All about partial discharge and Bushing monitoring

What are partial discharge and Bushing monitoring? Let’s take it one step at a time. Partial discharge is a term commonly used in electric engineering to define an electrical breakdown of a small portion of an electrical insulation system (solid or liquid), which is under high voltage stress, such as power plants’ transformers. The term “electrical breakdown” may refer to the failure of an electric system or to the quick drop of an electrical insulator’s resistance. This may lead to the apparition of a spark traversing the insulator, a short circuit or a blown fuse and so on.

Electrical breakdown occurrences are various: across strings suspended above power lines, underground cables or through lines that encounter tree branches along their way, but partial discharge mostly occurs within systems (which can be solid, liquid as well as gas) under high-voltage stress. Partial discharge is usually caused by cracks within the electric interfaces and very often takes place at the boundary between two different insulating materials, where the gap is not fully bridged.

Partial discharge is encountered especially in equipment deteriorated with age and in new tools improperly installed or poorly crafted. Some discharges are almost harmless, but others can be really dangerous to the integrity of the high-voltage systems. Therefore it is imperative to any circuit inspector or test engineer to determine the exact type of discharge and its cause, so there won’t be further complications. Also, testing is really important within known high-risk power plants. There are numerous plants that for some reason or another, such as old equipment or previous partial discharge records, tend to need more attention.

What about Bushing monitoring? A high voltage electric bushing consists in a hollow elongated dielectric metal enclosure containing a high voltage conductor. A collar made of high voltage dielectric material is placed over the metal enclosure and is bonded by an interface material which prevents moisture corrosion between the bonded portions.

High voltage bushings are made of porcelain and may be coated with glass. They’re also often filled with oil, to improve insulation. Some of them are called “capacitor bushings” due to their feature of acting similar to a low value capacitor between the conductor and the wall. This aids in the reduction of the electrical field stress that could cause a partial discharge. Low and medium voltage bushing are usually made of resin reinforced with paper.

Bushing monitoring is as important as partial discharge monitoring as it may prevent a breakdown and all the other complications that may occur. Partial discharges are detected as very small fluctuations in the current pattern and are difficult to detect because of their small magnitude and short duration. That’s why a series of discharge detection schemes have been developed, along with numerous tools, such as transformer diagnostic monitors, partial discharge analyzers with reflectometers and so on.

The Internet is a valuable source of information regarding the partial discharge phenomenon.  Online, you can learn all about what it is, when it occurs, how it evolves and also how to prevent discharges from turning into short circuits and ending up with blown fuses.  One of the sites specialized in this matter is elec-di.com. With a couple of clicks, you’ll be up to date with the latest partial discharge and Bushing monitoring equipment, being provided with downloadable technical documents and information as well as a list of services.


Resource box: For more information regarding partial discharge and Bushing monitoring you can always log on our website and learn how to protect your systems from failure as well as what professional tools to use to ensure proper and safe development for your installations: elec-di.com!