Induction Motor Problem, How to find Rc

In summary: Once you have taken account of Rc losses separately, you can then neglect Rc in the equivalent circuit. Which equivalent circuit are you using?
  • #1
TheRedDevil18
408
1

Homework Statement


A three phase 220 V , 60 Hz, six poles 10 hp induction motor has the following circuit. Parameters on a per basis referred to the stator:
Rs = 0.334 Ω,
R’R = 0.147 Ω,
Xs = 0.498 Ω
X’R = 0.224 Ω ,
Xm = 12.6 Ω
The rotational losses including the core losses amount to 262 W and may be assumed constant. For a slip of 2.8 % determine (a) The line current and the power factor (b) The shaft torque and output horsepower (c) The efficiency

Homework Equations

The Attempt at a Solution


To get the line current, I need the equivalent impedance. But how do I get Rc (core resistance) ?, Is their a way to get it or is it just neglected because it is very large ?
 
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  • #2
TheRedDevil18 said:
the core losses amount to 262 W and may be assumed constant.
You're wondering how to involve this detail in your calculations?
 
  • #3
NascentOxygen said:
You're wondering how to involve this detail in your calculations?

For question a), it says determine the line current, so IL = Vphase/Z, but they haven't given Rc. They also said that the core losses and rotational losses amount to 262W
 
  • #4
Can you express these fixed losses as their equivalent in line current and then add that in after you have done the other calculations?

N.B., I'm not sure this is the accepted approach, but it seems a valid approximation.
 
  • #5
NascentOxygen said:
Can you express these fixed losses as their equivalent in line current and then add that in after you have done the other calculations?

N.B., I'm not sure this is the accepted approach, but it seems a valid approximation.

Not sure how to do that, I have this equation

IL = Vphase/Zeq

Where Zeq would be the equivalent impedance of the circuit, but then I would have to neglect Rc
 
  • #6
TheRedDevil18 said:
Not sure how to do that, I have this equation

IL = Vphase/Zeq

Where Zeq would be the equivalent impedance of the circuit, but then I would have to neglect Rc
Once you have taken account of Rc losses separately, you can then neglect Rc in the equivalent circuit. Which equivalent circuit are you using?
 

Related to Induction Motor Problem, How to find Rc

1. What is an induction motor?

An induction motor is an AC electric motor that works by creating a rotating magnetic field. It is commonly used in industrial and commercial applications due to its reliability and low maintenance requirements.

2. What is the "Rc" in induction motor problems?

"Rc" refers to the rotor resistance in an induction motor. It is an important parameter in analyzing the performance of the motor, as it affects the speed and efficiency of the motor.

3. How do I find the value of Rc in an induction motor?

The value of Rc can be found by conducting a no-load test on the motor and measuring the stator current and voltage. Using this data, the rotor resistance can be calculated using the formula Rc = (Vs/Vr - 1) * Rs, where Vs is the stator voltage, Vr is the rotor voltage, and Rs is the stator resistance.

4. What are some common problems with induction motors?

Some common problems with induction motors include overheating, bearing failures, and stator winding failures. These issues can be caused by factors such as overloading, voltage imbalances, and lack of maintenance.

5. How can I troubleshoot an induction motor problem?

If you are experiencing issues with an induction motor, it is important to first check for any obvious signs of damage or wear. You should also check the motor's power supply and make sure it is operating at the correct voltage and frequency. If the problem persists, it is best to consult a professional technician who can diagnose and repair the issue.

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