Abstract:
Insulation in electrical equipment is a very crucial
aspect while designing any electrical system especially in case of
high voltages in any part of a power system. Hence it is crucial to
determine the properties and performance of an insulating
material. The experiments deal with the measurement of
breakdown voltages and determination of ageing of an insulating
material under accelerated AC fields. The insulating material
used in our experiments is Low Density Polyethylene (LDPE) as
it is an extensively used insulator for power cables. LDPE makes
an excellent electrical insulator because of its high resistivity and
good tracking resistance. While insulation is essential for
designing any electrical system, its failure often leads to the
subsequent failure of the system. Every insulating material
undergoes degradation with time even if it is subject only to
operating or working stress. The test method used, to relate the
stress and time till breakdown, in our experiments is steppedstress
testing. This type of tests gaining momentum due to their
certainty of completion of ageing experiments compared to
constant-stress testing where incomplete data leads to
censoreddata analysis. Also the times consumed can be low
depending on the choice of voltage step size and time step
duration. The variations were in terms of voltage levels and the
time of exposure of the specimen to a particular voltage level. The
distribution of breakdown voltages for the specimen for different
step sizes can be studied using Weibull distribution. Inverse
Power Law and Miner’s Theory of cumulative damage gives a
quantitative insight of the breakdown phenomena in insulators
and can be used to estimate the equivalent life of the material
under test. Using these statistical methods, the ageing and
expected performance of the insulating material can be obtained.
