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IEEE SENSORS JOURNAL, VOL. 15, NO. 3, MARCH 2015
Detection and Monitoring of Leakage Currents in
Power Transmission Insulators
Marcelo Martins Werneck, Daniel Moreira dos Santos, Cesar Cosenza de Carvalho,
Fábio Vieira Batista de Nazaré, and Regina Célia da Silva Barros Allil
Abstract— An optoelectronic sensor for real-time leakage
current monitoring on high-voltage (500 kV) and mediumvoltage (13.8 kV) power line insulators was developed. The leakage current drives an ultrabright light-emitting diode producing
an amplitude modulated light signal. The optically intensityencoded signal is coupled to a plastic optical fiber cable and
transmitted from the high potential measurement point to the
remote unit in ground potential. After the demodulation, the
leakage current root mean square values are concentrated in a
data logger and sent to a remote station 150-km away by general
packet radio service technology. Field tests at real operational
conditions on coastal regions have been performed; all data
collected are stored in a structured database, which can be
consulted from the Internet, while a serially produced head was
developed and the sensor is ready for commercialization. Since
leakage current on high-voltage insulators depends on local air
pollution and microclimate changes, several sensors have to be
used to cover the region monitored. For this reason, research has
been conducted to determine the sensor representativeness, i.e.,
the actual area, which can be covered by only one sensor.
Index Terms— Current, distribution, leakage, monitoring,
optical, sensor, transmission lines.
I. I NTRODUCTION
I
NSULATORS are key components in energy distribution
systems, and, after being installed, remain in field for long
periods of time. Insulator leakage current is the current flowing
from high voltage conductor to ground over the outside surface
of the insulator. Leakage current occurs in any high voltage
insulator, either in transmission lines (TL) or in distribution
lines installed outdoors due to the progressively coating of
conductive deposit from environment pollution.
These pollutants can be dust, ashes, smoke, clay powder,
chemicals from nearby industries or salt-spray on seashore
areas. In the presence of wet atmospheric conditions, particles
Manuscript received July 1, 2014; revised October 3, 2014; accepted
October 3, 2014. Date of publication October 8, 2014; date of current
version December 11, 2014. This work was supported by the Ampla
Energia e Serviços S.A., Niterói. The associate editor coordinating the review
of this paper and approving it for publication was Prof. Aime Lay-Ekuakille.
M. M. Werneck, D. M. dos Santos, C. C. de Carvalho, and
F. V. B. de Nazaré are with the Photonics and Instrumentation Laboratory,
Federal University of Rio de Janeiro, Rio de Janeiro 21941-901, Brazil
(e-mail: werneck@lif.coppe.ufrj.br; daniel@lif.coppe.ufrj.br; cesar@lif.coppe.
ufrj.br; fabio@lif.coppe.ufrj.br).
R. C. da Silva Barros Allil is with the Biological Defense Laboratory,
Brazilian Army Technology Center, Rio de Janeiro 20031-144, Brazil (e-mail:
regina@lif.coppe.ufrj.br).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/JSEN.2014.2361788
on the insulator surface will dissolve with the water droplets
and will provide an alternative path from high-voltage to
ground potential [1], [2]. Although these currents are around
a few miliamperes, when multiplied by the total number of
insulators located in that particular transmission line, the total
current can reach high values that can engage protection
devices, leading to electrical power line interruptions, thus
leading to financial and operational losses to distribution
companies and unsatisfied customers.
Additionally, night dew or light rain increases the conductance of the polluted layer leading to arcs. Depending
on the conductivity of the layer, these arcs can develop and
cause what is known as a flashover, when the air around the
insulator ionizes becoming a conductor, leading occasionally
to the destruction of the whole insulator followed by outages.
In general, this phenomenon happens in the following stages:
• Settling of pollutants on the insulator surface
• Compounding soluble pollutants with rainwater or dew
and formation of a conductive layer
• Starting of leakage currents
• Surface of the insulator gets hot followed by the
formation of dry areas
• Partial discharges
• Occurrence of flashover.
Consequently, the insulator leakage current monitoring as an
indicative parameter of a possible flashover incident, enabling
a proper planning of insulator predictive maintenance,
becomes significant.
