The rotating speed of three-phase asynchronous motor is graded and determined by the "pole number" of the motor.

The "pole number" of three-phase asynchronous motor is the number of magnetic poles in the specified sub-magnetic field. Different connection modes of stator windings can form different poles of stator magnetic field. The number of poles of the motor is determined by the required speed of the load. The number of poles of the motor directly affects the motor speed, and the motor speed =60x motor frequency/motor pole number. The current of the motor is only related to the voltage and power of the motor.

Large-capacity synchronous motors all rotate with magnetic poles, that is, the rotor is a magnetic pole, which is generated by the direct current of the excitation winding or the permanent magnet on the rotor. The logarithm of the magnetic pole of the synchronous machine is the logarithm of the rotor magnetic pole. Eight-pole motor means that the rotor has eight poles, 2p=8, that is, the motor has four pairs of poles.

Generally, turbo-generators are mostly hidden-pole motors with few pole pairs, generally 1 and 2 pairs, n=60f/p, so its rotating speed is very high, reaching 3000 revolutions (power frequency), while hydro-generators have many poles, and the rotor structure is convex, so the process is complicated. Because of its many magnetic poles, its rotation speed is very low, perhaps only a few revolutions per second.

Besides the efficiency of the pump and the motor, the power of the motor is approximately equal to that of the pump. The efficiency of the motor is generally 0.85, and your corresponding motor power is 5.5KW, 15KW, and the speed is 2900. Then the motors are 5.5KW-2P and 15KW-2P, respectively, and the motor speed = frequency ×60S÷ (the number of motor poles ÷2).