Transformer bushings are insulating devices that connect the high-voltage and low-voltage leads inside a transformer to the outside of the tank. They not only provide insulation between the leads and ground but also fix the leads and support current carrying capacity, making them one of the most important external insulation and current-carrying components of a transformer.
Based on their structure and insulation method, transformer bushings are mainly classified into the following categories:
Pure Porcelain Bushings
Mostly used in transformers of 10kV and below. They have a simple structure, consisting of a porcelain bushing and a conductive copper rod passing through it, with air insulation inside.
Oil-Filled Bushings
Commonly used in 35kV transformers. The porcelain bushing is filled with insulating oil, and the conductive rod is wrapped with insulating paper to enhance insulation performance. They are often connected to the transformer tank.
Capacitive Bushings
Used in transformers of 110kV and above. Utilizing the principle of capacitive voltage division, multiple layers of metal foil and insulating material are interleaved to form a capacitor core, ensuring uniform voltage distribution along the bushing and improving insulation strength. Depending on the insulation material, they can be further divided into oil-paper capacitors and adhesive-paper capacitors, with the latter having higher mechanical strength.
Fiberglass Dry Bushings
Used in dry-type transformers, they are made of composite materials such as fiberglass and have good insulation and mechanical support capabilities, suitable for oil-free environments.
