I. Overview
Needle insulator is an old type of insulator in high-voltage transmission and distribution lines. Due to its simple manufacturing, low cost, easy installation, and ability to reduce tower height (due to the upright installation of insulators, the grounding part is located below), it is widely used in high-voltage overhead power lines in ordinary and polluted areas with a nominal voltage of 6-35kV and a frequency of 100Hz in three-phase power systems, as insulation and supporting conductors.
Needle insulators consist of insulating components and steel feet, and are a type of rigid insulator that uses steel feet fixed inside the insulator to rigidly install the insulating components on a supporting structure. An insulator can be composed of one or multiple insulating components connected to each other. The insulation components of porcelain insulators are porcelain parts, usually coated with brown glaze or white glaze on the surface. The fixation of porcelain parts and feet can be separable or sexual (needle insulators with adhesive feet).
Insulators are divided into two types based on their structural form: adhesive type and zinc sleeve threaded connection type. Adhesive type refers to the direct bonding of ceramic parts with cement and feet. The steel feet are pressed into the ceramic parts with deep grooves to prevent the steel feet from loosening. An elastic pad is placed between the top of the steel feet and the ceramic parts. The zinc sleeve threaded connection type is that the inner hole of the ceramic part is first fitted with a zinc screw sleeve through cement glue, and then connected to the steel foot by the thread of this screw sleeve. The zinc screw sleeve has a buffering effect and is also convenient for replacing ceramic parts. Some also use mechanical connections with porcelain threads.
The old model needle type porcelain insulators specified in GB1000-1981 standard are divided into five levels according to rated voltage: 6, 10, 15, 20, and 35 kV. Each type is divided into two specifications based on the type of steel leg: iron leg straight leg and wooden leg straight leg.
The rated voltage of the new type of needle type porcelain insulator specified in GB/T1000.2-1988 standard is 10kV, and it is divided into three types according to applicable environmental conditions: ordinary type, reinforced insulation type 1 (medium pollution type), and reinforced insulation type 2 (extra heavy pollution type).
To reduce radio interference, there are also edge glazed insulators (for those with semi conductive glaze above the side groove and with the letter "B" in the model).
