T&D World Magazine

Acoustic Insulation Analyzer Allows GIS Testing with No Disturbance

The Acoustic Insulation Analyzer (AIA) from Doble Engineering gives users the opportunity to detect, locate, and identify most common defects in gas-insulated substations, such as particles and partial discharges. Produced by Doble's TransiNor office, the AIA has unique sensitivity that enables the user to classify whether a flaw is harmful or not.

The analyzer is portable, battery-powered, and easy to use via menu-controlled software. It detects particles and protrusions as small as 2 mm in-service, whereas 5 mm particles are detectable by conventional methods in the laboratory.

The user can determine whether a flaw is present in the insulation of GIS system, such as bouncing particles or partial discharges from protrusions and/or loose shields. The analyzer can perform condition-based monitoring of GIS during commissioning and in service. It can be used for design and factory tests during manufacturing.

AIA offers three measuring modes: continuous, pulse and phase.

Continuous mode provides:

  • RMS signal during one power cycle
  • Peak signal during one power cycle
  • Degree of modulation with the power cycle
  • Degree of modulation with twice the power cycle

Continuous mode gives initial information about the signal, indicating the type of flaw. 50 Hz (Frequency 1) or 100 Hz (Frequency 2) content suggests that a partial discharge is present. A fluctuating peak signal suggests that one or more particles are present.

Pulse mode provides:

  • Peak value of impulse signal
  • Time since last pulse

Both are plotted in an elevation time vs. amplitude plot.

Phase mode provides phase angle of pulse occurrence.

Using AIA to measure in GIS is easy. A cable connects the sensor to the front plug of the instrument, and may be held by hand or mounted to the GIS by a flexible band. Locate defects by moving the sensor to the place where the signal level is highest.

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