Thermal studies for HV GIS compartment design

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1 hermal studies for H GS compartment design Mariusz Stosur Pawel Dawidowski Marcin Szewczyk Przemyslaw Balcerek ABB Corporate Research Center, Poland Kacper Sowa AGH University of Science and echnology, Krakow, Poland Starowislna 13A Str., Krakow, Poland mariusz.stosur@pl.abb.com pawel.dawidowski@pl.abb.com marcin.szewczyk@pl.abb.com przemyslaw.balcerek@pl.abb.com Mickiewicza 30 Av., Kraków, Poland sowa@agh.edu.pl Abstract - n development of electric power products power devices and apparatus, aspects related to thermal phenomena are becoming very important due to the fact that they guarantee the correct operation of products. he temperature limits specified by the standards cannot be exceeded which makes the knowledge of the temperature behavior an important factor in order to predict reliability and performance of the product component in its working environment. n this paper hermal Network Method (NM) is used for modeling of temperature conditions in GS compartment arrangements. Additionally models implemented in AP-EMP software were validated with high-current laboratory measurement results. On the bases of the NM presented as the network approach composed of heat sources, thermal resistances and capacitances which can be easily represented and calculated by means of AP-EMP simulation software. his paper addresses the thermal behavior of GS compartment. Modeling in application to design rating calculations of the typical GS compartment arrangements are presented and analyzed. Keywords: hermal Network Method, thermal parameters, GS compartment, temperature rise test, AP-EMP, modeling, simulation, comparison 1 ntroduction hermal analysis is a very important aspect in electrical devices and apparatus design, especially for high current ratings. According to the international standard EC [1], a temperature rise type test has to be performed, in order to make sure that the allowed temperature limits are not exceeded. o reduce the number of design tests, it is important to predict the temperature rise with a simulation tool. Different approaches are available to the thermal simulation, selection of which is always a matter of balance between the modeling complexity and accuracy [2-7]. Among them, the hermal Network Method (NM) [3 5] has extremely low computational cost with sufficient accuracy for design work. Hence, it is a good alternative to resourceful and time demanding Finite Elements Method calculations, where main computational cost comes from the necessity of choosing a proper mesh-grid and a long time of calculations [7]. he basic idea of NM is to describe a thermal problem by an equivalent circuit network and then solve the network equations. he approach is based on the similarity between the electrical

2 and the thermal parameters. he method requires the user to specify more geometrical parameters than FEM-models, however it significantly reduces the computation time. his paper presents a brief description of thermal behavior of a typical GS ELK-3 compartment using AP/EMP program [4], [8], by setting up an equivalent electrical circuit of thermal network. n particular, using developed for this purpose models, described extensively in further sections. Additional simulations were also carried out in OrCAD Capture software, where thermal library, created and built is available [5]. Quality of the proposed model was compared to the real heat transfer distribution, obtained during laboratory experiment. 2 hermal Network Method general hermal Network Method (NM) utilizes the analogy between electric and thermal quantities, as shown in able 1, also Ohm s law in both, electric (2) and thermal circuits (2) are similar: Ohm s law for electrical circuit: = Ohm s law for thermal circuit: = (1) (2) able 1 hermal-electrical analogies [2 7] Quantity Electrical System hermal System Potential U [] [K] Flow [A] Q [W] Resistance R [Ω] R [K/W] Conductance 1 / R [S] G [W/K] Capacitance C [F] C [J/K] Ohm s Law = E / R Q= G Similar to the Ohms law for electric streaming fields, the following relation results between temperature difference ΔQ, thermal resistance R and the transferred heat rate P is presented by formula (3): Θ=P R (3) where: voltage U and current corresponds to temperature Q and heat transfer rate P, sources in thermal network mean power losses and are equivalent to current sources in electrical circuit [5], [8]. here are four mechanisms of changing electric energy into heat: resistance of conductors, magnetic hysteresis of materials in magnetic field, eddy currents, selected phenomena in dielectric materials. here are also three ways of heat transfer in electric devices: conduction, radiation, convection. t is commonly known, that differential equations for heat transfer are similar to the equations, which describe electric current flow. his fact enables simplification of thermal simulations by using NM. Main aspect of this method is replacement of real geometrical elements and

thermal phenomena by electrical elements such as resistors, current sources and capacitances. he network model for a thermal problem could be created and solved using a circuit simulator.

