TIPS FOR LOW VOLTAGE SWITCHGEAR PROTECTION

TIPS FOR LOW VOLTAGE SWITCHGEAR PROTECTION

Let us discuss some common practices for Switchgear protection.

The following guidelines are offered on how to inspect and what to look for when inspecting Switchgear.  Note that they may also be used for inspecting medium voltage Switchgear:

1. Equipment (Supply ON Mode):

  • Listen for popping, spitting, or cracking sounds produced by electrical discharges – also humming noises or vibration produced by resonance.
  • With lights out, look for blue or purple corona halos. Orange or red sputter arcs are created by intermittent sparking.
  • Ozone – produced by corona or overheating of organic materials, can usually be detected by their odors.




















2. Equipment(Supply OFF Mode):

  • Look for physical damage – cracks, breaks, delaminations, warping, blisters, flaking, or crazing of insulated parts.
  • Check for foreign objects and loose hardware, warped or distorted insulated bus, and rusty or bent structural framework.
  • Powdery deposits, carbon tracks, moisture stains or rust, flaking paint, or varnish are signs that moisture is, or has been, present

3. Moisture:

The term moisture, usually associated with water, includes vapors which can readily conduct leakage currents. They are often present as air pollutants in industrial atmospheres. The main source of moisture is highly humid air which is subject to climatic type cycling.
Detection of moisture usually depends on signs, rather than the presence of actual moisture.

4. Corona:

Corona is an electrical discharge phenomenon occurring in gaseous substances. High electrical gradients, exceeding the breakdown level of the gas, lead to corona discharges. Pressure, temperature, humidity, and the type of gas affect breakdown levels.

NOTE! It should be noted that corona usually occurs in MV switchgear rated at 5 kV and higher. Corona is not a problem in 600 V switchgear. The inspection for corona is listed here only for completeness since this inspection guide may also be used for inspecting medium- and high- voltage switchgear.

5. Heat:

Temperatures (even slightly over design levels) for prolonged periods can significantly shorten the electrical life of organic insulating materials. A prolonged exposure to higher than rated temperatures will cause physical deterioration of organic materials, resulting in lower mechanical strength. Localized heating (hot spots) sometimes occur.






















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