“Insulator Sealing” refers to the sealed interface between the rod, the end fitting and the Silicone Rubber housing to protect it against environmental impact.

This is an essential process for the reliability of the composite insulator: The sealing area covers the so-called triple point as well, which is the point of highest electrical stress concentration along the insulator.
Composite insulator has been applying both sealing processes since decades. This is a result of the multiple processes used in-house for the application of the Silicone Rubber housing.
Field performance and field experiences had conclusively confirmed that, when properly designed and manufactured, both sealing processes work perfectly. Overmoulding is the more challenging method, because the adhesion to the metal end fitting is absolutely necessary and requires special attention during manufacture.

Regarding the electrical field, overmoulding can be used to a certain extent for a field grading. However, for voltages above 200 kV or under critical conditions above 145 kV, corona rings or combined corona/arc protection devices are used and predominantly determine the field distribution.

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