The temperature difference between copper and oil of natural oil circulation power transformer is bigger than that of forcedoil circulation.
自然油循环变压器较以往强油循环变压器铜油温差加大，热问题就更加突出。
2
Since primary transformer of electric locomotive adopts the forcedoil-circulation cooling method, its heating computation is rather complicated and difficult.
电力机车主变压器采用强迫油循环吹风冷却方式，其发热计算较为复杂和困难。
3
The villagers were forced to use oil lamps, which are not only expensive but also dangerous because of the harmful gases they produce.