This manual introduces the cause, hazard and measurement method of local discharge. Local discharge refers to the discharge of only part of the area in the insulation system under the action of electric field, but not yet punctured. Local discharge may occur on the side of the conductor, or on the surface or inside of the insulation, and local discharge on the surface is called surface local discharge. Local discharge in the interior is called internal local discharge. And for the local discharge near the conductor surrounded by gas, it is called corona. The main causes of local discharge are: 1. Uneven electric field. 2. Inhomogeneous dielectric. 3. Bubble or impurity in the manufacturing process.
