All the transformer's power passes through a few insulating parts bolted to the tank. Discreet, inexpensive, and yet involved in a notable share of avoidable failures.
A conductor at 20 000 V must enter a metal tank bonded to earth without striking an arc to it. The bushing is exactly that: an insulator crossed by the conductor, holding the voltage between conductor and earth, while staying tight (the oil is behind it) and carrying the rated current without heating. Every transformer carries at least six: three on the MV side, three on the LV side (plus the neutral).
Unlike a winding fault, a damaged bushing gets replaced, with the unit isolated and, depending on the case, the oil partially drained. The condition is availability of the right reference: our technical file documents the bushings fitted, our bushings & terminals line covers the replacements, and visual inspection plus thermography during maintenance catches most of it in time (see also common failures).
General overview; exact interfaces, ratings and creepage distances are defined at quotation stage according to the voltage, the cable and the site's environment.
In an enclosed or compact substation, plug-in wins: compact, touch-protected, insensitive to pollution. Porcelain remains relevant for outdoor overhead connections. The choice follows the connection mode, not an aesthetic preference.
Most often by surface flashover: a layer of damp pollution creates a conductive path on the surface and the arc jumps along the insulator. A creepage distance matched to the environment and periodic cleaning remove most of the risk.
Yes: unlike a winding fault, a damaged bushing is replaced with the unit isolated and, depending on the case, the oil partially drained. The condition is having the right reference available: our technical file documents the bushings fitted.
Two pieces of information are enough: overhead or cable connection, and if cable, its cross-section and type. We then align bushings and connectors; a specification detail that avoids a bad surprise at installation.