Does it seem right a 10 Kva transformer draws 1.5A static?

[Paperman]

Been tracking my electric use over the last month. With nothing being used it was showIng a 12 KWh/day usage. So I pulled out the fluke and with the breaker panel off the 10kva transformer is pulling between 1.5-1.6A. It cost about $65 to keep that transformer warm. Economics say I should get a single phase service installed.

 

[LXCam]

What are you using it for? Yes transformers have a no load loss, but that seems really high for such a small amount of core material in hysteresis loss. You're not using it as a step up transformer are you?

And please explain what you mean with your last sentence.

 

[Bert_]

Keep in mind that the 1.5A you measured is apparent power. That number does not directly relate to watts.

It would also be helpful to know the voltage that the transformer is operating on. 1.5A at 120V is very different from 1.5A at 480V

 

[Paperman]

Sorry for the lack of information. This is a step down transformer. Taking 2 legs of my 480D service down to 240 single phase for the shops lighting. Its an old GE finned aluminum American made transformer. It has served as only lighting loads and 2 outlets for the last 30 years.

I just purchased this building and have been tracking the power usage. It seemed high for the amount of time I have been working in there. So I grabbed my Fluke T5 and checked the legs going to the transformer with all the breakers off in the lighting panel. It was bouncing between 1.5-1.6A. If that is what I can expect for a draw it makes economic sense to install another single phase service. There is already 4 single phase services here, one for each retail shop that is on the road frontage of the property. It cost over $2/day to keep the transformer on and less than 1/2 to pay the standard monthly service fee.

View media item 75272

 

[American Locomotive]

If it was truly drawing 700 watts with no load, it should feel pretty hot even after sitting all night.

Are you billed based on power factor?

 

[sberry]

Something is wrong with the math. 1.5 would be 2 kwhr a day. But the reading is not valid because its a transformer. To get 65$ it would take 120 hrs vs 12? There is a base fee anyway for service. Even on single its probably 20 a month. But 12kwhr isn't much, a dollar or 2 for usage. Something is fuzzy with the math here.

 

[Paperman]

Using round numbers 1.5ax480v=720w=.72kw. .72x24=17.28Kwh per day. .13 per KWh is about $2.25 per day 30 days is $67.50 per month. I can get a single phase service for less each month and have more capacity. With a new 15Kva transformer I only have 60ish amps of current available. Enough but more is always better right!!

I agree it should be warm, is have to do the fat guy shimmy up a ladder and give it a feel. I do not understand the power factor question. PF has never been mentioned in my talks with the POCO.

 

[sberry]

Ok, the 12 kwh is usage rate and not total? The poco has a 15K ****** on mine, 400 service.

 

[Paperman]

Yep 12kwh per day. If this is typical for a trans. I need to get a new service installed. We have dozens of these lighting transformers at work and my assumption has always been they are rather efficient in doing what they do. I never really considered the excitation current draw when looking at them. But now that that cost comes out of my pocket it becomes more important.

 

[sberry]

How much power are you using for 65 dollars and is it not standing service for other machinery8 you are contemplating using? You could buy big welder, motor, air comp on the cheap. A couple dollars a day, cost of a telephone service and half a cup of designer coffee or a bottle of water you got power.
I might even be tempted to take advantage of that in some form of value added service or equipment. We don't even know what the plans for all this is?

 

[American Locomotive]

PF has never been mentioned in my talks with the POCO.

So when dealing with alternating current, there are three types of "power": "real", "reactive", and "apparent". The combination of "reactive" power and "real" power is called "apparent" power. The ratio between real/reactive is called your power factor. A power factor of 0 is a purely reactive load, and a power factor of 1 is a completely "real" load.

Real power is straight forward. It's any power actually consumed by the device - either turned into something useful (like light or motion), or wasted as heat. An incandescent light bulb has a power factor of 1, as it has no appreciable inductance/capacitance, and all the current it consumes does something.

"reactive" power is more complicated. To simplify it: Things like capacitors and inductors (an unloaded transformer is basically a big inductor) rapidly "store" and "release" energy when connected to alternating current power. So while there is current flowing through the wires feeding the device, the device isn't "consuming" any power. It's just putting all the current right back into the grid - 60 times a second. That is called reactive power.

