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Reference: ISH2017_145

Type:
ISH Collection
ISH Collection
Title:
Need of standardized adhesion test for composite insulators: lessons learned from service experience and testing
In the beginning of 2016 two failures of line composite insulators were
experienced on the 130 kV transmission line. The two failed insulators were inspected in
the laboratory and the root cause of the damage was considered as weak adhesion
between the fibreglass rod and housing which finally resulted in the so-called “flashunder”
type of failure. The results of IR inspection of the rest of the insulators in service were in
line with this assumption, revealing a lot of hot spots on different insulators. This indicated
some kind of internal conducting path inside the insulators (in the interface silicone
rubber/fibreglass rod). Two batches of new composite insulators of two different types
were then evaluated in the laboratory by sample testing. The program for sample testing
included:
? Visual inspection and hydrophobicity classification.
? Test on interfaces according to the appropriate selection of tests from the IEC
standard (reference dry power frequency test, water immersion pre-stressing,
visual examination, steep-front impulse voltage test, dry power frequency voltage
test).
? Adhesion test not defined by the IEC. A special procedure was developed and
applied, which will be described in detail. Based on general insulator knowledge
good adhesion should result in separation in rubber material before the
separation between the fibreglass and the silicone rubber housing. This method
is generally accepted and performed by many manufacturers as an internal check
of the quality during the production of composite insulators.
All insulators have passed the selection of electrical tests according to the IEC standard
aiming for test of interfaces. However, obvious weakness in adhesion has been revealed
for one type of the insulators (the same as being detected in service), which would
influence the long-term performance. This indicates that the requirements of the present
standard cannot reveal the insulators with internal weakness of such type. Revealing of
poor adhesion should be an important topic for CIGRE/IEC in the future, i.e. to develop
new representative test methods and to revise relevant IEC standards.
File Size: 720,3 KB
Pages NB: 6
Year: 2017

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