what do u mean by a universal motor?

Question

what is the basic principle of universal motor?how does it work?

Answer 1

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 wound field DC motor the current in both the field and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) 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 (impedance must be taken into account, as must the pulsating force), and the resultant motor is generally less efficient than an equivalent pure DC motor. Operating at normal power line frequencies, the maximum output of universal 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 were also 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 such motors 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 several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave DC with 0.707 of the RMS voltage of the AC power line).

Unlike AC motors, universal motors can easily exceed one revolution per cycle of the mains current. This makes them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high-speed operation is desired. Many vacuum cleaner and weed trimmer motors will exceed 10,000 RPM, Dremel and other similar miniature grinders will often exceed 30,000 RPM. A theoretical universal motor allowed to operate with no mechanical load will overspeed, which may damage it. In real life, though, various bearing frictions, armature "windage", and the load of any integrated cooling fan all act to prevent overspeed.

With the very low cost of semiconductor rectifiers, some applications that would have previously used a universal motor now use a pure DC motor, usually with a permanent magnet field. This is especially true if the semiconductor circuit is also used for variable-speed control.

The advantages of the universal motor and alternating-current distribution made installation of a low-frequency traction current distribution system economical for some railway installations. At low enough frequencies, the motor performance is approximately the same as if the motor were operating on DC. Frequencies as low as 162/3 hertz were employed.

Answer 2

This article might help you in understanding the Universal Motor working principle and applications.

Answer 3

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. Therefore the 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 power switch and a fast power diode. The advantage is higher efficiency, less acoustic noise and better EMC behavior.



Page Contents
Key Characteristics
Parameters
Applications
Products
Documentation

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
* Terrible EMI (brushes create sparks and ozone)
* Driven by Rheostat, Chopper or Phase Angle (SCR or Triac) controllers
* Some degree of sensorless speed control possible
* Good power to weight ratio


Application Parameters


Voltage Motor Power Speed Range
115/230 Vac

50-1kW

20,000 RPM




Applications

* Blenders
* Power tools
* Simple fluid pumps (washing machines)
* Vacuum cleaners



* Tools
* Washers
* Food processors
* Fans
* Hair dryers

Answer 4

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 wound field DC motor the current in both the field and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) 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 (impedance must be taken into account, as must the pulsating force), and the resultant motor is generally less efficient than an equivalent pure DC motor.
Operating at normal power line frequencies, the maximum output of universal 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 were also 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.
Unlike AC motors, universal motors can easily exceed one revolution per cycle of the mains current. This makes them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high-speed operation is desired. Many vacuum cleaner and weed trimmer motors will exceed 10,000 RPM, Dremel and other similar miniature grinders will often exceed 30,000 RPM.

Answer 5

A universal motor is a motor which can run on either DC or single phase AC supply. The basic construction of a universal motor is similar to the construction of a DC series motor. It's working is also very similar to a DC series motor. To understand briefly about universal motor read at, http://www.electricaleasy.com/2014/02/universal-motor-construction-working.html

Answer 6

It's a motor that has a multipurpose.
It's basic principle of operation is because of the interaction of magnetic fields between the stator and the rotor when power is supplied to the motor.
It works like any other motor.

Answer 7

The universal motor go anywhere,utilizing every kind of energy.More details need too much time.