3 thermal phenomena by electrical elements such as resistors, current sources and capacitances. he network model for a thermal problem could be created and solved using a circuit simulator. Full set of thermal-electrical system s analogies is presented in able 1 [2-7]. he heat sources of a switchgear device are the temperature dependent ohmic losses of current carrying conductors, contacts, and connections. Heat is conducted along the current path and dissipated to the gas and enclosure through convection and radiation. he heated enclosure is cooled down through convection and radiation to the ambient. Using NM, the power loss of a conductor is calculated by its geometrical dimensions and material properties. Heat dissipations via radiation and convection are described by thermal resistances, which are calculated based on the surface areas, emissivity numbers and the installation conditions. An iterative solver is necessary due to the dependency of the conductor resistivity, the convective heat transfer coefficient and radiation coefficient of the temperature. 3 H GS compartment model for thermal analyses he purpose of this section is to establish the technical parameters of GS busduct elements and magnetic materials that were used for calculation of thermal behavior of a H GS compartment. he object of these analyses is a typical ELK-3 GS busduct. he simplified GS busduct assumed for the analyses is shown in Fig. 2 and Fig. 3 (GS busduct with magnetic material). able 2 Electrical and physical parameters using for simulations and analyses [11 16] Physical properties aluminum alloy (Al) not painted thermal conductivity (Al) 2 W/(m K) electrical resistivity (Al) Ω m thermal conductivity (magnetic material) 80 W/(m K) Emissivity (magnetic material) 0.5 Boundary conditions for simulations Fig 2 ELK-3 GS view [11, 14 16] rated current 00, 6300 A frequency 50 Hz SF6 absolute pressure 5 bar surrounding air pressure bar ambient temperature 25 C A A-A f 1 A f 1 Fig. 3 Sketch of GS ELK-3 type compartment with magnetic material layer-marked in gray (accord. to Fig. 2), without magnetic material (uncovered ends) green dash-line zone [12 16]

4 Nominal parameters of the GS ELK-3 compartment for which the solution is intended are indicated. ypical GS busduct parameters for modeling and analysis (Fig. 3) are presented in able 2. Magnetic materials are well known as a solution for reducing High Frequency (HF) transients propagating through cable systems in low voltage applications. n order to apply this solution in the H GS components, its impact on the GS thermal performance should be investigated [9 10]. t should be verified that with the inclusion of the additional material, the temperature for the modified GS busduct design is within the limits according to EC standard [1]. his work investigates an impact of such a material on thermal performance of the GS busduct. For that purpose, the worst case scenario was assumed in this paper, when the material was installed directly on the inner GS conductor, providing highest impact on the thermal performance. n order to investigate this impact, the simulation model developed and simulations conducted for different cases are presented in the following sections of this paper. 4 hermal analyses description and simulation results n this section an example of NM simulation conducted for the GS compartment as specified in able 2 is presented. he purpose of this analysis was to estimate the temperature rise for different current ratings of the GS busbar. he NM method was applied for the simplified GS conductor model, which was built using AP-EMP (by APDraw/S). Modeling and calculations were made for the three cases, as presented in able 3, in order to obtain appropriate values of the parameters describing in established models of thermal resistors (e.g. emissivity). able 3 Case studies of thermal analyses Case studies GS busduct without enclosure surrounding air pressure GS busduct with enclosure SF6 pressure inside GS busduct with enclosure and magnetic materials SF6 pressure inside model 1 (Fig. 4) model 2 (Fig. 5) model 3 (Fig. 6) Studies were carried out for the typical GS compartment with aluminum conductor/pipe, enclosure, surrounding by air environment, typical magnetic material and pressured SF6 gas. Based on paper [4, 12 16] thermal network components (thermal resistance, heat source, thermal capacitance) were realized in S and built in AP-EMP environment, fulfilling standard program procedures [8]. he voltages taken from the circuit are used to determine a non-linear resistance R(t) (ACS-controlled time-dependent resistor, YPE 91). n this equivalent model, the voltages represent temperatures of different components. hermal capacitance values of the materials used in modeling and simulation are presented in able 4.

able 4 hermal capacitance values Material hermal capacitance [kj/k] Conductor 15.06 SF6 gas 0.92 GS enclosure 157.47 Magnetic material as extra layer.