What gets even more complicated, is that residential and many small commercial properties are almost always only billed based on the "real" power they consume. However, many large commercial and industrial facilities are billed based on their power factor and apparent power. This is because if you have a large facility with really bad power factor, the current you're "releasing" back into the grid can cause significant load on the power lines. So while your giant machine may only be using 2KW of "real" power, to the power grid it might as well be using 6KW, because it's consuming/returning so much current.

Things like transformers and induction motors work best when they're fully loaded. When partially loaded or unloaded, they're almost purely reactive loads with really bad power factor. So even though they may not be using much "real" power doing nothing, to your power company they are a significant load.

Since you have 3 phase, there's a good chance you're being billed based on "apparent power", in which case having a transformer sitting around doing nothing most of the time will cost you money.

 

[Paperman]

How much power are you using for 65 dollars and is it not standing service for other machinery8 you are contemplating using? You could buy big welder, motor, air comp on the cheap. A couple dollars a day, cost of a telephone service and half a cup of designer coffee or a bottle of water you got power.
I might even be tempted to take advantage of that in some form of value added service or equipment. We don't even know what the plans for all this is?

The $65 in question here is in essence doing me nothing other than getting my 480 down to 240/120.

Yes the 480 is here for the other large machines but I also need single phase for everyday items. The trans. was already installed and we use them by the dozen at my work so I figured it would be the best way to go. I pay a flat $30 to have the 480D service plus actual usage, I figured if the trans. used 100w to stay alive I'm not spending another $30 monthly fee for a second single phase service. But now that I have actual usage that is more inline with $60+ each month for the trans. to stay warm it makes more economical sense to just pay the extra fee to the POCO for their single phase meter.

That was why I came here asking if the usage is inline with what a dormant transformer should draw or is my 30+ yr. old unit sucking more than its fair share. I can get a 15Kva Square D trans. that covers my needs but if it takes the same 1.5A load to keep it warm I'm going backwards. I was hoping the brain trust here would tell me a standard trans. takes 1% FLA at idle.

So in the end 30+65=$95 for the 480D service and the 240V/60A transformer or 30+30= $60 for the 480D service and a 200A 240V service. I can spend that $400 a year on better things than a warm block of iron and copper.

American Loco. Thanks for the lesson. There are 2 CT's on the incoming line running to the meter, I'll have to look over the bill to see if they make mention of how its calculated.

 

[rlitman]

...Since you have 3 phase, there's a good chance you're being billed based on "apparent power", in which case having a transformer sitting around doing nothing most of the time will cost you money.

To me, it sounds like a typical commercial secondary service. I've never heard of them being billed on apparent power. That's something usually reserved for a primary service.

...I can get a 15Kva Square D trans. that covers my needs but if it takes the same 1.5A load to keep it warm I'm going backwards...

Different transformers come in different energy efficiency classes. You get what you pay for.

 

[Paperman]

Different transformers come in different energy efficiency classes. You get what you pay for.

It was free, came with an expensive wrapper

 

[sberry]

Seems to me that if we pay 35 a month for one meter and we add another one with a base fee of at least 20 if they will do it then we are looking for 10 or 15$ a month juice in it? I may be looking at this wrong?

 

[sberry]

This is a pretty significant building, the savings and the power expense here are but a minor piece of the pie at this point I would think. If it was 800 a month vs 800 a year then saving 400 per would be significant and worth investment in another layer of equipment.

 

[Bert_]

If the transformer is really not supplying anything while your not there, then perhaps you could just shut it off when it's not needed.

 

[walta]

Check with your service provider. It is my understanding most commercial accounts are billed not for the actual power used like residential meters. But the meter records the peak wattage and that is billed 24/7 for that billing period with an up charge if the power factor is not zero. So you need to find ways to lower your peak as the valleys are irrelevant.


Walta

 

[Matt Matt]

My 6KVA draws between .7 to .8 A. My 15KVA draws between 1.5 to 1.8A. I have both mine on disconnects. I never leave them hot all the time.

