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A three-phase motor is more compact and less costly than a single-phase motor of the same voltage class and rating, and single-phase AC motors above 10 hp (7.5 kW) are uncommon. Three-phase motors also vibrate less and hence last longer than single-phase motors of the same power used under the same conditions. [32]
Notice the concentrated windings on the stator poles. Cross-section of switched reluctance machine with 6 stator and 4 rotor poles. Notice the concentrated windings on the stator poles. A reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. The rotor does not have any windings.
The induction motor's (d,q) coordinate system can be superimposed to the motor's instantaneous (a,b,c) three-phase sinusoidal system as shown in accompanying image (phases b & c not shown for clarity). Components of the (d,q) system current vector allow conventional control such as proportional and integral, or PI, control, as with a DC motor.
A typical 3 phase linear induction motor. The "primary" core (grey) has grooves, and the windings are laid into them on top of each other. An aluminium plate above (not shown) serves as "secondary" and will move relative to the primary if a 3 phase AC is applied.
The phase windings of a polyphase transformer can be connected internally in different configurations, depending on what characteristics are needed from the transformer. In a three-phase power system, it may be necessary to connect a three-wire system to a four-wire system, or vice versa.
Universal motors also lend themselves to electronic speed control and, as such, were an ideal choice for domestic washing machines. The motor can be used to agitate the drum (both forward and in reverse) by switching the field winding with respect to the armature. The motor can also be run up to the high speeds required for the spin cycle.
The synchronous stator winding consists of a 3 phase winding. It is provided with a 3 phase supply, and the rotor is provided with a DC supply. DC excited motors require brushes and slip rings to connect to the excitation supply. [30] The field winding can be excited by a brushless exciter. [31]
A basic three-phase induction motor will have three windings, each end connected to terminals typically numbered (arbitrarily) as L1, L2, and L3 and sometimes T1, T2, T3. A three-phase induction motor can be run at two-thirds of its rated horsepower on single-phase power applied to a single winding, once spun up by some means.