This is another way of obtaining improved starting performance without affecting its running performance. Though it is more expensive it gives better performance than deep bar rotor construction. The stator of double cage rotor induction motor is same as that ordinary induction motor. Rotor consists of two cages or two layers of bars short circuited … Continue reading Double cage rotor

# Category: Induction Machines

# Deep bar Rotor

There is no constructional difference between stator of seep bar rotor motor and that of ordinary induction motor. The rotor consists of deep bars, short circuited by two end rings one on each side. The magnetic leakage flux lines are shown by dotted lines. Now consider that the bar consists of many number of layers … Continue reading Deep bar Rotor

# High torque Cage Machines

In case of slip - ring induction motor an external resistance can be added in the rotor circuit during starting which gives higher starting torque and lower starting line current at an improved power factor. This resistance is then gradually cut from the rotor circuit which would otherwise result in decrease of full load speed, … Continue reading High torque Cage Machines

# Blocked Rotor Test

In this test, the rotor is locked and it is not allowed to rotate. Thus the slip s = 1. When s = 1 ⇒ Electrical equivalent of Mechanical load becomes equal to Zero. If the motor is slip - ring induction motor then the windings are short - circuited at the slip rings. The situation … Continue reading Blocked Rotor Test

# No load test on Induction Motor

In this test, the motor is made to run without any load i.e. no Load condition. The speed of the motor is very close to the synchronous speed but less than synchronous speed. The rated voltage is applied to the stator. The input line current and total input power is measured. The two wattmeter method … Continue reading No load test on Induction Motor

# Constant V/f speed control

We have seen the Stator Frequency control. In stator frequency control ⇒ Two things gets changed different as to Constant V/f speed control. (i). Here maximum torque remains unaltered (As ratio of V/f = Constant) (ii). Magnetic condition of machines also gets unaltered. (Φm = K V1 / f) In case of Only stator frequency control : In case … Continue reading Constant V/f speed control

# Stator Frequency control

We know that Synchronous speed in rpm is given by : Ns = 120 f / P Here f : Stator frequency And P : Number of poles in stator Torque - Slip characteristics At s = 0 ⇒ Speed of machine N = Ns. And that point is marked by a circle in the above diagram. … Continue reading Stator Frequency control

# Speed Control of Induction Machines

We have seen the Derivation for Torque expression in earlier post Torque Expression for Induction Motor. T = KT s α / (s2 + α2) Here KT is Torque constant = 3 E21 / ωs X’2 And α is the machine constant = R’2 / X’2 At running condition : α = 0.1 and s = 0.06 / 0.07 Means ⇒ α2 >> s2 T ≈ KT s / … Continue reading Speed Control of Induction Machines

# Theory of Induction machines with varying flux (Φ)

As we have discussed earlier the Equivalent circuit of an Induction machine Equivalent circuit of Induction Machine. Here Rotor rectance has become independent of speed (N) or Slip (s). But Rotor resistance has become a function of speed or Slip. Illusion : Never forget that the Rotor rectance is the function of Slip. Analysis of Induction … Continue reading Theory of Induction machines with varying flux (Φ)

# Starting of Slip-Ring Induction motors

It is known that in slip ring induction motor, externally resistance can be added in the rotor. Let us see the effect of change in rotor resistance on the torque produced. We know that torque produced by an induction motor is given by T = KT s α / (s2 + α2) Where KT is torque constant = 3 … Continue reading Starting of Slip-Ring Induction motors