5 able 4 hermal capacitance values Material hermal capacitance [kj/k] Conductor SF6 gas 0.92 GS enclosure Magnetic material as extra layer.05 his kind of S usage together with controlled time-dependent resistor element R(t) [4, 12 13] were widely applied in dynamic NM modeling. Cross section of the analyzed cases (model 1, model 2, model 3) and drawings diagrams with simulation results are presented in Fig. 4, Fig. 5 and Fig. 6 respectively. n able 5 AP-EMP simulation results are presented and compared with OrCAD Capture results. a) b) = 4kA / 6.3kA as a joul heat source Pipe radiation to air Pipe temp hradiati heatsrc M Recalculate current [A] into joule heat source [W] Pipe convection to air Ambient emp

c) d) 80 1 70 1 temperature [C ] 50 30 temperature [C ] 1 100 80 0 50 100 150 0 250 0 50 100 150 0 250 Fig.

6 c) d) temperature [C ] temperature [C ] Fig. 4 Analyzed GS compartment for model 1; a) cross-section and equivalent thermal network; main conductor with surrounding air pressure, R1 thermal resistance for radiation, R2 thermal resistance for convection to air, C1 conductor thermal capacitance; b) hermal network diagram for model 1 AP-EMP program; AP-EMP simulation dynamic results for model 1: c) rated current 00 A, d) rated current 6300 A a) b) = 00/ 6300A as a joul heat source SF6 radiation enclosure radiation to air hradiati hradiati heatsrc M SF6 convection pipe -> gas SF6 convection gas -> enclosure enclosure convection to air Recalculate current [A] into joule heat source [W] Ambient emp

c) d) conductor enclosure 1 conductor enclosure 50 100 t e m p e r a t u r e [ C ] t e m p e r a t u re [C ] 80 30 0 50 100 150 0 250 0 50 100 150 0 250 Fig.

7 c) d) conductor enclosure 1 conductor enclosure t e m p e r a t u r e [ C ] t e m p e r a t u re [C ] Fig. 5 Analyzed GS compartment for model 2; a) cross-section and equivalent thermal network; main conductor in enclosure; R1 thermal resistance for radiation, R2 thermal resistance for convection to SF6, R3 - thermal resistance for convection from SF6 to enclosure, R4 thermal resistance for radiation to air, R5 thermal resistance for convection to air, C1 conductor thermal capacitance, C2 SF6 thermal capacitance, C3 enclosure thermal capacitance; b) hermal network diagram for model 2 AP-EMP program; AP-EMP simulation dynamic results for model 2: c) rated current 00 A, d) rated current 6300 A a) b) Pipe radiation to enclosure hradiati Pipe convection pipe ->SF6 = 4kA / 6.3kA as a joul heat source coating pipe thermal conductivity SF6 radiation enclosure radiation to air hconduct hradiati hr adiati Pipe temp heatsrc U Coat temp Enclosure temp M Recalculate current [A] into joule heat source [W] coating convection coating ->gas SF6 convection gas -> enclosure enclosure convection to air Ambient emp

8 c) d) Fig. 6 Analyzed GS compartment for model 3; a) cross-section and equivalent thermal network; main conductor with magnetic material and enclosure; R1 thermal resistance for conduction in coating, R2 thermal resistance for radiation from magnetic material to enclosure, R3 thermal resistance for convection to SF6, R4 thermal resistance for convection from SF6 to enclosure, R5 thermal resistance for radiation to air, R6 thermal resistance for convection to air, R7 thermal resistance for radiation (uncovered ends, Fig. 3, Fig. 8), R8 thermal resistance for convection to SF6 (uncovered ends, Fig. 3, Fig. 8), C1 conductor thermal capacitance, C2 magnetic material thermal capacitance, C3 SF6 capacitance, C4 enclosure thermal capacitance; b) hermal network diagram for model 3 AP-EMP program; AP- EMP simulation dynamic results for model 3: c) rated current 00A, d) rated current 6300A able 5 Simulation results and comparison (temperatures on GS tube) Rated current AP-EMP OrCAD Capture Case studies [A] [ C] [ C] model model model model model model Results presented in able 5 indicate the AP-EMP models estimate the final temperature of the whole compartment correctly. Differences between OrCAD and AP-EMP results comes from the fact that the OrCAD utilizes more detailed thermal model of thermal resistances to calculate the temperature. he AP-EMP software has allowed us to achieve the approximate value based on the initial assumptions. 5 Experimental verification of realized hermal Network Models he purpose of this section is to compare heat transfer distribution in GS busduct with the magnetic material installed in the GS conductor, as presented in section 3. Data obtained from lab experiment were compared with AP-EMP and OrCAD Capture models.

