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2011 11th International Conference on Control, Automation and SystemsOct. 26-29, 2011 in KINTEX, Gyeonggi-do, Korea
1. INTRODUCTIONThere many applications of infrared thermography for
non-destructive testing. EvaWulsten et.al [1] measured
droplet surface temperature in dry air from the droplet
temperature predicted by acoustic levitation theory. J.M.
Laskar et.al [2] report measurement of thermaldiffusivity of solid samples by using a continuous heat
source and infrared thermal imaging. Their technique, a
continuous heat source is used for heating the front
surface of solid specimen and a thermal camera for
detecting the time dependent temperature variations at
the rear surface. The incorporation of heat loss
correction in the solution of heat equation provides the
values of thermal diffusivity for aluminum, copper and
brass. A. Brosse et.al [3] proposed the inspection of
grinding process. A perfect control of this process is
thus necessary to ensure correct final parts and limit
damage. The experience on this subject has shown that
the main effects on ground surface are residual stressesor metallurgical change, which are directly linked with
the temperature and the power absorbed during the
process. These example applications are pointed that the
advantage of thermal image camera but they did not
explain about the accuracy of thermal image. The most
important of heat radiation effect is emissivity of the
measured object. Therefore the accurate emissivity istaken into account. P. Herve et.al [4] derived a direct
measurement method for the total directional emissivity
of various coatings of interest for satellites applications.
The effective spectral range chosen the measurementscovers 6800 m. The design of the measurement
apparatus for several coatings was presented. TadeuszWalach[5]described a special relationship of thermal
image camera and signal. Conventional and
unconventional methods of the emissivity
measurements together with a detailed analysis of the
accuracy of typical methods are presented in his paper.
A criterion and a procedure of choosing the emissivity
measurement method are also proposed.Xiaogang Sun
et.al [6] investigated the temperatures and emissivities
of the metallic thermal protection blanket at 9001,300C experimentally by using a multi-wavelength
pyrometer. A linear relation between the emissivity and
true temperature at different wavelengths is assumed.
Some experimental results for the practical dataprocessing of measurements performed on the metallic
thermal protection blanket show that the difference
between the calculated temperature and the temperature
measured by a standard thermocouple.
This paper is presented the properties of heat
radiation of the object (Emissivity), using thermal image
camera (Thermal Image: TI) with 8 to 14 m of
wavelength in order to apply preventative maintenancemonitoring the quality of material and equipment in the
electrical distribution system.
2. PRINCIPLE OF THERMOGRAPHY
From the principles of the radiation, it is important to
understand about to the laws of radiation. In this
concept, each body at a temperature Temits a radiation
with a wavelength inside the electromagnetic spectrum.
The radiation emitted can be measured by a value called
luminance and noted as L0. The value ofL0 is given
analytically by the Plancks law as in equation 1.
Emissivity Measurements on Material and Equipment in Electrical
Distribution System
T.Suesut1, N.Nunak1, T.Nunak1 and A.Rotrugsa2 Y.Tuppadung 21
Faculty of Engineering, King Monkuts Institute of Technology Ladkrabang
(Tel : +66-2-326-0000; E-mail: [email protected])
2Power System Maintenance Division, Provincial Electricity Authority,Thailand
Abstract:
This paper studies on the emissivity of electrical distribution equipments using infrared thermography with 8-14 m of
wavelength. The infrared thermography camera is widely used for preventive maintenances propose in many industries.
It can be captured a thermal image for identifying fault on electrical equipment and measuring the temperature as well.
The most important factor to use the thermal image accurately is the emissivity of materials. Therefore, this project
aims to define the unknown emissivity of electrical devices in order to apply with the infrared thermography camera.The heat chamber to control the operating temperature 30
oC 200
oC has been created to maintain the temperature of
material for measuring the emissivity. To ensure the emissivity measurement technique, the general used material
such as iron, stainless steel, brass, copper and aluminum were done the experiment and compared with the standard
emissivity table. The selected electrical equipments (new and old) are cable lug, P.G. connector, some part of fuseholder and disconnecting switch. Finally, the emissivity data of selected devices can be used to input to thermal image
camera for a better accuracy of temperature measurement.
Keywords: Infrared Thermography, emissivity measurement
1259978-89-93215-03-8 98560/11/$15ICROS
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5
10
2[exp( / ) 1]
CL
C T
=
(1)
Where c1 is the first radiation constant:3.7418321016Wm
2, c2 the second radiation constant:
1.4388102mK; the wavelength [m]; Tthe absolutetemperature [K] andL0 the energetic spectral luminance
[Wm3
Sr1
].However, for a real body at the same temperature T,
the luminance measured will not be equal to L0 butL =
L0. Where is called emissivity of the material and
takes values in the range [0,1]. Most often the electrical
distribution equipment emissivities range from 0.1 to
0.95 depending on the type of material and surface
characteristic. The basic idea of thermography is then to
measure the luminance of a body in a range ofwavelength chosen to obtain the temperature of the body.
