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 (since the insulators 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 35 kV and frequencies not exceeding 100 Hz, 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 support structure using a steel foot fixed inside the insulator. The insulator can be made up of one or multiple interconnected insulating components. The insulating parts of the porcelain insulator are porcelain pieces, usually coated with brown glaze or white glaze 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: glue-mounted and zinc-sleeve threaded connections. The glue-mounted type connects the porcelain piece directly to the base with cement, with a deep groove pressed into the porcelain part of the steel base to prevent loosening. An elastic pad is placed between the top of the steel base and the 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's threads to the steel base. 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 porcelain insulators specified in GB1000-1981 standard are divided into five grades according to rated voltage: 6, 10, 15, 20, and 35kV. 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. 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 are provided, which are made of upper conductive glaze above the side slots and have a letter "B" in the model.