How Do You Calculate Torque and Efficiency in a Three Phase Induction Motor?

In summary: Thank you for replying NascentOxygen! , unfortunately it does not state synchronous speed and i haven't got a textbook containing the answer since its a homework sheet :frown:Thank you for replying NascentOxygen! , unfortunately it does not state synchronous speed and i haven't got a textbook containing the answer since its a homework sheet :frown:
  • #1
Student96
2
0

Homework Statement



A three phase cage rotor induction motor running at full load draws a stator current of 60A at a power factor of 0.8 lagging from a 415v, 50Hz Supply. Under the conditions the stator loss is 3.6kW, the rotor loss is 1.3kw and percentage slip is 4.5%. If the shaft power output is 29.4kW, calculate the shaft output torque, efficiency & mechanical friction and windage loss.

Homework Equations



Torque = Force * distance

The Attempt at a Solution



At first i tried using the power output 29.4kw to try to work out the torque but then realized that its not used for force.

Now unfortunately this is were I'm stuck at, I really need help on this and I can't get my head around the question. I am uncertain of what formulas to use and would really appreciate it if someone could guide me and tell me which ones to use :confused:.
 
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  • #2
Hi Student96! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

They don't tell you the motor's synchronous speed?

Does the textbook give you the answers?
 
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  • #3
Torque = Force * distance

Perhaps more relevant is..

Power = Torque * angular velocity

and as NascentOxygen said they don't give you the angular velocity.
 
  • #4
NascentOxygen said:
Hi Student96! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

They don't tell you the motor's synchronous speed?

Does the textbook give you the answers?

Thank you for replying NascentOxygen! , unfortunately it does not state synchronous speed and i haven't got a textbook containing the answer since its a homework sheet :frown:
 
Last edited by a moderator:
  • #5
Student96 said:
Thank you for replying NascentOxygen! , unfortunately it does not state synchronous speed and i haven't got a textbook containing the answer since its a homework sheet :frown:
In which case, to demonstrate that you really do understand the work, you could represent synchronous speed algebraically, e.g., Ns RPM, and work through the exercise based on that in place of a numerical value.

Alternatively, perhaps all of the induction motor exercises you have worked through in class have involved a particular synchronous speed, for convenience? If so, maybe you could assume that value for this exercise, too?

Have you asked other students in your class how they are going to answer this?
 
  • #6
assume that the number of poles is 2 (or some other number) state this assumption the Ns=120f/p
 
  • #7
Hi kevinj. :welcome:

You may not have noticed that the thread you responded to here is over 12 months old. Most likely the poster by now has moved on (one way or another). :smile:

kevinj said:
assume that the number of poles is 2 (or some other number) state this assumption the Ns=120f/p
... or some other even number.
 

Related to How Do You Calculate Torque and Efficiency in a Three Phase Induction Motor?

1. What is an induction motor and how does it work?

An induction motor is a type of electric motor that uses electromagnetic induction to produce rotational motion. It consists of a stator (stationary part) and a rotor (rotating part). When alternating current is passed through the stator windings, it creates a rotating magnetic field which induces a current in the rotor. This current creates its own magnetic field, causing the rotor to rotate.

2. What are the main components of an induction motor?

The main components of an induction motor include the stator, rotor, bearings, shaft, and frame. The stator consists of the outer housing and the stator windings, while the rotor is made up of the rotor core, rotor bars, and end rings. The bearings, shaft, and frame provide support and stability for the motor.

3. What are the common problems with induction motors?

Some common problems with induction motors include overheating, bearing failure, and electrical faults. These issues can be caused by factors such as overloading, insufficient cooling, poor maintenance, and voltage fluctuations.

4. How can I troubleshoot a problem with an induction motor?

If you are experiencing issues with an induction motor, the first step is to check for any visible signs of damage or wear. You can also use a multimeter to test the electrical connections and check for continuity. Additionally, it is important to ensure that the motor is not overloaded and that it is receiving the correct voltage and frequency.

5. How can I prevent problems with induction motors?

To prevent problems with induction motors, it is important to properly maintain them by regularly inspecting and cleaning them. It is also important to ensure that the motor is not overloaded and that it is receiving the correct voltage and frequency. Additionally, using high-quality components and following proper installation procedures can help prevent issues with induction motors.

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