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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: kstaweep@kmitl.ac.th)

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

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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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