Microsoft Word - 41_PE_03_14_183-186_sebok PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 90 NR 3/2014 183 Milan ŠEBÖK1, Miroslav GUTTEN1, Matej KUČERA1, Daniel KORENČIAK1, Tomasz N. KOŁTUNOWICZ2 University of Žilina, Zilina, Slovakia (1), Lublin University of Technology, Lublin, Poland (2) Nondestructive diagnostics of electrical systems and equipments Abstract. This paper analyses the problem of thermal sensors, it examines the principles, functions and application for a non-contact temperature measurements. The knowledge in measurements of infrared radiance allows us to use the methods of thermovision diagnostics more effectively and to localise the disturbance which determines the quality of connection in distribution of electric energy. For technical testing of electrical systems and equipment thermography is an important diagnostic method for determining of failure of electrical systems and equipment as well as for detection of worsened condition of these systems. Streszczenie. W artykule przedstawiono problematykę termicznych sensorów, zasady badań uwzgledniające bezdotykowe pomiary temperatury, ich funkcje oraz wnioski. Dotychczasowa wiedza o pomiarach w podczerwieni pozwala na efektywniejsze wykorzystanie metod termowizyjnych celem lokalizacji zakłóceń związanych z jakością połączeń odpowiadających za dystrybucję energii elektrycznej. Termografia jest nieniszczącą metodą diagnostyczną pozwalającą na badania instalacji elektrycznych i sprzętu w celu określenia uszkodzeń urządzeń i systemów elektrycznych, a także do wykrywania pogarszania się ich stanu. (Nieniszcząca diagnostyka systemów elektrycznych i urządzeń). Keywords: Thermovision, radiation, calculation, thermogram. Słowa kluczowe: Termowizja, promieniowanie, kalkulacja, termogram. doi:10.12915/pe.2014.03.41 1. Introduction In measurement of electrical equipment and wires we deal with warming of contacts, switches, power cables, clamps, contacts of fuses. In electrical substation, temperature of each object is measured, focusing on the expansion joints, junctions, bends and coats drivers. Thermovision is used to measure warming of connections and clamps in electrical machines, as well as to the measurement of electrical equipments in the internal and external electrical distributing systems. Fundamental for a non-destructive diagnostics of electrical equipments using thermovision, is the ability to record and to transform infrared radiation (heating) to the form of real thermal images of objects, for a detection of a failure (defect) [6]. Infrared radiation is generated as a result of physical processes that take place in the object of radiation; moving atoms, molecules, vibration in crystal lattice, and transition of electrons from one energy level to another. The basic source of infrared radiation is elevated temperature of the source of radiation [3]. Radiation of hot sources acts (in respect of surrounding conditions), like visible light. To display temperature fields we can use visualization techniques used in optics. The only differences are materials used for elements of visualization systems, size of values which are derived from the wavelength of radiation, and also sensitivity of sensors for recording the signal [6]. The surface of the measured object in a state of thermodynamic equilibrium emits electromagnetic radiation and the radiated power depends on the thermodynamic temperature and properties of the surface object. Fig.1. Termogram and real picture of transformer For thermovision diagnostics of infrared radiation in the inside distribution of electric energy, we need to take into account many important factors affecting the accuracy of measurement. Results of the measured values of specific electric contact are often biased by measurement defects. In determining the classification of degrees to correct the defects, it is necessary to correct measured values due to disruptive effects of other objects [1]. 2. Theory Thermal Sensors are equipment, which transform input physical quantity (temperature) to electric signal. Transformed signal can be used in automatic control systems for data records elaboration and archivation [2]. Infra-radiation, which is absorbed to the active part of a sensor, increases its temperature. Temperature changes in the sensitive part of a sensor are represented by a relative slow process. In Fig.2 is a model – by construction of the thermal sensor [5]. Fig.2. Model – Simple construction of thermal sensor: 1 - sensitive part of sensor with temperature TD, active area of sensor S and thickness d, 2 - thermal bridge with thermal conductivity G, 3 - base with temperature TA If the sensitive part of sensor is characterised with heat capacitance C, absorbtance α and it is conducted surround area with temperature TA, with thermal conductivity G and active sensor is radiated with radiance current Φ(t), that changes with time, then if holds: if Φ(t) = 0 then TD = TA (1) if Φ(t) > 0 then TD > TA The state of the thermal balance occurs when the absorbed energy is equal conductive thermal energy of the thermal bridge [5]. By the following differential equation is described: G 3 21S Φ(t) TA 184 PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 90 NR 3/2014 T0 ΔTm ΔT(t) 0 t (2)       tTGtT dt d Ct  , where: ∆T = TD -TA is temperature increase