I. Overview
Needle 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 (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.
Needle-type insulators are composed of insulating parts and steel feet, which are rigidly mounted on a support structure by fixing the steel feet inside the insulator. The insulator can be made up of one or multiple interconnected insulating components. The porcelain insulator parts are glazed with brown or white porcelain. The fixation of the porcelain parts and feet can be separable or permanent (needle-type insulators with glued feet).
Insulators are categorized by structure into two types: glued and threaded zinc sleeve connections. The glued type connects the porcelain piece directly to the base with cement, featuring a deep groove in the porcelain part where the steel base is inserted to prevent loosening, with an elastic pad between the steel base and porcelain piece. The threaded zinc sleeve connection type first glues the porcelain inner hole with cement to a zinc screw sleeve, and then connects the screw sleeve to the steel base via threading. The zinc sleeve serves as a buffer and facilitates the replacement of the porcelain piece. There are also those using 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 model needle-type 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: Standard Type, Reinforced Insulation Type 1 (Medium Pollution), and Reinforced Insulation Type 2 (Heavy Pollution).
To reduce radio interference, edge insulators with insulating glaze above the side slots, and models containing the letter "B," are also provided.
