Application of CPI to metal oxide surge arresters and insulators
Experience
form CIGRE and IEC studies with surge arresters exposed to pollution,
indicate that the combination of the charge of the leakage current
pulses and the duration of the current pulse activity, rather
than the amplitude of the leakage current pulse alone, are decisive
for the heating of the zinc oxide varistor in MOSAs in polluted
conditions.
The
CPI is installed on arresters and insulators on site to collect
data regarding the site severity with special reference to
MOSAs and insulators.
These data are used to classify the site severity and to establish
pollution zones relevant to MOSAs. Furthermore, the CPI is
used during artificial pollution tests of MOSAs and insulators
in the laboratory.
By
comparing recorded data from site and laboratory, it will
be possible to correlate service stresses with laboratory
stresses and in that way establish pollution tests in the
laboratory that are realistic and related to the relevant
pollution zones.
The
CPI is used on post insulators and long rod insulators in
principle the same way as on MOSAs. In case of cap-and-pin
insulators the shunt unit should be connected between the
first and the second insulator disc from the earthed end of
the string.
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