About the knowledge of motors, the most selected and comprehensive! (1)
Electric motors are ubiquitous in the field of equipment. This is not a lonely device. A reliable pump also requires a reliable motor, and the quality of the motor directly affects the normal operation of the equipment. Motor type, soft start method, selection steps, damage causes and handling methods, and the differences between good and bad motors Each of these questions is an important reflection of the motor's happiness index. Let's take a look together. Basic knowledge of motors: Differences between various types of motors: 1. Differences between DC and AC motors. As the name suggests, DC motors use direct current as the power source. And AC motors use AC power as the power source. In terms of price, merit
Motor type, soft start method, selection steps, damage causes and handling methods, and the differences between good and bad motors Each of these questions is an important reflection of the motor's happiness index. Let's take a look together.
Differences in various types of motors
1. Differences between DC and AC motors
As the name suggests, DC motors use direct current as the power source. And AC motors use AC power as the power source.
In terms of price, DC motors with the same power are higher than AC motors, including speed control devices. The price of DC speed control devices is also higher than that of AC speed control devices. Of course, there are also significant differences in structure and maintenance.
In terms of performance, due to the stable speed and precise speed control of DC motors, which cannot be achieved by AC motors, DC motors have to be used to replace AC motors under strict speed requirements.
AC motor speed regulation is relatively complex, but it is widely used due to the use of AC power in chemical plants.
2. Differences between synchronous and asynchronous motors
The rotation speed of the rotor is the same as that of the stator, which is called a synchronous motor. If it is not consistent, it is called an asynchronous motor.
3. Differences between ordinary and variable frequency motors
Firstly, ordinary motors cannot be used as variable frequency motors.
Ordinary motors are designed according to constant frequency and voltage, and cannot fully meet the requirements of frequency converter speed regulation, so they cannot be used as frequency conversion motors.
1、 The impact of frequency converters on motors mainly lies in their efficiency and temperature rise
The frequency converter can generate varying degrees of harmonic voltage and current during operation, causing the motor to operate under non sinusoidal voltage and current. The higher-order harmonics inside can cause an increase in stator copper loss, rotor copper loss, iron loss, and additional losses of the motor, with the most significant being rotor copper loss. These losses will cause the motor to generate additional heat, reduce efficiency, and output power, and generally increase the temperature rise of ordinary motors by 10-20%.
Variable frequency motor with independent cooling fan for ordinary motors
2、 Insulation strength issues of electric motors
The carrier frequency of the frequency converter ranges from several thousand to over ten kilohertz, making the stator winding of the motor withstand a high voltage rise rate, which is equivalent to applying a steep impulse voltage to the motor, causing the insulation between turns of the motor to withstand a more severe test.
3、 Harmonic electromagnetic noise and vibration
When ordinary motors are powered by frequency converters, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors become more complex. The harmonics contained in the variable frequency power supply interfere with the inherent spatial harmonics of the electromagnetic part of the motor, forming various electromagnetic excitation forces and increasing noise. Due to the wide operating frequency range and large speed variation range of electric motors, it is difficult to avoid the natural vibration frequency of various structural components of the motor due to the frequency of various electromagnetic force waves.
4、 Cooling issues at low speeds
When the frequency of the power supply is low, the losses caused by higher harmonics in the power supply are relatively large; Secondly, when the speed of the variable motor decreases, the cooling air volume decreases proportionally to the third power of the speed, resulting in the inability of the motor to dissipate heat and a sharp increase in temperature rise, making it difficult to achieve constant torque output.
How to distinguish between ordinary motors and variable frequency motors?
Differences in structure between ordinary motors and variable frequency motors
1. Higher insulation level requirements
The insulation level of general variable frequency motors is F level or higher, and the strength of ground insulation and wire turn insulation should be strengthened, especially considering the ability of insulation to withstand impulse voltage.
2. The vibration and noise requirements of variable frequency motors are higher
Variable frequency motors should fully consider the rigidity of the motor components and the overall structure, and strive to increase their natural frequency to avoid resonance with various force waves.
3. 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.
4. Different requirements for protective measures
For variable frequency motors with a capacity exceeding 160KW, bearing insulation measures should be taken. The main reason is that it is prone to magnetic circuit asymmetry and also generates shaft current. When the currents generated by other high-frequency components combine, the shaft current will greatly increase, leading to bearing damage. Therefore, insulation measures are generally taken. For constant power variable frequency motors, when the speed exceeds 3000/min, special high-temperature resistant lubricating grease should be used to compensate for the temperature rise of the bearings.
5. Different heat dissipation systems
The variable frequency motor cooling fan adopts an independent power supply to ensure continuous cooling capacity.