Mechanical Rating Criterion
Maximum Design Cantilever Load (MDCL) is a mechanical
characteristic by which Composite Line Post Insulators (CLPI) are rated. This
is the maximum cantilever load that the insulator is designed to withstand
continuously throughout its service life.
At this level of load, which generally represents 40% to 50%
of failing load (as defined by failure data provided by manufacturers), there
will be no reduction in strength due to mechanical damage of the insulator’s
components.
At this point in time, universally accepted definitions of
cantilever load characteristics, including failure and failing load, have not
been agreed upon and are under consideration by ANSI and IEC.
Tension loads
Tensile strength of composite line post insulators is
dependent on the mechanical characteristics of the end fittings, and on those
of the core-to-end fitting interfaces.
Compression loads
Compression loads on line post insulators do not usually
result in damaging stresses until buckling occurs. Generally, elastic buckling
of long posts, while not desirable, is not damaging. However, for further
information on this, the manufacturer should be consulted.
Torsion loads
Some designs of line post insulators may have low torsional
capability. In this event, cracking of the fibreglass rod or permanent rotation
of the end fittings can occur by twisting. The manufacturer should be consulted
to determine the torsional capability of a given insulator.
Combined loads
Actual line loads are rarely single loads. Usually, they are
a combination of loads. When comparing actual mechanical load conditions with
composite line post mechanical strength ratings, it must be recognized that
vertical transverse and longitudinal loads each contribute to the total bending
moment on the insulator, and therefore to total cantilever load.
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