Question

Universal motor works only with DC supply.

Hint:

The Universal motor is often referred to as an AC Series Motor. It is commonly used in high-speed, high-torque household appliances such as vacuum cleaners, food mixers, and portable power drills.

Answer 1

Step 1: Defining the Universal Motor:
A Universal motor is a series-wound motor specifically designed and optimized to operate on both single-phase Alternating Current (AC) and Direct Current (DC) electrical supplies.

Step 2: Analyzing AC Operation:
When connected to an AC supply, the alternating current reverses its direction periodically. Because the field winding and armature winding are in series, the polarities of both the field poles and the armature conductors reverse simultaneously. Since both variables change sign, the direction of the electromagnetic torque ($T \propto \Phi \cdot I_a$) remains positive and unidirectional, allowing the motor to rotate continuously.

Step 3: Design Modifications for AC Compatibility:
To run efficiently on AC without excessive energy loss, the stator core is constructed of thin silicon steel laminations to minimize eddy current heating, and the windings are designed with low inductance to reduce reactive voltage drops.

Step 4: Conclusion:
Since the motor runs on both AC and DC, the statement that it works “only with DC” is False.