What is the use of adding external resistance in a slip ring motor?
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What is the use of adding external resistance in a slip ring motor?
The external resistance reduces high resistance as soon as the motor obtains normal speed and increases the starting torque of a motor. The tweaking of external resistance also aids in decreasing of rotor and stator current but improves the power factor of a motor.
How does the external resistance of slip ring induction motor influence the motor performance?
In the case of slip ring motors, the rotor resistance is increased by the addition of external resistance. This external resistance makes the rotor circuit current low. Hence by increasing the rotor resistance, we can improve the starting torque of the wound rotor induction motor (W.R.I.M.).
What is the purpose of connecting external resistor to slip ring induction?
The slip rings in a wound rotor motor form a secondary, external circuit. Inserting resistance to this circuit allows the motor to produce very high torque at start-up, which is necessary for moving loads with high inertia.
What is the higher the resistance of the external cage of the motor?
The outer cage has high ‘resistance to reactance ratio’ whereas, the inner cage has low ‘resistance to reactance ratio’.
What is the formula for calculation of rotor resistance?
Example 5.3
| Step no. | Total rotor circuit resistance RΩ | Resistance between steps Ω |
|---|---|---|
| 3 | R23 = β · R22 = 0.676 × 0.435 = 0.294 | 0.294 – 0.199 = 0.095 |
| 4 | R24 = β · R23 = 0.676 × 0.294 = 0.199 | 0.199 – 0.135 = 0.064 |
| 5 | R25 = β · R24 = 0.676 × 0.199 = 0.135 | 0.135 – 0.09 = 0.045 |
| 6 | R2 = 0.09 = 0.09 | 0.09 – 0 = 0.090 |
How do you find the external resistance of a rotor?
I min = ss e 2 ( R 21 S 2 ) 2 + ss X 2 2 = ss e 2 ( R 22 S 3 ) 2 + s s X 2 2 etc . Once β is known, the resistance value for each step can be determined. In the above case, the slip Smax corresponds to the slip at the operating point of the torque or current curve, where the desired torque Tmax or current Imax occurs.
What is external resistance?
external resistance is the resistance offered to the flow of electricity in the external circuit.
What is the maximum value of slip in induction motor?
This is maximum value of slip s possible for induction motor which occurs at start. While s = 0 given us N = Ns which is not possible for an induction motor. So slip of induction motor can not be zero under any circumstances. Practically motor operates in the slip range of 0.01 to 0.05 i.e. 1 \% to 5 \%.
What is the value of slip in induction motor?
This is the reason; slip is never zero in an induction motor. Slip = 1, means that rotor is stationary. Negative value of slip in induction motor can be achieved when the rotor speed is more than the synchronously rotating magnetic flux.