Introduction
Insulting bushing is a crucial yet often overlooked component guarding the frontier of an oil immersed transformer. It serves as not only the sole passage for currents entering and exiting the oil tank but also the critical barrier that ensures the purity of the insulating oil.
Definition
Bushing is an insulating device installed on the cover or wall of a transformer's oil tank. The core of the bushing is a conductive rod used to connect the internal windings to the external circuits. The conductive rod is wrapped with efficient insulating materials. The exterior is usually designed with sheds - this corrugated structure aims to increase the creepage distance and prevent surface arcing under rainy, foggy, or dirty environmental conditions.
Function
Insulation: the bushing isolates the high-voltage conductor from the grounded tank wall, and withstands both operating voltages and lightning overvoltages, to prevent breakdown and short circuits.
Support: the bushing provides mechanical fixing to ensure the stable positioning of the central conductive rod, and withstands mechanical loads from connected busbars and environmental forces to guarantee the overall structural reliability.
Sealing: the bushing forms a perfect barrier to prevent the leakage of insulating oil while blocking the ingress of air and moisture to maintain a clean and dry internal environment within the transformer.
Material
Traditional porcelain
Features: long history; mature technology; high compressive strength and stability
Limitations: heavy and fragile; inconvenient to transport and install; poor surface hydrophobicity leads to the adsorption of contaminants, forming conductive pathways that trigger arcing in humid environments
Modern composite materials
Features: utilizes an epoxy glass fiber core rod as the framework, covered with high-temperature vulcanized silicone rubber sheds
Advantages: lightweight design; excellent hydrophobicity; high impact resistance; easy maintenance
Parameter
Creepage Distance: this value should be determined based on the pollution level of the installation site and is crucial for contamination flashover prevention.
Partial Discharge (PD): the lower the PD value, the better the insulation process and the longer the expected service life. High-quality bushings usually have PD values less than 5-10 pC.
Dielectric Loss Factor (tanδ): this indicator reflects the energy loss of insulation materials in an alternating electric field. A lower tanδ value indicates better insulation performance and reduced heat generation.
Conclusion
The bushing serves as an indispensable gatekeeper for the transformer. Its failure could lead to catastrophic consequences, including transformer breakdowns, grid outages and significant economic losses.
Therefore, when selecting a transformer, thoroughly understanding the bushing's type, material and performance is a strategic approach to ensuring power system reliability and long-term return on investment. A high-quality bushing remains one of the most effective protections for the entire transformer asset.