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Motor Speed and Slip Ratio

2021-01-25 14:16:02 Weima Electric (Shanghai) Ltd. read

The unit of rotational speed is round per minute r/m (rpm), round per second per r/s (rps).

ⅰ.Synchronous speed of motor

Because the rotation of the induction motor is caused by the rotating magnetic field and its speed is the same as the rotating magnetic field, so the synchronous speed of the motor refers to the speed of the rotating magnetic field, expressed in NS.

Synchronous speed of various frequencies and pole numbers (r/m)

Pole/P

50HZ

60HZ

Pole/P

50HZ

60HZ

2

3000

3600

6

1000

1200

4

1500

1800

8

750

900

ⅱ.Rated speed of motor

Rated speed refers to the speed of the motor at rated power. That is the motor speed at full load, so it is also called full load speed. It is indicated by the symbol "n".

ⅲ.Maximum safe speed of motor

Unless otherwise indicated on the nameplate, all single speed three-phase squirrel cage induction motors with voltage of 1000V and frame number of 400 and below shall be able to operate safely and continuously within the speed listed in the table below.

unit:r/m

Frame No.

2P

4P

6P

Frame No.

2P

4P

6P

≤100

5200

3600

2400

225

3600

2300

1800

112

5200

3600

2400

250

3600

2300

1800

132

4500

2700

2400

280

3600

2300

1800

160

4500

2700

2400

315

3600

2300

1800

180

4500

2700

2400

355

3600

2300

1800

200

4500

2300

1800

400

1800

Note: when the motor runs above the rated speed, for example, when the speed control is applied, the noise and vibration intensity will increase. Then the motor is required to do fine leveling to meet the acceleration capacity above the rated speed. In addition, bearing life may be reduced so attention should be paid to the interval of oil filling and the supplement of grease and its service life.

ⅳ.Transfer Ratio

The stator winding is connected with three-phase alternating current to generate rotating magnetic field, the rotating magnetic field cuts the rotor winding, and the rotor winding generates induced current. The induced current generates electromagnetic force under the action of the rotating magnetic field to drive the rotor to rotate (the rotating direction of the rotor is consistent with that of the rotating magnetic field). Without the influence of external force, the rotation speed of rotor is lower than that of stator magnetic field.

S=(ns- n)/ ns×100%。Slip ratio means the ratio of the difference between the speed of stator magnetic field rotation (synchronous speed) and the speed of rotor rotation (rated speed) and the rotation speed of stator magnetic field. S=(ns- n)/ ns×100%。

电机的转差率一般控制在3%~5%之间。The slip ratio of motor is generally controlled between 3% and 5%.

Note: motor mainly refers to three-phase asynchronous motor