In a three-phase motor, the speed of rotation of the magnetic field is referred to as the _____________ speed.

In a three-phase motor, the speed of rotation of the magnetic field is referred to as the _____________ speed.

• A. Synchronous
• B. Asynchronous
• C. Rotational
• D. Cyclical

Answer: (A)

The speed of rotation of the magnetic field in a three-phase motor is referred to as the synchronous speed. This term is used to define the speed at which the stator's magnetic field rotates, which is directly linked to the frequency of the electrical supply and the number of poles in the motor. Synchronous speed is calculated using the formula: \[ N_s = \frac{120 \times f}{P} \] where \( N_s \) is the synchronous speed in RPM, \( f \) is the frequency in hertz, and \( P \) is the number of poles. This concept is fundamental in understanding the operational characteristics of three-phase motors, as it sets the theoretical maximum speed at which the motor can operate. The motor's actual speed may differ due to various factors, such as load and slip, which means that while synchronous speed provides a crucial benchmark, most motors will operate at a speed slightly less than this value when under load. The other options do not accurately describe this concept in the context of three-phase motors. Asynchronous speed refers more generally to the speed of the motor when operating under load and not the speed of the magnetic field itself. Rotational and cyclical do not specifically relate to the

The speed of rotation of the magnetic field in a three-phase motor is referred to as the synchronous speed. This term is used to define the speed at which the stator's magnetic field rotates, which is directly linked to the frequency of the electrical supply and the number of poles in the motor. Synchronous speed is calculated using the formula:

[

N_s = \frac{120 \times f}{P}

]

where ( N_s ) is the synchronous speed in RPM, ( f ) is the frequency in hertz, and ( P ) is the number of poles.

This concept is fundamental in understanding the operational characteristics of three-phase motors, as it sets the theoretical maximum speed at which the motor can operate. The motor's actual speed may differ due to various factors, such as load and slip, which means that while synchronous speed provides a crucial benchmark, most motors will operate at a speed slightly less than this value when under load.

The other options do not accurately describe this concept in the context of three-phase motors. Asynchronous speed refers more generally to the speed of the motor when operating under load and not the speed of the magnetic field itself. Rotational and cyclical do not specifically relate to the