Inverter overcurrent fault causes and treatment methods - Database & Sql Blog Articles

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In today's world, energy scarcity has become a growing concern, with energy prices rising rapidly and industries pushing for greater efficiency. The power industry, in particular, is highly energy-intensive, and the use of frequency converters has proven to be an effective way to reduce energy consumption. As a result, inverters are now widely used in both large and small equipment. They play a crucial role throughout the entire power plant, and their safe operation is vital. If an inverter fails, it can lead to serious damage or even explosions, creating critical safety issues and causing significant economic losses. Therefore, it's essential for power industry personnel, especially those working in power plants, to have a basic understanding of inverter faults, their causes, and how to detect and address them quickly.

1. Phenomenon: Overcurrent (OC) – This is the most common inverter alarm. It often occurs due to various reasons:

(1) Tripping during startup: This is a severe overcurrent situation. Possible causes include a short circuit in the load, mechanical jamming, a damaged inverter module, or insufficient motor torque.

(2) Tripping upon power-on: This type of fault is usually not resettable. Common causes include a faulty module, a defective drive circuit, or a problem with the current detection circuit. For example, some industrial washing machines or pump systems may experience this issue.

(3) Tripping during acceleration: This typically happens after the inverter starts and begins to accelerate. Causes may include a too-short acceleration time setting, a low current limit, or excessive torque compensation (V/F).

2. Example: An LG-IS3-43.7kW inverter triggered an "OC" alarm immediately after startup. Upon opening the cover, no signs of burning were observed. Online testing of the IGBT (7MBR25NF-120) showed no major issues. To further diagnose, the high-power transistors connected to the IGBT were tested individually, revealing a potential problem.

3. Fault Handling: When checking the upper half-bridge drive circuit, a noticeable difference was found between the three paths. After a detailed inspection, it was discovered that one optocoupler (A3120) had a short between its output pin and the negative supply rail. Replacing the component resulted in balanced performance across all three paths. After powering up the module, everything operated normally, confirming the successful repair.