2.3.2.2 FLASHOVER TEST EVALUATION
METHOD
When the pollution layer on insulator surfaces was
completely wetted, a series of flashover tests were carried
out 4-5 times for per polluted specimen at the same
pollution degree. The test method applied with
even-rising voltage method and can be summarized as
follows:
(1) First, increase the voltage at a random rate to the
value of about 40% of predicted flashover voltage Up, and
then change the rate to the value of (10%-20%)×Up /s till
the flashover. Finally, record the flashover voltage Uf ;
(2) 1-2 minutes later, repeat the above procedures.
During the tests, the variation of ambient temperature
is less than 2°C by means of the refrigeration system and
the temperature in the chamber was kept below 35°C to
obtain the valid test data despite hot steam fog in the
paper.
For a polluted specimen, a series of flashover voltage
obtained by above procedure are expressed as Uf1, Uf2, ···,
Ufn (n is the number of flashovers), then the minimum
flashover voltage of the polluted insulator is