A relationship between the leakage current and
wind velocity, which is the first of its kind, has been
proposed in this paper. This relationship has been derived
based on Dimensional Analysis technique. The
proposed relationship has been applied for prediction
of leakage current in the 275 kV insulators of
YTL (Yeoh Tiong Lay) Power Station, which situated
at the coast of South China Sea, Terrengannu,
Malaysia. The calculated results were compared with
the measured leakage current data. There was an excellent
concordance between the experimental results
and those calculated from the mathematical model.
Keywords: Leakage current, Wind velocity, Dimensional
analysis, Insulator.

The insulators of power lines, switchyards and
other power installations sited near seacoast get contaminated
with wind borne salt and dust particles
and formed contamination layer. Such a layer is
composed of largely inert and often conductive compounds
as carbon, metal oxides and salts. This layer
may form conductive path, usually in the presence of
fog or dews or light rain. This conductive layer allows
the flow of leakage current through the insulator
surface under system voltage. It results in the ohmic
heating on the insulator surface and drying of the contaminated
layer by rapid evaporation of the moisture
at the location oh high current density. This phase
of development is known as the dry band formation
[1]. The dry band has a high resistance, across which
the entire energized voltage of the insulator existed.
This causing a localized breakdown or arc bridging
over the dry band and leading to a widening of the
dry band due to moisture evaporation and finally arc
extinction. These intermittent arc bridging and arc
extinction produce leakage current pulses with sharp
peaks [2]. If the insulation resistance of the insulator
decreases abruptly due to excess contamination
on its surface, then leakage current becomes large.
When the rate of current change is extremely high,

full flashover occurs on the insulator surface. During
the flashover on the insulator surface the leakage
current increases tremendously. This is due to the
non-uniformity of the distribution of the contamination
on the insulator surface [3-4].
In order to prevent wetting and hence formation of
conducting film in the presence of contaminants that
give rise to uncontrolled leakage currents resulting in
flashover, polymers are presently used as alternative
materials instead of glass and porcelain for outdoor
insulators [5]. Though polymers help in attaining
high flashover voltage these are expensive compared
to commonly used porcelain and glass insulators.
The porcelain and glass insulators of YTL (Yeoh
Tiong Lay) Power Station at Terrengannu, Malaysia
are facing contamination problems due to wind velocity
at the seacoast. The location of YTL Power
Station is shown in Fig. 1.
For getting better performance, the insulators of
that power station should be washed at appropriate
times. The decision for washing is taken by
YTL Power Station engineers through measurement
of leakage current of selected insulators. It appears
from a review of the literature [6-9] that although a
number of measurement techniques on leakage current
and other parameters are available, no mathematical
relationship between leakage current and
wind velocity has yet been proposed. This paper presented
the development of a mathematical model considering
the effect of wind velocity on the variation of
leakage currents in the contaminated insulators using
Dimensional Analysis technique [10]. The results calculated
from the proposed model are compared with
the available measured leakage current data made
available from YTL Power Station.
List of Symbols
- I Leakage current in the insulator;
- wa Wind velocity
- N Static arc constant;
- w Weight of the insulator;
- et Exposure time
- L Length of fundamental SI units;
- M Mass of fundamental SI units;
- T Time of fundamental SI units;
- A Current of fundamental SI units;
- n Arc constant;
- k1 Exponent of the variable I;
- k2 Exponent of the variable wv;
- k3 Exponent of the variable N;
- k4 Exponent of the variable w;

k5 Exponent of the et.

The insulators in YTL (Yeoh Tiong Lay) Power
Station are located at a height of about 50 meters
from the sea level. For measuring leakage current,
the artificial electrode is fixed near the first shed of
the 275 kV line post test insulator and tightened by
a screw. This arrangement is shown in Fig. 2 (a).
A cable is connected between the electrode and the
leakage current measuring instrument, which is shown
in Fig. 2(b).
The Leakage Current Monitor (LCM) measures
the leakage current and the highest leakage current
is printed and remains on display until a next higher
value occurs or the instrument is reset. The leakage
current of the insulators in two sections, i. e.,
blocks of the switchyard (Block No. 10 and Block
No. 20) at the YTL power station was measured at
various times of a day. At the same time the corresponding
wind velocities at YTL Power Station were
measured using velocity meter. All instruments used
in the experiment are calibrated with the standard
instruments before commencing the leakage current
measurement. The percentage of error of comparison
results between the standard and LCM instrument is
found to be 0.01.