II. L EAKAGE C URRENT E VALUATION
Superficial leakage current is the result of the interaction
between the climate and the contaminants deposited over the
surface of the insulator, an approximate expression for the
leakage current is given by
U πγm D
U
= Eπγm D
=
(1)
I L E AK AG E =
Rm
l
where I L E AK AG E is the leakage current, U is the distribution/
transmission line voltage, Rm represents the insulator surface
resistance (which is related to the contaminant density), l is
the insulator creepage distance, γm is the conductivity of the
dewy and contaminated surface, D is the insulator diameter,
and E is the electric field intensity through the creepage
path [3]. The variables described in (1) are shown in Fig 1.
The accumulation of contaminants over the insulator
surface, combined with the environmental high humidity,
1530-437X © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
WERNECK et al.: DETECTION AND MONITORING OF LEAKAGE CURRENTS IN POWER TRANSMISSION INSULATORS
Fig. 1.
Representation of the variables from (1).
causes the increase of the conductivity (γm ) that enables
the leakage current emergence. The electric companies need
to maintain a continuous monitoring of leakage current and
for this they rely in parameters that help establishing a
preventive strategy of water-jet-cleaning or substitution of
insulators placed on the area with favorable conditions to
flashover occurrence. In recent years, many studies have been
carried out to improve pollution assessment, such as [1], [4],
and [5]. There are also many standards that help technicians
to improve insulator performance, such as the IEC60815 [6],
which defines parameters for insulator selection, for instance,
pollution severity level, creepage or arcing distance.
Particularly, the in-field tests which were carried out for this
work showed that the quantity of deposited contaminants and
environmental humidity are directly related to the leakage
current value.
The usual method to assess insulator pollution is the ESDD,
meaning Equivalent Salt Deposit Density. The ESDD is by
definition the amount of sodium chlorine deposited over the
insulator surface that would produce the same conductivity
at a given natural pollution. In order to measure ESDD it is
necessary to wash the polluted insulator with distilled water,
carefully collect the water and then measure its conductivity.
Now, the amount of salt that would produce the same conductivity divided by the surface of the insulator area will give the
ESDD factor in mg/cm2. The washing is performed on what is
known as “sacrifice insulator”, that is, an insulator of the same
type as those used on that specific location but without electric
wires. This insulator is hoisted to the top of the tower and left
there for a specific amount of time until it gets polluted as
much as the others. Then, this insulator is lowered down and
washed.
Leakage current assessment is not a new concern of the
electric company personnel. Accidents involving flashover
events in insulators employed in transmission/distribution
lines, especially near seashore areas, have been a major
issue for energy companies for a long time. Consequently,
several sensor types and on-line monitoring techniques have
been developed and widely used for protection systems [7].
Also, current literature presents several techniques to
monitor insulator pollution. Classic techniques apply resistive
dividers [8], [9], induction coil, as described in patent [10] and
a magnetic toroid around the insulator [11]. Optical methods
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have also been employed by [12] and, more recently,
by [7], [13], and [14]. Particularly, in [14], the authors
describe the first development stages of the employment of
plastic optical fibres in leakage current detection. However, in
order to be useful for the electric company, a leakage current
monitoring system needs to present, at least, four basic characteristics: ease of use (i.e., be practical), low cost, safety and
reliability.
In this paper an optoelectronic system is described, being
capable of measuring, storing and radio transmit by GPRS
(General Packet Radio Service) data link the insulator
leakage current data as well as local temperature and air
relative humidity using plastic optical fiber (POF) technology.
Comparing with other solutions available in literature, this
system presents some advantages, such as immunity to
electromagnetic interference; low cost; lightweight, easy
installation at the power line without the need to turn it off,
and does not need a power supply close to high voltages. Other
benefits can also be mentioned, that is: optimization and monitoring of energy losses, increase of the distribution network
reliability yielding a reduction of intervals between turn-offs,
optimization of the insulators washing routine and easy way
to compare different kinds of anti-pollution insulators.
III. T HE L EAKAGE C URRENT M ONITORING S YSTEM
An optoelectronic transducer intended for measuring
leakage currents from both high voltage transmission line (TL)
and medium voltage distribution line was developed. The
working principle of the sensor is very simple, based on
the fact that an LED output light is proportional to its
direct current. So, a high efficient LED is installed inside
the transducer so as to the leakage current flowing from
high voltage line to ground potential over the insulator
surface drives the LED supplying enough energy to make it
lighten. Then the LED output light, modulated by the leakage
current, is fed into a POF that transmits the signal to the
Remote Unit (RU) installed at ground potential.
