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In the process of using the frequency converter, if you find that the frequency converter is subject to signal interference, then you need to first determine the source of the interference signal.
And combined with the actual situation to take the appropriate method to block the signal interference, you can also take certain methods to prevent the frequency converter from being interfered with, so that the frequency converter in the process of work in the process of the state of more stable.
General frequency converter in the process of work is very susceptible to radiation interference.
If in the production work, the frequency converter is subject to radiation signal interference, you need to propagate the interference signal through the radiation method, the specific way is through the wiring and the radioactive source and the line to be interfered with the shielding to weaken its interference signal.
If the frequency converter is affected by the line propagation of interference signals, then it is necessary to install filters through the input and output sides of the frequency converter, through the reactor or magnetic bad and other ways to deal with.
The specific way can take the signal line and power line vertical cross for vertical cross to sub-slot wiring. Shield tube should be grounded as far as possible, and need to maintain the entire length can be continuously and reliably grounded.
Frequency converter is affected by line propagation interference, need to let the shield grounding away from the frequency converter, at the same time should maintain and frequency converter grounding distance between the grounding point, should be separated from the frequency converter grounding point.
In order to avoid frequency converter by line propagation signal interference, you can let the magnetic ring in the frequency converter input power line and output line to use, the input line should be together towards the same direction of the circle, the output line also needs to be towards a direction of the circle, in the process of winding, you should let the magnetic ring close to the frequency converter, so that you can avoid the frequency converter by the line interference signal influence.
Frequency converter anti-interference measures
(1) The basic control circuit of frequency converter
There are two types of basic circuits, analog and digital, for communicating signals with the outside:
① 4～20mA current signal circuit (analog); 1～5V/0～5V voltage signal circuit (analog).
② Switch signal circuit, frequency converter start/stop command, forward/reverse command, etc. (digital).
External control instruction signals are introduced into the frequency converter through the above basic circuits, and at the same time, the interference source also generates interference potentials on its circuits to invade the frequency converter with the control cable as the media.
(2) The basic types of interference and anti-interference measures
① Electrostatic coupling interference: refers to the control cable and the surrounding electrical circuit of electrostatic capacitive coupling, the potential generated in the cable.
Measures: Increase the distance from the interference source cable, up to 40 times the diameter of the conductor above, the degree of interference is not obvious.
In the two cables set between the shielding conductor, and then the shielding conductor grounding.
② Electrostatic induction interference: refers to the magnetic flux generated by the surrounding electrical circuit changes in the cable induced potential. The size of the interference depends on the size of the flux generated by the interference source cable, the closed loop area formed by the control cable and the interference source cable and the relative angle between the control cable.
Measures: Generally, the control cable and the main loop cable or other power cables are laid separately, the separation distance is usually more than 30cm (minimum 10cm), separation is difficult, the control cable will be laid through the iron pipe. The control conductor stranded, the smaller the stranded spacing, the shorter the route laid, the better the anti-interference effect.
③Radio wave interference: This means that the control cable becomes an antenna, and electrical potential is generated in the cable by foreign radio waves
Measures: Same as those described in 1 and 2. If necessary, the frequency converter into the iron box for wave shielding, shielding with the iron box to be grounded.
④ Poor contact interference: refers to the frequency converter control cable electrical contacts and relay contacts poor contact, resistance changes in the cable generated by the interference.
Measures: poor contact of relay contacts, using parallel contacts or gold-plated contacts relay or selection of sealed relays. The cable connection points should be regularly tightened and reinforced.
⑤ Power line conduction interference: refers to various electrical equipment from the same power supply system to obtain power supply, by other equipment in the power supply system directly generates electric potential.
Measures: If the control power of the frequency converter is supplied by another system, install line filter on the input side of the control power; install insulated transformer and shielding and grounding.
⑥ Grounding interference: refers to the body grounding and signal grounding. For the weak voltage and current loop and any unreasonable grounding can be induced by a variety of unexpected interference, such as setting up more than two grounding points, grounding will produce potential difference, resulting in interference.
Measures: Take 1 point of grounding for the control cable for speed determination, and the grounding line is not used as a signal path. Cable grounding in the frequency converter side, the use of dedicated grounding terminals, not shared with other grounding terminals, and minimize the resistance of the grounding terminal lead point, generally not more than 100d.
(3) Other precautions
① The control cabinet with frequency converter should be as far away as possible from large-capacity transformers and motors. Its control cable lines should also avoid these leakage flux of large equipment.
② Weak voltage and current control cables should not be close to circuit breakers and contactors that are prone to arcing.
③ The control cable is recommended to be 1.25mm×2 or 2mm×2 shielded stranded insulated cable.
④ The shielding of the shielded cable should be continuous to the same length of the cable conductor. When cables are connected in the terminal box, the shielded terminals should be connected to each other.
