Zhou Yongming (Guangzhou Cement Factory) In the cement industry, the speed control systems of major large equipment such as kilns and mills will directly affect the service life of these equipment and the quality of the products. Frequency conversion speed control system overcomes many shortcomings of traditional DC speed control systems, such as low speed operation system instability, high energy consumption, high maintenance costs, with a large speed range, hard characteristics, high precision, low energy consumption, convenient braking Flexibility and other advantages are getting more and more applications. However, due to the interference problem of the frequency converter, the placement of the frequency converter is very knowledgeable.

1Distance between inverter and motor installation In the field of industrial use, the distance between the inverter and the motor can be roughly divided into three situations: long distance, medium distance and close distance. Within 20m for close range, 20 ~ 100m for middle distance, and 100m for long distance.

Because the inverter output voltage waveform is not a sine wave, the waveform contains a large number of harmonic components, in which higher harmonics will increase the inverter output current, causing the motor winding heat, resulting in vibration and noise, accelerated insulation aging, and may also The motor is damaged; at the same time, the harmonics of various frequencies will emit different levels of radio interference to the space, which will interfere with the normal operation of the electronic device and may cause other devices to malfunction. Therefore, place the inverter as close as possible to the motor being controlled. However, due to the limitation of production site space, there is always a certain distance between the inverter and the motor. If the distance between the inverter and the motor is within 20m, it can be directly connected with the inverter. For the medium distance between the inverter and the motor of 20m to 100m, the carrier frequency of the inverter needs to be adjusted to reduce harmonics and interference. However, for a long-distance connection between the inverter and the motor of more than 100 m, not only should the carrier frequency be moderately reduced, but an output AC reactor should also be installed.

2 The distance between the central control room and the frequency converter can be monitored in a highly automated central control room. The signals of the frequency converter system are also sent to the central control room. If the position of the frequency converter is in the central control room, the total control Between the station and the frequency converter, it can be connected directly, through the 0'5/10V voltage signal and some switch signal control. However, the high-frequency harmonic electromagnetic radiation of the high-frequency switching signal of the inverter will cause some interference to the PLC main control system and weak control signal, so it does not have to be neat and tidy, and put the inverter in the central control room. If the frequency converter is far from the central control room, 4~20mA current signal and some switch quantity can be used for control connection; if the distance is farther, you can use RS485 serial communication method to connect; if you want to increase the distance, you can use The communication relay reaches the distance of 1km; if the fiber connector is used, the distance can reach 23km. With the use of communication cable connections, a multi-stage drive control system can be easily constructed to implement master/slave and synchronous control. Connecting with the currently popular fieldbus systems will greatly increase the data conversion rate. The extension of the distance between the central control room and the frequency converter cabinet helps to shorten the distance between the frequency converter and the motor, so as to improve the system performance with a more reasonable layout.

In short, when installing the inverter, it is necessary to comprehensively consider the distance between the inverter, the motor, and the central control room to minimize the influence of harmonics, improve the stability of the control, and reduce the impact on other devices. !

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