37V voltage of the control circuit
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Hello, experts! Our low-voltage cabinets drive the motors of the field circulation pumps; the distance between them is 500 meters. Both the 380V power cables and the 220V control cables are run in metal conduits, and everything is operating normally. But there is a strange phenomenon with the 220V intermediate relays installed in the low-voltage cabinet at the low-voltage chamber end: the indicator lights for the relays that are engaged show a bright green light, while those for the relays that are not engaged display a faintly bright green light. I used a multimeter to measure the voltage across the coil of the relays that were not engaged, and it read 37V. Additionally, the normally closed contacts of these relays did not conduct electricity, which should be the case! But why does this coil have a voltage of 37V? ? And it’s not just one; all the relays that are not engaged in this cabinet show a faint green light, and the coils have a voltage of 37V. What’s going on here? The induced voltage in the cable tray? It’s that powerful? Can the induced voltage reach 37V? Could the induced voltage cause the relay to be activated? How can these induced voltages be eliminated? ? Have any of you experts encountered such a situation? Anyone who knows something about this, please give some advice! ! Thank you! !
The phenomenon you described, namely a 37V voltage appearing across the terminals of the unactivated relay coil, is likely caused by electromagnetic induction or a \"voltage leakage\" in the circuit. During long-distance cable transmission, especially when power cables and control cables are placed close to each other in the same metal conduit, induced voltages are generated due to electromagnetic induction. This situation is not uncommon in industrial control systems. Here are some possible causes and solutions: 1. Electromagnetic induction: In the same conduit, the alternating current in the 380V power cable may induce a voltage in the 220V control cable through electromagnetic induction. This induction phenomenon becomes more pronounced if the cables in the cable tray are arranged closely together, especially when the power cables and control cables run parallel to each other and are very close. Solution: - Run the power cables and control cables separately as much as possible to increase the distance between them. - Cables with metal shielding or an additional shielding layer around the control cable can be used to reduce induced voltage. - Select an appropriate cable cross-section for the control cable and ensure proper grounding to reduce the impact of induced voltages. 2. Series connection in the circuit: There may be some unintended parallel paths in the control cables, and voltage drops can occur through these paths. Solution: - Check the insulation of the control cable to ensure it is in good condition and free from damage. - Check whether the relay and its associated devices are properly grounded. - Check the wiring for incorrect connections or damaged components. 3. Leakage voltage of the relay itself: Some relays may have a slight leakage current when in the off state, resulting in a low voltage across their terminals. Solution: - Check the relay specifications to confirm that it is suitable for your application. - If the leakage voltage affects the proper operation of the system, it may be necessary to replace the relay with one that has a lower leakage current or better performance. The induced voltage is generally not sufficient to activate the relay, as the relay’s coil usually requires a higher voltage (close to its nominal voltage) in order to generate enough magnetic force to close the contacts. However, this induced voltage may interfere with other electronic devices or have a negative impact on the lifespan of the relay over time. You can try one or more of the above measures to reduce or eliminate induced voltage and ensure the proper operation of the control system. .
Induced electricity: Check whether the grounding of each cabinet and the cables is properly done, as well as whether there are any strong sources of interference such as frequency converters in the vicinity of these cabinets.
1. The power supply distance is too long; it generally should not exceed 300 meters. Is a voltage drop at a distance of 500 meters considered normal? 2. The solutions are: first, use shielded control cables; second, ensure that the spare conductors in the control cables are grounded. 3. LED lights are not necessary for the indicator lights
Thank you to the experts for their professional guidance! ! The current situation is that the cables are provided by Party A, while the construction work is carried out by the contractor; we are only responsible for the low-voltage cabinet equipment. Although we do have some relationship with them, we cannot raise any demands, as doing so would threaten the interests of certain people! !