A.C. Machines and Motors

Front

What is a split-phase motor?

Back

A single-phase motor with different resistance and inductance in the run/start winding, creating a split phase and small starting torque. It uses a centrifugal switch to cut out the low-rated start winding.

Front

How is the direction changed in split-phase motors?

Back

By changing the polarity on the run or start winding, but not both.

Front

What is a capacitor start motor?

Back

A single-phase motor with increased phase split in the run/start winding, creating larger torque. It uses a capacitor to create a two-phase effect for starting.

Front

What happens at 75% full speed in a capacitor start motor?

Back

The centrifugal switch cuts out the low-rated start winding, and the motor continues running using the run winding.

Front

What is a capacitor-start/capacitor-run motor?

Back

A motor with two capacitors, one in series with the auxiliary/start winding, maintaining split phase for increased torque. The auxiliary winding stays in the circuit.

Front

What is a universal motor?

Back

A motor that operates on both A.C. and D.C., with stator and field windings in series, providing high start torque. It is lightweight and used in portable and domestic equipment.

Front

Why are universal motors not used in continuous-run equipment?

Back

Because they are noisy.

Front

What is a cage rotor in three-phase machines?

Back

A rotor with a three-phase rotating magnetic field around the stator, solid conductor bars, shorting rings, and rifling to help start.

Front

How is rotor speed calculated in three-phase machines?

Back

Rotor speed (nr) is calculated using synchronous speed (ns) and slip, which can be expressed as a percentage or per unit.

Front

What causes synchronous speed in A.C. motors?

Back

The connection of D.C. to the rotor synchronizes with the rotating field, causing synchronous speed.