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Join Date: Feb 2017
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Remaining Transformer Capacity

02/13/2017 7:03 PM

I was hired in 2011 as a extra set of hands in maintenance for a film company. Just last week I was given the maintenance manager position (trust me, it didn't come easy...I busted my butt!!!). We have recently had an expansion and we have 2 new 2500 kva transformers and was asked to do a utility and equipment information update. How do I know what current % load is? I'm sure I may be over thinking like I always do. Is it simply checking the max load at each breaker on the switchgear and totaling them? It's currently running 6084 kwh. I know that's no help but I was like dayum!! our company power bill is over 350,000 a month we have 6 of these transformers.

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Pathfinder Tags: Transformer. Percent load
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#1

Re: Remaining transformer capacity

02/13/2017 7:33 PM

It looks as though you are confusing kw and kwh.

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#2

Re: Remaining transformer capacity

02/13/2017 7:45 PM

If your current power bill is "over 350,000 a month" and those are dollars, call your power company and have them send someone out to help you.

Two more xformers means another 120,000 a month, they will be glad to help you.

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#4
In reply to #2

Re: Remaining transformer capacity

02/13/2017 8:08 PM

No I was just stating what our usage was, not to be confused with the possibility of my thought process. We have tons of heaters, I was throwing that info in as a wow factor. We also run 24/7 365.

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#3

Re: Remaining transformer capacity

02/13/2017 7:58 PM

It's currently running 6084 kwh.

Did you mean "6084 kw"? Kilowatt is power, "kwh" is kilowatt hours and is energy = power x time. (1 kwh is 1 kilowatt for 1 hour.)

Power is measured in kilowatts but transformers are rated in kva (1000 x volts x amps). The load is kilowatts will, in general, be less than kva, due to the characteristics of the load. The ratio is called power factor (power factor = kilowatts/kva), and you will need to know the power factor to convert between kva and kilowatts.

https://en.wikipedia.org/wiki/Power_factor

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#5
In reply to #3

Re: Remaining transformer capacity

02/13/2017 8:14 PM

Kw per hour

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#6
In reply to #5

Re: Remaining transformer capacity

02/13/2017 8:29 PM

There is no such unit, not in meaningful use, anyway.

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#7
In reply to #5

Re: Remaining transformer capacity

02/13/2017 8:42 PM

kilowatt•hours, not kilowatts/hour.

Kilowatts, or more fundamentally, watts, are a measure of rate of energy flow. Alternatively, one watt is one Joule per second. A rate.

Think of kilowatts as velocity. Velocity * time = distance. Kilowatts * time = energy. Energy is what you're billed for.

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#8

Re: Remaining Transformer Capacity

02/13/2017 8:57 PM

I hear my mother calling.

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#9

Re: Remaining Transformer Capacity

02/13/2017 9:12 PM

Best to get the power company involved like Lyn said. You need to measure the peak currents rather than the kWh as this will only give you an average power usage (kw over a period of time) not peak power usage. Using only the kWh reading off the meter could easily result in overestimating available capacity.

The power company will have the gear to properly, accurately and safely check this.

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#10

Re: Remaining Transformer Capacity

02/13/2017 9:26 PM

It sounds like they just want the information on the new transformers.....

Like capacity, location, company who installed and will service the equipment, serial number etc....I would just take a picture of the id plate and what section it serves and paint a big number on the sides of the transformers...unless they gave you a form to fill out....

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#11
In reply to #10

Re: Remaining Transformer Capacity

02/13/2017 9:48 PM

Thanks for a legitimate answer, it's clear to see most people want to ride around on there high horse and correct inexperience instead of actually helping! I have the nameplate information and took all the data from each breaker on the switchgear and sent it over to one of ourepairs many corporate engineers, sheeshe who knew trying to ask for help would make you feel like a fat kid on an elementary playground. Grow up guys! SOLAR EAGLE, THANKS AGAIN!!!

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#12
In reply to #11

Re: Remaining Transformer Capacity

02/13/2017 10:07 PM

Not everyone. Don't throw the baby out with the bathwater. There's a saying: "Ask an engineer the time and he'll tell you how to build a watch."

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#14
In reply to #11

Re: Remaining Transformer Capacity

02/13/2017 10:31 PM

I was hired in 2011 as a extra set of hands in maintenance for a film company. Just last week I was given the maintenance manager position

Please bare in mind that from the little you have said about yourself you could very well be totally unqualified to do the job.

We have many people asking questions here on CR4 that have turned out to be dangerously unqualified to do the work they are asking questions for. We have to be careful what we say because as Engineers we have an ethical responsibility about what information we give out least we cause more harm than good.

Transformer and breaker capacity will only give you a vague idea of the load. Performing a proper load profile study is important, especially with large 24/7 loads like yours.

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#15
In reply to #11

Re: Remaining Transformer Capacity

02/13/2017 10:44 PM

I believe that every response that you got here was an effort to help you.

The fact that you took offense does not speak well for you.

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#16
In reply to #11

Re: Remaining Transformer Capacity

02/13/2017 11:37 PM

No problem....I don't think these guys understood the question, we usually get technical questions that deserve scrutiny, don't be discouraged....You can learn a lot here, but you have to be able to take it on the chin....there are a lot of very smart knowledgeable people willing to help you for nothing more than a thank you....

