Special Machines - Relucatnce and Hysteresis Motors

8/17/2019 Special Machines - Relucatnce and Hysteresis Motors

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Reluctance Motors

• An induction motor with a modified squirrel-cagerotor

Stator - Single phase induction motor

• Split phase reluctance motor• Capacitor type reluctance motor

Rotor

• Asymmetric magnetic construction• By removing some rotor teeth

• Rotor turns in synchronism with the rotating

magnetic flux


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otch-!ype Rotor

• "otch# areas are "$igh-

Reluctance#

• "%ole# areas are &nown as

"Salient# %olesum'er of salient poles

must match the num'er of

stator poles


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(lat and Barrier Slot Rotors


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)peration

• *t starts li&e a induction motor 'ut

the rotor accelerates towards

synchronous speed

• At a "critical# speed+ the low-reluctance paths provided 'y the

salient poles will cause them to

"snap# into synchronism with the

rotating flux,


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)peration continued.

• /hen the rotor synchroni0es+

slip is equal to 0ero

• Rotor pulled around 'y

"reluctance torque#• (igure at right shows the

rotor synchroni0ed at no load


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)peration continued.

• A "step# increase in loadslows the rotor down+ andthe rotor poles "lag# the

stator poles,• !he angle of lag+ 1+ is calledthe "torque angle#,

• !he maximum torque angle+

1max 2 345,


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)peration at maximum load

• Maximum load is when 1 2 345,

• *f load increases so that 1 6 345+the flux path is "over stretched#and the rotor falls out ofsynchronism,

• Motor runs at slip speed


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Reluctance torque+ !rel

0

2

sin(2 ) srel rel

V

T K f δ

=

= × ÷ !rel 2 average value of reluctance torque

7 2 applied voltage 7.f 2 line frequency $0.

1rel 2 torque angle electrical degrees.

8 2 motor constant


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Reluctance torque+ !rel

• Maximum reluctance torque+ !relmax occurs

at 1rel 2 345


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9imitations

• 9ow power factor

• 9ow pull out torque

• 9ow efficiency


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Applications

• Constant speed applications

:, recoding instruments

;, timing instruments


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Documents

Special Machines - Relucatnce and Hysteresis Motors