Anyone have experience with stepping up 460V to 480V without swapping the utility transformer? We have a client who purchased a machine that has very tight voltage tolerance and and the 460V service knocks it offline. The quote from the utility company is substantial, so i am looking into other options.
460V to 480V
- Thread starter Rock86
- Start date
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If utility can't/won't do anything (chances are they are quite capable of changing some taps but want to be stubborn about it) a buck-boost transformer(s) is likely a lesser cost solution you can apply to just that one piece of equipment
I forgot to say... the existing transformer does not have the ability to change taps.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Does the load have a neutral?
No.
I am a bit rusty on buck boost, can someone confirm my calculations?
input: 460V 3ph
output: 480V 3ph
Load in Amps: 119A
(119A * (480V - 460V))/1000 = 2.38kVA <-- This kVA would be the transformer size required, correct?
input: 460V 3ph
output: 480V 3ph
Load in Amps: 119A
(119A * (480V - 460V))/1000 = 2.38kVA <-- This kVA would be the transformer size required, correct?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
They possibly need to open it up to change, particularly if pole mounted type. They won't necessarily volunteer this information easily.
Pad mount might be more fixed though.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
460V is not standard utility distribution voltage. My guess is that someone mistakenly INSISTED on the 460V transformer under some mistaken belief that it was “required”, and the utility eventually gave up and gave it to them. Now the user needs 480V and someone at the utility engineering dept. is saying “Nope, you forced us to buy this stupid one-off 460V transformer for you that we can’t use for anyone else, so now you deal with it.”
Its a Pad mounted transformer in NJ from 1986. The surrounding commercial area is/was fed with 460V transformers.
They did open it up and no luck. its fixed.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
simple single phase application yes, you need to have a boost coil that can handle 119 amps @ the boosted volts.
Commonly used buck/boost units have 12/24 or 16/32 volt low volt coils so the more basic configurations will be dealing with 12, 24, 16 or 36 volts of change.
three phase, the simple method is to connect them in an open delta and one of your phases is still same conductor for both input and output.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
or there is enough demand on it that it draws it down to that level or even tap changer on primary side is set low or malfunctioning - though if OP has been told they can't change without replacing that is probably not the case, but high demand drawing voltage down could still be a possibility. That could be sign things need upgraded anyway, there may be more load now then there once was when what is there was selected.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
That's why I asked about a neutral.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
This use of autotransformers would seem to be prohibited NEC 215.11 / 210.9 unless the 460V 3-wire delta is corner grounded, in which case you must use 2 autotransformers that leave the grounded conductor untransformed.
Although I guess you could call the "460V" a nominal 480V and use 2 sets of autotransformers to transforms to 600V and back to 480V under Exception 2. Which would be pretty stupid, so perhaps just claim that Exception 2 should apply from 460V to 480V.
Cheers, Wayne
Although I guess you could call the "460V" a nominal 480V and use 2 sets of autotransformers to transforms to 600V and back to 480V under Exception 2. Which would be pretty stupid, so perhaps just claim that Exception 2 should apply from 460V to 480V.
Cheers, Wayne
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Strange. Is it ungrounded?
JoeStillman
Senior Member
- Location
- West Chester, PA
460V used to be a standard voltage in parts of NJ. I don't know about any other states. A client of mine had to modify a bunch of ATS's when the old service got upgraded to 480V.
The existing equipment is a 3-wire system. my intent was design the system such that it would utilize two transformers. thank you for that code reference.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
While the _equipment_ only requires the three 'hot' conductors, is the supply a 460/266V _system_?
As I read 215.11/210.9, you can use autotransformers to derive a 480/277V feeder or branch circuit, even if the load does not _use_ the neutral; the key is that you are not deriving a new neutral conductor, but instead keeping the same neutral between supply and load side of the transformer.
On top of this, I'd guess that a very sensitive system (designed for 480V but can't tolerate 460V) is also sensitive to the L-G voltage anyway; if the source is ungrounded I'd look into an isolation transformer to fix that as well.
Ideally you would use a set of 3 transformers, each rated 266V:11V in a wye autotransformer configuration to boost voltage. Those won't be available.
But you could use common 240/480 : 24/48V transformers. Use the 480V primary at 266V, that makes the 24V operate at 13.3V. In a wye configuration that would boost your 460/266V system to 483/279V. You would need 3 1kVA rated transformers.
-Jonathan
As I read 215.11/210.9, you can use autotransformers to derive a 480/277V feeder or branch circuit, even if the load does not _use_ the neutral; the key is that you are not deriving a new neutral conductor, but instead keeping the same neutral between supply and load side of the transformer.
On top of this, I'd guess that a very sensitive system (designed for 480V but can't tolerate 460V) is also sensitive to the L-G voltage anyway; if the source is ungrounded I'd look into an isolation transformer to fix that as well.
Ideally you would use a set of 3 transformers, each rated 266V:11V in a wye autotransformer configuration to boost voltage. Those won't be available.
But you could use common 240/480 : 24/48V transformers. Use the 480V primary at 266V, that makes the 24V operate at 13.3V. In a wye configuration that would boost your 460/266V system to 483/279V. You would need 3 1kVA rated transformers.
-Jonathan
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I agree that if the load is 480V 3P3W, and the supply is 460V/266Y with the neutral conductor available, you could use 3 autotransfomers to make 480V/277Y and just feed the equipment with the 3 derived ungrounded legs, and that would comply with 215.11/210.9.
Cheers, Wayne
hillbilly1
Senior Member
- Location
- North Georgia mountains
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- Owner/electrical contractor
