Rating of composite suspension insulators related to the long term mechanical strength of rods

The long duration mechanical strength of rods used in composite insulators is a major problem for the line designer. The previous approach to the problem and the requirements of standards give an extrapolation for the long term performance of the rod which is not confirmed by accurate analysis of test results. So, a new model for the load-time curve is determined. Based on the analysis of the behaviour of the rod under tensile stresses with acoustic emission and the determination of the physical “damage limit”, a mathematical model of the breakage process is proposed. This model takes into account two damage mechanisms; at high stresses, the slope of the load-time failure curve is governed by the relaxation of the resin matrix, then the curve tends to a horizontal asymptote corresponding to the intrinsic mechanical strength of the glass fibres. The model can solve any problem related to the ultimate behaviour of the fibreglass rod after various load histories. The conditions required to have no reduction of the ultimate strength of the rod in relation with the SML of composite suspension insulators are established