Autotransformer for 550volt equipment

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powerplay

Senior Member
An Adolph Mohr "Cutter" model Polar 82-ST has a requirement of three phase 550volts 60hz on it's label for a printing shop. The autotransformer that came with it has an output of 575/230volt which are both connected to the equipment from separate cables from either side of the autotransformer winding labelled 575 and 230volt. The place it was hooked up at previously was a typical 208 volt three phase, but the voltage metered at the new location is 249 three phase delta. The Lovett RC 6445 autotransformer has no labelled primary voltage, but an labelled secondary output of 575/230volts....when i applied the 249volts from a disconnect switch the output was 630 volt no load.

Two questions I have (so far) are:

a) Is hooking up an autotransformer meant for 208volts to 240+volts primary damaging the windings badly?
b) Is a decent quality motor requiring 550volts able to handle 600volts no problem? ...can it handle more?

Thanks again!
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
I think you might be pushing it a little bit. Are there any other taps in the autotransformer to get the voltage down a bit?


What is the full load amperage of this machine
 

templdl

Senior Member
Location
Wisconsin
I find it unusual to see an autotransformer with such a great difference between the input and output voltage. Auto or buck/boost transformers are more likely applied would smaller voltage differences because all that you need to pay for is the KVA that is required to make that voltage adjustment and as such you save a boat load of money if you don't require isolation.
With this application the kva required to step up the voltage to what it appears to be 550v from 230v would end up to be close to the same as what an isolation transformer would cost, by isolation I mean a transformer with a separate primary and secondary winding. The cost of an auto transformer and an isolation transformer would be about the same. So, what would be the cost benefit of using an autotransformer?

As a sales engineer for a transformer manufacturer who manufactured a lot of custom transformers and I would never recommend this unless there is a specific reason as to want no isolation between the line and load.

I do find this application a bit unusual but there may be something that I am overlooking and could learn from. That's what is so great about this forum.
 

powerplay

Senior Member
The autotransformer provided two voltages...550volt for the motor, 230volt for controls from the same transformer. I have heard the autotransformer isn't recommended for electronics... pros/cons?

I was told the winding's insulation can handle 10-20% more voltage than labelled.... possibly true, or wishful thinking? I am thinking it is reducing the lifespan of the transformer but by how much?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
I find it unusual to see an autotransformer with such a great difference between the input and output voltage.
I notice these frequently on 'older' generation servo controlled equipment like CNC equipment. I have seen them from the US, Japan, and Germany, so it must be more of what was a common recommendation 15-20years ago from manufacturers like Fanuc. I think this falls into the 'it worked in once so lets stick with it' mentality.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
That's a German built paper cutting machine, and I'll bet it's close to 30 years old.

I guess you could have a transformer built to put out 230 and 550 from a 208 volt source. Probably be easier to find a 240 to 208 trans. If worse came to worse I guess you could use 3 boost bucks, but I'll bet that machine is only worth about 3500 or 4 grand. How much money are you going to spend adapting it?
 
T

T.M.Haja Sahib

Guest
An Adolph Mohr "Cutter" model Polar 82-ST has a requirement of three phase 550volts 60hz on it's label for a printing shop. The autotransformer that came with it has an output of 575/230volt which are both connected to the equipment from separate cables from either side of the autotransformer winding labelled 575 and 230volt. The place it was hooked up at previously was a typical 208 volt three phase, but the voltage metered at the new location is 249 three phase delta. The Lovett RC 6445 autotransformer has no labelled primary voltage, but an labelled secondary output of 575/230volts....when i applied the 249volts from a disconnect switch the output was 630 volt no load.

Two questions I have (so far) are:

a) Is hooking up an autotransformer meant for 208volts to 240+volts primary damaging the windings badly?
b) Is a decent quality motor requiring 550volts able to handle 600volts no problem? ...can it handle more?

Thanks again!
For (a),it is a safety issue on the LV side of the auto transformer.
For both (a),(b),check with the manufacturers.
 
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