Fig. 7 Laboratory arrangement: laboratory setup with analyzed H GS conductor, current power source, high current connections and 7 thermocouples type K he measurements were carried out for the rated

he H GS conductor was placed horizontally (Fig. 8a, 8b), surrounded by free flowing air at atmospheric pressure, the ambient temperature was 23 C. he tests were performed with blinded ends (Fig.

Arrangement of calibrated thermocouples type K, attached to the H GS conductor, is presented in Fig. 7. a) b) c) Uncovered end - conductor without magnetic material Fig.

tests with 00 A current are presented in Fig. 9a and corresponding simulation results (Fig. 9b). he overall duration of the laboratory tests was approximately 250 min (each test).

9 Fig. 7 Laboratory arrangement: laboratory setup with analyzed H GS conductor, current power source, high current connections and 7 thermocouples type K he measurements were carried out for the rated current of 00 A. All tests were stopped after achieved steady temperature rise conditions. he temperature tests were carried out using the circuit depicted in Fig. 7. he H GS conductor was placed horizontally (Fig. 8a, 8b), surrounded by free flowing air at atmospheric pressure, the ambient temperature was 23 C. he tests were performed with blinded ends (Fig. 8c) modeling real operating conditions where the GS conductor is mounted to the busbar spacers. he steady state current of 00 A was applied. Arrangement of calibrated thermocouples type K, attached to the H GS conductor, is presented in Fig. 7. a) b) c) Uncovered end - conductor without magnetic material Fig. 8 H GS conductor during laboratory test H GS; a) conductor placed horizontally, b) conductor with magnetic material layer, c) blinded end of conductor emperature curves obtained during laboratory tests with 00 A current are presented in Fig. 9a and corresponding simulation results (Fig. 9b). he overall duration of the laboratory tests was approximately 250 min (each test). During simulation, computation of the temperature measured by the thermocouples: 1 (on conductor), 3 (on conductor under magnetic material), 4 (on magnetic material) is only possible, due to the structure of the thermal network. he temperature values in the steady conditions are presented in able 6. Detailed comparison of single waveforms from the lab tests and simulation are presented in Fig. 10. As can be seen the results are in closed proximity to measurement and simulation, which confirms high accuracy of the model developed and high efficiency of the proposed method.

10 a) b) hermocouple 1 hermocouple 3 hermocouple 4 80 temperature[c] Fig. 9 emperature rise in test with 00 A - a) original measurement results, b) simulation results able 6 est and simulation results for 00 A - comparison of final values of temperature emp point measurement Measurement AP-EMP Simulation OrCAD Capture hermocouple hermocouple hermocouple a) b) simulation measurement hermocouple 1 70 simulation measurement hermocouple 3 temperature [C] 50 temperature [C] c) hermocouple temperature [C] simulation measurement Fig. 10 emperature rise test with rated current 00 A; comparison of AP-EMP dynamic simulations (red line) and measurement results (blue dashed line) for different temperature measurement points

