In the range of 5000m above sea level, the air pressure decreases by about 1.07kPa for every 100m increase in altitude. Above 1000m, every 100m increase in air temperature will decrease the temperature by 0.6 degrees on average. The impact of air pressure drop on electrical products mainly has two aspects:

 

1. A decrease in air pressure will reduce the insulation strength of the air medium, resulting in a decrease in the insulation performance of electrical products
 

The dielectric strength of the air changes into a concave curve with the air pressure (Bassen’s law). There is a lowest point of the dielectric strength in the middle. When the air pressure is higher than this point, the dielectric strength increases with the air pressure. At air pressure, the insulation strength increases as the air pressure decreases. This is because when the air density is high, the ions formed by electrons or free electrons attached to the gas molecules accelerate in the electric field. Because the gaps between gas molecules are small and the collisions between molecules are frequent, the ions cannot be accelerated enough. The kinetic energy to collide with other molecules to make them ionize. In the case of low air density, although the ions in the electric field can be accelerated to sufficient kinetic energy, the probability of collision with gas molecules is greatly reduced, which is also not conducive to the ionization of the gas medium. Under normal pressure, the dielectric strength of air gradually decreases with the decrease of air density.

 

 

High-altitude areas require corrections to the dielectric strength-related indicators of electrical products, such as power frequency withstand voltage and impulse withstand voltage, electrical clearance and creepage distance, etc.; corrections to the rated capacity of electrical products are also required.

 

Table of correction coefficients for power frequency withstand voltage and impulse withstand voltage correction

 

Note: The dielectric test of low-voltage electrical appliances, such as the dielectric test between phase and phase, between phase and neutral line and ground, and between the disconnected contacts of the same phase, includes the insulation test of solid insulation and electric gap. Therefore, the test voltage should be corrected according to the requirements of the table. Since the dielectric properties specially used for solid insulation are not affected by altitude, the test voltage does not need to be corrected.

 

3. Electrical clearance correction
 

The clearance correction coefficient of low-voltage electrical appliances can be calculated according to the chart given in "Special Environmental Conditions Plateau Electrical and Electronic Products Part 1: General Technical Requirements" (GB/T20626.1-2006):

 

Clearance correction factor table

 

4. Rated capacity correction
 

As mentioned above, low air density will reduce the heat dissipation capacity of electrical products. Although the temperature rises as the altitude increases, the temperature rise can partly compensate for the increased temperature rise due to the decrease in heat dissipation capacity, but in general, due to the decrease in heat dissipation capacity, the temperature rise of electrical appliances The increase is an indisputable fact, so it is necessary to revise the rated capacity of electrical products. The specific correction factor varies with the product's heat dissipation conditions and methods, and generally requires derating.

 

 

The solar pumping system is applied in high altitude areas. The pumping inverters, combiner boxes, control cabinets and other electrical equipment in the system need to be corrected for the dielectric strength related indicators and the rated capacity as described above. And this needs to consider the influence of altitude from the product design stage, this method will bring greater R&D investment. Another way is to adopt some selective measures for the photovoltaic pumping system, so that it can be safely used in high-altitude areas, which may be a more realistic method.

 

Take Siemens MICROMASTER 440 universal inverter as an example. As shown in the figure below, when used in high altitude areas, the output current and input power voltage are derated.

Solar pumping systems can also use a similar method to derate the input power supply voltage and rated capacity, so as to be suitable for high-altitude areas. For pumping inverters, the correction coefficient can be given according to the product design standards provided by the manufacturer, and the coefficients are different for products of different manufacturers; for the power distribution equipment such as the combiner box and control cabinet in the solar pumping system, it is affected. Altitude has a greater influence on the switching elements used, such as DC circuit breakers. The following table shows the correction value of a manufacturer's DC circuit breaker at an altitude of 2000m or more. The breaking capacity remains unchanged. The correction factor of the related equipment can be determined by consulting the instruction manual of the switching element.

 

Correction coefficient table of DC circuit breaker in different altitude areas

                 

Solartech solar pumping system adopts international leading technology and is composed of solar pumping inverters, combiner boxes and control cabinets independently developed by the company. Shenzhen Solartech solar pumping system has been successfully applied to many high-altitude areas at home and abroad. solar water pumping has a wealth of project experience, and the corresponding correction parameters of the system can be given according to customer needs. The reasonable configuration of the system realizes the safe and reliable application of solar water pumping systems in different altitude areas.