SYNCHRONOUS

RELUCTANCE MOTORS

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SYLLABUS Constructional features – Types – Axial

and Radial flux motors – Operating

principles – Variable Reluctance and

Hybrid Motors – SYNREL Motors –

Voltage and Torque Equations - Phasor

diagram - Characteristics.

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RELUCTANCE TORQUE

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.

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BASIC FACT 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.

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RELUCTANCE MOTOR

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 and the reluctance is

minimum.

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CONSTRUCTION Broadly classified into two parts

1. Stator

2. Rotor

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STATOR CONSTRUCTION

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.

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STATOR CONSTRUCTION

Usually three phase winding are provided.

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ROTOR CONSTRUCTION

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.

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WORKING PRINCIPLE

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.

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WORKING PRINCIPLE

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.

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WORKING PRINCIPLE

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.

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WORKING PRINCIPLE

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.

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ADVANTAGES 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.

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DISADVANTAGES 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.

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APPLICATIONS 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.