[Design Requirements for Insulation Coordination of Connection Terminals in Electrical Connection Application of Low Voltage Equipment]: Insulation Coordination of Low Voltage Equipment has higher requirements for connection terminals from design structure to material selection. This paper attempts to analyze the application and design requirements of connection terminals in Low Voltage Electrical Appliances from the principles of insulation coordination and insulation coordination requirements of low voltage equipment: Insulation Coordination principle, insulation co-or.

Insulation coordination of low-voltage equipment has higher requirements for terminal from design structure to material selection. This paper attempts to analyze the application and design requirements of terminal in low-voltage electrical appliances from the principle of insulation coordination and insulation coordination requirements of low-voltage equipment.

Insulation co-ordination principle

Insulation coordination refers to the selection of electrical insulation characteristics according to the use requirements of products and the surrounding environment. Only based on the strength of various functions (such as voltage and other factors) endured during its lifetime, can the final goal of product insulation coordination be achieved.

1. Considering the working environment of low-voltage equipment, there are roughly the following factors affecting insulation coordination:

Rated voltage related to equipment; rated insulation voltage; rated impulse voltage determined by overvoltage during operation of equipment. In addition, environmental conditions such as temperature, humidity, solar radiation, heating, ventilation, dust, water vapor, etc. Other factors such as pollution, material properties (CTI), voltage action time, frequency, altitude (atmospheric pressure), electric field conditions, uniform electric field, and non-uniform electric field.

2. Analysis of Insulation Damage and Influencing Factors

One is insulation breakdown (thermal breakdown), that is, under the action of strong electric field, the dielectric inside the dielectrics is heated by dielectric loss. If the heat can not be dissipated, the temperature rises continuously, resulting in the escape of low molecular volatiles and the destruction of the molecular structure of the material, and finally the insulation breakdown.

Influencing factors of insulation breakdown:

The breakdown voltage decreases with the increase of temperature-temperature.

The breakdown voltage decreases with the increase of humidity-humidity

The breakdown voltage of materials decreases with the increase of voltage-action time and voltage-action time.

The breakdown voltage of materials decreases with the increase of frequency-frequency

Material Thickness-Increasing Material Thickness, Disadvantageous Heat Dissipation and Decreasing Breakdown Voltage

The second is insulation aging, that is, the irreversible physical and chemical changes of insulating materials under the action of various factors in the process of equipment operation, which lead to the rapid changes of electrical and mechanical properties of materials and destroy them, which is insulation aging.

For example: thermal aging, low molecular volatiles or products escaped from insulating materials under the action of heat, oxygen and water alone or in combination; free radicals formed participated in chain reaction to break molecular chains; autocatalytic action induced accelerated material destruction; hydrolysis degradation; or polymer chain polymerization, which resulted in material performance degradation or complete destruction;

In addition, electrical aging, due to the partial discharge of ozone, nitrogen oxides, high-speed particles, as well as dielectric loss caused by partial discharge increases, resulting in material heating, resulting in material performance degradation or complete destruction.

Insulation aging factors:

Electric Field Strength-Increasing Electric Field Strength Accelerates Insulation Aging of Materials

With the increase of temperature-temperature, the insulation aging of materials will accelerate.

With the increase of humidity-humidity, the insulation aging of materials will accelerate.

With the increase of frequency-frequency, the insulation aging of materials will accelerate.

Pollution-Pollution Causes Partial Discharge and Accelerates Insulation Aging of Materials

In summary, the electrical strength of insulating materials used in connection terminals of low voltage electrical equipment is far greater than that of air. Therefore, when the insulation design of connection terminals with electrical gap fails to meet the requirements, the method of creeping distance should be adopted, that is, adding solid insulation between the two conductors for isolation.

Due to the defects in solid insulating materials (such as impurities and air gap), although the voltage is far less than the breakdown level, it will still damage its life due to partial discharge. The damage of solid insulating materials has a cumulative process during its life, and its irreversibility will eventually lead to breakdown or aging and loss of effectiveness. Under the action of high frequency voltage, the increase of dielectric loss and partial discharge will reduce the service life.

It is inappropriate to simply increase the thickness of the insulation structure of the terminal in order to obtain long-term voltage withstanding ability. Only through reasonable structural design can satisfactory results be achieved. Specifically, the design method must determine the minimum electrical clearance; the minimum creepage distance; or add some auxiliary measures: coating insulating materials; adding insulating sleeve or insulating liner; laying insulating film; anti-pollution and anti-moisture, etc.