Speed regulation principle It can be seen from the spee […]
Speed regulation principle
It can be seen from the speed relationship n=n1(1-S)=60(f1/P)(1-S) of asynchronous motor.to change the speed of asynchronous motor, we can start from the following 3 aspects:
1.Changing the pole number P of stator winding of asynchronous motor to change the speed n1 of stator rotating magnetic field, which is called pole-changing speed regulation (not uniform speed regulation).
2.Change the frequency of the power supply connected to the motor to change n1, the so-called variable frequency speed regulation.
3.Changing the revolutional slip of motor S
Pole changing speed regulation
Because the revolutional slip S of general asynchronous motor is very small in normal operation, the speed n = N1 (1-S) of the motor is determined by the synchronous speed n1. From n1=60f1/P, it can be seen that the synchronous speed n1 will change if the pole logarithm P of stator winding is changed with the power frequency f1 unchanged. For example, when the pole logarithm doubles, the synchronous speed will decrease by half, and the speed of motor will also decrease by about half. Obviously, this kind of speed regulation method can only change the speed one step at a time, rather than smooth speed regulation.
Squirrel cage rotor is commonly used in pole-changing motors, because the pole number of the squirrel cage rotor can automatically change with the change of the pole number of the stator, so that the pole number of the stator and rotor magnetic field is always equal and the average electromagnetic torque is generated. If it is a winding rotor, when the stator pole logarithm is changed, the connection method of the rotor winding must be changed accordingly to get the same pole logarithm as that of the stator, which is very inconvenient.
In order to make the stator have two pole logarithms, the method is to use two sets of stator windings with different pole logarithms, one of which is called double winding pole-changing. Obviously, this is an uneconomical method, which is only used in special cases. The ideal way is to install only one set of stator windings and change the winding connection to obtain two or more pole logarithms, namely the so-called single winding pole change. For the case of double pole ratio (such as 2/4 pole, 4/8 pole, etc.), single-winding pole-changing has long been adopted by people. With the development of science and technology, non-double pole ratio (such as 4/6 pole, 6/8 pole, etc.) and three-speed (such as 4/6/8 pole) using single-winding pole-changing have also been widely used.
The next article will talk about variable frequency speed regulation.