of sensitive part of sensor, when this part is heated with absorbed input radiance current αΦ(t). Let the radiance input current change in time (3) Φ(t) = Φ0 + Φm e jωt The result for the temperature increase is (4) ∆T(t) = T0 + ∆Tm e j(ωt-φ) The first term is the d.c. part and the second term is the harmonic part this equation [6]. On the basis of formulations (3), (4) we can design electrical (substitute) structure of thermal sensor Fig.3. Fig.3. Electrikal structure of thermal sensor Temperature increase ∆T is delayed against input radiance current Φ(t). For amplitude ∆Tm and shift movement period φ we write (5)  22 CG T mm      and        G C arctg   Fig.4. Input radiance current and delay of the temperaturel of thermal sensor 3. Radiation Heating is defined by the relationship α/ε, where α is the absorption coefficient of energy and ε is the emission coefficient (emissivity) of the measured body [1]. Ratio of intensity radiation of actual body and ideal black body at the same temperature is defined by spectral coefficient of emissivity [8]: (6)    TH TH T , , ),( 0        It is clear that the coefficient of spectral emissivity is equal to the spectral absorption coefficient. By Kirchhoff’s law the black body is an ideal emitter. Plank defines the spectrum of black body radiation [8]: (7) 1 2),( 52    kT hc e hc d TdH     Plank’s law is a function of spectral distribution of values. Win’s law clearly defines the shift of visible and invisible body radiation (when it is heated) to the side of the shorter waves. Stefan-Boltzmann’s law, as an integration of Planck's law by λ, defines an integral radiant flux density of black body at the temperature T [3]: (8)   4 0 /),( TddTdHH T     where: σ = 5,67.10-8 W/m2K4 – Boltzmann constant. Flux density of blackbody radiation (Fig.5) on the range of wavelengths λa, λb is received by integrating Planck equation by λ [6]. (9)   4/),( TddTdHH b a T      Fig.5. Flux density of black body radiation Derivation of Planck’s equation by temperature dT gives the change of spectral flux density emitted from black body as a function of temperature [6]: (10)       d dH eT ekhc T ddH kThc kThc . 1 )/(/( )/(2 )/(     Real objects generally do not behave as black bodies. No-black bodies absorb only a part of α(λ)Φ (incident radiation), part of the reflected radiation ε(λ)Φ and part τ(λ)Φ is a transient radiation. If the system is in thermodynamic equilibrium, according to conservation of energy, the reflected and transient energy is equal to the energy absorbed. Emissivity ε(λ) (coefficient of radiation), compensates absorption coefficient α(λ) then ε(λ) = α(λ). It follows that: (11) 1)()()(   The result of object temperature measurement T0, which is registered in the spectral range of wavelengths ∆λ ΔT(t) C αΦ(t) G αΦ0 Φm Φ(t) Φ0 0 t PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 90 NR 3/2014 185 (surface density of radiant flux), is the registered radiant flux density Hreg [6]: (12)             ddTdH ddTdH ddTdHH ff aareg          ),()( /),()( /),()( 00 When an object is transparent τ(λ) = 0 and if T0 is much larger than Ta, the first part of the equation is very small. In this case the task is easier and it is essential to know ε0(λ). Difficulties arise when the body is surrounded by other objects, which have high temperature and these temperatures are higher than the examined object. In this case, its own radiation depends on the T0 and ε0 affected by reflected radiation error caused by parasitic (surrounding) objects with a temperature Te and emissivity εe. For measurements of this type it is necessary to know ε0 and T0 parameters and the number of equations, which are equal to number of unknown parameters. Radiation of measured object is formed by the sum of two parts; its own H1 radiation and parasitic H2 radiation in the infrared spectral range: (13)               1 1 1 /),()( /),()( /),()()( 2 00 1       ddTdHH ddTdH ddTdHSH ee eee where: S - geometric parameter which depends on the distance of two objects and on their surfaces. 4. Experimental In measurement of electrical equipment and wires we deal with warming of contacts, switches, power cables, clamps, contacts of fuses. In electrical substation temperature of each object is measured, focusing on the expansion joints, junctions, bends and coats drivers. A circuit containing conductor was set up in the laboratory. Fig.6. Thermogram of breaker The conductor was divided into three parts connected to the staples. The three phase breaker was derived from harmonic current. The thermogram of the circuit is on the Fig. 6. The measured circuit was load by the current from 5% to 100% of the conductor's nominal current load [7]. The measurements were taken under the following conditions:  clean and well closed terminal,  loose terminal (terminals were loose and conductors were connected only through their asymmetric position),  loose terminal and staple and conductor connection was tained with oil and sand. Measured results are graphicaly illustrated on the Fig. 7. Staple connected to the conductor cant be warmer than free conductor, if it is not damaged. On the picture we can see the negative area of the staple temperature increase compared with the closed conductor. The result of the smaller staple temperature is caused by the bigger load. Fig.7. Relation