If my memory serves me correct, 10 kVA single phase transformer can be hooked up to 20 A at 480 V. It has an output of 41 1/2 A 240 single phase. If you are fused before the transformer, You could use a contactor relay to turn on the transformer. But I would suggest using 3 wire control for outages. It is generally not advised to start a transformer and load at the same time. A transformer can draw up to six times it’s idle amps in start up. Additional load can trip fusing.

I have done some jobs that have a three wire control console for lighting at each door of the shop, and one lighting switch that goes back to a main contactor lighting switch. This is was done to not overload metal hilide lightbulbs in short term outages.

This one contactor controlled 5 rows of 6 metal hilide 100 W lightbulbs.

 

[Matt Matt]

So when dealing with alternating current, there are three types of "power": "real", "reactive", and "apparent". The combination of "reactive" power and "real" power is called "apparent" power. The ratio between real/reactive is called your power factor. A power factor of 0 is a purely reactive load, and a power factor of 1 is a completely "real" load.

Real power is straight forward. It's any power actually consumed by the device - either turned into something useful (like light or motion), or wasted as heat. An incandescent light bulb has a power factor of 1, as it has no appreciable inductance/capacitance, and all the current it consumes does something.

"reactive" power is more complicated. To simplify it: Things like capacitors and inductors (an unloaded transformer is basically a big inductor) rapidly "store" and "release" energy when connected to alternating current power. So while there is current flowing through the wires feeding the device, the device isn't "consuming" any power. It's just putting all the current right back into the grid - 60 times a second. That is called reactive power.

What gets even more complicated, is that residential and many small commercial properties are almost always only billed based on the "real" power they consume. However, many large commercial and industrial facilities are billed based on their power factor and apparent power. This is because if you have a large facility with really bad power factor, the current you're "releasing" back into the grid can cause significant load on the power lines. So while your giant machine may only be using 2KW of "real" power, to the power grid it might as well be using 6KW, because it's consuming/returning so much current.

Things like transformers and induction motors work best when they're fully loaded. When partially loaded or unloaded, they're almost purely reactive loads with really bad power factor. So even though they may not be using much "real" power doing nothing, to your power company they are a significant load.

Since you have 3 phase, there's a good chance you're being billed based on "apparent power", in which case having a transformer sitting around doing nothing most of the time will cost you money.

This is brilliantly said. The only thing I can add is,... how are you billed? as most often there is for three phase service, there is a delivery and usage premium.

Off-topic, but in mid August 2003 I almost worked for almost two days straight because there wasn’t enough reactive power on the system. In some places it lasted three days. It was one of the biggest black outs I’ve ever seen. The 8 hours Per day I had off brought neighbours closer together. Candles on front porches and Coleman lanterns in driveways with lawn chairs and a few generators humming in the background.

Besides actually having to work more, I think it would be cool shut down electricity occasionally now and then and make everybody camp in their own house. It’s funny how there was a small baby boom in May 2004, In the affected areas,lol.

 

[Paperman]

If the transformer is really not supplying anything while your not there, then perhaps you could just shut it off when it's not needed.

I use the single phase for normal stuff. Part of that is the security system, garage door openers and the emergency/exit signs that need to be active 24/7. This building is billed as small commercial not industrial so I am billed by usage. One fee for having the service and another for actual KwH consumed.

 

[American Locomotive]

When you did your current draw test, did you disconnect all the signs and security system?

 

[Lightman]

[/QUOTE]American Loco. Thanks for the lesson. There are 2 CT's on the incoming line running to the meter, I'll have to look over the bill to see if they make mention of how its calculated.[/QUOTE]

Had simular situation at job while working. Idea to downsize the step down for the devices that require 24/7 power and a larger stepdown for equipment that is used working hours only, (timer? manual switched relay control for larger stepdown). this may be cheaper than new entrance, if they allow two diffrent services to same building.???


Used to work at a Power co., is the service three wire or four wire? two 480 volt to between all phases the 0 to ground on one of the legs? or two CT with one having two wires and a seperate neutral, four wire service to building?

Quick story, found a asphalt plant with 480 volt delta, 1500KVA, ungrounded from power company side, metered for grounded leg, customer grounded the leg with one of the CT's, after metering corrected business went out of business. was only paying for 1/3 of power usage.

