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Partial Discharge Detection Using Acoustic Ultrasound

Partial discharges (according to IEC standard 60270) are harmful electrical discharges in electrical systems. The early detection of these anomalies, as well as the identification of the exact location of the emission, will help to carry out corrective actions on time and with high efficiency. These discharges release energy from time to time, creating a distinctive acoustic signature that can be captured by an ultrasound listening device (ULD).

According to current statistics, 85% of power failures occur in medium and high voltage transformers. Partial discharges such as the corona effect are the main causes of power loss and damage to electrical equipment insulation, hence the need to have an inspection tool for these discharges at hand. This is more so the case in acoustic inspection, where there is often no temperature increase in corona discharges.

Partial Discharge – Corona

Corona discharge is the luminescent or electrical discharge around conductors when the surrounding air is stressed beyond its point of ionization without developing disruptive discharges. Corona looks for a path to land through the air. These high energy discharges can cause mechanical, electrical and thermal damage.

Corona is a changing zone of ionized gases, identifiable to the inspector through airborne ultrasound. Corona discharge occurs when the voltage in electrical conductors, such as an antenna or a high-voltage transmission line, exceeds the threshold value. The air around the high transmission line begins to ionize to form a blue or purple glow, generally visible in total darkness and with high humidity in the environment.

Partial Discharge – Tracking (or Electrical Treeing)

Tracking discharge is an initial stage of the Electric Arc. It follows a path over the damaged insulation looking for ground. This charred path will lead to reduced insulation and the possibility of current leak from the conductor. Heat is not generated, but as the condition becomes more intense, a temperature rise will be produced that can be detected by an infrared camera. This discharge requires serious attention, as the problem is imminent.

Tracking creates a carbonized current leak path in the form of lightning-like fractals, these over the dielectric that lost its capacity and are prematurely damaged by the discharge. This form is also known as Lichtenberg Figures in honor of the German physicist, Georg Christoph Lichtenberg. This tree structure is associated with the progressive deterioration of components and equipment under voltage. The higher the voltage, the more problematic and risky a possible event is.

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