Amplitude modulated fiber optic sensors have been
abandoned some decades ago due to several side-effects such
as optical power drift due to temperature and ageing, modal
instability and macro-curvature losses. However, with the
availability of POFs at low cost, these sensors were re-visited
and some examples appeared in the literature lately [11], [12].
For the reasons stated above, when using an amplitude
modulated fiber optic sensor it is necessary to address all the
mentioned conditions. For instance, when dealing with plastic
optical fiber waveguides, all rays in a bent fiber are leaky,
that is, they can traverse the core-cladding interface and never
return. At successive reflections the guided light inside the
fiber loses power. However, some rays reflect back in the cladair interface returning to the core [15], and become guided
again. The higher the numerical aperture (NA) of the fiber,
the more these returning rays are allowed to penetrate back
into the core. This effect happens with POFs that possess
millions of guided modes and very large NA. Indeed, for a
bending radius of 32 mm, a standard 1-mm-diameter POF
loses only about 0.1 dB per turn [16]. Therefore, bend losses
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IEEE SENSORS JOURNAL, VOL. 15, NO. 3, MARCH 2015
Fig. 2.
Temperature dependence for Nichia LEDs. (a) NSPB300 Blue,
(b) NSPG310 Green and (c) NSPR510 Red (graphs available at [17]).
are negligible in a POF cable connecting the transducer and
the receiver.
The other issue to account for is the temperature dependence
of the LED, whose output light fades as temperature rises. This
thermal drift depends on semiconductor material and dopants,
that is, for different LED colors (wavelength), different drifts
apply. In order to find the LED type which best complies
with transmission requirements, three different LEDs were
investigated, namely: blue, green and red LEDs. In reality,
the best wavelength for a silicon photodetector is around
850 nm, which corresponds to its peak response. However,
we decided to use visible LEDs for the project because it
facilitates maintenance since the operator can see whether the
transducer is working or not just by looking into the POF
output connector. Fig. 2 shows three temperature dependence
graphs for three LEDs manufactured by Nichia Corporation:
NSPB310 Blue, NSPG310 Green and the NSPR510 Red [17],
[18], [19].
Notice the smaller dependence of the blue and green LEDs
with temperature variation. However, since the wavelength
of all three LEDs fall outside the peak sensitivity of the
photodetector, one has also to check the wavelength drift
with temperature, since for different wavelengths there will be
different gains. Fig 3 shows the wavelength performance for
the three LEDs with the same current in different temperatures.
As it can be seen in Fig. 3 (a), (b) and (c), the peak
wavelength (that is, the wavelength at which the maximum
value of the optical power is obtained) of both blue and green
LED drifts are negligible with temperature, i.e. the peak wavelength does not considerably vary, whereas red LED presents
a large drift. From these results the green LED was chosen
since it provides lower optical losses when employed in POF
light transmission systems while its temperature dependence
characteristic is similar to the one presented by the blue LED
(Figs. 2 and 3); its drift under temperature was recorded in
Fig. 3. Temperature drift in the spectra of three different Nichia LEDs:
(a) NSPB310 Blue, (b) NSPG310 Green and (c) NSPR510 Red. φ is the
LED diameter.
order to be compensated by the software.
The circuit diagram of the sensor is shown in Fig 4.
Since the LED only conducts in one direction, the full wave
rectifier allows the detection of an alternate leakage current
signal. The two transient voltage suppressors (transorbs)
protect the sensor from transients which may occur in the
high voltage line.
The transducer, shown in Fig. 5, is comprised of a ceramic
cup in which the circuits are located, a polymeric insulator
and a POF cable to transmit the current signal to the receiver
system.
For a high voltage TL application, the sensor taps the
leakage current from the top skirt of the insulator string as
shown in Fig. 6 (a). The medium voltage distribution line
version is intended to be installed on the top of the insulator
WERNECK et al.: DETECTION AND MONITORING OF LEAKAGE CURRENTS IN POWER TRANSMISSION INSULATORS
Fig. 4.
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Circuit diagram of the sensor.
