Switchgear--- Capacitor Panel Noise (Fuse–VCS Connection)

Switchgear--- Capacitor Panel Noise (Fuse–VCS Connection)

“Why Is  Capacitor  is Talking to Me?” 🤔

Ultrasonic noise at the capacitor panel, especially between the fuse and VCS connection, is mainly caused by corona discharge. This happens when a high electric field forms at a connection point and ionizes the surrounding air. It is common at bolted joints where small imperfections exist. This noise can occur due to loose tightening, small air gaps, sharp edges, or dust contamination. Even minor irregularities can concentrate the electric field and produce ultrasonic energy, which is detected by devices like Fluke ii910.


 Why 0–25 dB is OK

Values up to 25 dB are common because:

  • Electrical equipment naturally produces vibration and energy
  • Ultrasonic sensors are highly sensitive
  • Sound reflects inside metal panels
  • Early-stage discharge is very weak

So, low to moderate readings do not necessarily indicate a fault.

When it becomes risky

A reading becomes concerning when:

  • The dB value increases over time
  • The signal is highly localized at a connection
  • Frequency is high (30–60 kHz range)
  • The value rises above 25–30 dB

Even a lower value (like ~20 dB) can be important if it is concentrated at a single point.

What to check

At the fuse–VCS connection:

  • Ensure proper tightening torque
  • Remove dust or contamination
  • Check for sharp edges or uneven surfaces
  • Confirm good contact without gaps