Classification and characteristics of composite insulators

At present, the composite insulators developed and produced in the world include: line post composite insulator, long rod composite insulator, post composite insulator, hollow multiple insulator, interphase composite spacer and multiple insulator for electrified railway.

The structure of line post and post composite insulators is similar to that of long rod composite insulators. Hollow composite insulator can be used in oil immersed capacitive bushing, circuit breaker, transformer, capacitor, cable terminal, voltage divider, lightning arrester and other capacitors.

Compared with porcelain bushing, this hollow composite insulator has the advantages of small size tolerance, light weight and high mechanical strength, and it also eliminates the risk of breakage. In gas filled electrical equipment, even if the insulator breaks, there will be no threat to the surroundings.

The interface and connection structure are the parts of composite insulators that often fail during operation. The close connection between interfaces shall be considered in the design, and no air gap is allowed. The air gap is the gathering point of moisture and partial discharge, which is easy to cause burn marks and corrosion, and expose the core to wet conditions, causing insulator damage.

The design and manufacture of composite insulators involve high voltage, machinery, chemical engineering and other related knowledge. Generally speaking, the design of composite insulators is given according to the electromechanical performance requirements of insulators. Each component shall be designed, selected and calculated separately. The results of design calculation should be combined with the test measurement. The design of composite insulator includes: determination of insulator distance and insulation level, determination of creepage distance, core rod design, material and structure selection of umbrella skirt, and structural design of fittings joint. Equalizing ring shall also be designed for insulators above 220kv. In the design and manufacture, the materials of umbrella skirt sheath, mandrel and adhesive should be selected. These designs need to comprehensively consider the electrical and mechanical loads undertaken by composite insulators in the operating environment, as well as the impact of environmental factors on insulator performance.