Partial Discharge Testing with an Acoustic Imaging Camera | SonaVu™

Electrical discharge is more common than we’d like to believe; even in new installations. Unreliable electric power systems not only cost millions of dollars in downtime and repairs, but they also have the potential to maim and kill. Detecting these electrical defects poses a serious challenge, particularly at an early stage when there is still time to initiate corrective actions.

Now, there is a new class of condition monitoring technology that helps reduce the risk of arc flash explosion while enhancing overall electrical asset reliability.

SonaVu™, is a multi-frequency acoustic imaging camera that blends visual and auditory senses to faults that threaten the safety and reliability of electrical assets. With an array of 112 highly-sensitive ultrasound sensors, SonaVu™ listens to a wide field of detection which it displays on a 5” color screen. Sources of ultrasound created by the presence of partial discharge are superimposed on the image allowing inspectors to intuitively pinpoint their location.

Partial Discharge Testing

Electrical Safety Risk

Any discussion about risk must include health and safety. But it should not ignore asset reliability. One certainty is that safety and reliability risks are both linked to unscheduled downtime, costly legal exercises, and ultimately, lost profit. A perfect solution identifies safety and reliability as one and the same and marginalizes their impact on the other three.

Ultrasound is the best technology for reducing the risk of electrical arc flash exposure while ensuring equipment reliability. It does this by detecting defects which, when left to deteriorate, could lead to an arc flash event. This doesn’t suggest that ultrasound removes the need for personal protective equipment and other safety measures. Inspectors must still adhere to all safety protocols in place for working near electrical assets.

The long-distance sonic imagery capabilities of the SonaVu™ acoustic imaging camera make it an essential tool for inspecting electrical systems for partial discharge while maintaining electrical safety and reliability.

Origins of Electrical Defects

Figures produced by the IEEE point to insulation failure in as much as 90% of electric switchgear defects. Age has very little influence over reliability. In fact, 80% of failures are associated with poor workmanship or quality issues. IEEE concluded that the most likely cause of electrical asset failures includes water ingress, cracked insulators, and incompetent workmanship during installation or maintenance.

Ultrasound acoustic camera for finding switchgear defects

What is Partial Discharge?

Partial Discharge is a localized electrical discharge or spark in an insulation system that does not completely bridge the gap between two conducting electrodes. It can occur at any point in the insulation system, where the electric field strength exceeds the breakdown strength of that portion of the insulating material. This could be due to voids within a solid insulation material.

Across the surface of insulating material, in gas bubbles within liquid insulation, or around electronic gas in the form of corona.

Visualizing ultrasound caused by partial discharge

Partial discharge is an atomic reaction which, due to the movement of electrons ionizes the air molecules at locations of high stress. Ionization splits the oxygen molecule to form ozone and nitrous oxide which in their normal states are generally harmless. But when mixed with water vapour, become corrosive. If you’ve ever walked into a substation and noticed the smell of ozone, then you have witnessed the presence of partial electric discharge firsthand.

Now, with the SonaVu™ acoustic camera from SDT, the smell of partial electrical discharge is brought to visual and audible life.

Partial Discharge Effects

Partial discharges emit energy in several ways producing electromagnetic emissions in the form of radio waves, light and heat, acoustic emission in the audible and ultrasonic ranges, and ozone and nitrous oxide gases. These emissions enable us to detect, locate, measure, and analyze partial discharge activity so we can identify faults before they develop into failures.

Partial discharge activity may be intermittent, or it may vary in intensity over time, but once it starts the damage always increases.

Where do we Find Partial Discharge?

You will find activity in all types of high voltage power assets. From switchgear… to transformers… to overhead lines… and underground cables. Partial discharge causes degradation and failures. Experience shows that Partial discharge activity is a contributory factor in over 80% of disruptive substation failures. It is the most reliable indicator of the true condition of insulation in live assets.

Finding partial discharge and corona with an acoustic imaging camera

The procedure for scanning is straightforward. Connect the noise attenuating headphones to the SonaVu™ and position the sensors towards potential sources. The ultrasound produced by partial discharge excites the sensors while their location is revealed on the display. Tap the icon to capture either a video or still image to place it into your inspection report. It’s that easy!

SonaVu™, the world’s favourite ultrasound company. If you are going to buy an ultrasonic acoustic imaging camera for electrical asset management, doesn’t it just make sense to choose one from an ultrasound company?

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