External insulation and discharge characteristics of transmission and transformation equipment

Insulation in power system can be divided into external insulation and internal insulation from insulation structure and characteristics. External insulation: air gap insulation and surface insulation of insulators exposed to the atmosphere; The withstand voltage of external insulation is closely related to atmospheric conditions and is generally designed by the electric power design department. Air gap breakdown and surface flashover are the manifestations of external insulation loss. After breakdown or flashover occurs, the insulation performance of air can be automatically restored, belonging to self-recovery insulation. Internal insulation: insulation from direct contact with the atmosphere; Its tolerance voltage is independent of atmospheric conditions. Generally designed by the manufacturer;Internal insulation can be composed of solid, liquid, gas (SF6) and other media combination (mainly liquid, solid); Once the internal insulation breakdown often can not automatically recover, is a non - self - recovery insulation. External insulation of electrical equipment: Air clearance and insulators constitute the external insulation of electrical equipment, which directly bears the influence of the atmosphere and other external conditions. Air gap breakdown and insulator flashover are often referred to as destructive discharge of external insulation. The ring-breaking discharge voltage of external insulation is related to atmospheric conditions. Under different atmospheric conditions, the discharge voltage of external insulation can be converted according to the law of a lot of experiments.

The function of insulator: the conductive body at different potential is connected with each other mechanically and insulated from each other electrically. Insulators are usually composed of insulating parts, metal attachments for mechanical fixation, adhesive insulation parts and adhesives for metal attachments.

1. Classification of insulators

Into line insulator: (1) according to the purposes and insulating structure used for high voltage overhead line suspension or support the insulation of the conductor parts used for hanging wire suspension insulator, used to support the conductor is the pillar of composite insulator, such as: post insulator used for high voltage and high voltage electrical distribution equipment busbar charged part of the insulation support used in high isolation switch for fixed contact post insulator and porcelain cover: Used for electrical insulation within the container, within and insulated from the surrounding environment factors such as voltage transformer's porcelain sleeve, lightning arrester porcelain sleeve casing, such as: used as a conductor through the electrical enclosure, grounding transformer winding insulation parts partition or wall will qualify, wall casing pipe (2) according to the insulating material such as divided into porcelain insulator: anti-aging performance is good, have enough electrical and mechanical strength; Heavy and fragile, high cost of transportation and installation, high energy consumption in manufacturing. Glass insulator: has the same environmental stability as electric porcelain, mechanical and electrical strength is higher than electric porcelain; Suspension type tempered glass insulator has the characteristic of "self-explosion" after being damaged, which is convenient to find in time during line inspection. Composite insulators: have good electrical performance, mechanical strength and environmental stability; Simple process, production process pollution, light weight, small volume, convenient transportation and installation; The material has hydrophobicity, strong anti-pollution flashing ability; The aging resistance is not as good as porcelain and glass insulators, and the production cost is high.

2. Insulators are required to have sufficient electrical strength, to withstand certain mechanical loads, and to withstand adverse environmental and atmospheric effects. Electrical performance: flashover voltage (dry flashover voltage, wet flashover voltage, pollution flashover voltage), breakdown voltage and visible corona voltage; Mechanical properties: tensile load, bending load and torsional load; Cold and hot properties and anti-aging properties.

3. Line insulators are divided into pin type, column type and suspension type according to their different structures. Pin type insulators are widely used in 6-10kV power distribution lines. (line post type porcelain insulators: below 35kV, porcelain cross arm insulators, insulation to the ground and cross arm function (to separate each phase of the wire a certain distance)) line suspension type insulators are used for high voltage lines above 35kV, can be divided into disk and rod shape.