I. Overview
Pin-type insulators are an older type of insulator used in high-voltage transmission and distribution lines. Due to their simple manufacturing, low cost, easy installation, and ability to reduce tower height (as they are installed vertically with the grounding part at the bottom), they are widely employed in overhead power lines for three-phase power systems with nominal voltages of 6 to 35kV and frequencies not exceeding 100Hz, in both ordinary and polluted areas, for insulation and support of conductors.
The needle insulator is composed of an insulating part and a steel foot, which is a rigid insulator that rigidly mounts the insulating part to the supporting structure using a steel foot fixed within the insulator. The insulator can be made up of a single part or multiple insulating components connected together. The insulating parts of the porcelain insulator are porcelain pieces, typically glazed with brown or white porcelain. The fixation of the porcelain pieces and the foot can be separable or permanent (needle insulators with adhesive feet).
Insulators are categorized by structural type into two types: glued and zinc-sleeve threaded connection. The glued type involves the porcelain piece being directly glued to cement and connected to the base, with the steel base having a deep groove in the porcelain section to prevent loosening, and an elastic pad is placed between the steel base and porcelain piece. The zinc-sleeve threaded connection type first glues the porcelain inner hole with cement and then connects it to the steel base using the zinc threaded sleeve. The zinc sleeve serves as a buffer and facilitates the replacement of porcelain pieces. There are also types that use mechanical connection through porcelain threads.
The old model needle-type porcelain insulators specified in the GB1000-1981 standard are divided into five grades according to rated voltage: 6, 10, 15, 20, and 35 kV. Each grade is further divided into two specifications based on steel foot type: iron pole straight foot and wood pole straight foot.
The new model needle porcelain insulators specified in GB/T1000.2-1988 standard have a rated voltage of 10kV. They are classified into three types based on applicable environmental conditions: General Type, Reinforced Insulation Type 1 (Medium Pollution), and Reinforced Insulation Type 2 (Heavy Pollution).
To reduce radio interference, edge glaze insulators with upper conductive glaze above the side slots and a model containing the letter "B" are also provided.
