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 the height of towers (since the insulators are installed vertically with the grounding part at the bottom), they are widely used in overhead power lines for three-phase power systems with nominal voltages of 6 to 35 kV and frequencies not exceeding 100 Hz in ordinary and polluted areas, serving as insulation and support for conductors.
The needle-type insulator consists of an insulating component and a steel foot, which is a rigid insulator that rigidly mounts the insulating component to the support structure by a steel foot fixed inside the insulator. The insulator can be composed of one or multiple interconnected insulating parts. The insulating components of the porcelain insulator are porcelain pieces, typically glazed in brown or white. The fixation of the porcelain pieces and the foot can be separable or permanent (needle-type insulators with glued feet).
Insulators are categorized by structure into two types: glued and zinc-threaded connection. The glued type connects the porcelain piece directly to the base with cement, featuring a deep groove in the porcelain piece where the steel base is inserted to prevent loosening, and an elastic pad is placed between the steel base and porcelain piece. The zinc-threaded connection type involves first cementing a zinc threaded sleeve into the porcelain piece's inner hole, and then connecting the sleeve to the steel base via its threads. The zinc threaded sleeve serves as a shock absorber and facilitates the replacement of the porcelain piece. There are also those that use mechanical connections via 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 type needle porcelain insulators specified in GB/T1000.2-1988 standard have a rated voltage of 10kV, which are categorized into three types according to applicable environmental conditions: General Type, Enhanced Insulation Type 1 (Medium Pollution), and Enhanced Insulation Type 2 (Heavy Pollution).
To reduce radio interference, edge glaze insulators are also provided (for the upper portion above the side slots, with models containing the letter "B").
