Which motor is referred to as a universal motor?

• A. Synchronous
• B. Series
• C. Single-phase induction
• D. Shunt

Answer: (B)

Universal motors may be powered by either AC or DC power sources.
The universal motor is constructed in the same way as a series-wound DC motor. However, it is designed to operate with either AC or DC applied.
The series-wound motor is the only type of DC motor that will operate with AC applied.
The windings of shunt-wound motors have inductance values that are too high to allow the motor to function with AC applied.
The series-wound motors have windings that have low inductances (few turns of large diameter wire), and they, therefore, offer a low impedance to the flow of AC.
The universal motor is one type of AC motor that has concentrated or salient field windings. These field windings are similar to those of all DC motors.