Also saw a large plant that had ungrounded 4 wire 480D v. service, indicator light to each phase, when one light went out that phase had developed a ground meaning to be service at next scheduled outage, if second phase develped a ground then this is fault causing outage or a breaker trip. Probally not to code now, old stuff.

 

[Paperman]

Yes all single phase breakers were switched off.

On service I will have to say its a 3 wire. No neutral coming in with the 3 large conductors. They do have them paralleled, two conductors for each leg but I do not see any others coming in. Pics would help, let me work on that.

 

[Paperman]

Here are a few pics of what I have. Still in demo/clean phase so excuse the mess.

Trans. and single phase panel.

View media item 75399
1200A 480D panel with feeder for above Trans.

View media item 75401
View media item 75402
Incoming 480D at right, single phase for retail stores to left. CT's for 480 as well.

View media item 75403
480V meter.

View media item 75410

3Phase at the pole.

View media item 75407
Another view of the pole.

View media item 75409

 

[wyliesdiesels]

If theres only 2 CTs then you have corner grounded delta.

Theoretically, you could wire a load between the grounded leg and ground and get free power.

 

[Lightman]

Here are a few pics of what I have. Still in demo/clean phase so excuse the mess.

Trans. and single phase panel.

View media item 75399
1200A 480D panel with feeder for above Trans.

View media item 75401
View media item 75402
Incoming 480D at right, single phase for retail stores to left. CT's for 480 as well.

View media item 75403
480V meter.

View media item 75410

3Phase at the pole.

View media item 75407
Another view of the pole.

View media item 75409

The fouth cutut is a solid blade, this is connected to the "center point" or ground of the high side "Y" connection. only closed when closeing or opening the three other primary fuses. when this is not allowed to float, when connected to ground you may get either a back feed out of the bank to other connected transformers, up and down the line, burning out other transformers in this bank or ferroresonance of the bank with extemely high voltage if other incomming phase goes down up line or a fuse opens. Always float the center of the "y" on " Y - Delta " banks.

 

[wyliesdiesels]

The fouth cutut is a solid blade, this is connected to the "center point" or ground of the high side "Y" connection. only closed when closeing or opening the three other primary fuses. when this is not allowed to float, when connected to ground you may get either a back feed out of the bank to other connected transformers, up and down the line, burning out other transformers in this bank or ferroresonance of the bank with extemely high voltage if other incomming phase goes down up line or a fuse opens. Always float the center of the "y" on " Y - Delta " banks.

How could you tell that its Y on the high side?

 

[Lightman]

How could you tell that its Y on the high side?

Convential two bushing high side, only one phase connected to each H1 of each transformer, H2 bushing tied together , with temp cutout for switching, to temp ground center of high side Y.

If delta connection each phase would commect to H1 and H2 of each transformer. making it Delta - Delta.


Delta - Y in all of out 69KV to 14400/25KV substations.

Most all standard padmount ground mount transformer were Y-Y, 120/208, or 277/480 four wire services.

Most distrubition line construction is four wire, Y connection to make sure there is a solid ground fault current to operate breakers and fuses, (neutral is grounded each pole and service point), if something touches the phases. delta connnection, fault to ground is less. saw much delta inside of plants to reduce the ground fault currents and save a neutral wire.

 

[Paperman]

WOOOOH, that's some info that going to take some time and pencil to digest. Thank you.

I'm a bit lost, this is not my profession as I like to see the things I work with and I cant see electrons!!!

There is a y Delta? So there are 3 different connections available in 480v?

 

[wyliesdiesels]

WOOOOH, that's some info that going to take some time and pencil to digest. Thank you.

I'm a bit lost, this is not my profession as I like to see the things I work with and I cant see electrons!!!

There is a y Delta? So there are 3 different connections available in 480v?

Yes there is 3 different types of 480v 3 phase.

480Y/277
480D corner grounded
480D ungrounded

The last one is very rare on line side of meter. But still common as a seperately derived system for plants with critical operations where a power loss due to ground fault would be costly such as food manufacturing. On these ungrounded deltas there is an indicator panel to alert maintenance personnel of a ground fault.

At the service panel, there is a bank of 3 lights wired in wye. All bulbs are at the same brightness when there is no fault. Upon a leg going to ground, the corresponding bulb will go out and the other 2 will be brighter.