of the staple temperature increase and current load The final data of the staples temperature increase compared to the conductors are illustrated on the Fig.7 which means ΔT = TSV – TL, (TSV is the terminal temperature and TL is conductor temperature) and they were obtained by the temperature measurements of the electric joints and conductors. Fig.8 Termogram high voltage breakers On the Fig. 8 we can see the thermogram of measured object at a temperature T1 and emissivity ε1 which we want to know (radiant 1. and 3. phase with temperature T1 and T3) and from the other side we can see parasitic object with temperature Te, which is larger than T1 and T3 (radiant phase 2). Emissivity εe of parasitic object is high and the distance from measured object d is small. The temperature value Te and emissivity εe is unknown. The thermal camera distinguishes this different temperature of objects, i.e. temperature, which would have absolutely black body in this spectral range. The result of calculated equation is the temperature of 2. phase (parasite object) Te = 352.65 K. Value of calculated 186 PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 90 NR 3/2014 temperature Te is near to measured temperature Te = 352.65 K. The size of radiation flux density of parasite object BR2 (εe = 0.96 and temperature Te = 352.65 K) is: (14)     1 /),(   ddTdHH eee Then the radiant flux density of the 1 and 3 phase measured object is: (15)     reflectionddTdHS radiationddTdHH eee           /),()1( /),( 00 If S = 1 then we have result calculated temperature of measured object (1. phase of breaker) with T1 = 293.15 K, and (3. phase of breaker) with T3 = 294.45 K For Measured data: F1: T1 = 327.45, K = 54.30ºC, ε1= 0.96 F2: Te = 352.65, K = 79.50ºC, εe= 0.96 F3: T3 = 338.19, K = 65.04ºC, ε3= 0.96 Following values were calculated: F1: T1 = 303.25, K = 30.10ºC, ε1 = 0.85 F2: Te = 348.45, K = 75.30ºC, εe = 0.92 F3: T3 = 306.19, K = 38.04ºC, ε3 = 0.89 5. Conclusion Comparing the results of calculated and measured values; we see that real measured temperature values are influenced by parasite object. The differences between the calculated and measured values are illustrated on the graph (Figs. 9, 10, 11). On the graph we see measured and calculated temperature differences of breaker phase F3 at the current load. Measured temperature of breaker (phase F1 and F3) is higher than calculated because close parasite object breaker F2 influences its temperature. As we can see on the graph (Fig. 6) temperature differences depend on the value of current load (In). Experimental measurements and mathematical calculations show the advantage of thermovision application on the illustrated diagnostics of the conductors and staples temperature increase. It is necessary to consider the parasitic effects of warming measured electrical systems. Fig.9. Measured and calculated data (phase F1) Fig.10. Measured and calculated data (phase F2) Fig.11. Measured an calculated data (phase F3) This work was supported by the Grant Agency VEGA from the Ministry of Education of Slovak Republic under contract 1/0624/13. Dr. T.N. Koltunowicz is a participant of the project: “Qualifications for the labour market – employer friendly university”, cofinanced by European Union from European Social Fund. REFERENCES [1] B e n k o I . , Determination of the Infrared surface Emisivity, Budapest, 1990 [2] P e n d e r C . W . , R o u x J . A . , Microcomputer System for controling and Infrared Scaning Camera. Microcomputer in optical System, USA,1999 [3] T o t h , D . , Infrared System Helps with Energy Efficiency, USA, 1995 [4] K l a b a c k a E . , Surface modifications for Thermovision Measurement, ČVUT, Prague 2001 [5] L y s e n k o V . , Detectors for noncontact temperature measurement, Prague 2005 [6] Š e b ö k M . , G u t t e n M . , K uč e r a M . , Diagnostics of electric equipments by means of thermovision, Przeglad Elektrotechnicny, 87 (2011), n. 10, 313-317 [7] K ú d e l čí k J . , B u r y P . , D r g a J . , K o pča n s k ý P . , Z á v i š o v á V . , T i m k o M . , Structure of transformer oil-based magnetic fluids studied using, Journal of Magnetism and Magnetic Materials,326 (2013), n.1, 75-80 [8] Š i m k o M . , C h u p áč M . , The theoretical synthesis and design of symmetrical delay line with surface acoustic wave for oscillators with single-mode regime of oscillation, Przeglad Elektrotechniczny, 88 (2012), n.12A, 347-350 Authors: Dr. Milan Šebök, Ph.D. (Eng), Prof. dr. hab. Miroslav Gutten, Ph.D. (Eng), Dr. Matej Kučera, Ph.D. (Eng), Dr. Daniel Korenčiak, Ph.D. (Eng), Department of Measurement and Application Electrical Engineering, Faculty of Electrical Engineering, University of Žilina, 1, Univerzitná Str, 01026 Žilina, E-mail: milan.sebok@fel.uniza.sk, gutten@fel.uniza.sk; Dr. Tomasz N. Kołtunowicz, Ph.D. (Eng), Faculty of Electrical Engineering and Computer Science, Department of Electrical Apparatus and High Voltages Technology, Lublin University of Technology, 38a, Nadbystrzycka Str., 20-618 Lublin, Poland, E-mail: t.koltunowicz@pollub.pl. 0 10 20 30 40 50 60 5 15 25 40 50 60 70 80 90 10 0 measured calculated In, % T, ºC 0 20 40 60 80 100 5 15 25 40 50 60 70 80 90 10 0 measured calculated In, % T, ºC 0 10 20 30 40 50 60 70 5 15 25 40 50 60 70 80 90 10 0 measured calculated In, % T, ºC