The relationship between synchronous speed and rotor speed.

The synchronous speed is not necessarily greater than the rotor speed, as in some cases the rotor speed can be higher than the synchronous speed.

Synchronous speed is not necessarily greater than rotor speed, as in some cases the rotor speed can exceed synchronous speed.

1. The concepts of synchronous speed and rotor speed

Before understanding the relationship between synchronous speed and rotor speed, we need to first understand these two concepts. Synchronous speed refers to the speed of the rotating magnetic field, usually calculated using the formula Ns=120f/p, where f is the frequency of the power supply and p is the number of pole pairs. For example, a power supply of 50Hz and a 4-pole motor has a synchronous speed of 1500rpm.

Rotor speed refers to the actual rotational speed inside the rotor, usually calculated using the formula N=120f/p(1-s), where s is slip. Slip refers to the difference between rotor speed and synchronous speed.

2. The relationship between synchronous speed and rotor speed

The relationship between synchronous speed and rotor speed depends on the operating state of the motor. When load is low or current is weak, slip is very small, and rotor speed approaches synchronous speed; however, when load increases, slip increases, causing rotor speed to decrease. Therefore, when the motor load is too heavy, rotor speed may be lower than synchronous speed.

In addition, there are some special cases; for example, during startup of single-phase motors and induction motors, since there is no initial rotational torque inside the rotor, rotor speeds may exceed synchronous speeds. However, as load increases, their slip also increases, causing rotor speeds to decrease and approach synchronous speeds.

3. Applications of synchronous speed and rotor speed

Synchronous speed and rotor speed are important parameters in motor design and maintenance; they directly affect motor performance and lifespan. In motor maintenance, measuring the difference between rotor speeds and synchronous speeds helps assess the condition and health status of the motor.

Additionally, understanding the relationship between synchronous speeds and rotor speeds helps us select appropriate motor models based on load conditions to ensure that motors can operate stably and efficiently.