The supplier of the supporting equipment of the inverter reminds you that the voltage waveform output by the inverter is similar to a sine wave, but not a real sine wave. Its waveform contains a large number of harmonic components, especially the higher harmonics will increase the output current of the inverter, cause the motor winding to heat, produce oscillation and noise, accelerate the aging of insulation, and even may damage the motor; At the same time, harmonics of various frequencies will emit radio disturbances of different programs into space, which may lead to malfunction of other electromechanical equipment.
Therefore, when installing the inverter, it is necessary to comprehensively consider the interval between the central control room, the inverter and the motor, so as to reduce the influence of harmonics as much as possible and improve the stability of control.
(1) The boundary of the interval is said:
1. Near spacing: the spacing between the inverter and the motor ≤ 20m;
2. Intermediate spacing: the interval between the inverter and the motor > 20m, and the ≤ is 100m;
3. Remote spacing: the spacing between the inverter and the motor > 100m;
(2) Occasions for industrial use:
1. Near spacing: the inverter and the motor can be directly connected;
2. Intermediate spacing: the inverter and the motor can be directly connected, but the carrier frequency of the inverter needs to be adjusted to reduce the harmonic disturbance;
3. Remote spacing: the inverter and the motor can be directly connected, not only the carrier frequency of the inverter needs to be adjusted to reduce the harmonic interference, but also the output communication reactor needs to be installed.
(3) In highly automated factories:
In a highly automated factory, all equipment needs to be monitored and controlled in a central control room. Therefore, the signal of the inverter system should also be sent to the central control room.
1. Near interval: that is, if the inverter is installed in the central control room. The control console and the inverter can be directly connected and controlled by a voltage signal of 0-5/10V and some switching signals. However, the electromagnetic radiation of the high-frequency switching signal of the inverter will cause some disturbance to the weak current control signal, so it does not have to be beautiful and neat, and the inverter is placed in the central control room.
2. Intermediate spacing: that is, the frequency converter is far away from the central control room, and the current signal of 4-20mA and some switching quantities can be selected for control connection; If the interval is farther, RS485 serial communication mode can be used to connect;
3. Far spacing: that is, the interval between the inverter and the central control room is greater than 100m. At this time, it is possible to use a communication intermediate relay to achieve a distance of 1 km; If it is farther away, it is necessary to choose a fiber optic adapter, which can reach 23km far.
The communication cable connection can easily form a multi-stage drive control system, and then realize the requirements of master/slave and synchronous control. Connecting with the currently prevalent fieldbus system will greatly increase the data conversion rate. The extension of the interval between the central control room and the inverter cabinet is conducive to shortening the interval between the inverter and the motor, so as to improve the system performance with a more reasonable layout.
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