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Constructional features – Types – Axial and Radial flux motors – Operating principles – Variable Reluctance and Hybrid Motors – SYNREL Motors – Voltage and Torque Equations - Phasor diagram - Characteristics.
2
The torque exerted by the reluctance motor because of the tendency of the salient poles to align themselves in the minimum reluctance position. This torque is called reluctance torque. 3
When a piece of magnetic material is loaded in a magnetic field a force acts on the material tending them to bring it into the most dense portion. Force tends to align the specimen of material in such a way that the reluctance of the magnetic path lies through the material will be minimum. 4
Defined as an electric motor in which torque is produced by the tendency of the rotor to move to a position where the inductance of the excited winding is maximum minimum.
and
the
reluctance
is 5
Broadly classified into two parts 1. Stator 2. Rotor
6
Similar to induction motor.
Outer frame to cover whole machine.
Next to frame stator core is available.
Stator core made up of silicon material – to reduce hysteresis and eddy current loss
Core have slots.
Slots used for housing the stator winding. 7
Usually three provided.
phase
winding
are
8
No permanent magnets. No separate field winding for excitation on rotor. Have salient pole rotor core. Made up of solid steel material or laminated sheets. Low cost, high efficiency and capable of operating at very high speeds. 9
Works on the basic principle of minimum reluctance position. Sinusoidal rotating field is produced in the air gap when stator winding is excited by AC supply. Produced field exerts reluctance torque on the unsymmetrical rotor. Tending to align the salient pole axis of the rotor with the axis of revolving magnetic field. 10
Rotor tries to align with the minimum reluctance position by developing reluctance torque in between stator and rotor. No core in the rotor so no core or copper loss.
11
The reluctance torque developed in the type of motor can be expressed as
If reluctance torque is sufficient to start the motor, the rotor will pull into step with revolving field. 12
The rotor continue to run at the speed of the revolving field. The rotor revolves synchronously, its poles lag behind the stator pole by a certain angle known as torque angle. The reluctance torque increases with the increase in torque angle. 13
No need field excitation at zero torque.
More reliable then PM machines.
Rotors are constructed from high strength and low cost materials. The motors can be operated from standard PWM ac inverters.
Have capability to survive very high temperature.
Motor has simple and rugged construction.
High speed capability. 14
Compared to induction motor it is slightly heavier and has low power factor.
But Increasing the saliency ratio
the power
factor can be improved.
2. High cost than induction motor.
15
Pumps and conveyors.
Synthetic fiber spinning mills.
Motor pumps.
Metering pumps.
Widely used for constant speed applications such as 1. recording instruments. 2. Timing devices. 16