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#17
In reply to #11

Re: Remaining Transformer Capacity

02/13/2017 11:42 PM

If you need the assistance from the forum to give you some general idea how to go about calculating these power and loading, you need to let us know more details. All the answer that posted in here may not be 100% correct as each of us have different idea and method but then again, these answer in this forum are just some references for you to understand and to apply to it. For example,

"In your question that you had an expansion and you have 2 new 2500 kva transformers and was asked to do a utility and equipment information update. How do I know what current % load is?"

So in this case we dont know whether if you want us to calculate the total current that the 2500kvA transformer can provide or maybe you want to know whether the 2500kvA transformer is enough to cater for your expansion project?

Sometime, some OP just give us a very simple sentence and let us do all the guessing works. Like there is one OP asking us to provide a PCB layout by just showing an IC. See what I mean.

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#20
In reply to #10

Re: Remaining Transformer Capacity

02/15/2017 6:46 AM

Looking at the Howard Industries transformer nameplate (see post number 10 SolarEagle).

The capacity of the transformer is P = I x U X sqrt (3)

P = 76.74 x 18810 x 1.73 = 2497 kVA

This is in conformity with the 2500 KVA as indicated on the nameplate.

-

When I suppose the efficiency of the transformer is 100% and the nominal current at the low voltage side equals to 480A (low voltage in Wye as indicated on the name plate and according to the connection diagram).

Then the nominal voltage at the low voltage side equals to U = P / (I x sqrt(3))

U = 2500/1.73x480 = 3.0kV

Which seems correct to me.

-

-

But what is the meaning of the 277 A ?

The ratio 480/277 equals to sqrt(3) which gives me the idea that this transformer can be wye/delta connected, but this is in contradiction with the connection diagram (only 3 + N leads are accessible) and the delta current must be higher than the wye current.

-

What is the meaning of the HV 125 LV 30 kV ?

When the high voltage side is made for 125kV this is in contradiction with the different taps-voltages (18810 – 21780V)

When the low voltage side is made for 30kV then the current in the low voltage side (in Wye) would be only 48A. This is in contradiction with the 480Y and 277A on the transformer nameplate.

Who can guide me ?

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#21
In reply to #20

Re: Remaining Transformer Capacity

02/23/2017 7:49 AM

Just to help, rudy.leurs.

The first line on rating plate gives kVA rating and BIL [Basic Insulation Level] - that's the 125 kV HV and 30 kV LV - it is what impulse voltage level the insulation can withstand when lightning or switching surges occur.

The second line gives HV & LV voltages line to line / line to junction point of the three phase windings, the usual √3:1 for 3 phase, e.g. 480/277. If you look at bottom right, you see a vector diagram which shows the HV - LV as Y-Y also called star-star connection. Note that GRDY following voltage means "grounded Y" meaning star point must be grounded, Y means Y winding but it can be without earth. The final item is "Amps 3005" - you assumed units letters followed number along line but if you look at whole diagram it starts "kVA 2500" & puts rating definition before number, left to right.

480/277 is 3 phase line-line/line-common voltage normally used in USA, often without ground connection for 3 wire supply to motors and other large loads.

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#13

Re: Remaining Transformer Capacity

02/13/2017 10:19 PM

It is not easy job but do you have any information of all the equipment for the expansion projects? I presume that you want to know how much the these 2500kvA transformer can supply the power to these equipment’s.

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#18

Re: Remaining Transformer Capacity

02/13/2017 11:52 PM

If the 6 transformers are all identical, you have 15,000 kva total capacity. If all the loads are resistive, the power factor would be 1.00, and you would have 15,000 kw capacity also. If many of the loads are inductive, the power factor could be 0.80, in which case you would have 12,000 kw capacity. If your 6084 number is actually kw instead of kwh, you are loaded only to about 40-50% of capacity.

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#19

Re: Remaining Transformer Capacity

02/14/2017 1:33 AM

If it is no fixed charge and you pay 0.08 $/kWh then 6086 kWh it is the measured in an hour.

So your demand is 6086 kW.

This is an average demand. What do you need is the maximum consumed.

Then you have to measure the kWh each hour in a day and pick the maximum up.[It has to be measured in a most charged day].

Now you need the kVA [the kWh per hour when the power factor is 1 [maximum].

Let's say the power factor is 0.9 [no penalty charge] then the kVA will be 6086/0.9=7600 kVA.

If all 6 transformers are equally loaded then 7600/6=1270 kVA from each one.

If you can read what is written on name plate as "kVA" compare with the consumed.[Since it is a dangerous action to be close to a transformer, a licensed electrician has to do it].

If 1270 kVA is the maximum demand and on name plate is 1500 kVA then you have 1500-1270=230 kVA reserve-230*0.9=207kW [or kWh/hour] on each transformer.

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Users who posted comments:

67model (1); 7anoter4 (1); Andrew Westman (2); jack of all trades (2); josh9999 (3); lyn (3); Rixter (1); rudy.leurs (1); Simon Wan (2); SolarEagle (2); Tornado (3)

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