1. Insulation and stress categories

1.1 Different types of insulation

The insulation of an electrical structure or device is its ability to withstand the voltage or, more generally, the electrical stresses applied to it. Insulation is the material element or set of constructive devices that ensure this insulation.

On a three-phase electrical network, whatever the rated voltage, there are three insulation configurations to be considered when carrying out insulation coordination studies (figure 1 ).

• Insulation between one of the three phases and earth...