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When using magnetic pumps, customers often choose variable frequency motors instead of ordinary motors. Many people don't know the difference between the two, so let's take a brief look.
1. The difference in the design of ordinary motors and variable frequency motors
1. Structural design: When designing the structure, it is also important to consider the influence of non-sinusoidal power supply characteristics on the insulation structure, vibration, and noise cooling methods of the variable frequency motor.
2. Electromagnetic design: For ordinary asynchronous motors, the main performance parameters considered when redesigning are overload capacity, starting performance, efficiency and power factor. The variable frequency motor, because the critical slip is inversely proportional to the power frequency, it can be started directly when the critical slip is close to 1. Therefore, overload capacity and starting performance do not need to be considered too much, but the key issue to be solved is how to improve the motor Adaptability of non-sine wave power supply.
2. Design requirements of variable frequency motors
1. The structural design is mainly to improve the insulation level; fully consider the vibration and noise of the motor; the cooling method adopts forced ventilation cooling, that is, the main motor cooling fan adopts an independent motor drive mode, and the function of the strong cooling fan is to ensure that the motor is in Cooling at low speeds.
2. Minimize the stator and rotor resistance and reduce the fundamental copper loss to compensate for the increase in copper loss caused by higher harmonics.
3. The distributed capacitance of the coil of the variable frequency motor is smaller, and the resistance of the silicon steel sheet is larger, so that the influence of the high frequency pulse on the motor is smaller, and the inductance filtering effect of the motor is better.
4. Ordinary motors, ie industrial frequency motors, only need to consider the starting process and the working conditions of one point of the industrial frequency, and then design the motor; while the variable frequency motors need to consider the starting process and the working conditions of all points within the frequency conversion range, and then design the motor.
5. In order to adapt to the PWM wide wave analog sine alternating current output by the frequency converter contains a large number of harmonics, the specially made frequency conversion motor can actually be understood as a reactor plus an ordinary motor.
6. The main magnetic field is not saturated design. One is to consider that higher harmonics will deepen the saturation of the magnetic circuit, and the other is to consider that the output voltage of the inverter can be appropriately increased in order to increase the output torque at low frequencies.
Three, the difference in structure between ordinary motors and variable frequency motors
1. The vibration and noise requirements of the frequency conversion motor are higher: the frequency conversion motor must fully consider the rigidity of the motor components and the whole, and try to increase its natural frequency to avoid resonance with each force wave.
2. Different heat dissipation system: the frequency conversion motor cooling fan adopts independent power supply to ensure continuous heat dissipation.
3. Higher requirements for insulation class: Generally, the insulation class of variable frequency motors is F or higher. Strengthen the insulation to the ground and the insulation strength of the turns, especially considering the ability of the insulation to withstand impulse voltage.
4. Different cooling methods for variable frequency motors: variable frequency motors generally use forced ventilation cooling, that is, the main motor cooling fan is driven by an independent motor.
5. Different requirements for 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.
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