Tag: AC motors

Charles Proteus Steinmetz’s first job after arriving in America was to investigate problems encountered in the design of the alternating current version of the brushed commutator motor. The situation was so bad that motors could not be designed ahead of the actual construction. The success or failure of a motor design is not known until…

Normally, the rotor windings of a wound rotor induction motor are shorted out after starting. During starting, resistance may be placed in series with the rotor windings to limit starting current. If these windings are connected to a common starting resistance, the two rotors will remain synchronized during starting. This is useful for printing presses…

Shaded Pole Induction Motor An easy way to provide starting torque to a single-phase motor is to embed a shorted turn in each pole at 30° to 60° to the main winding. (Figure below) Typically 1/3 of the pole is enclosed by a bare copper strap. These shading coils produce a time lagging damped flux…

A three-phase motor may be run from a single-phase power source. However, it will not self-start. It may be hand started in either direction, coming up to speed in a few seconds. It will only develop 2/3 of the 3-φ power rating because one winding is not used. 3-φ motor runs from 1-φ power but…

A wound rotor induction motor has a stator like a squirrel cage induction motor, but a rotor with insulated windings brought out via slip rings and brushes. However, no power is applied to the slip rings. Their sole purpose is to allow resistance to be placed in series with the rotor windings while starting (figure…

Most AC motors are induction motors. Induction motors are favored due to their ruggedness and simplicity. In fact, 90% of industrial motors are induction motors. Nikola Tesla conceived the basic principles of the polyphase induction motor in 1883 and had a half horsepower (400 watts) model by 1888. Tesla sold the manufacturing rights to George…

Brushless DC motors were developed from conventional brushed DC motors with the availability of solid-state power semiconductors. So, why do we discuss brushless DC motors in a chapter on AC motors? Brushless DC motors are similar to AC synchronous motors. The major difference is that synchronous motors develop a sinusoidal back EMF, as compared to…

The variable reluctance motor is based on the principle that an unrestrained piece of iron will move to complete a magnetic flux path with minimum reluctance, the magnetic analog of electrical resistance. Synchronous Reluctance If the rotating field of a large synchronous motor with salient poles is de-energized, it will still develop 10 or 15%…

Synchronous motors load the power line with a leading power factor. This is often useful in canceling out the more commonly encountered lagging power factor caused by induction motors and other inductive loads. Originally, large industrial synchronous motors came into wide use because of this ability to correct the lagging power factor of induction motors.…

Single Phase Synchronous Motors Single-phase synchronous motors are available in small sizes for applications requiring precise timing such as timekeeping, (clocks) and tape players. Though battery-powered quartz regulated clocks are widely available, the AC line operated variety has better long term accuracy—over a period of months. This is due to power plant operators purposely maintaining…

After the introduction of the DC electrical distribution system by Edison in the United States, a gradual transition to the more economical AC system commenced. The lighting worked as well on AC as on DC. Transmission of electrical energy covered longer distances at a lower loss with alternating current. However, motors were a problem with…