Dear Friends,

I need to control the speed of 4 3 phase AC motors 0f 2.2kw each powered from the same Bus without using Frequency controllers. Please suggest methods with their Pros and Cons...

Any help would be highly appreciated.

Anshuman

 

Get the power company to change their frequency :^).
If they are generally synchronous motors, there aren't
many effective ways to do that.

Regards

cww

 

Anshuman,

It would be difficult to control the motor speed, but
you could fit vari-speed gearboxes to the outputs and
vary the speed of the load. DO THE MATHS though, nowadays, it can be cheaper to use inverters than gears

Siemens do an inexpensive no frills range as do Eurotherm and Danfoss.

If you only need start up ramping - soft starts are even cheaper.

regards

Marc Sinclair
http://www.germainesystems.co.uk

 

I want to visit my customers without having to spend time travelling.
I want to own a yacht without having to pay for it...
I could draw up a fairly long list like this.

 

Responding to Anshuman Patra's query:

1) Do the motors have to change speed together?

2) Have you investigated using an AC reluctance motor with an integral mechanical speed changer?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected]) {[email protected]}

 

thanx a lot ;-).I shall pass on the messsage to the power company. Meanwhile can u suggest me any other means by which I can manage till the power company manages to pull their Stunt...? The motors are AC asynchronous motors.

regards

Anshuman

 

Why can't you use a drive? Don't think you really have a choice...

 

If I could, I'd be rich! Nearly all AC motors you will see are very stubborn in regard to the angular velocity of the rotating magnetic field. I'm afraid you are left with mechanical or fluid power dodges while the power company agonizes. This is why there has been such tremendous development and activity in the VFD market, producing
price points that have obsoleted the alternatives. Still not cheap, just cheaper than most alternatives. This has also lead to a rash of VFDs being missapplied as a cure-all. And a rise in noise problems, toasted motors, etc. etc.

Regards

cww

 

If you are satisfied with a half speed / full speed solution you might change the number of poles of the motor on the fly with a contactor.

Some motors are made in a way that the electrical connection determines if the motor have two or four poles (some other pole combinations probably exist too) and changing from two to four poles would (almost exactly) give half the speed.

I don't think this is what you are asking for however and almost all other answers are as the rest have suggested: use either those drives or something mecanical...

There are some other solutions, but you don't want them
considering the price of a modern drive...

/Johan Bengtsson

Do you need education in the area of automation?
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Is using a wound rotor motor feasible?

Chris

 

You may what to look at http://www.payback.com They acomplish speed control by varying the magnetic coupling between the motor's output shaft and the load.

Hope this helps.