What is Transformer Bushing?

Basically a transformer is a device which is used to step up or step down the voltage as per requirement. Transformers are required in power transmission and generation stages, they involve high voltages. Since the transformer works at very high voltage, it is also necessary to take care that it functions properly without any leakage or damage. Now, it is worth noting that there is one very important factor in helping the transformer to function properly; That is its bushing. Without a bushing, it is not possible to operate the transformer in any high-voltage condition (usually in KV).

A bushing is an electrical insulator that allows safe passage of electrical current. It is similar to any insulator surrounding the conductor, which helps prevent any untoward incident from occurring. A transformer consists of two windings - primary and secondary (HV and LV). It makes connections to external wires to carry electricity. Even though the transformer also includes LV, it is not so low that it is negligible. When current flows through a conductor, it creates an electromagnetic field around it. So, the greater the current and voltage, the greater the field generated.

When approaching a transformer, the current around the windings (ie the outer transformer case) is strong enough to ionize the insulator to the outside (air, gas or vacuum) and make it conductive. If the dielectric strength of the insulator is broken, it will start to conduct and once the insulator becomes conductive, it can either pass leakage current or even create a short circuit under the ground. This would be very harmful as the transformer is close to it, which may also damage the transformer. Bushings are used immediately before and after the windings, to protect the transformer body from that.