Why choose AC motor for cold rolling? (I) Disadvantages of DC Motor

Why choose AC motor for cold rolling? (I) Disadvantages of DC Motor

Motor structure determines the disadvantage of DC motor.

At present, most strip cold rolling mills in operation use DC motors as the main drives. The wide speed range, simple control, low speed and high torque DC motor meet the requirements of cold strip rolling mills. However, the maintenance of DC motor carbon brush and commutator is accompanied by the whole operation process of DC motor. Fragile and delicate, if careful maintenance is not in place, it is easy to cause the commutator ignition and affect the power supply device, such as burning SCR, fast fuse, etc.

Because of the high operation and maintenance requirements of DC motors, with the development of AC variable frequency speed regulation technology and the application of vector control technology, inverter speed regulation motors have almost completely replaced traditional DC motors in low power applications. The newly designed large and medium-sized tropical rolling mill, medium plate rolling mill and section steel mill at home and abroad have completely selected AC frequency conversion motor.

Dc motor structure

Ac motor structure

At present, AC main drive frequency conversion speed regulation of cold rolling mill generally adopts AC-DC-AC frequency conversion device.

Ac - DC - AC variable frequency speed control system has the characteristics of good performance, strong function, high reliability, using pulse width modulation (PWM) vector control or direct torque control. Ac to AC frequency conversion has the advantages of high frequency, high power factor, low grid side harmonics and no reactive power compensation, which can meet the technical performance requirements of the main drive of large rolling mills. The rectifier transformer capacity is small and the no-load loss of the transformer is small.