The property of internal friction between the molecules of a liquid when it flows is called the viscosity of the liquid. The size of the viscosity, expressed in terms of viscosity, is a resistance factor that is used to characterize the properties of the liquid. The viscosity of the insulating oil is the same as the concept of the viscosity of a general liquid, which is the internal friction of the liquid, that is, when the insulating oil acts against the laminar flow under the action of an external force. The insulating oil molecules ask about the nature of the internal frictional resistance. The greater the internal friction of the insulating oil, the greater the viscosity, the more difficult the flow, and the poor heat dissipation.
There are many ways to express viscosity, which can be roughly divided into two categories: The viscosity measured directly according to the definition of viscosity is called "absolute viscosity", such as dynamic viscosity and kinematic viscosity. The viscosity measured under a certain condition in comparison with a liquid of known viscosity is referred to as "relative viscosity" or "conditional viscosity", such as Engel's viscosity and the like.
According to the measurement method, the viscosity is generally divided into three types: dynamic viscosity, kinematic viscosity, and Engelt viscosity.