1. The effect on the strength of the insulating medium The reduction of air pressure or air density will cause the reduction of the external insulation strength. In the range from altitude to 5000m, for every 1000m increase, the average air pressure will decrease by 7.7~10.5kPa, and the external insulation strength will decrease by 8%~13%.
2. The impact on the breakdown voltage of the electrical gap For the designed product, since the electrical gap has been fixed, the breakdown voltage will also decrease with the decrease of the air pressure. In order to ensure that the product has sufficient breakdown resistance when used in a plateau environment capacity, the electrical clearance must be increased.
3. Effect on corona and discharge voltage
a. High altitude and low air pressure reduce the initial voltage of partial discharge of high-voltage motors, reduce the initial voltage of corona, and cause serious corona corrosion;
b. High altitude and low air pressure reduce the internal air pressure of the power capacitor, resulting in a decrease in the initial voltage of partial discharge;
c. High altitude and low air pressure reduce the inner cavity voltage of the arrester, resulting in a lower power frequency discharge voltage.
4. Influence on arc extinguishing performance of switchgear
The reduction of air pressure or air density will reduce the arc extinguishing performance of the air medium arc extinguishing switch, reduce the on-off capacity and shorten the electrical life.
a) The arcing time of the DC arc prolongs as the altitude increases or the air pressure decreases;
b). The arcing distance of DC and AC arcs increases with the increase of altitude or decrease of air pressure.
5. The cooling effect of the medium, that is, the influence of the temperature rise of the product
A reduction in air pressure or air density causes a reduction in the cooling effect of the air medium. For electrical products that use natural convection, forced ventilation or air radiators as the main heat dissipation methods, the temperature rise increases due to the decline in heat dissipation capacity. In the range from altitude to 5000m, for every 1000m increase, the average air pressure will decrease by 7.7~10.5kPa, and the temperature rise will increase by 3%~10%.
a. The increase rate of temperature rise of static electrical appliances with the increase of altitude is generally within 0.4K per 100m, but for high heating appliances, such as electric furnaces, resistors, electric welding machines and other electrical appliances, the increase rate of temperature rise with altitude increases, Every 100m reaches more than 2K. the
b. The temperature rise of power transformers is related to the cooling method as the altitude increases. The increase rate per 100m is: oil-immersed self-cooling, 0.4% of the rated temperature rise; dry-type self-cooling, 0.5% of the rated temperature rise; oil-immersed forced wind Cold, 0.6% of rated temperature rise; dry forced air cooling, 1.0% of rated temperature rise;
c. The increase rate of the temperature rise of the motor with the increase of altitude is 1% of the rated temperature rise per 100m.
6. The impact on the mechanical structure and sealing of the product
a. Cause changes in the physical and chemical properties of low-density, low-concentration, porous materials (such as: electrical insulation materials, heat insulation materials, etc.);
b. Evaporation of lubricants and acceleration of volatilization of plasticizers in plastic products;
c. Due to the increase of the internal and external pressure difference, gas or liquid is easy to leak from the sealed container or the leakage rate increases, and electrical products with sealing requirements indirectly affect the electrical performance;
d. Cause pressure changes in the pressure vessel, causing the pressure vessel to break easily.
