# Design 50 HP Auto Transformer Starter



## maddhatter (May 7, 2012)

Sounds like a homework question...

You need to convert HP to KW, get a TX to suit, and create a control circuit to suit.

You'll need several contactors, a timer or two, electrical and mechanical interlocking, motor protection, etc.


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## wildleg (Apr 12, 2009)

hi cletis


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## NC Plc (Mar 24, 2014)

I have a hard enough time forcing myself to do my own homework.


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## John Valdes (May 17, 2007)

Sounds more like an engineer with little experience and has been asked to do this by his employer.
I would suggest they go soft start and not use this starting method.


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## Ultrafault (Dec 16, 2012)

My vote is for a vfd.


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## sparkywannabee (Jan 29, 2013)

Are there a lot of cowboys in Gujarat, India.


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## micromind (Aug 11, 2007)

1) What type of load is the motor starting, this will determine the KVA rating of the transformer, as well as the starting voltage applied to the motor. 

2) In addition to the above, how long can the motor stand starting current? A NEMA motor can take a LOT more than an IEC one. This will determine how long the transformer stays in the circuit. 

3) Design the control circuit around the above.


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## JRaef (Mar 23, 2009)

Motor starting autotransformers are sold as definite purpose devices based on HP (or kW). So when you find a supplier, just tell them the motor size, they will already have a design for it. You do not do this by using an off the shelf distribution transformer, it will not have the necessary taps, it will be too expensive and too big. 

Why you would do this is questionable. By the time you are done with your engineering time component cost and wiring time, you could have bought two solid state soft starters.


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## RIVETER (Sep 26, 2009)

cowboy3307 said:


> Dear All,
> I need to design 50 HP Auto Transformer Starter. Please need help. I need Material list with rating. Please suggest Transformer rating and steps .
> 
> Thanks in advance...


What do you think that auto transformers are for?


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## cowboy3307 (Oct 19, 2014)

A client need 50 HP Auto Transformer Starter for Pump application. 3 Taping in Transformer at 50%,65%,80% . Now i find to rating of power contactor for ATS.


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## micromind (Aug 11, 2007)

I don't know how it is in India, but in the USA it's almost always less money to but an assembled unit rather than build one.


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## JRaef (Mar 23, 2009)

micromind said:


> I don't know how it is in India, but in the USA it's almost always less money to but an assembled unit rather than build one.


I don't believe there is any "almost" involved...


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## micromind (Aug 11, 2007)

JRaef said:


> I don't believe there is any "almost" involved...


Lol.....

I doubt if you could buy the transformer alone for less that the whole assembly......


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## Vintage Sounds (Oct 23, 2009)

cowboy3307 said:


> A client need 50 HP Auto Transformer Starter for Pump application. 3 Taping in Transformer at 50%,65%,80% . Now i find to rating of power contactor for ATS.


Is there a reason they specifically want an autotransformer starter and not a VFD?


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