Phasor Diagram of 3 Phase Induction Motor
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Phasor Diagram of 3 Phase Induction Motor
Phasor Diagram of 3 Phase Induction Motor
In a 3-phase Induction motor, the rotor winding is Short-circuited while the stator winding is connected to the 3-phase supply. The rotor winding that has been Short-circuited receives the energy magnetically from the stator winding. As a result, a Transformer with a Rotating Secondary could be used to describe an Induction motor (Short-circuited). Transformer primary and Secondary are represented by the stator winding and rotor finding, respectively. So One can Anticipate that the Equivalent circuit of an Induction motor will Resemble that of a transformer given how similar the flux and voltage conditions are to those in a Transformer. The Equivalent circuit for an Induction motor is shown in Fig. 3.8 for each phase. Let’s talk about the rotor and stator Circuits Independently.
Stator circuit.
The events in the stator closely resemble those in the Transformer primary. R1 and X1 are the stator resistance and leakage reactance per phase, respectively, and V1 is the applied voltage to the stator per phase. A magnetic flux created by the applied voltage V1 connects the primary stator winding and the rotor winding (i.e., secondary). Self-induced Electromagnetic fields (e.m.f.) E1 is an induced and mutually induced e.m.f. in the stator winding.
E’2 (= s E2 = s K E2 where K is Transformation ratio) is induced in the rotor winding. The flow of stator current I1 causes voltage drops in R1 and X1.
V1 = – E1 + I1(R1+jX1) …… phasor sum
When the motor is at no-load, the stator winding draws a current I0. It has two components viz.,
(i) which supplies the no-load motor losses and
(ii) Im, the Magnetising Component, creates magnetic flux in the air gap and the core. Therefore, the no-load motor losses and Magnetic flux generation are Represented by the parallel combination of Rc and Xm.
I0 = Iw + Im
Rotor circuit.
Here R2 and X2 represent the rotor resistance and standstill rotor reactance per phase respectively. So At any slip s, the rotor reactance will be X2 .The induced voltage/phase in the rotor is E’2 = s E2 = s K E1 . Since the rotor winding is short-circuit, the whole of e.m.f. E’2 is used up in circulating the rotor current I’2.
E’2 = I’2 (R2 + jsX2)
The rotor current I’2 is reflect as I”2 (= K I’2) in the stator. The phasor sum of I”2 and I0 gives the stator current I1.
It is significant to remember that a transformer’s primary input and secondary output are both electrical. However, in an induction motor, the rotor’s output is mechanical while the stator’s and rotor’s inputs are electrical. It is desirable and necessary to substitute an equivalent electrical load for the mechanical load in order to simplify calculations. The induction motor’s transformer equivalent circuit is what follows.
Phasor Diagram of 3 Phase Induction Motor
The magnetic fields caused by the stator and rotor currents rotate at synchronous speed Ns, despite the fact that their frequencies are different. A magnetic flux that rotates at a speed of Ns is create by the stator currents. So In the direction of the rotor’s rotation at slip s, the speed of rotation of the rotor field in relation to the rotor surface is
But the rotor is revolving at a speed of N relative to the stator core. Therefore, the speed of rotor field relative to stator core
The magnetic fields of the stator and rotor are thus synchronous when observed by a space observer, regardless of the value of slip s. As a result, it is possible to think of a 3 phase induction motor as being analogous to a transformer with an air gap separating the iron portions of the magnetic circuit carrying the primary and secondary windings. The Phasor Diagram of 3 Phase Induction Motor is show in Figure 3.9.