Inductance L = 2 H
Rate of change of current di/dt = 5 A/sec
Self induced EMF = − (Rate of change of current × Inductance) = −L(di/dt)
= −(5 × 2) = −10V
Universal motors may be powered by either AC or DC power sources.
The universal motor is constructed in the same way as a series-wound DC motor. However, it is designed to operate with either AC or DC applied.
The series-wound motor is the only type of DC motor that will operate with AC applied.
The windings of shunt-wound motors have inductance values that are too high to allow the motor to function with AC applied.
The series-wound motors have windings that have low inductances (few turns of large diameter wire), and they, therefore, offer a low impedance to the flow of AC.
The universal motor is one type of AC motor that has concentrated or salient field windings. These field windings are similar to those of all DC motors.
L0ad impedance Z = R + jX
z = 10 + 10j
Phase angle θ= tan−1(IL/IR)
tanθ = 1
Torque speed characteristic of induction motor
Motoring mode: 0 ≤ s ≤ 1
For this range of slip, the load resistance in the circuit is positive, i.e. torque developed is in the direction in which the rotor rotates.
In this region the value of slip lies between 0 to 11 i.e., slip is positive.
The motor rotates in the same direction as that of a rotating magnetic field.
At s = 0 (synchronous speed), the torque produced by the motor is zero because the induced voltage in the rotor is zero when N= Ns.
The torque increases as the slip increases while the air gap flux remains constant.
The torque-slip characteristic from no-load to somewhat beyond full-load is almost linear.
Generating mode: s <0
In this operating mode, the slip s is negative i.e., s < 0. The slip will be negative if and only if the rotor speed N is greater than the synchronous speed Ns (N> Ns). However, the rotor and R.M.F both rotate in the same direction.
In this region, the motor acts as a generator and return the power back to a.c. source.
Braking or plugging Mode: s > 1
In this region, the value of slip is greater than 1 and the rotor rotates in the opposite direction of the rotating magnetic field.
This is achieved by interchanging any two phases of the stator supply.
The total number of the conductor in stranded cable is given by
N = 3x2 − 3x + 1
x = no. of layer
For layer 1
N1 = 3(1)2 − 3(1) + 1
N1 = 1
For layer 2
N2 = 3(2)2 − 3(2) + 1
N2 = 7
In layer 2 no. of conductor = N2 − N1 = 7 − 1 = 6
For layer 3
N3 = 3(3)2 − 3(3) + 1
N3 = 19
In layer 3 no. of conductor = N3 − N2 = 19 − 7 = 12