Moreover, inside the electromagnetic spectrum there are
many kinds of radiation from the radio waves to the Xand rays, the principle of infrared thermography is tomeasure the radiation in the infrared domain where the
luminance reached maximum value.
Radiosity (J, W/m2)[7] accounts for all the radiant
energy leaving a surface). It represents the rate at which
radiation leaves a unit area of the surface. This radiation
includes the reflected portion of the irradiation (G
W/m2), as well as direct emission from the surface (E,
W/m2) (see Fig.1). It is generally different from theemissive power depending on the emissivity value.
Reflected
portion of
irradiation
Irradiation
Emission
Radiosity
Fig.1 Surface radiosity
The irradiation (G, W/m2) is defined as the rate at
which radiation is incident on a surface per unit area of
the surface. As shown in Figure2, portions of the
radiation may be reflected, absorbed, and transmitted.
From a radiation balance on the medium, it follows that
G = Gref+ Gabs + Gtr (2)
Then division by G
G/G = Gref /G+ Gabs /G+ Gtr/G
or 1 = + + (3)
Where , and are defined as the fraction of the
total irradiation absorbed, reflected and transmitted by a
surface, respectively
Finally, the thermography method gives very reliable
non-contact measurement with many advantages for
preventive maintenance in electrical power and
distribution system.
Absorption
Transmission
IrradiationReflection
Semitransparent
medium
Fig.2 Absorption, reflection, and transmission processes
associated with a semitransparent medium.
3. MEASUREMENT SYSTEM
3.1 Experimental set-up
The basic concept of emissivity measurement using
infrared thermography is measuring the surface
temperature by standard thermometer and adjusting the
emissivity on infrared thermography camera until the
temperature being similar. The environment temperaturehas to be controlled constantly during measurement
process. Therefore this research has designed the heat
and environment control chamber. The chamber can be
provided the temperature from room temperature to 3000C.
Fig.3 Heat chamber for control the environment
Inside the chamber has a jig and fixture for hold thesample on the suitable position. The user can open thedoor and change the sample easily. The opposite side of
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the door is the hole with the gate for measuring the
temperature by thermal image camera. The thermalimage camera from Fluke company model TI32 has
been used in this experiment with 8 to 14 m of
wavelength. Temperature measurement range is (not
calibrated below -10 C) -20 C to +600 C (-4 F to
+1112 F). The refresh rate of Image capture frequencyis 9 Hz or 60 Hz refresh rate depending upon model
variation. Detector type is 320 X 240 Focal Plane Array,
uncooled microbolometer with operating temperature at-10 C to +50 C (14 F to 122 F). The dual channel
digital thermometer with thermocouple type K is used in
the experiment as shown in figure 4.
Fig.4 Jig and fixture for hold the sample.
Fig.5 Experiment setup for thermal image camera
3.2 Measurement procedure
Step1 determine the background temperature
In the heat chamber, the background temperature (TBG)
is emitted from inside environment such as stainless
steel wall and fixture. Because of the background
temperature generated from several source, measuring
of TBG is defined from the average temperature by
varying the emissivity of 0.1 to 0.95 on the thermal
image camera.
Step2 determine the emissivity of the object
From step1, the background temperature is entered into
the thermal image camera. The emissivity measurement
using infrared thermography is measuring the surface
temperature by standard thermometer and adjusting the
emissivity on infrared thermography camera until the
temperature being the same temperature.
Fig.6 The steel plate
Fig.7 Thermal image of the sample
4. EXPERIMENTAL RESULT
The experiments were started by heating up temperature
at 200oC. Afterward, the temperature of material was
maintained during measurement emissivity. To ensure
the emissivity measurement technique, the general used
material such as iron, stainless steel, brass, copper and
aluminum were done the experiment and compared with
the standard emissivity table as shown in table1. Theemissivity of electrical equipment is illustrated on
table2.
