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

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In today’s fast-paced world, energy scarcity and rising costs have made energy efficiency a top priority across industries, especially in the power sector. Power systems rely heavily on energy, and inverters play a crucial role in reducing consumption. They are widely used in both large-scale and small equipment, making their safe operation essential for the entire power plant. Any malfunction in an inverter can lead to serious damage, even explosions, creating safety crises and causing significant economic losses. Therefore, it's vital for power industry professionals to understand inverter faults, identify their causes quickly, and monitor their performance in real time.

1. Phenomenon: Overcurrent (OC) – This is the most common inverter alarm. It can occur under various conditions:

(1) Tripping during startup: This is a severe overcurrent situation. Possible causes include load short circuits, mechanical jams, damaged inverter modules, or insufficient motor torque.

(2) Tripping upon power-on: This type of issue is usually not resettable. Common reasons are faulty modules, damaged drive circuits, or issues with the current detection circuit. For example, problems with valve imported pumps in industrial washing machines may also trigger this.

(3) Tripping during acceleration: The inverter doesn’t trip immediately after restarting but only during acceleration. This might be due to too short acceleration time settings, low current limits, or excessive torque compensation (V/F) settings.

2. Case Study: LG-IS3-43.7kW Inverter Trips “OC” at Startup: Upon opening the unit, no signs of burnout were visible. Online measurements of the IGBT (7MBR25NF-120) showed no immediate issues. To further diagnose, the high-power transistors were tested after removing the IGBT, and a detailed check was performed on all seven units.

3. Fault Resolution: When checking the upper half-bridge drive circuit, a clear difference was found between the three paths. After a thorough inspection, it was discovered that one optocoupler (A3120) had a short circuit between its output pin and the negative supply rail. Replacing the component restored balance across all three paths. After powering up the module, everything operated smoothly without any issues.