A Method for Calculating the Derating Factors of Low Voltage Apparatus in High Altitude

At present, Low Voltage Apparatus is often required to reduce the capacity when they are used at high altitudes, but the method of determining the derating factors still needs further research. To address this problem, firstly, a formula for calculating the derating factors is derived, and a method is proposed to quickly calculate the derating factors based on a small amount of simulation or experimental data using the formula. Then, the electrical-thermal coupling model of a certain type of DC universal disconnecting switch was constructed and the derating factors was solved to verify the accuracy of the calculation method. Finally, the derating factors of different low voltage apparatuses were calculated and analyzed. The results show that the calculation method can accurately and conveniently calculate the derating factors of low voltage apparatuses at high altitude. In the range of 3000 m − 5000 m, the derating factors are almost linearly related to the altitude. The calculation method and conclusion can provide a reference for the design and use of low voltage apparatuses in high-altitude environment.