Reasons for Damage to Electric Arc Furnace Thermal Capacitors

In industrial fields such as steel smelting and alloy melting, electric arc furnaces are typical load equipment characterized by high energy consumption, high impact, and high harmonics. To improve power factor, stabilize grid voltage, and enhance energy utilization, thermal capacitors are typically configured in arc furnace systems. However, many users frequently encounter capacitor failures during operation. What are the common reasons for this?

I. Common Reasons for Damage to Electric Arc Furnace Thermal Capacitors

1. Overheating Damage Due to Excessive Harmonic Current
Electric arc furnaces are highly nonlinear loads and generate a significant amount of high-order harmonics (especially the 2nd, 3rd, 5th, 7th, and 11th harmonics) during operation. These harmonic currents superimpose on the capacitors, causing them to withstand currents far exceeding their rated values. Excessive capacitor current leads to a rise in the internal dielectric temperature and accelerates dielectric aging.

Recommended Solution: Install filtering reactors (typically with a reactance rate of 5% to 14%) in series with the capacitor circuit to effectively suppress harmonic currents and protect the capacitors from harmonic overload.

2. Grid Voltage Fluctuations and Arc Impact
The startup and extinguishing of the arc furnace cause severe grid voltage fluctuations and even generate impact voltages. Such repeated high-voltage stress can lead to capacitor insulation breakdown, internal metallized film layer separation, casing bulging, oil leakage, and other faults.

Recommended Solution: Incorporate dynamic reactive power compensation devices (such as SVG or TSC) into the system to absorb impact reactive power.

3. Accumulated Mechanical and Thermal Stress Due to Frequent Switching
During the operation of the arc furnace, the reactive power changes rapidly, requiring frequent switching of the capacitor banks. If ordinary contactors or mechanical switches are used, this can result in instantaneous current impacts during switching, contact erosion, and repeated heating and cooling of the capacitor dielectric, ultimately reducing insulation performance.

Recommended Solution: Use composite switches or thyristor switches to control capacitor switching. These devices operate at voltage zero-crossing points, avoiding impact currents and extending capacitor lifespan.