Corner grounded delta came out as a way to save on wire, CTs, cut-outs, and breaker costs as well as a way to ground an otherwise ungrounded service. Since one phase leg is grounded, only 2 CTs and 2 pole breakers are needed. On primaries that are corner grounded delta(rare) only 2 cut-outs are needed.

Since you have corner grounded delta, code REQUIRES that the grounded leg NOT have fuses or breakers protecting it UNLESS all phase legs are disconnected simultaneously.

Also, the grounded leg is to be colored the same as a neutral even though it is NOT a neutral.

And only breakers listed for corner grounded delta can be used. This means they have a straight rating (240v or 480v) rather than a slash rating(120/240 or 277/480) because line to ground faults are the same voltage as line to line faults.

Be careful when working on that service. It can be deadly to an uninformed person.

 

[wyliesdiesels]

Convential two bushing high side, only one phase connected to each H1 of each transformer, H2 bushing tied together , with temp cutout for switching, to temp ground center of high side Y.

If delta connection each phase would commect to H1 and H2 of each transformer. making it Delta - Delta.


Delta - Y in all of out 69KV to 14400/25KV substations.

Most all standard padmount ground mount transformer were Y-Y, 120/208, or 277/480 four wire services.

Most distrubition line construction is four wire, Y connection to make sure there is a solid ground fault current to operate breakers and fuses, (neutral is grounded each pole and service point), if something touches the phases. delta connnection, fault to ground is less. saw much delta inside of plants to reduce the ground fault currents and save a neutral wire.

Yeah i shouldve phrased my wuestion differently.

I know how the primary hookups vary between wye and delta.

What i meant was, how can you see the hookups? Im having a hard time seeing it. Maybe its just because Im on a phone.

 

[Lightman]

Yeah i shouldve phrased my wuestion differently.

I know how the primary hookups vary between wye and delta.

What i meant was, how can you see the hookups? Im having a hard time seeing it. Maybe its just because Im on a phone.

No need for the fourth cutout if Delta high side, Delta or Y secondary.

And only need fourth switch on Y - Delta connection.

Y-Y always grounded, no fourth switch

Also fourth 480V service ,, open Y-open Delta using two transformers, 240/480 four wire with wild leg, and corner grounded three wire service.

 

[Paperman]

Yes there is 3 different types of 480v 3 phase.

480Y/277
480D corner grounded
480D ungrounded

The last one is very rare on line side of meter. But still common as a seperately derived system for plants with critical operations where a power loss due to ground fault would be costly such as food manufacturing. On these ungrounded deltas there is an indicator panel to alert maintenance personnel of a ground fault.

At the service panel, there is a bank of 3 lights wired in wye. All bulbs are at the same brightness when there is no fault. Upon a leg going to ground, the corresponding bulb will go out and the other 2 will be brighter.

Corner grounded delta came out as a way to save on wire, CTs, cut-outs, and breaker costs as well as a way to ground an otherwise ungrounded service. Since one phase leg is grounded, only 2 CTs and 2 pole breakers are needed. On primaries that are corner grounded delta(rare) only 2 cut-outs are needed.

Since you have corner grounded delta, code REQUIRES that the grounded leg NOT have fuses or breakers protecting it UNLESS all phase legs are disconnected simultaneously.

Also, the grounded leg is to be colored the same as a neutral even though it is NOT a neutral.

And only breakers listed for corner grounded delta can be used. This means they have a straight rating (240v or 480v) rather than a slash rating(120/240 or 277/480) because line to ground faults are the same voltage as line to line faults.

Be careful when working on that service. It can be deadly to an uninformed person.

So can the POCO reconfigure the service with the equipment they have hanging? I ask as this service/set of transformers also feed the building next door. That building is currently empty and owned by the bank, for sale. Now would’ve the time if it’s possible.

 

[wyliesdiesels]

No need for the fourth cutout if Delta high side, Delta or Y secondary.

And only need fourth switch on Y - Delta connection.

Y-Y always grounded, no fourth switch

Also fourth 480V service, open Y-open Delta using two transformers, 240/480 four wire with wild leg, and corner grounded three wire service.

Never seen an open Y.

And why would it be 4-wire delta?

