Electrical Engineering ⇒ Topic : Universal motors

UNIVERSAL MOTOR

• Fractional-horsepower series motors that are adapted for use on either D.C. or A.C. circuits of a given voltage are called universal motors.
• The universal motor is designed for commercial frequencies from 60 cycles down to D.C.(zero frequency), and for voltage from 250 V to 1.5 V. A commercial universal motor may have a somewhat weaker series field and more armature conductors than a D.0 series motor of equivalent horsepower. It is manufactured in ratings up to 314 H.P., particularly for vacuum cleaners and industrial sewing machines. In smaller size of 14 H.P or less, it is used in electric hand drills.

               Like all series motors, the no-load speed of the universal motor is universally high. Quite frequently, gears trains are built into the motor housing of some universal motors to provide exceedingly high torque at low speeds.

            When these motors are used in commercial appliances such as electric shavers, sewing machines, office machines, and small hand hair diyers or vacuum cleaners, they are always directly loaded with little danger of motor run away