Ultrasound Inspection scanning

Ultrasound Scanning Inspection is performed to detect insulation based problems at  the electrical installation. If there is an insulation based problem on the surface of the installation, the air around the defective area will be ionised. These ionised air will vibrate. The vibration of the ionised air produces Ultrasound in the range of > 20kHz which is not audible to human ear. This is called “Partial Discharge”.

Partial Discharge can be extremely dangerous due to the fact that at a critical stage, this problem could turn into a catastrophic “Flash Over” phenomena resulting in explosions. The Ultrasonic Detector will “convert” the Partial Discharge sound from Ultrasound range to the human audible range through a process called “hetrodyning”.

Hence, if an Ultrasound is detected at the electrical installations i.e. Partial Discharge activities, this could lead to the detection of surface insulation based defects. The types of Partial Discharge activities that can be detected by Ultrasonic Inspection are Corona, Tracking, Arcing and Mechanical Vibrations. The detected sound can be digitised and subsequently analysed using the “Spectrum Analysis” software. This allows the classification for the type and severity of the defects.

Ultrasound Defect

The specific sound quality of each type of emission is heard in the headphone while the intensity of the signal is observed on a decibel meter (dB). The ultrasonic sound that are normally detected due to partial discharge problem have the characteristics of erratic, sizzling frying, uneven and popping sound of an electrical discharge.

There are 4 basic electrical problems that can be detected via Ultrasonic Scanning Inspection. There are :-


When voltage of an electrical conductor, such as an antenna or high voltage transmission line exceeds threshold value, the air around it begins to ionize to form a blue or purple glow.

Destructive Corona Tracking

Often referred to as “baby arcing”, follows the path of damaged insulation.



An arc occurs when electricity flows through space. A good example of an arc is lightning.


Mechanical Vibration

Loose nuts and bolts causing the equipment to make noise and operate less than efficiently.