Can electrical partial discharges be detected using ultrasound?

Electrical partial discharges can generate sound signals in both the audible and ultrasonic frequency ranges. These signals can be detected and located using suitable airborne ultrasonic testing devices.

Partial discharges occur within localized areas of electrical insulation. They may arise, for example, at damaged, contaminated, or aged insulation and can indicate developing deterioration.

Inspection using the SONAPHONE

The SONAPHONE can be used with the BS10 or BS30 airborne sound sensors to locate ultrasonic signals at electrical systems.

• The BS10 is suitable for targeted inspections at short and medium distances.
• The BS30 has strong directivity and is suitable for locating more distant sound sources.

The ultrasonic signals are made audible and can be assessed and documented using their level curve and spectrogram.

Inspection using the SONASCREEN 2

The SONASCREEN 2 displays the position of the sound source directly in the camera image. This enables larger system areas to be inspected quickly and several sound sources to be displayed simultaneously.

The Partial Discharge mode is optimized for locating and analyzing partial discharges. It provides functions including:

• visual localization of the sound source,
• a live PRPD diagram,
• storage of the measurement,
• further evaluation and documentation using PDReport.

PRPD stands for “Phase Resolved Partial Discharge” and displays the detected acoustic events in relation to the phase of the line voltage.

Limitations of ultrasonic inspection

Reliable detection of a partial discharge depends on factors including:

• the type and intensity of the discharge,
• the distance to the sound source,
• the propagation path of the ultrasonic signal,
• shielding by enclosures or closed switchgear,
• the orientation of the testing device,
• ultrasonic background sources.

Ultrasonic inspection provides indications of possible partial discharges and supports their localization. The final assessment of the electrical equipment must be performed by qualified personnel and may require additional testing methods.

When inspecting electrical systems, the required safety distances and all applicable operational and statutory safety regulations must always be observed. The testing device must not be used as a reason to approach energized or damaged components beyond the permitted distance.