the nameplate voltages. This will saturate the magnetic core, more than necessary and produce losses in the form of heat and higher magnetizing current.

    Tap #3 is standard for 480V input, your input is listed at 494V in a loaded condition.
    You should check the voltage in an unloaded condition, during the evening hours, when the local grid is less loaded. Voltages will rise higher during times of reduced loading on the local grid. You likely will need to adjust to tap #1 or #2, to reduce the magnetizing current to its lowest value.

    While your in there, check that X4 is connected to a grounding electrode conductor, as required by the NEC.
    Bond it to building steel, or cold water pipe at the water service entrance.

    SAF Ω

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    if you just google "typical iron loss for 150KVA transformer" and open the first pdf from Eaton.

    302 Found

    you will see that a typical 150KW aluminum wound dry transformer:

    Type KT-4 K-Factor 4, 150 °C Rise DOE 2016 Efficient weighs 1237 pounds, 350 no load and 2600 full load losses
    Type KT-4 K-Factor 4, 115 °C Rise DOE 2016 Efficient weighs 1607 pounds, 489 no load and 1376 full load losses

    anyhow, the pdf is 44 pages, i tried to pick a good example, also located a missprint or two.


    anyhow you should be nowhere near 4KW load for a disconnected building with a transformer that size or two.

    the amps you're measuring seem right to me for a 90% inductive load of an unloaded transformer, but i don't have an explanation for the current imbalance.

    you can buy cheap KVA meters off ebay,
    100A AC Digital Power KWh Watt Meter Volt Amp Voltmeter Ammeter Open Close CT 711463667401 | eBay
    or more expensive ones.
    this looks interesting CEM DT3353 Digital 1000A AC 3-Phase Watt Volt Current True RMS Power Clamp Meter | eBay but it only handles balanced 3 phase loads.

    there are a few of these on ebay (i've never seen them before, may be 220vac only)
    NICE TIF MODEL KW-220-3 KILOWATT HOUR METER WATTMETER VOLT AMP DISPLAY | eBay

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    Several commentators here seem to have missed a major item in this line in post #3:
    3400 kWh / 720 = 4.722 KWH draw all the time (ignoring actual usage)

    "Ignoring actual usage" Meaning the calculations will be some unknown amount higher than actual.

    With as a qualifier, actual numbers for your transformer losses will be a bit lower than these calculations.

    If this is used to power several smaller machines in addition to the office etc. several smaller units of suitable size that are
    turned off when not in use, and a suitable sized one for things that are powered up all the time may be very cost effective.

    Bill

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    Average phase current is 9.3A from the provided numbers. 9.3 x 480 = 4464 VA, 4464 x 1.73 for 3 phase gives 7722 VA total. Presumably the average is actually a bit lower current than 9.3A, so the VA is closer to the 4464 VA.

    4.46kVA x 720 hours = 3211kVAH for the month. Close.

    This has come up before, when a transformer of decent size (IIRC the last one was 500kVA) is left powered and there is no load on it. It runs to money especially if there is a low power factor penalty.

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    Thank you all for the help. They sent out another electrician yesterday to do some measurements. The electrician is going to call the transformer manufacture and see what the transformer losses should be. I might have to look into buying or renting a power analyzer.

    We are considering going with a smaller transformer or putting a disconnect on the larger transformer and running small transformer for the lights and office.

    Meanwhile I will check what the voltage tap is set at on the primary and measure the 480V line voltage during the off hours. Setting it for a higher voltage should reduce the losses.

    I will post with what we come up with.

    Thanks again.

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    Update: The landlord tells me that the electrician contacted GE and was told that our transformer has been revised several times since installation. They claim that their new transformer will only draw 1.5A VS the 8A we are drawing now. The landlord wouldn't tell me if the 8A was normal. However he did say he would split the $3000-4000 cost of installing a new transformer. Does anyone know the contact number for GE technical support? I am still not sure if the transformer is defective or the landlord is trying to get me to chip in for a repair. I have a hard time believing transformer technology has improved 5 fold in 20 years.

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    Quote Originally Posted by Richie V6 View Post
    I have a hard time believing transformer technology has improved 5 fold in 20 years.
    It has not, but... for a hundred-plus years, no one had to make many changes. Then Copper went serious-dear, Aluminium was improved, energy went more costly, and Hoovermints mandated higher efficiencies by fiat.

    Your 20-year-old transformer as to date of winding may be a great deal older as to DESIGN. Nor is a new one a FIVE fold improvement, overall, even if the cited figures are correct. They may not be. There are trade-offs.

    You don't need a contact person. Specifications are published by transformer model line and SKU. It's the utility company that needs those.

    All that said, at the end of the day, the offer from the landlord seems reasonable as such things go.

    Speaking now not as a machinist, but rather as a person who has had energy and facilities management responsibility more than one company, more than 20 years, many US states, more than one foreign country, usually over a dozen buildings at a time.

    I'd grab it. It should have a sub one-year payback, your share, and stay beneficial going forward, both as to energy savings, and "cooperative tenant" credentials with the landlord.

    Either of you or the landlord goes spring-loaded into the cranky position, the price of a transformer will turn out really small beer in due course.

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    Quote Originally Posted by thermite View Post
    It has not, but... for a hundred-plus years, no one had to make many changes. Then Copper went serious-dear, Aluminium was improved, energy went more costly, and Hoovermints mandated higher efficiencies by fiat.

    Your 20-year-old transformer as to date of winding may be a great deal older as to DESIGN. Nor is a new one a FIVE fold improvement, overall, even if the cited figures are correct. They may not be. There are trade-offs.

    You don't need a contact person. Specifications are published by transformer model line and SKU. It's the utility company that needs those.

    All that said, at the end of the day, the offer from the landlord seems reasonable as such things go.

    Speaking now not as a machinist, but rather as a person who has had energy and facilities management responsibility more than one company, more than 20 years, many US states, more than one foreign country, usually over a dozen buildings at a time.

    I'd grab it. It should have a sub one-year payback, your share, and stay beneficial going forward, both as to energy savings, and "cooperative tenant" credentials with the landlord.

    Either of you or the landlord goes spring-loaded into the cranky position, the price of a transformer will turn out really small beer in due course.

    Thank you for advice. I think I will take him up on the offer. Just have to save up some funds. Turns out moves are expensive.

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    Quote Originally Posted by Richie V6 View Post
    Thank you for advice. I think I will take him up on the offer. Just have to save up some funds. Turns out moves are expensive.
    Sooner it gets done, ONCE, sooner the recurring bill drops. And stays down. So you know the money is coming.

    It needs to be done soon. or the waste is gone forever.

    Enjoyed a training course on commercial building lighting management, long time ago. Applied that, plus other stuff, saved my employer twice my then-salary year one. Earned a nice raise. Plus - we had genuine profit-sharing.

    A very friendly and helpful classmate I exchanged a lot of notes and thoughts with had to have done better yet.

    I was responsible for eighteen retail stores and a central warehouse. As an "additional duty".

    He.... was full-time Facilities Manager for a larger retailer.

    Direct report to a guy named "Sam Walton".

    Sometimes one learns more USEFUL stuff from the other students than from the "professors.."

    Be that at GE, Nela Park, Ohio.

    Or "right here, on PM".

    The usual catch applies. Advice of any kind is irrelevant.... if it is not actioned.



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