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Participant

Join Date: May 2009
Posts: 3

Higher Capacity Motor

05/27/2009 1:25 AM

I'm planning to buy one machine, which requires 30HP motor.

I've transformer of 25HP capacity. I've applied for increased capacity, it will take time.

Can i use 30 HP motor till 1 month?

What are the possible problems?

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Commentator

Join Date: May 2009
Location: Centurion, South Africa
Posts: 87
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#1

Re: Higher capacity motor

05/27/2009 1:39 AM

Yes, you can use the system temporarily.

You need to set the overcurrent protection of the motor, to the rated current of the transformer and not to the rated current of motor. This will prevent the transformer from overheating and insulation failure.

Depending what type of machine the motor is driving, you may encounter problems such as:

Reduced output from the machine (less product over time), machine might take longer to do the work.

Motor may not get up to speed (overcurrent protection will protect motor and transformer)

Make sure you have overcurrent protection in the circuit...

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Participant

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#2
In reply to #1

Re: Higher capacity motor

05/27/2009 1:42 AM

Thanks buddy...

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Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

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Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
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#3
In reply to #2

Re: Higher capacity motor

05/27/2009 4:33 AM

With the motor protection applied to protect the transformer, instead of the motor, it may or may not work, though it will be safe.

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Power-User

Join Date: Mar 2006
Location: Valdosta, GA
Posts: 361
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#4

Re: Higher Capacity Motor

05/28/2009 7:39 AM

Transformers are rated lower than they are actually capable of for a margin of safety. Motors are rated higher than they usually have to perform in real life. This all has to do with safety but in your case I think your margins may overlap and you would be safe. Don't blame me if you blow your transformer though. It's your choice. If you decide to go ahead with this, at the very least, you should monitor the actual power being transferred to the motor for awhile to try to learn if this will work. The easiest way to do this is use a clamp on ampmeter to monitor the actual amperage and then calculate your horse power. I am sure that some of the math whizzes on here can provide you with formulas and details about how to do this. Just ask.

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Power-User

Join Date: Dec 2006
Posts: 346
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#5

Re: Higher Capacity Motor

05/31/2009 4:28 PM

vivek; most transformers can take a 25% over load ,if you are worried put a cooling fan to dissipate the heat generated. perry

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Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
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#6

Re: Higher Capacity Motor

06/05/2009 3:23 PM

A good way to cheat the system is to power factor correct the transformer on the supply side and then further power factor correct the motor on the secondary side of the transformer. (standard issue AC power factor correction capacitors)

By reducing the VA load of the motor its apparent power Vs true power will become much closer. You may see as much as a 40% drop on the motors amp load at the transformer when done properly. That effect will free up considerable amperage capacity over head on the transformers windings. That will equate to a more efficient transformer too simply from less internal heating!

Doing it on the primary side of the transformer also will free up more line amp capacity on the primary feed source as well. Secondary side power factor correction does the motor. Primary side power factor correction does the transformer.

If properly done you may likely see a 50% reduction in the amperage drawn at the circuit breakers!

Your 30 hp motor could balance out as having the same apparent power draw as a 15 - 20 hp motor!

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Guru
Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2008
Location: CHENNAI, TAMIL NADU, INDIA.
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#7

Re: Higher Capacity Motor

08/16/2009 2:58 AM

Yes, Mr. Vivek.

You can temporarily use with the following care. For that you have to study the actual temperature rise in your Transformer. If the actual temperature rise at 25 H.P and the max range permissible to be looked in to.

1. If the margin is narrow, you take steps to increase the cooling of the transformer, by providing additional cooling surface in the oil circulation and operate the transformer.

2. What is the power fctor in the system.If it is less take steps to improve thePower factor.

Provide the details to my mail sd610@rediffmail.com and I will study and suggest, if possiblhanks,

DHAYANANDHAN.S,

CR4 MEMBER,

INDIA.

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Users who posted comments:

Aldego (1); dhayanandhan (1); Keywalker (1); perry (1); PWSlack (1); tcmtech (1); Vivek P H (1)

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