Cant use the 416v wild leg line to neutral for anything.

So can the POCO reconfigure the service with the equipment they have hanging? I ask as this service/set of transformers also feed the building next door. That building is currently empty and owned by the bank, for sale. Now would’ve the time if it’s possible.

Reconfigure it to what?

 

[Lightman]

Never seen an open Y.

And why would it be 4-wire delta?

Cant use the 416v wild leg line to neutral for anything.



Reconfigure it to what?

Wyliediesel, you are right open y delta can be either three or four wire service, depends on customer if he has two or three pole breakers and equipment?, I guess. I have built both per customer request and work order????

Have used the the open Y-Delta when there are only two phase line close to service or there is mixed services area ( think residential area, someone puts in small back yard shop with one or two three phase devices) only have to add second transformer to pole and pull Four wire service to shop, rest of single phase services stay same. 240/480 only used small, remote lift stations or small irrigation location only require two phase and two transformers.

Other good thing about Y- Delta banks, in a pinch on the loss of one transformer, bad transformer can be disconnected and remaining two can be put back in service at slightly reduced loading, till perm replacemnt.

 

[Paperman]

Thank you guys for the insight into the workings of 480. I work on the mechanical side of a papermill and we use LOTS of 480D ungrounded and a fair amount of 4160 on most things above 250HP. We have ground fault indication on all of the MCC's and main bus distribution gear.

When I asked about reconfiguring I was asking if it could be go from corner grounded to ungrounded. Seems the corner ground is the oddball that is not very standard which makes getting the proper gear to hand it harder. While I'm far from poor I'm on a commercial or industrial operation so cost is a factor and I am buying most of my gear on the secondary market as either used or old stock.

On a corner grounded 480D would I see 480v P-P and P-G on all 3 legs? My head says on leg should not have any voltage potential to ground if it is already grounded at the pole. Ive tried calling the POCO to get a person out to explain what exactly this service is but that has gone nowhere. All/most of the sparkys here have only worked here and know what we do and what we have, they haven't been out and around.

Again thanks for holding my hand RK

 

[wyliesdiesels]

Yes a corner grounded delta can be changed to ungrounded.

But you need to put it in ground fault monitoring and PoCo would need to come out, remove grounding, add a CT. You would also need to recolor the grounded leg from white or gray and remove the bonding on your end.

Just out of curiosity, why would you want to convert it?

The voltage measurements on corner grounded delta are 480v line to line and 480v line to ground on 2 phases. The ground phase will have no potential to ground because it is bonded to ground.

Wyliediesel, you are right open y delta can be either three or four wire service, depends on customer if he has two or three pole breakers and equipment?, I guess. I have built both per customer request and work order????

Have used the the open Y-Delta when there are only two phase line close to service or there is mixed services area ( think residential area, someone puts in small back yard shop with one or two three phase devices) only have to add second transformer to pole and pull Four wire service to shop, rest of single phase services stay same. 240/480 only used small, remote lift stations or small irrigation location only require two phase and two transformers.

Other good thing about Y- Delta banks, in a pinch on the loss of one transformer, bad transformer can be disconnected and remaining two can be put back in service at slightly reduced loading, till perm replacemnt.

Ok and what would someone do with the neutral? Im not seeing the purpose of running the neutral on a 480D. 240v loads line to neutral?

 

[Lightman]

The neutral? 480 corner ground has two pole breaker, ground and neutral tied to one phase, (breaker not to break Grounded phase) four wire would be 240/480 four wire. 240 volt stuff connected to phase to ground two phases , wild leg for three phase stuff, three pole breaker.

More common to use 277/480 four wire, more common equipment. Light ballast, exit lights and such. Haven't see much 240V equipment. (240V would probally work at 277V +- 10%)

 

[Paperman]

Just out of curiosity, why would you want to convert it?

You made mention of the special breakers needed and the "oddball" nature of the grounded delta. Im used to working with and have access to knowledge of ungrounded therefore it would be a safer and likely cheaper to go the route of ungrounded.

I will have to do it again but I am pretty sure I pulled 500V on all 3 legs to ground when I was installing the mill. I was checking to be sure the disconnect was open/closed when starting/finishing the install. Ill check that out tonight.