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, ease of installation, and ability to reduce tower height (since the insulators are installed vertically with the grounding part below), they are widely used in overhead power lines with nominal voltages of 6 to 35kV and frequencies not exceeding 100Hz in ordinary and polluted areas for three-phase power systems, serving as insulation and support for conductors.
The needle-type insulator is composed of an insulating component and a steel foot, which is a rigid insulator that rigidly mounts the insulating component to the support structure using a steel foot fixed within the insulator. The insulator can be made up of a single piece 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 adhesive feet).
Insulators are categorized by structure into two types: glue-mounted and zinc-sleeve threaded connection. The glue-mounted type directly bonds the porcelain piece 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 between the steel base and porcelain piece. The zinc-sleeve threaded connection type involves first cementing the porcelain piece's inner hole with a zinc threaded sleeve, and then connecting the sleeve to the steel base via threading. The zinc sleeve serves as a shock absorber and facilitates the replacement of the porcelain piece. There are also types that use mechanical connections via porcelain threads.
The old model needle 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 the 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 categorized into three types according to 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 models containing the letter "B" are also provided.
