I. Overview
Needle-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 transmission lines in standard voltage ranges of 6 to 35kV for three-phase power systems in ordinary and polluted areas, serving as insulation and support for 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 by fixing the steel foot inside the insulator. The insulator can be made up of a single piece or multiple insulating parts interconnected. The insulating parts of the porcelain insulator are porcelain pieces, usually glazed with brown or white on the surface. The fixation of the porcelain pieces and the foot can be separable or permanent (needle insulators with adhesive feet).
Insulators are categorized by their structural forms into two types: glued and zinc-sleeve threaded connection. The glued type directly bonds the porcelain piece to the base with cement, featuring a deep groove in the porcelain section of the steel base to prevent loosening. An elastic pad is placed between the steel base and porcelain piece at the top. The zinc-sleeve threaded connection type involves first cementing the porcelain inner hole with a zinc threaded sleeve, and then connecting it to the steel base using this threaded sleeve. The zinc sleeve serves as a buffer and facilitates the replacement of the porcelain piece. There are also those that use mechanical connections relying on 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-type porcelain insulators specified in GB/T1000.2-1988 have a rated voltage of 10kV, which are divided into three types according to applicable environmental conditions: Standard 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 models containing the letter "B" are also provided.
