Jan 22, 2021
How to solve inverter interference
Electric power processing and production units have extremely high requirements for the working efficiency of mechanical equipment. Therefore, in order to make the working efficiency of mechanical equipment to meet production needs, many electric power processing units will install and use inverters. Because there are many types of machinery and equipment used in the processing and production units, the inverter is prone to interference during the production process. Once the inverter is disturbed, it will seriously affect its work efficiency.
In the process of using the frequency converter, if the frequency converter is found to be interfered by the signal, it is necessary to judge the source of the interference signal first, and take appropriate measures to block the signal interference based on the actual situation. You can also take certain measures to prevent the frequency converter from being interfered by the signal. Interference makes the inverter more stable in the working process.
Generally, the inverter is susceptible to radiation interference during operation. If the frequency converter is interfered by radiation signals during production work, the interference signals need to be transmitted through radiation. The specific method is to weaken the interference signals by wiring and shielding the radioactive source and the interfered line.
If the inverter is affected by the interference signal propagated by the line, it needs to be processed by installing a filter on the input and output side of the inverter, through a reactor or a magnetic failure. The specific method can be to adopt the signal line and the power line to cross vertically and cross vertically to divide the slot wiring. The shielding tube should be grounded as much as possible, and it needs to be continuously and reliably grounded over the entire length.
Inverter is affected by line propagation interference, so the shielding layer should be grounded far away from the inverter, and at the same time, the distance between the grounding point of the inverter and the grounding point of the inverter should be kept apart. In order to prevent the inverter from being affected by the interference of the line propagation signal, the magnetic ring can be used on the input power line and output line of the inverter. The input lines should be wound in the same direction together, and the output line should also be wound in the same direction. During the winding process, the magnetic ring should be close to the inverter, so as to prevent the inverter from being affected by line interference signals.
How to solve inverter interference
Inverter anti-interference measures
Due to the non-linearity of the main circuit (switching action), the inverter itself is a source of harmonic interference, but its peripheral control loop is a small energy and weak signal loop, which is very susceptible to interference from other devices, causing the inverter itself and its surroundings. The device is not working properly. Therefore, when the inverter is installed and used, anti-interference measures must be taken for the control loop.
1) The basic control circuit of the inverter
There are two basic circuits for signal exchange with the outside: analog and digital:
① 4～20mA current signal circuit (analog); 1～5V/0～5V voltage signal circuit (analog).
②The switch signal circuit, the start and stop commands of the inverter, forward and reverse commands, etc. (digital).
The external control command signal is introduced into the inverter through the above-mentioned basic circuit, and at the same time, the interference source also generates interference potential on its circuit, and the control cable is used as a medium to invade the inverter.
2) Basic types of interference and anti-interference measures.
①Electrostatic coupling interference: refers to the electric potential generated in the cable by the electrostatic capacitance coupling between the control cable and the surrounding electrical circuits.
Measures: Increase the distance between the cable and the interference source. When the diameter of the conductor is more than 40 times, the degree of interference is not obvious.
Set a shielding conductor between the two cables, and then ground the shielding conductor.
②Electrostatic induction interference: refers to the electric potential induced in the cable by the magnetic flux changes generated by the surrounding electrical circuits. The magnitude of the interference depends on the magnetic flux generated by the interference source cable, the closed loop area formed by the control cable and the relative angle between the interference source cable and the control cable.
Measures: Generally, the control cables are laid separately from the main circuit cables or other power cables. The separation distance is usually more than 30cm (minimum 10cm). When separation is difficult, the control cables are laid through iron pipes. Twist the control conductors. The smaller the twisting distance and the shorter the route, the better the anti-interference effect.
③Radio interference: refers to the control cable becoming an antenna, and the electric potential is generated in the cable by external electric waves.
Measure: Same as described in 1 and 2. If necessary, put the frequency converter into an iron box for electric wave shielding, and the iron box for shielding must be grounded.
④ Poor contact interference: Refers to the interference in the cable caused by the electrical contact of the inverter control cable and the contact of the relay, and the change of resistance.
Measures: For poor contact of the relay contacts, use parallel contacts or gold-plated contact relays or use sealed relays. The cable connection points should be tightened and reinforced regularly.
⑤Power line conduction interference: refers to when various electrical equipment receives power from the same power system, other equipment directly generates electric potential in the power system.
Measures: The control power supply of the inverter is supplied by another system, a line filter is installed on the input side of the control power supply; an insulating transformer is installed, and the shield is grounded.
⑥Grounding interference: refers to the body grounding and signal grounding. Various unexpected interferences can be induced by weak voltage current loops and any unreasonable grounding. For example, if more than two grounding points are set, a potential difference will be generated at the grounding, which will cause interference.
Measures: Take one point of the control cable for the given speed to ground, and the ground wire is not used as a signal path. The grounding of the cable is done on the side of the inverter. Use a special grounding terminal instead of sharing it with other grounding terminals, and try to reduce the resistance of the grounding terminal lead point, generally not more than 100d.
3) Other matters needing attention
①The control cabinet with frequency converter should be kept away from large-capacity transformer and motor as far as possible. The control cable circuit should also avoid these devices with large leakage flux.
②The weak voltage and current control cables should not be close to circuit breakers and contactors that are prone to arcing.
③It is recommended to use 1.25mm×2 or 2mm×2 shielded twisted insulated cables for control cables.
④The shield of the shielded cable should be continuous until the cable conductor is the same length. When the cables are connected in the terminal box, the shield terminals should be connected to each other.