2. Abstract
• For a better wetting property during Solid layer tests, relative humidity shall be higher
and temperature shall be lower. This poses problem that the solid layer tests shall have to
be conducted only during the period when Relative humidity is higher and temperature is
lower.
• Since these tests are time consuming, alternative tests methods were attempted.
• In this study attempts were made to carry out the solid layer pollution test at any time of
the day. The polluted insulator is kept at the centre of the nozzle column assembly and
the plain water spray is directed on to the test object.
• Various tests at different distances from the centre point were also carried out. The results
• will be helpful in arriving at a test method overcoming the difficulties of the solid layer
pollution test.
• It was possible to conclude from the study that solid layer pollution tests can also be
conducted by clean fog wetting.
3. Introduction
• The flashover voltage and withstand ability of external insulation
is governed by the degree of pollution and the type of pollution
as well as by weather conditions, which vary to a great extent in
nature.
• In order to obtain reliable and comparable results for assessing
the quality and the right choice of insulation under pollution
conditions, it becomes necessary to perform investigations
under controlled laboratory conditions with different pollution
severities and several test methods have been evolved in this
frame work.
• The advantage of such artificial pollution test over naturally
polluted insulator studies is the availability of useful results
within limited time duration.
4. • Two methods viz., salt fog and solid layer methods are
generally used for artificial pollution test on insulators.
Salt fog method can be reproduced in all types of weather
conditions. However, the Solid layer method of pollution test is
difficult to be carried out at tropical countries, wherein, wetting at
lower humidity
and at higher temperature is difficult.
• Therefore, alternate method of wetting, i.e., by indirect water fog
has been carried out and the results are presented in this paper.
5. • Solid layer method
• The procedure for pollution test by solid layer method has been
given in IEC-60507, 1991.
• It also suggests two types of wetting procedures namely,
Wetting
before and during energisation (Procedure-A) and Wetting after
energisation (Procedure-B).
In tropical countries like India, wetting the pollution layer on the
insulators is very difficult.
We have to wait till the Temperature comes down to a lower
value and the Relative humidity value increases.
6. • Instead of steam fog wetting during solid layer tests, alternate
wetting by plain water fog was carried out.
• In order to assess the validity of test procedure, it was
necessary to check the repeatability of wetting characteristics.
• The wetting characteristics were determined on the strings of
three-disc insulators of glass and porcelain insulators.
7. • The wetting characteristics of various insulators were
determined when kept at centre of the nozzle column assembly,
0.6metre and 1.2 metre away from the centre of the nozzle
column assembly.
• The results are presented in the following sections. After
determining
the optimal position of the insulator for the indirect fog, repetitive
tests were performed in order to find out the repeatability of the
wetting characteristics.
