Ingles

Industrial Electricity






































1 Summary


Industrial Electricity

The Universal Motor . . .


The AC Motor . . .

The Single Phase Motor . . .


The Split-phase Single Phase Motor . . .


The Capacitor-start Motor


The Permanent Capacitor Motor


The StartPermanent Capacitor Motor . . .

The Three-phase AC Motor

Machines Control










THE UNIVERSAL MOTOR

The universal motor is a rotating electric machine similar to a DC motor but designed to operate either from direct current or single-phase alternating current. The stator and rotor windings of the motor are connected in series through the rotor commutator. Thereforethe universal motor is also known as an AC series motor or an AC commutator motor. The universal motor can be controlled either as a phase-angle drive or as a chopper drive.

In the phase-angle application, the phase-angle control technique is used to adjust the voltage applied to the motor. A phase shift of the gate's pulses allows the effective voltage, seen by the motor, to be varied.The phase-angle drive requires just a triac.

In the chopper application, the Pulse Width Modulation (PWM) technique is used to adjust the voltage applied to the motor. Modulation of the PWM duty cycle allows the effective voltage, seen by the motor, to be varied. Compared to a phase-angle drive, a chopper drive requires a more complicated power stage with an input rectifier, a powerswitch and a fast power diode. The advantage is higher efficiency, less acoustic noise and better EMC behavior.

Key Characteristics

Substitutes another field winding for DC motor’s permanent magnets.
Can be driven by AC or DC (hence ‘universal’).
High construction complexity.
Low reliability.
Low efficiency.
Driven by Rheostat, Chopper or Phase Angle(SCR or Triac) controllers.
Some degree of sensorless speed control possible.
Good power to weight ratio.



















A variant of the wound field DC motor is the universal motor. The name derives from the fact that it may use AC or DC supply current, although in practice they are nearly always used with AC supplies. The principle is that in a woundfield DC motor the current in both the field and the armature will alternate at the same time, and hence the mechanical force generated is always in the same direction. In practice, the motor must be specially designed to cope with the AC current, and the resultant motor is generally less efficient than an equivalent pure DC motor. Operating at normal power line frequencies, the maximum output ofuniversal motors is limited and motors exceeding one kilowatt are rare. But universal motors also form the basis of the traditional railway traction motor. In this application, to keep their electrical efficiency high, they were operated from very low frequency AC supplies, with 25 Hz and 16 2/3 hertz operation being common. Because they are universal motors, locomotives using this design werealso commonly capable of operating from a third rail powered by DC. The advantage of the universal motor is that AC supplies may be used on motors which have the typical characteristics of DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is the maintenance and short life problems caused by the commutator. As a result suchmotors are usually used in AC devices such as food mixers and power tools which are used only intermittently. Continuous speed control of a universal motor running on AC is very easily accomplished using a thyristor circuit, while stepped speed control can be accomplished using multiple taps on the field coil. Household blenders that advertise many speeds frequently combine a field coil with...