Fig. 5. The optoelectronic transducer. Left - Ceramic head and optoelectronics, Right - Bottom view after epoxy filling, Inset: Optoelectronic printed
circuit board.
under test and then energized from the high voltage line, as
shown in Fig 6 (b). Notice that in both cases the leakage
current from high voltage to ground is forced to traverse the
transmitter LED.
The optical fiber from the current transducer goes from the
high voltage line all the way down to a mid-tower location
that can be easily accessed by the operators. The Remote Unit
receives the optical fiber and converts the optical amplitude
modulated signal to a voltage one, which is proportional to
the monitored current. The block diagram of the RU is shown
in Fig. 7. The RU’s interface section demodulates the optical
signal into digital data that is stored in memory together
with local temperature and air relative humidity. After been
codified, the data are transmitted by GPRS to the cellular
communication network. The electronic hardware of the RU
is composed of a CPU board associated with a datalogger
system, the sensor interrogation system, power supply
(which can be implemented by a battery, for instance) and a
GPRS modem transmitter. Figure 7 shows the block diagram
of the overall system.
As mentioned before, the RU can communicate with the
data server through GPRS cell phone network. In this way all
RUs can send data to the electric company’s Internet server
where data is stored and analyzed. Any authorized user can
access the web page to check for the data in order to observe,
for instance, the trend line of the leakage current in any
specified location.
In a medium voltage application, the RU is energized by
the 127 VAC available on the poles. In this case the RU box is
compact as shown in Fig. 8. In high voltage applications there
is no AC voltage available to powering the RU, therefore we
Fig. 6. Installation scheme of the high voltage TL sensor (a) and medium
voltage distribution lines sensor (b). In both cases the leakage current from
high voltage to ground is forced to traverse the sensor.
Fig. 7.
Block diagram of the Remote Unit.
used batteries with enough ampere-hour capacity to power
the transmitter for one year in continuous operation. In this
case the RU was accommodated in a larger box as will be
seen later (in Fig. 12).
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IEEE SENSORS JOURNAL, VOL. 15, NO. 3, MARCH 2015
TABLE I
U NCERTAINTY OF L EAKAGE C URRENT M EASUREMENT
Fig. 8.
The remote unit box.
Fig. 9. Calibration of the sensor. The fitting shows a third order polynomial
that is used by the software for calculating the leakage current.
IV. P ERFORMANCE T ESTS
Three tests have been applied to the sensor in order to
calibrate it and collect data to perform software compensations
where necessary. They are: input/output relation (sensitivity);
uncertainty at fixed temperature and temperature drift of the
sensor/receiver outside the case (ceramic cup) for different
currents.
measurements: First, the standard deviation (SD) of the output
voltage was calculated by applying a current source to the
input and covering all input range, in this case, from zero to
60 mArms . This procedure was done ten times for each value
shown in the first column of Table I, resulting in the second
column of the table (Averaged Output Voltage). The next step
was to evaluate the SD of the output voltage for each value,
resulting in the third column of the table (Standard Deviation)
which is the uncertainty of the voltage measurement. The
output voltage SD results obtained so far were produced
for calibration purpose. In field applications, when leakage
currents are to be measured, there is a need to know the
uncertainty of the input current measurements.
In order to calculate the uncertainty of the input current,
the first step was analyze the regression curve and evaluate its
derivative at each current value shown in the first column of
Table I (Input Current). The SD of current is the projection of
the SD in voltage over the x-axis by the slope of the curve at
that point. This can be found by dividing the SD of the output
voltage by the derivative of the regression curve shown in
Fig. 9 at each point. The results are shown in the fourth column
of the table (Uncertainty). Table I shows the measurements, the
averages, the standard deviations obtained and the calculated
accuracy.
A. Input/Output (Sensitivity)
The LED output optical power responds parabolically to
the input current, whereas photodiodes in photoconductive
configuration responds linearly to the input light. Therefore we
must expect a parabolic sensitivity of output voltage against
input current for the transducer chain. In order to measure the
input current by observing output voltage, a calibration curve
must be obtained. This is shown in Fig 9 where each dot
in the curve is the result of an average of 50 measurements
at constant temperature. The regression line drawn over the
input/output plot is a third order polynomial with regression
coefficient R2 = 0.999908. This polynomial is used by the
software to calculate the leakage current from the output
voltage.