11 6 Conclusions Heat phenomena in working electrical devices and apparatus are the condition which define their current limits. herefore using the computational techniques allows engineers to analyze thermal aspects of systems in the early design stage. Simulation models with proven accuracy are a must for thermal design of electric apparatus. Such analyses support the estimation of the required cooling or modification of the construction to meet thermal requirements. herefore, the thermal network concept offers an approach which is efficient and intuitive, especially for electric engineers with high speed of computations and good precision it is worth to be considered. he thermal networks S of GS busduct have been built. Calculations and simulation results were obtained for three cases: GS busduct without enclosure surrounded with the air pressure (Model 1), GS busduct with enclosure SF6 pressure inside (Model 2) and GS busduct with the enclosure and the magnetic material wound on the GS conductor SF6 pressure inside (Model 3). All calculations were made for simplified GS busduct design and were simulated for operating currents of 00 and 6300 A. S provided relatively close simulations for the compartment temperature as compared to the measurement results. Additionally, with the use of the AP-EMP software the time constants for the temperature increase was read. he AP-EMP model overestimates the thermal value by the several degrees Celsius as compare to the OrCAD model. his is due to fact that in the AP-EMP model only fundamental thermal dependencies were implemented. Further expansion is possible. mportant fact is that AP-EMP allows for fast and easy assessment if the thermal conditions are meet or are close to their limits. Based on the simulation results presented in this paper, the following conclusions can be listed: for typical atmospheric pressure without an enclosure the temperature on the GS conductor was equal to approx. 150 C (not acceptable according to EC standard [1]); for the GS busduct with the enclosure and with the SF6 gas pressure inside the temperatures are below the limiting value 105 C [1]; additionally the GS busduct with a magnetic material (as extra layer) within the enclosure and SF6 gas pressure inside the temperatures are also below the limit 105 C [1]; laboratory examination of GS conductor (with magnetic material) and obtained results confirm high accuracy of realized AP-EMP S. Generally, AP-EMP program with created and validated S can be utilized as a tool for thermal behavior modeling and dynamic heat rise simulations during electrical devices and apparatus design process. he analyses presented in this paper can serve as a base for development of more advanced AP-EMP models with the use of hermal Network Method approach. Acknowledgements he authors would like to acknowledge Waldemar Chmielak, Ph.D. Eng., Marek Piskała, M.Sc. Eng. and adeusz Daszczyński, M.Sc. Eng. from the Warsaw University of echnology for performing heating tests of GS conductor in single-phase system and for providing experimental data used in this paper.

12 7 References [1] EC Standard: High-voltage switchgear and controlgear Part 3: Gas-insulated metal-enclosed switchgear for rated voltages above 52 k, 11 [2] Dong X., Summer R., Kaltenborn U.: hermal network analysis in M GS design, th nternational Conference on Electricity Distribution, No. 0637, 09 [3] Grossmann S., Lobl H., Kaltenborn U.: ABB and the echnical University of Dresden collaborate on the thermal design of power equipment, ABB Review No. 2, 05 [4] Kałat W.: AP-EMP as a Practical ool for hermal Network Modeling and Heat ransfer Simulation, EEUG News echnical Paper, ol. 7, No. 4, 11/01, page -53 [5] Platek R., Banas M.: hermal analyses of transformers and medium voltage products with hermal Network Method, Electrical Review, No. 2/08, page [6] Loebl H.: Basis of hermal Networks, Material of High oltage nstitute, Dresden University of echnology, 02 [7] Obrączka A., Kowalski J.: Heat transfer modeling in ceramic materials using fractional order equation, Advances in the heory and Applications of Non-integer Order Systems, 5th Conference on Non-integer Order Calculus and ts Applications, Cracow, Poland Lecture Notes in Electrical Engineering, ol. 257, Springer 13 [8] Dommel H.W.: Electromagnetic ransients Program, Reference Manual (EMP) heory Book, BPA, Portland, Oregon, 1986 [9] Stosur M., Kuczek., Szewczyk M., Piasecki W., Fulczyk M., Florkowski M., mpact of high voltage GS substation configuration on lightning overvoltages, Electrical Review, ol. 88, No. 5a, 12, page [10] Kuczek., Stosur M., Szewczyk M., Piasecki W., Steiger M., nvestigation on new mitigation method for lightning overvoltages in high voltage power substations, Journal E Generation, ransmission & Distribution, ol. 8/13, ( /iet-gtd ), page 1-8 [11] ABB official webside: [12] Stosur M., Dawidowski P., Szewczyk M., Samul B., Balcerek P., hermal analysis of typical GS compartment with hermal Network Method using AP-EMP program, Electrical Review, ol. 90, No. 4, 14, pp [13] Stosur M., Dawidowski P., Szewczyk M., Balcerek P., Sowa K., Modeling and simulation of thermal behavior within typical GS busduct using AP-EMP program, EEUG Meeting, European EMP-AP Conference, European EMP-AP Users Group Association, Cagliari, Sardinia - taly, September 14, Conference Proceeding 14, page [14] Purnomoadi A. P., nvestigation of Free Moving Particles on the Breakdown oltage in Gas nsulated Switchgears (GS) under Different Electrical Stresses, MSc hesis, Delft University of echnology, June 12 [15] ABB AG Mannheim, High-oltage Switchgear nstallation manual, Mannheim 07 [16] Graber L., hronicker., hermal-network Simulations and Computational Fluid Dynamics for Effective Gas Leakage Detection in SF6 Switchgear, CGRE Session 08, page 1-8

I, THERMAL ANALYSIS OF BUS-BAR FOR SWITCH BOARD

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