Inverter interference case problem analysis and processing - Database & Sql Blog Articles

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1. How to Identify Inverter Interference Issues Inverter interference problems typically manifest in the motor’s operation. For example, the motor might suddenly stop while running, or it may run at inconsistent speeds, accelerate and decelerate unpredictably, or fail to stop even when the stop button is pressed. These issues are common signs that the inverter is being affected by external interference. 2. The Third Method to Address Grounding Interference: Proper Grounding One of the most effective ways to tackle grounding-related interference is to ensure a solid and correct grounding system. The grounding terminal should be connected via a "third method" — meaning it's completely separate from the neutral line. The grounding wire should be as short as possible and firmly connected to earth. Additionally, control circuit cables should use shielded wires, with the shielding grounded at the near end and left unconnected at the far end. Following manufacturer guidelines for wiring is essential — keeping high-voltage and low-voltage lines separated, avoiding parallel runs, and using proper distribution methods. Installing filters or reactors on both input and output sides can also help reduce interference. Shielding the inverter with a metal enclosure and reducing the carrier frequency are further steps that can improve performance. If communication functions are used, twisted-pair cables should be employed for RS485 connections. Below, I’ll go into more detail about specific cases encountered in real-world applications. 3. Case Study: Grounding Issues in a Three-Phase Five-Wire System A typical issue occurs when an inverter is operating but fails to stop when the stop button is pressed. Upon inspection, it was found that the inverter’s ground wire was only connected to the transformer’s neutral line, which itself wasn’t grounded. After the transformer’s neutral line was properly grounded, the inverter functioned normally again. Many small factories overlook proper grounding during installation. When machines leave the factory, they are usually set up with strict separation between ground and neutral lines according to national electrical codes. However, some users connect only the neutral line to the “N” terminal, neglecting to connect the ground wire. Even if shielded cables are used, improper grounding prevents effective shielding. This leads to interference issues, such as the inverter failing to stop and the motor not responding. Connecting the ground wire directly to earth or ensuring the neutral and ground are properly bonded in the power panel resolves this problem. While some users opt to connect the ground to the neutral, this practice can be dangerous if the neutral line becomes disconnected, potentially causing electric shocks. 4. Case of External Equipment Interfering with the Inverter (1) Symptom: The motor occasionally fails to stop. (2) Diagnosis: The shielding was properly grounded, and reducing the carrier frequency had no effect. Both the input and output side filters were also ineffective. After investigation, it was found that the inverter’s power distribution cabinet was too close to another power room where large currents flowed. The strong magnetic field from the current caused interference, leading to unstable inverter operation. Moving the inverter away from the power room resolved the issue, showing that the interference came from external equipment. 5. Case of Inverter Interference Affecting External Devices (1) Symptom: The motor doesn’t start after the inverter is turned on. (2) Diagnosis: The inverter received a 4–20 mA signal from an external transmitter, but the frequency displayed on the panel was 0.00. Measuring the transmitter’s output showed no signal. After adding a 102 pF capacitor across the transmitter’s output, the system worked normally. This indicated that the signal was being disturbed by the inverter. Using a simple shunt capacitor proved to be an effective solution in this practical engineering scenario. This case highlights how an inverter can interfere with external devices.