B. Uncertainty of Leakage Current Measurement
Accuracy of measurement can be done by sweeping the
input range several times, from zero to 60 mA and calculating
the standard deviation for each value. The steps below were
used in order to calculate the uncertainty of the input current
C. Thermal Drift Tests
LED optical power fades as temperature increases. This
is clear by observing in Fig. 2 the output power of the
green LED which drifts about 5% for a temperature range
of 20 to 50 °C. Therefore, it is expected to observe this drift
in the transducer chain. The transducer thermal drift evaluation
was performed by inserting both transmitter and receiver into
an oven and varying the temperature covering the temperature
range expected in the field. Figure 10 shows the results of
this test.
As expected, for all input currents, the output voltage
decreases as temperature rises, particularly for 60 mA at 65 °C.
However, as it will be seen, maximum currents observed in
real applications rarely exceed 20 mA and local temperatures
are limited to the range of 25 to 40 °C. In this range the error is
about 3%, quite acceptable for this kind of application, when
the idea is to monitor leakage current increase rather than to
know it precisely.
WERNECK et al.: DETECTION AND MONITORING OF LEAKAGE CURRENTS IN POWER TRANSMISSION INSULATORS
Fig. 10.
Temperature drift of the set transmitter-receiver.
Fig. 11. Installation sequence. 1) The tower at left was chosen for the
installation; 2) Equipment being hoisted to the top; 3) Transmitter box being
fixed; 4) Arrows indicate the position of the sensor and the transmitter box;
5) Transmitter box in place and being tested by technician.
V. F IELD I NSTALLATION AND DATA A SSESSMENT
As stated above, the system was designed for monitoring
currents in both high voltage TL and medium voltage
distribution lines. Two Brazilian electric companies allowed
the installation of the system in their operational grids: one in
a 500 kV TL and another one in a 13.8 kV distribution line.
The first prototype was installed in a single 500 kV TL tower
and was kept there for several months while transmitting
data. In a second row of experiments, several sensors were
installed at a medium voltage distribution line. This section
describes the installation of both systems.
A. Installation in 500 kV Transmission Line
The TL chosen for installation of the 500 kV monitoring
system was located in the island of São Luis, at the Brazilian
northern state of Maranhão where strong winds blowing from
the seashore bring severe pollution to the insulators. Fig. 11
shows the installation sequence. The transmitter box (Fig.11-5)
contains two 45 Ah batteries, enough for powering the receptor
and GPRS transmitter for as much as 12 months.
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Fig. 12. Satellite picture showing the location of the measurement units
(adapted from Google Maps).
Fig. 13. Pictures of the installation sequence in a 13.8 kV line. 1) The pole
chosen for the installation; 2) Equipment being hoisted to the top of insulator;
3) Complete system installed on the pole; 4) Indication of the sensor position
and the high voltage line.
B. Installation in 13.8 kV Distribution Line
The medium voltage system was installed in a seashore area
where the local electric company has had many problems due
to flashovers and electric shortages. We installed five units in
different locations of a large area so as to map and identify
similar meteorological conditions. Fig. 12 shows a satellite
picture of the area under study with the location of the remote
units (RU).
The installation in the field was performed without
de-energizing the high voltage line using appropriated highvoltage procedures, Fig. 13 shows the installation sequence.
After installation, the transducer starts acquiring data to the
RU which are sent in real time to a specially designed web
page where each RU can be accessed separately in order to
check for the actual status of each insulator.
VI. R ESULTS AND D ISCUSSION
A. Real Time Analysis
After installation, in both high- and medium-voltage lines,
the RU started transmitting data immediately so it was possible
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IEEE SENSORS JOURNAL, VOL. 15, NO. 3, MARCH 2015
Fig. 14. Data collected from sensor installed on an insulator at 500 kV.
Upper trace is the temperature; lower trace the leakage current. Each peak in
the upper trace represents one complete day cycle in which the temperature
rises from 25 °C during the night to about 40 °C at noon.
Fig. 15. Data collected from 500 kV insulator show leakage currents in
excess of 12 mA.
to check locally on the Internet the adequate operation of
the system. The high voltage version transmits to its web page
the data acquired; in this case the leakage currents together
with local temperature. Fig. 14 shows one of these graphs.
