How To Calculate Rotor Resistance Of Induction Motor

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How is rotor resistance calculated in an induction motor?

Where, δ is the duty ratio of the transistor. From this equation we can suggest that rotor circuit resistance per phase is increased by 0.5(1-δ)R. Thus total circuit resistance can be evaluated. Therefore the total rotor resistance is varied from Rr to 0.5(1-δ)R as δ is varied from 1 to 0.

What is rotor resistance in induction motor?

Rotor resistance (IM): It is the resistance of the AC induction motor rotor; From: Heavy-Duty Electric Vehicles, 2021.

How is motor resistance calculated?

after you know the amount of the current, use this formula to determine the resistance of each phase: R = V/ (2*I) ohm the result of the calculation of the formula above will give you the amount of the resistance of each phase of the IM.

What does rotor resistance do in a 3-phase induction motor?

Rotor Resistance Control of Induction Motor: While maximum torque is independent of rotor resistance, speed at which the maximum torque is produced changes with rotor resistance. For the same torque, speed falls with an increase in Rotor Resistance Control of Induction Motor.

What is rotor reactance?

The reactance of the induction motor rotor depends upon the inductance of the rotor, voltage frequency, and rotor’s current. If L2 = inductance of rotor, the rotor reactance is given by. X2=2πf2 L2 But f2=sf1 ∴ X2=2π sf1 L2=s(2π f1 L2) Or X2=sX20.

Why do rotors have resistance?

Advantages of Rotor Resistance Starter High starting torque may be obtained with the rotor resistance starter. It improves the power factor of the motor. Absence of line current harmonics. Reduced starting current.

How do you increase rotor resistance?

By adding resistance in the rotor circuit of a slip ring induction motor, the starting current. 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.

What is the relation of the rotor resistance with respect to the starting torque in induction motors?

What is the relation of the rotor resistance with respect to the starting torque? Explanation: The rotor resistance is directly proportional to the starting torques.

What is the resistance formula?

The formula to calculate the resistance using Ohm’s Law is given as follows: R = V I. where, R is the resistance of the resistor R in ohms (Ω) V is the voltage drop in the resistor in volts.

What is the resistance of a motor?

A good motor should read less than 0.5 ohms. Any value greater 0.5 ohms indicate trouble with the motor.

How do you find the resistance?

R = V ÷ I Question 3 A flows through a 240 V lamp. What is the resistance of the lamp? To calculate the resistance of an electrical component, an ammeter is used to measure the current and a voltmeter to measure the potential difference. The resistance can then be calculated using Ohm’s Law.

How do you find the resistance of a 3 phase motor?

Check the motor winding resistance or ohms reading using a multimeter or ohmmeter for phase to phase terminal ( U to V,V to W ,W to U ). The ohms reading for each winding must be the same (or nearly the same). Remember that the three phases have identical windings or nearly so!

What is the effect of rotor resistance on the maximum torque?

The higher the rotor resistance R2, the higher will be the torque.

How do starting and maximum torque vary with rotor resistance?

Rotor resistance can be increased upto that when Starting torque becomes equal to Maximum value of torque, because after that Starting torque gets reduced. This value of resistance is called Critical Resistance. When slip at starting becomes equal to slip corresponding to maximum torque.

When 3 phase induction motor is at no load the slip is?

Q1 A 3-phase, 6-pole, 50 Hz induction motor has a slip of 1% at no-load and 3% at full-load. Find (i) synchronous speed, (ii) no-load speed (iii) full-load sped (iv) frequency of rotor current at standstill (v) Frequency of rotor current at full-load.

How is rotor current calculated?

Consequently, the rotor current frequency f’ is given by; i.e., Rotor current frequency = Fractional slip x Supply frequency (i) When the rotor is at standstill or stationary (i.e., s = 1), the frequency of rotor current is the same as that of supply frequency (f’ = sf = 1× f = f).

How is induction motor reactance calculated?

Equivalent Circuit of a Single Phase Induction Motor Also, the sum of forward and backward slip is 2 so in case of backward slip, it is replaced by (2 – s). R1 = Resistance of stator winding. X1 = Inductive reactance of the stator winding. Xm = Magnetising reactance.

What is the formula for rotor frequency?

The frequency of the rotor current fr = Ns x P/120, so fr = 0 if the slip is zero. If the operating speed is zero, Ns = N and the frequency of the rotor current is the same as the frequency of the stator current . f = source frequency in Hz.

What is the disadvantage of rotor resistance control method?

The major disadvantage of the rotor resistance control method is that the efficiency is low because of the additional losses present in the resistors connected within the rotor circuit. The efficiency is greatly reduced at low speeds because of the higher value of the slip.

What is the higher the resistance of the external cage of motor?

The outer cage has high ‘resistance to reactance ratio’ whereas, the inner cage has low ‘resistance to reactance ratio’.

How does rotor resistance increase torque?

In the normal operating range, increasing R2 increases the rotor impedance, necessitating higher slip for a given torque. Slip at maximum torque is directly proportional to R2 but the maximum torque is not changed by changing R2. R2/s = R2 + R2(1-s)/s.

How do you calculate the starting torque of an induction motor?

Torque of a three phase induction motor is proportional to flux per stator pole, rotor current and the power factor of the rotor. T ∝ ɸ I2 cosɸ2 OR T = k ɸ I2 cosɸ2 .

Can we use rotor resistance method for starting?

The easiest method of starting wound rotor (slip-ring) induction motors is to connect some extra resistance in the rotor circuit as shown in fig. Connection of extra resistance in the rotor circuit decreases the starting current and at the same time increases the starting torque.

How do you calculate starting torque?

By adding the proper value of the external resistance (i.e., R2 = X2), maximum starting torque can be obtained.

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