The variable frequency motor is used for the motor with special frequency converter. The difference between the variable frequency motor and the common motor is that the strong cooling fan is added, and the power of the fan comes from a separate power supply, which can not be led out from the main motor. The strong cooling fan is used to ensure the cooling of the motor at low speed.
Answer 1: variable frequency motor can adjust the speed of motor, and then realize the purpose of energy saving according to the load situation. Ordinary motor is a device with fixed speed, which can not be adjusted.
Answer 2: there is no big difference, but its coil distribution capacitance is smaller, the resistance of silicon steel sheet is larger, so the impact of high-frequency pulse on the motor is smaller, and the motor's inductive filtering effect is better.
Answer 3: the manufacturing process of ordinary motor and variable frequency motor is quite different.
Ordinary motor, namely power frequency motor, only needs to consider the starting process and the working condition of one power frequency point, and then design the motor; while variable frequency motor needs to consider the starting process and all the working conditions of all points within the range of variable frequency, and then design the motor.
The differences are:
1. From the perspective of power frequency, the variable frequency motor is of poor quality, while the ordinary motor is a good motor.
2. Because the PWM width modulation wave output by the frequency converter simulates sinusoidal alternating current, which contains a lot of harmonics, it usually needs to be filtered by the reactor before entering the ordinary motor, otherwise the ordinary motor will generate heat.
3. In order to adapt to the output of the frequency converter PWM PWM PWM analog sinusoidal AC contains a lot of harmonics, the purpose of the specially made frequency conversion motor can be understood as reactor plus ordinary motor.
4. That is to say, the frequency conversion motor with the same power has larger iron core section, more coil turns, larger wire diameter, higher insulation and special cooling fan motor.
5. In order to meet the needs of speed regulation with weak magnetic field, bearing capacity and dynamic balance of high-speed rotor are considered.
6. This kind of variable-frequency motor does not have better torque characteristics, but it overcomes the need that the ordinary motor does not adapt to PWM PWM PWM PWM width modulation to simulate sinusoidal alternating current.
7. If the variable frequency motor does not have the above characteristics and requirements, it is the false variable frequency motor variable frequency motor than the ordinary motor (constant frequency and constant voltage).
The structural differences are:
1. The insulation grade is generally f or higher. Strengthen the insulation strength to the ground and wire turn, especially consider the ability of insulation to withstand impulse voltage.
2. For the vibration and noise of the motor, it is necessary to fully consider the rigidity of the motor components and the whole, and try to improve its natural frequency so as to avoid resonance with each force wave.
3. Cooling mode: forced ventilation cooling is generally adopted, that is, the main motor cooling fan is driven by an independent motor.
4. Measures to prevent shaft current, bearing insulation measures shall be taken for motors with capacity over 160kW. It is easy to produce asymmetric magnetic circuit and shaft current. When the current generated by other high-frequency components is combined, the shaft current will increase greatly, resulting in bearing damage. Therefore, insulation measures should be taken generally.
5. For constant power variable frequency motor, when the speed is more than 3000/min, special grease with high temperature resistance shall be used to compensate the temperature rise of bearing.
What are the disadvantages of long-term low-frequency operation of ordinary motors: 1. Resonance at a certain frequency; 2. Heat dissipation. When the power frequency is low, the loss caused by high-order harmonics in the power supply is large. In addition, the fan she brought is not enough to cool herself at low frequency, and the life of the motor drops abruptly.
Supplement: in addition, the motor speed can also be adjusted by the hydraulic coupling.
Hydraulic coupling is a kind of mechanical equipment that uses liquid medium to transfer speed. Its active input shaft end is connected with the original transmission machine, and its driven output shaft end is connected with the load shaft end. By adjusting the pressure of liquid medium, the speed of the output shaft can be changed. In ideal condition, when the pressure tends to infinity, the output speed is equal to the input speed, which is equivalent to the steel coupling. When the pressure is reduced, the output speed will be reduced correspondingly, and the output speed can be adjusted steplessly lower than the input speed by continuously changing the medium pressure.
However, the hydraulic coupling in the speed range, speed accuracy, efficiency and other links, are worse than the inverter motor, but the price is cheaper.
What are the disadvantages of long-term low-frequency operation of General Motors?
A: ordinary motors are not allowed to work at low frequency for a long time, or they may burn out if they are heated seriously.
The wiring method of the variable frequency motor is the same as that of the common motor, which is generally the star connection method. The difference is that the variable frequency motor is equipped with an independent cooling fan to force the motor to cool.
Connect the end, x, y and Z of the three windings of the three-phase power supply together to form a common point O, and lead out three end lines from the start a, B and C. this connection method is called "star connection method" or "Y-connection method". The three-phase power supply is a system which is connected by three sinusoidal power supplies with the same frequency, the same amplitude and the phase difference of 120 ° in turn. There are two connection modes of three-phase power supply: Y-type and △ type.