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Rabaacca
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Induction Motor

12/15/2016 3:55 PM

slip of induction motor is difference in speed of rated speed and synchronous speed.The rated speed varies because of load Then how can we vary slip of induction motor
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lyn
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#1

Re: induction motor

12/15/2016 4:08 PM

Google is your friend.

Read these!

Slip in Electrical Induction Motors - Engineering ToolBox

AC Induction Motor Slip – What It Is And How To ... - Power/mation
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Rixter
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#2

Re: induction motor

12/15/2016 4:11 PM

Put more load on it. The greater the load the more the slip. Higher slip means greater torque. Slip will increase until motor torque equals torque required by the load.

http://www.globalspec.com/reference/10795/179909/chapter-3-ac-and-dc-motors-ac-motors-control-of-speed-torque-and-horsepower
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Andy Germany
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#7
In reply to #2

Re: induction motor

12/16/2016 3:38 AM

GA.

You beat me to it!!

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JRaef
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#3

Re: induction motor

12/15/2016 4:21 PM

What do you mean by "vary slip of induction motor"? Do you want to vary the DESIGN slip of a motor you are manufacturing?

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James Stewart
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#4

Re: induction motor

12/15/2016 4:41 PM

You can vary the slip by adding or subtracting load in the pseudo-linear region of rotor response.

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RAMConsult
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#5

Re: induction motor

12/16/2016 1:32 AM

You can also control the speed by using a wound rotor induction motor and either variable resistance or electronics to alter the speed-torque curve characteristics and slip. If you only have a squirrel cage IM then you can use a VFD or VSD to accurately control the torque/speed/slip.

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PWSlack
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#6

Re: induction motor

12/16/2016 3:13 AM

Easy. Vary the mechanical load that it is driving.

The thinking is sdrawkcab: it is the variation in load that causes the variation in slip, and not the other way round. Slip is something that one "lives with".

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7anoter4
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#8

Re: Induction Motor

12/16/2016 8:55 AM

First of all the rated slip is connected with rated rpm that means it is not a variable as all other parameters are- frequency, voltage, load, pf, efficiency, ambient temperature rated are constant.

May be you mean: “how to vary the rotor velocity”? The usually way is VFD.

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Codemaster
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#9

Re: Induction Motor

12/17/2016 4:40 AM

As others have said - by varying the load. You gave the answer in your 2nd sentence. To be precise, should say actual speed varies because of load. Rated speed is at rated load.

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RAMConsult
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#10

Re: Induction Motor

12/17/2016 11:51 PM

Excuse me, but there are only two variables that can be changed at the terminals of an IM, voltage and frequency, and both of these affect the load and hence the slip. Everyone seems to be thinking that the mechanical load is somehow a fixed quantity, when in fact the mechanical load presented at the shaft is a function of the power available at the shaft; i.e., they're in balance. That's why the speed-torque curve of a pump or blower is superimposed on the speed-torque curve of the motor, and the place where they cross represents the operating point of the pump/motor combination; i.e., the load at a certain speed, and hence the slip.

As many of you have stated in other posts, if the voltage is reduced 20% then the amount of torque available is reduced to 64%. Surely nobody believes that an IM that can only supply 64% of its rated torque can possibly supply 100% of rated HP, or that the slip is somehow going to be the same either. Unless the motor is impedance-protected, the current will increase towards the LRA (Locked Rotor Amps) and overheat until the protective means operate.

That's the beauty of modern VFDs, the ability to vary the voltage and/or frequency to "force" the desired operating mode, be it constant power, constant torque, or variable torque, according to what the mechanical load requires.

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Andy Germany
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#11
In reply to #10

Re: Induction Motor

12/18/2016 8:04 AM

The voice of reality. Well put, thanks.

GA my friend!!

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James Stewart
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#12
In reply to #11

Re: Induction Motor

12/19/2016 3:02 PM

That will be about enough of that voice of reality for today, thank you. We were doing all this in our heads anyway, and anything is possible in the noodle.

I agree about load, the motor will put forth enough power to match the load at the shaft. If the shaft is not doing much work, then neither is the motor, and there will be less slip.

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7anoter4 (1); Andy Germany (2); Codemaster (1); James Stewart (2); JRaef (1); lyn (1); PWSlack (1); RAMConsult (2); Rixter (1)

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