Table 1. Emissivity of common used material
Iron Copper Stainless Aluminium Brass
50 0.88 0.24 0.52 0.51 0.65
60 0.84 0.28 0.48 0.46 0.57
70 0.84 0.24 0.46 0.42 0.52
80 0.83 0.21 0.45 0.37 0.49
90 0.83 0.2 0.44 0.36 0.48
100 0.84 0.18 0.43 0.36 0.46
110 0.84 0.19 0.43 0.36 0.46
120 0.84 0.2 0.41 0.36 0.45
130 0.84 0.21 0.41 0.37 0.44
140 0.84 0.2 0.4 0.37 0.44
150 0.84 0.19 0.4 0.36 0.43
160 0.84 0.19 0.39 0.35 0.44
170 0.83 0.18 0.38 0.35 0.44
180 0.82 0.19 0.37 0.34 0.43
190 0.82 0.18 0.36 0.33 0.42
200 0.81 0.16 0.34 0.33 0.4
Temperature (C)
Emissivty (e)
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Table2. Emissivity of electrical distribution equipment
Group / Object Emissivity () at 30-200 CAluminum
Aluminum Compression Terminal Lug 0.45 - 0.71
Aluminum Bare Insulated 0.71 - 0.79
Bail Clamp 0.69 - 0.88
Compression Connectors 0.45 - 0.73
Connector Dead End 0.50 - 0.67
Connector Splice Compression (Partial Tension) 0.63 - 0.73
Hot Line Clamp 0.49 - 0.68
PG Clamp Connector 2 Bolt 0.70 - 0.80
PG Clamp Connector 3 Bolt 0.61 - 0.75
Bronze with tin plated
New Parts Of Fuse Cutout 0.43 - 0.64
Old Parts Of Fuse Cutout 0.51 - 0.85
Cast bronze with silver plated
Cap (drop fuse) 0.49 - 0.64
Stainless Steel
New Driving Stud 0.47 - 0.77
Old Driving Stud 0.56 - 0.78
Copper with silver plated
New Connector Of Insulators 0.48 - 0.58
Old Connector Of Insulators 0.43 - 0.69
Parts Of Disconnecting Switch 0.66 - 0.85
Copper with tin plate
Terminal lug of Load Break Switch SF6 0.32 - 0.69
Others
New Parts Of Disconnecting Switch 0.49 - 0.78
Old Parts Of Disconnecting Switch 0.75 - 0.85
Parts Of Lt. Switch 0.76 - 0.89
5. CONCLUSION
Emissivity of electrical equipment is up to thematerial properties of each type of equipment. The
emissivity values were achieved by controlling the
surface temperature of an object with constant
temperature. The common used material such as iron,copper, stainless steel, aluminum, brass was selected for
measuring and comparing to ensure the accuracy of this
method. The selected electrical equipments (new and
old) are cable lug, P.G. connector, some part of fuseholder and disconnecting switch. Finally, the emissivity
data of selected equipment can be used to input to
thermal image camera for a higher accuracy of
temperature measurement. This research can be
provided advantages for preventive maintenance inelectrical power and distribution system.
ACKNOWLEDGMENT
This work was supported by the research and
development funding of Provincial Electricity Authority,
Thailand.
REFERENCES[1] EvaWulsten and GeoffreyLee, Surface temperature
of acoustically levitated water microdroplets measuredusing infra-red thermography Chemical Engineering
Science Vol. 63(2008)54205424
[2] J.M. Laskar, S. Bagavathiappan, M. Sardar, T.
Jayakumar, John Philip, Baldev Raj Measurement ofthermal diffusivity of solids using infrared
thermography, Materials Letters Vol. 62 (2008)
27402742
[3] A. Brosse, P. Naisson, H. Hamdi, J.M. Bergheau
Temperature measurement and heat flux
characterization in grinding using thermography,Journal of materials processing technology Vol. 2 0 1
( 2008 ) 590595[4] P. Herve, N. Rambure, A. Sadou, D. Ramel, L.
Francou, P. Delouard, E. Gavila,Direct measurement of
total emissivities at cryogenic temperatures,
Application to satellite coatings, Cryogenics 48 (2008)
463468
[5] Tadeusz Walach Emissivity measurements on
electronic microcircuits Measurement Vol.41 (2008)
503515
[6] Xiaogang Sun, Peng Xiao, Guibin Yuan, Jingmin
Dai, Research on the Temperature and Emissivity
Measurement of the Metallic ThermalProtectionBlanket, International Journal ofThermophysic Vol.30 (2009) 249256
[7]Incropera, DeWitt, Bergmann and Lavine.
Fundamentals of Heat and Mass Transfer. 6th
ed. Willey
Asia.2005.
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Appendix : Electrical distribution equipment
Picture Name Picture Name
Aluminum Compression
Terminal Lug
Aluminum Bare
Insulated
Bail ClampCompression
Connectors
Connector Dead End
Connector Splice
Compression
(Partial Tension)
Hot Line ClampPG Clamp Connector 2
Bolt
PG Clamp Connector 3 Bolt
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