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The transmission and distribution of electricity include many waypoints, from the power generation facility to eventual points of use. Along the way, the job of the polymeric insulator is to support and separate electrical conductors without allowing current to pass through.

Insulators come in a variety of sizes, shapes and materials. One of the most widely used types of polymeric insulators is composite materials containing silicone rubber. They are picked based on how they withstand a range of harsh environments, including hot desert climates as well as variable temperature regions such as those found in Europe as well as the northern United States and Canada.

Image Credit: SDT Ultrasound Solutions

While climate contributes to the degradation of polymeric insulators, it is not the only factor that plays a role in their shortened longevity. Their early demise is also somewhat due to the partial discharge of electrical current.

Partial Discharge (PD) is a localized electrical discharge or spark in an insulation system that does not entirely bridge the gap between a pair of conducting electrodes. It can happen at any point in the insulation system, where the electric field strength is greater than the breakdown strength of that portion of the insulating material.

PD is a reaction that takes place at an atomic level. At locations of high stress, the movement of electrons ionizes the air molecules. Ionization splits the oxygen molecule to create nitrous oxide and ozone, which, alone in their normal states, are considered harmless. But if combined with water vapor, they will become corrosive.

Partial discharge is something that many of us may have witnessed firsthand; you can often smell ozone in a substation, for example.

Polymeric insulators are designed to withstand harsh climates and vast swings in temperature. They can, to an extent, even withstand the presence of PD. Each asset has its breaking point, however, and the corrosiveness of PD eventually leads to the degradation of polymer insulators too. Frequent condition monitoring is therefore crucial in order to gauge their remaining life.

Infrared thermography and ultrasound are both technologies that have become synonymous with inspections and condition monitoring of electrical assets. Infrared is highly regarded for its ability to see heat traces at safe distances, while ultrasound is preferred for its ability to hear partial discharge in the form of arcing, surface tracking, and corona.

New technology in the form of Acoustic Imaging Cameras is gaining favor because it can spot PD anomalies in any light condition from safe distances. SonaVu™ is an example of this kind of technology.

The SonaVu™ is an acoustic imaging camera that can hear sources of ultrasound from distances of fifty meters or greater and then visualize the sound on a full-color video or image.

Equipped with 112 digital MEMS sensors, operators can see the ultrasound source while listening to it through both a heterodyned circuit and Bluetooth headphones. The videos and images are stored in memory and transferred to a PC for convenient report generation.

A diagnostic report was recently conducted by Craig Casler, principle technical inspector with Absolute Infrared Inspection Services in Erie, Pennsylvania on a substation. Casler was called in to inspect a range of different assets within the substation, such as transmission and distribution lines fitted with polymer insulators.

His technologies include both infrared cameras and ultrasound detection systems. An inspection with his SonaVu™ Acoustic Imaging Camera allowed for the safe reveal of insulations degradation from the ground.

Image Credit: SDT Ultrasound Solutions

Polymer insulators, such as the one pictured in this article, are commonly used in the world of electrical power transmission and distribution. Casler quickly spotted it as a source of partial discharge and confirmed the source of the PD using his SonaVu™.

Despite being a seasoned electrical inspector and well-trained in the use of ultrasound and infrared, this was only the second time Craig has used his SonaVu™ to carry out field inspections. Casler’s success after receiving only one hour of virtual online training before using it in the field indicates the ease of use of modern technologies and short learning curves.

Image Credit: SDT Ultrasound Solutions

In Casler’s client report, he recommended corrective action in the form of cleaning or full replacement of affected components.

It is known that ultrasound can detect the presence of PD at very early stages. Since the PD was not present during previous inspections and given the routine nature of the inspections carried out on this substation, it was concluded that the defect was in its early stage, and the necessary corrective action was not urgent. There was time to plan the repair.

Image Credit: SDT Ultrasound Solutions

In many cases, inspectors conduct their work and are never made aware of the good they created. In this case, however, Craig’s customer shared their findings and appreciation. After the arranged outage to replace the polymer insulator, the customer took this photo and shared it.

A closer examination revealed how the polymer coating was corroded as a result of the corona effect. When looking at the image below, it was clear that the lines tracing downward from where the cable rests was a result of destructive surface tracking.

Image Credit: SDT Ultrasound Solutions

Often, like so many assets, run-to-failure is the only reliability strategy employed. When corona and other forms of partial discharge go unchecked or excluded from routine condition monitoring, catastrophes do happen.

The burning around the insulator in this image was caused by the same PD activity as previously shown. The sole difference is that it was left undetected. Maintenance was carried out as a reaction to the damage on an emergency basis, with collateral damage to the power lines. Worse than that, the fire damaged a key transformer and resulted in a plant-wide shutdown.

In addition to costing millions of dollars in downtime and repairs, unreliable electric power systems have the potential to maim and kill. Reliability leadership must focus on the preservation of human as well as physical assets.

Ultrasound represents an easy, safe, reliable technology for assessing the presence of risk and the need for maintenance intervention. It is an inexpensive technology with a short competency curve.

The original article can be found here. 

This information has been sourced, reviewed and adapted from materials provided by SDT Ultrasound Solutions.

For more information on this source, please visit SDT Ultrasound Solutions.

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