Note that the temperature fluctuates from 25 °C during the
night to about 40 °C at noon. On the other hand, the leakage
current is nearly zero during the hotter part of the day but
rises during the night when temperature drops and eventually,
reaches the dew point. Notice also that the leakage current
keeps a tendency of increasing from day to day, starting on
Day 1 and increases progressively up to Day 7. Then, suddenly
at Day 8 it is low again. This is because there was a tropical
rain that day (notice the drop in temperature on Day 7) and
the insulator was washed out from the deposited salt. After
that day the current starts to rise again until the next raining
event. Strong rain washes the insulator, fine rain or dew, on the
other hand, makes the salt conducting, increasing the leakage
current. Another example of information that can be extracted
from these data is shown in Fig. 15, where very high peaks
of currents occur in dry seasons without rains.
This graph shows several peaks in excess of 12 mA. These
currents represent a power of more than 5.000 W over the
insulator. In an LT of 400 km, with each insulator burning such
power, an enormous amount of energy is lost. These currents
not only decrease the lifetime of the insulator but can also
trigger the TL protection devices if many peaks occur at same
time.
The data obtained from RUs installed in medium voltage
distribution lines can be seen in the system web page.
Figure 16 shows the main page which can be accessed
by authorized users. In this page there is a list of all the
Fig. 16.
Fig. 17.
Web page screens of the system.
Graph from field data obtained from the system web page.
units installed. When a unit is chosen, its parameters are
displayed in the screen as shown in Figure 16.
Figure 17 shows the data collected from two RUs installed
in the field. It is possible to create graphs of all parameters
WERNECK et al.: DETECTION AND MONITORING OF LEAKAGE CURRENTS IN POWER TRANSMISSION INSULATORS
such as temperature, dew point, humidity and leakage current
of any location.
During the generation of the graph in Fig. 17 (upper) all
monitored parameters were selected: leakage current, humidity
and temperature. However, just two or one type of data can
be selected such as in Fig 17 (lower), where only the leakage
current is shown. The data has been analyzed for two months
in order to establish relationships between leakage current
and climate parameters, and between two different sites of
installation.
It is possible to observe that the leakage current is strongly
related to the humidity. One can note in Fig 17 (upper)
that larger humidity (green) leads to larger leakage current
(orange), that is, high humidity increases the conductance of
the polluted layer leading to arcs. It can also be observed
that as the ambient temperature approaches the dew point the
leakage current increases.
Observing the two graphs of Fig. 17, a slightly similarity
can be seen in the leakage current behavior. Despite the fact
that these two RUs were installed about 3 km away from each
other, their leakage current increasing patterns are similar. The
intensity difference, however, can be explained by the fact that
the RU 52237 (Fig. 17 (lower) is sheltered from pollutants
by large trees and buildings. This analysis is important to
determine the maximum distance that the RUs can be installed
from each other.
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page proving, therefore, to be reliable. The small thermal drift
observed in the sensor-transmitter set was unimportant for
the data analysis. The LED/POF technology applied for the
leakage current sensor presented some advantages over other
techniques adopted previously: efficiency, easy installation,
robustness and reliability.
The objectives of this project were reached. However,
in order to this technique be of any usefulness to electric
companies, it is necessary to transform the data into information. This means to establish parameters which can determinate
the real status of the insulator regarding the leakage current
that flows to the ground. After such parameters have been
established, it will be possible to issue the “washing warnings” meaning that if the set of insulators were not washed
immediately, a flashover may occur. The establishment of these
parameters will produce the logistic insertion of this activity in
companies, reducing the risk of a failing insulator causing an
energy shortage. To create these parameters it will be necessary to analyze a great diversified amount of data from different critical points of maritime pollution inside the area under
study. Thus, it will be possible to determinate the optimal time
to intervene, i.e., to carry out the washing of insulators.
The data obtained from the sites of installation will be
evaluated in order to be possible to increase the distance
between them. All external parameters have to be taken into
account, such as the buildings and trees around, the distance
from the sea and roads.
