Effect of Altitude on Impulse and 60-Cycle Strength of Electrical Apparatus

The air strength of electrical apparatus to long waves (1½×40 microseconds) is essentially proportional to the RAD. The impulse strength of apparatus applied at high altitudes and exposed to lightning should be rated accordingly. The RAD corrections for front-of-wave impulses (1,000 kv/microsecond) are one half and less than one half of those for long waves. Sixty-cycle strength and corona are also affected in direct relation to the RAD. Voltage ratings naturally should recognize this. The oil strength of apparatus is practically unaffected by altitude. Data on the effect of humidity are presented. Other influencing factors that may be present at high altitude are discussed. Corona effects may need more attention.