The maximum voltage that a transformer bushing can withstand before failing is indicated by the bushing's voltage rating. The kind of insulation used in a bushing and the bushing's design affect the voltage rating of a bushing.
Porcelain is the insulation material most frequently used in transformer bushings. A good insulator, porcelain can handle high voltages. However, porcelain is very fragile and can crack if not handled carefully.
The insulation utilised in transformer bushings also includes silicone rubber, epoxy resin, and synthetic resin-bonded paper. These materials are less likely to break and are more flexible than porcelain. They are not, however, as effective insulators as porcelain.
The voltage rating of a bushing is also influenced by its design. Greater voltages can be handled by bushings having a bigger diameter than by those with a smaller diameter. This is so that there is more insulation between the conductor and the ground due to the bigger diameter.
A transformer bushing's voltage rating is often stamped on the bushing. Kilovolts (kV) are typically used to express voltage ratings. A bushing rated for 132 kV, for instance, can resist a maximum voltage of 132,000 volts.
When choosing a transformer bushing for a specific application, it's crucial to take the voltage rating into account. For the highest voltage that the transformer will be exposed to, the bushing needs to be rated. The bushing could malfunction and result in a transformer failure if it is not rated for the maximum voltage.
Here are some examples of voltage ratings for transformer bushings:
Low voltage bushings: 12 kV, 24 kV, 36 kV
Medium voltage bushings: 69 kV, 115 kV, 138 kV
High voltage bushings: 230 kV, 345 kV, 500 kV
Ultra high voltage bushings: 765 kV, 1100 kV, 1500 kV
An essential safety aspect of a transformer bushing is its voltage rating. It aids in preventing electrical fires and damage to the transformer.
