Aging Effect on Leakage Current Flow in Wooden Poles


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ABSTRACT

Insulation degradation leading to leakage current flow through high voltage insulators
could result in catastrophic failures such as pole fires and damages to nearby
equipment. This paper examines the leakage current distribution originating from the
high voltage conductor to various locations through the wooden pole of various age
profiles. The specimens that are investigated in this paper range from a new sample to
an aged pole sample of more than 20 years in service.

INTRODUCTION

IN Australia and many other countries in the world
with vast bush lands, power transmission lines on the
distribution level, are carried on wooden poles [1-2].
These distribution lines suspended on insulators, which
are fixed to wooden poles, pass cities as well as bush
lands. Under different weather conditions, insulators
become contaminated, and in particular, with damp
weather, these insulators lose their ability to provide a
perfect insulation between the high voltage wire and the
ground [3]. When excessive leakage current starts
flowing through the high impedance support such as the
wooden pole, the fire starts at the loosen metal-wood
junction. The high voltage drops across the junction
causes minor arcing that heat up the wood and later leads
to fire.

LEAKAGE CURRENT AT VARIOUS
LOCATIONS

Under the dry condition, the leakage current at the metal
pin of the insulator was measured by switching on switch
S1 and average current of 1630 μA was recorded. This
current represents the total leakage current produced by the
insulator. Later, the leakage current through the wood was
measured and an average value of leakage currents at S2,
S3 & S4 was calculated. The entire testing procedure for
specimen A was repeated for specimens B and C. The
leakage current value over a 60 second period of specimen
A, B and C are shown in Figure 5 and the average leakage
current based on 60 second period at switch S2, S3, and S4
are tabulated in Table 2. Under wet condition, the moisture
level between 25% and 30% was applied to the timber
specimens. The result obtained for the wet and dry
specimen was compared to evaluate the performance of
wood. Figure 6 shows the leakage current of specimen A, B
and C during both the wet and dry condition test.