Transformer oil is used for insulation and heat dissipation. The coil immersed in oil can be well isolated from the outside air to prevent dust and moist air from entering and improve the insulation performance of the winding.

变压器油的另一个重要作用是散热。通过油的流动把变压器内部热量传导致变压器表面，然后散发到周围空间。尽管水的散热性能要好于变压器油，但普通水是导电的故不能直接用于变压器散热，大型变压器也有间接用水散热的。

Another important function of transformer oil is heat dissipation. Through the flow of oil, the heat inside the transformer is transferred to the surface of the transformer and then dissipated to the surrounding space. Although the heat dissipation performance of water is better than that of transformer oil, ordinary water is conductive, so it can not be directly used for transformer heat dissipation. Large transformers also have indirect water cooling.
              

由此可见变压器油的主要特征是绝缘性和流动性及高温下的安全性。

It can be seen that the main characteristics of transformer oil are insulation, fluidity and safety under high temperature.

而润滑油的基本要求是两项，一是能在机件表面保持油膜，从这个角度说粘稠度越高越好，但过于粘稠要增运行阻力。二是有较好的流动性、有利于散热同时起到清洗金属屑作用，这就要求粘稠度低一些。选择机油就是要在二者间找到平衡点。

The basic requirements of lubricating oil are two. One is to keep oil film on the surface of machine parts. From this point of view, the higher the viscosity, the better. However, if it is too viscous, the running resistance will be increased. Second, it has better fluidity, is conducive to heat dissipation, and plays a role in cleaning metal chips, which requires lower viscosity. The choice of oil is to find a balance between the two.

对于负荷较大且转速低的运转部位，一般用粘稠度高的黄油，既可在机件间形成油膜起到润滑作用，又可通过运转使其实现循环流动。如果你在这里使用粘稠度很低的钟表油是无法保持油膜的，而过度的流动性还会使油很快流失根本起不到润滑作用。

For the operating parts with large load and low speed, the grease with high viscosity is generally used, which can not only form an oil film between the parts to play the role of lubrication, but also realize the circulation flow through the operation. If you use a watch oil with low viscosity here, you can't keep the oil film, and the excessive fluidity will make the oil lose quickly and can't play a lubricating role at all.

变压器油和车用润滑油相比，稠度要低得多，它虽可满足散热和流动性两项，但无法形成足够厚的油膜，必然导致机件很快磨损。

Compared with vehicle lubricating oil, the consistency of transformer oil is much lower. Although it can meet the requirements of heat dissipation and fluidity, it can not form enough thick oil film, which will inevitably lead to rapid wear of parts.

由此可见把变压器油作车用是不行的。车用油一定要按说明书要求选择比较合适的，粘稠度过高过低都不行。联想到一个修自行车的老师傅把高速润滑油脂用到自行车上，殊不知高速黄油在常温、低速时流动性很差，还不如普通黄油效果好。

It can be seen that transformer oil can not be used for vehicles. Car oil must be selected according to the requirements of the manual, too high or too low viscosity is not good. Think of a teacher who repaired bicycles who used high-speed grease on bicycles, but they didn't know that the fluidity of high-speed grease was very poor at room temperature and low-speed, and it was not as good as ordinary butter.