What are the two factors that determine the synchronous speed of the rotating magnetic field of an induction motor?

The synchronous speed of the rotating magnetic field in an induction motor is fundamentally determined by two key factors: the number of stator poles and the frequency of the electrical supply.

The synchronous speed (Ns) can be calculated using the formula:

[

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

]

where (f) is the frequency of the supply in hertz and (P) is the number of poles in the stator winding. As the frequency increases, the synchronous speed increases, and similarly, a higher number of poles will result in a lower synchronous speed. This relationship illustrates how the interplay between the electrical frequency and the pole configuration directly influences the speed at which the magnetic field rotates.

The other options provided focus on factors like torque, voltage, magnetic field strength, current, rotor speed, and insulation type, which do not influence the synchronous speed itself. Instead, these factors relate more to the performance characteristics of the motor, such as its ability to produce torque or handle electrical stresses, rather than the basic synchronous speed determined by the motor's design and electrical supply characteristics.