MECHANICAL FATIGUE OF COMPONENTS OF OVERHEAD LINES
WITH SPECIAL ATTENTION TO COMPOSITE INSULATORS:
LABORATORY AND THEORETICAL INVESTIGATION TO EVALUATE
THEIR LONG TERM PERFORMANCE UNDER THIS STRESS
(1990)Abstract
The overhead line components can
be submitted in operation to mechanical
fatigue stresses, mainly caused by the wind
actions on the conductor span. The
behaviour of a component under this kind of
stress will be considered and its strength
evaluated, in order to prevent the failure
of the component during its operation life
as well as an oversizing in its design.
So far quite poor information was available
on the response of composite insulators in
organic materials to stresses transmitted
by aeolian vibrations of the conductor. On
the other hand, there is some concern that
this kind of stress has caused, or taken
part in, the core fractures noticed on some
insulator types during operation.
The paper refers an investigation performed
on a conductor span about 100 m long, built
up in laboratory. The conductor, anchored
on both ends of the span with· composite
insulator strings, .was excited by a shaker
generating vibrations like those caused in
service by wind. The vibration frequency
ranged from 5 to 50 Hz.
The dynamic behaviour of the conductor as
well as that of the anchor composite
insulators was investigated. This allowed
to determine the inflexion modes and the
highest relevant strains that can occur on
insulators in operation. Then a rig was
conceived and built to submit the insulator
unit to a bending fatigue cycle,
reproducing on it in a conservative way the
determined strain values. The resulting
mechanical fatigue test was also
implemented with intervals of immersion of
the insulator in an acid solution, in order
to simUlate attacks in service from
chem"ical agents like acid rains and fogs,
moisturewi th addition of ni treous gases, etc ....
Preliminary test results have been obtained
and are briefly referred.
