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Select 460V to 208V transformer
2

Select 460V to 208V transformer

Select 460V to 208V transformer

(OP)
For a 15 HP motor, 208V, six lead three phase motor that is wound for 208V delta or 416V star, what is the best low cost selection for a transformer 460V primary and 208V secondary so that the motor can be run on 208V?

RE: Select 460V to 208V transformer

Get some quotes from your local vendors.
You need to spec your requirements, especially copper vs. aluminum.  Outdoor/ indoor, temperature rise etc.

Look up the standard features offered and review that thye meet your needs.
 

Rafiq Bulsara
http://www.srengineersct.com

RE: Select 460V to 208V transformer

(OP)
I was not looking for a specific recomendation, just a good direction to start in before contacting a vendor with unknown product knowledge. I have seen articles describing using two transformers.  

RE: Select 460V to 208V transformer

Better go back to the start and hire an electrician.
There are no motors wound for 208V delta/416V star.
If you can't accurately describe your equipment, I don't want the responsibility of advising you.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Select 460V to 208V transformer

Many IEC motors are wound for operation at a high voltage if connected in Star and the low voltage if connected in Delta, with the ratio being based on the sq. rt. of 3 rule, or 1.732. For the UK and Australia, the high voltage was/is 415V, which makes the low voltage 415/1.732, or 240V. The new "harmonized" standard is now 400Y230V, but many motors built for use in the UK are still labeled 415/240V. Sounds as though you have one of those. Motors, as a general rule, are fine with a voltage range that is +-10% of their nameplate rating. So 240V - 10% is 216V, still a little too high for a 208V service. What you need is a simple type of transformer called a "buck-boost transformer". These are low cost autotransformers (meaning not isolation transformers) and can be connected to provide small increments of voltage change, i.e. 208V to 240V.

Per what Bill said, a decent industrial electrician will know this and be able to properly select and connect some buck-boost transformers for you.


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RE: Select 460V to 208V transformer

"...but many motors built for use in the UK are still labeled 415/240V."

I wish they were!! A true 415V motor in the UK is a 'special' now, which is a real PITA when you work on a site with legacy infrastructure and don't have the ability to get down to 400V on taps.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Select 460V to 208V transformer

(OP)
The motor data plate says 208V. Inside the cover though, it shows a delta low and star high volt connection diagrams.

The motor shop offered to rewind the motor for 460V at a reduced cost,we'll probably go that way. The customer is maxed out on 208V current but has plenty of 460.

I witnessed the motor shop test the Siemens motor on 416V and 460V. For the record, the motor shop's motor test stand uses a commercially made power supply box and one of the choices for voltage output selection was 416V. Just because 460V is not used in our country does not mean that it does not exist. Its a big world!

RE: Select 460V to 208V transformer

Quote:

Just because 460V is not used in our country does not mean that it does not exist.
Don't quite understand this statement.
208V and 480V are both standard North American voltages. The standard motor voltages for use on 208V and 480V are 200V and 460V respectively.
A star delta motor for use on 200V would be rated either 200V/346V or 200V star delta/start.
The other option may be 230V/400V or 230V star delta start.
And it is possible to build a motor for 460V and underrate it so that it will have enough torque to develop full horsepower at 208V delta. Kind of wasteful for a 15HP motor.

But,thinking outside the box;
A 208V delta motor would want 360V on the star connection. 15 HP will need about 25 Amps at 360V. Two 480:120V dry type transformers in buck configuration will drop your standard 40V t0 360V. There will be 25 Amps in the 120V windings so you will need two 3KVA transformers in open delta.
If you are subject to heavy loading and/or frequent starting use 5KVA transformers.
May be cheaper than a rewind, depends on the labor cost to install.
Where are you located. In North America 460 went out as a standard voltage in the 50's. I saw a legacy 460 Volt transformer about 10 years ago, but there are not many legacy 460V systems left. If a transformer fails you will most likely be upgraded to 480 Volts. 480 Volt transformers are available off the shelf. A 460 Volt transformer may be a special build with a long delivery time.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Select 460V to 208V transformer

(OP)
True that most 480V systems I see in the Atlanta GA, USA area read from 478V to 488V. The nominal voltage on the motor data plates are 460V, 230/460, 208/230-460 or straight 200V which is best for 208 systems. I still see some labels on old panels that say 440V too.
 

RE: Select 460V to 208V transformer

(OP)
Sorry, I meant to say 416V not used in our country.

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