B. Statistical Analysis of the Data
The resulting data of the leakage current monitoring
performed by five RUs installed in field at the coastal region of
Rio de Janeiro –Brazil (Fig. 12), were submitted to statistical
analysis in order to obtain the climatic parameters necessary
for the occurrence of the critical levels of leakage current
and subsequent occurrence of flashover. The leakage current
is considered critical if its root mean square values become
higher or equal 5 mA. On the other hand, the occurrence of
leakage current is related to a wet environment, in the presence
of dew. The dew occurs when the local temperature is close
enough to the dew point temperature, so that to select the data
it was considered the points where the difference between the
local temperature and the dew point temperature was smaller
or equal than 1 °C. Respecting these boundary conditions, the
temperature and humidity figures related with the occurrence
of critical levels of leakage current were isolated from the raw
data collected in a 12 months interval. Then, a statistical analysis was performed using the selected data, from which, averages (AVG) and standard deviations (STD) were calculated:
Temperature: AVG = 20.3 °C; STD = 1.7 °C.
Humidity: AVG = 98.1%; STD = 1.8%
These calculated values establish the boundary climatic conditions necessary for occurrence of critical levels of leakage
current. In these cases it would be indicated the intervention of
the maintenance team for washing procedure of the isolators.
VII. C ONCLUSIONS
The system has been operating for several months in the
field with continuous monitoring and sending data to the web
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Marcelo Martins Werneck was born in Petrópolis,
Brazil. He received the Degree in electronic engineering from the Pontifícia Universidade Católica of
Rio de Janeiro, Rio de Janeiro, Brazil, in 1975, the
M.Sc. degree from the Biomedical Engineering Program, Federal University of Rio de Janeiro (UFRJ),
Rio de Janeiro, in 1977, and the Ph.D. degree from
the University of Sussex, Brighton, U.K., in 1985.
He has been with UFRJ since 1978, where he is
currently a Lecturer and Researcher. He is also the
Coordinator of the Instrumentation and Photonics
Laboratory at the Electrical Engineering Program, UFRJ. His research interests include fiber optics sensors, transducers, and instrumentation.
Daniel Moreira dos Santos was born in
Rio de Janeiro, Brazil. He received the Degree from
the Federal Centre of Technology Education Celso
Suckow da Fonseca, Rio de Janeiro, in 2010, as an
Electronic Engineer. He is currently pursuing the
M.Sc. degree at the Photonics and Instrumentation
Laboratory, Electric Engineering Program, Federal
University of Rio de Janeiro (UFRJ), Rio de Janeiro.
He is also a Researcher with the Institute for
Post-Graduate Studies and Research in Engineering,
UFRJ. His research interests include sensors,
instrumentation, and fiber optics.
IEEE SENSORS JOURNAL, VOL. 15, NO. 3, MARCH 2015
Cesar Cosenza de Carvalho was born in
Rio de Janeiro, Brazil, in 1966. He received
the B.Sc., M.Sc., and D.Sc. degrees in electronic engineering from the Federal University of
Rio de Janeiro (UFRJ), Rio de Janeiro, in 1989,
1994, and 2000, respectively. He is currently a
Researcher with the Instrumentation and Photonics
Laboratory, Electrical Engineering Program, UFRJ.
His research interests include fiber optics, sensors,
transducers, and optoeletronic instrumentation.
Fábio Vieira Batista de Nazaré was born in
Maceió, Brazil, in 1984. He received the Degree
in electronic engineering from the Universidade
Federal de Pernambuco, Recife, Brazil, in 2007.
He was a Research Engineer with the Nuclear Instrumentation Laboratory, Regional Center of Nuclear
Sciences, Recife. He received the M.Sc. degree
in electrical engineering from the Institute for
Post-Graduate Studies and Research in Engineering,
Federal University of Rio de Janeiro, Rio de Janeiro,
Brazil, in 2010, where he is currently pursuing the
D.Sc. degree at the Instrumentation and Photonics Laboratory, Electrical
Engineering Program, and is also an Electronic Engineer.
Regina Célia da Silva Barros Allil was born in
Rio de Janeiro, Brazil. She received the Degree in
electronic engineering from the Faculdade Nuno
Lisboa, Rio de Janeiro, in 1988, and the M.Sc.
degree from the Biomedical Engineering Program,
Federal University of Rio de Janeiro (UFRJ),
Rio de Janeiro, in 2004, and the Ph.D. degree from
the Electronic Engineering Program, Instrumentation
and Photonics Laboratory, UFRJ, in 2010. She is
currently a Researcher with the Brazilian Army
Technology Center, Rio de Janeiro. Her research
interest lies in fiber optics sensors and optoelectronic instrumentation.