The peel test is an important test for insulators in the updated version of IEC 61109-2025.
1. Overview
The peel test is a standardized method used to assess the adhesion quality between the housing (typically silicone rubber) and the fiberglass core of a composite insulator. This test provides both qualitative and quantitative evaluation of bond strength at any accessible location on the insulator—such as along the trunk or beneath a shed (if the shed is removed). It is especially useful when the composite insulator lacks sheds or features sheds that are incompatible with the pull-off test.
2. Specimen Preparation
For each composite insulator, the peel test is conducted at four distinct locations evenly distributed around the circumference. At each location:
Three parallel cuts are made in the housing, each approximately 5 ± 2 mm wide.
These cuts are then intersected at 90 degrees by additional perpendicular cuts, forming a lattice (grid) pattern.
This process creates four small grid-shaped test areas at the interface between the rubber housing and the core rod.
3. Test Procedure
A tensile testing machine (or a manual device equipped with a calibrated force gauge) is used to perform the peel test.
One grid-shaped rubber segment is clamped with pliers, and force is applied perpendicular to the insulator’s longitudinal axis to peel the rubber away from the core.
The elongation rate must be maintained between 50 mm/min and 55 mm/min.
The ultimate peel force (in newtons) is recorded.
The actual bonded cross-sectional area at the rubber-core interface is measured using a sliding caliper to enable accurate stress calculation.
4. Acceptance Criterion
To pass the peel test, the average breaking stress across all four tested locations on the composite insulator must exceed 1.5 N/mm².
