Welcome my friends to your site to learn electrical engineering .Today I present to youHigh Voltage Engineering Second Edition
Electrical treeing first happens and propagates when a dry dielectric materials is subjected to excessive and divergent electrical subject stress over a very long time. The areas the place impurities, gases voids, mechanical defects, or conducting projections create extreme electrical subject stress in small areas of the dielectric are the place electrical treeing happens. These may cause small electrical discharges between partitions of the dielectric by ionizing gases. A defect or impurity might even trigger the partial breakdown of the stable dielectric. These partial discharges (PD), that are ultraviolet gentle and ozone, react with the dielectric close by, decomposing it additional and additional lowering its insulation functionality. Gases are sometimes liberated because the dielectric degrades, creating new voids and cracks. These defects weaken the fabric’s dielectric energy, improve {the electrical} stress, and velocity up the PD course of.
Water bushes and electrical bushes
A diffuse, semi-conductive 3D plume construction is sort of a plume, fashioned within the presence of water. Water bushes plume could also be fashioned inside the polyethylene dielectric, which is used to make high-voltage cables. It’s believed that the plume consists of small, water-filled channels. These channels are outlined by the native crystal construction of the polymer. It’s troublesome to see particular person channels with optical magnification. Due to this fact, it’s needed to make use of a magnifying glass. Scanning electron microscope(SEM).
Water bushes begin as a tiny area round a defect. The excessive electrical subject and water proceed to assist them. Water bushes can finally attain the purpose that they cross the outer floor layer with the middle high-voltage conductor. At this level, the insulation turns into extra pressured. Water bushes may cause reliability issues if they’re able to initiating {an electrical} tree.
An alternate tree-like construction that may be fashioned with or with out water is the an. {The electrical} tree is. It may additionally type inside polyethylene or different stable dielectrics. The formation {of electrical} bushes can even happen in areas the place bulk stress enhancements or floor stress enhancements trigger dielectric breakdown to happen in a small space of the insulation. This completely damages that space of the insulation materials. Extra electrical breakdowns (referred to as “smaller”) can then trigger additional tree development. partial discharges. Speedy voltage modifications akin to utility switching operations can speed up the expansion {of electrical} bushes. Excessive voltage DC cables can also develop electrical bushes as {the electrical} prices migrate to the dielectric close to the HV conductor. The realm wherein the injected cost is situated (referred to as house cost dielectric’s electrical subject is amplified, which stimulates stress enhancement and the initiation {of electrical} bushes to boost pre-existing stress. {The electrical} tree is usually partially conducting so it might additionally improve {the electrical} stress between the tree’s conductor and it.
The person channels {of electrical} bushes are extra seen than water bushes. These partially conductive trails can develop into so giant that they finally trigger dielectric failure. The most typical failure mechanism for electrical energy insulations which have been uncovered to salt spray alongside coastlines is electrical monitoring. The branching 2D and 3D patterns are generally referred to as Lichtenberg figures.
2D carbonized electrical bushes (or monitoring), throughout the floor a polycarbonate plat that was a part of irrigation. These partially conducting paths finally led to the untimely failure and malfunction of the system.
Excessive-voltage gear can even expertise electrical treeing, or “Lichtenberg Figures”, simply earlier than it breaks down. These Lichtenberg figures can be utilized to find out the reason for insulation breakdown. A high-voltage engineer with expertise can decide the placement of the first trigger and determine the bushes and branches. This technique can be utilized to research broken-down transformers, excessive voltage cables, bushings, and different gear. The insulation is both unrolled (in case of paper insulation), or lower in skinny slices (in case of stable insulation). The outcomes are then sketched and photographed, making a helpful archive.