Basic knowledge of motor 2

The difference in structure between ordinary motor and variable frequency motor

01. Higher insulation requirements

Generally, the insulation class of the frequency conversion motor is F or higher. Strengthen the insulation to the ground and the insulation strength of the turns, and especially consider the ability of the insulation to withstand impulse voltage.

02. The vibration and noise requirements of variable frequency motors are higher

As for the frequency conversion motor, we must fully consider the rigidity of the motor components and the whole, and try to increase its original frequency to avoid resonance with each force wave.

03. Different cooling methods for variable frequency motors

For frequency conversion motors generally, we use forced ventilation cooling, that is, the main motor cooling fan is driven by an independent motor.

04. Different protection measures

Bearing insulation measures should be adopted for variable frequency motors with a capacity exceeding 160KW. The main reason is that the asymmetry of the magnetic circuit is easy to occur, and the shaft current is also generated. When the currents generated by other high-frequency components work together, the shaft current will greatly increase, resulting in damage to the bearing, so generally insulation measures must be taken.

For constant power variable frequency motors, when the speed exceeds 3000/min, special high-temperature-resistant grease should be used to compensate for the temperature rise of the bearing.

05. Different cooling systems

The frequency conversion motor cooling fan uses an independent power supply to ensure continuous heat dissipation.

Motor selection

The basic content needed for motor selection are:

Type of load driven, rated power, rated voltage, rated speed, and other conditions.

Load type:

·DC

·Asynchronous Motor

·Synchronous Motor

For production machinery with stable load and no special requirements for starting and braking, ordinary squirrel-cage asynchronous motors should be preferred, which are widely used in machinery, water pumps, fans, etc.

Starting and braking are more frequent, and production machinery that requires larger starting and braking torques, such as bridge cranes, mine hoists, air compressors, and irreversible rolling mills, we should use wound asynchronous motors.

Where there is no requirement for speed regulation, a constant speed or improvement of power factor is required, synchronous motors should be used, such as medium and large-capacity water pumps, air compressors, hoists, mills, etc.

The speed regulation range is more than 1:3, and the production machinery that needs continuous, stable and smooth speed regulation should adopt separately-excited DC motors or squirrel-cage asynchronous motors or synchronous motors with variable frequency speed regulation, such as large-scale precision machine tools, gantry planers, Rolling mills, hoists, etc.

If the production machinery that requires large starting torque and soft mechanical characteristics, we should use series-excited or compound-excited DC motors, such as trams, electric locomotives, and heavy-duty cranes.

Generally speaking, the motor can be roughly determined by providing the type of load driven, the rated power of the motor, the rated voltage, and the rated speed.

But if the load requirements are to be optimally met, these basic parameters are far from enough.

The parameters that need to be provided include:

Frequency, working system, overload requirements, insulation level, protection level, moment of inertia, load resistance torque curve, installation method, ambient temperature, altitude, outdoor requirements, etc. (provided according to specific conditions)

Reported by jessica