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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12) ISSN 1843-6188 THE USE OF ELECTROMAGNETIC FIELD IN MODELING AND MONITORING ELECTRICAL EQUIPMENT Monica ROTARIU, Adrian BARABOI, Maricel ADAM, Catalin PANCU Faculty of Electric Engineering, Department of Energetic „Gh. Asachi” Technical University of Iaşi, Bd. D. Mangeron, nr. 51-53, 700050 E-mail: [email protected] process of other electricity applications thereby, nor to exersize biological effects over living organisms including the human factor. This is the reason we consider as a very important aspect to take into account the electomagnetic pollution effects generated by electrical installations. Abstract: Electricity is more than energy: it is a vital component of our lives, playing an important role in the economy of many countries. Wherever electricity is generated, electromagnetic fields are created. The strong development of information technology had provided new possibilities in monitoring and diagnose of electrical equipment and devices. The purpose of this paper is to highlight the posibility of using the electromagnetic map of electrical equipment in the process of monitoring, diagnosing, controling and commanding them. The mathematical modelling and simulation of different operating status of the electrical equipment and devices, was accomplished by using the EMTP – ATP software. The paper also presents experimental results of the monitoring and diagnose of the electrical equipment using the information contained in their electric and magnetic field. The data is processed with the 6024 E National Instruments acquisition board. 2. ELECTRICAL EQUIPMENT AND DEVICES. MONITORING AND DIAGNOSE TECHNIQUES The electromagnetic field is generated by each electrical equipment and installation, which can lead to different kind of perturbations in the equipment functioning or can cause the malfunctioning of the equipment and devices nearby (over voltage, over currents, excessive heating of high voltage power line conductors). Taking into account the facts mentioned above, in this paper we have focused on developing modern monitoring and diagnose techniques that with the use of the information contained in the electromagnetic radiation field of each electrical equipment and devices can give us information about the different states the equipment or devices are facing while on service. In the chapters below are described some of the equipment that make part of our study, highlighting the parameters that are being analyzed using their own electromagnetic radiation field. Keywords: electromagnetic map, electrical equipment and devices, electromagnetic field, acquisition board. 1. INTRODUCTION The technological progress concerning data transmission and the development and expansion of the power systems worldwide was an important factor in increasing the electromagnetic field level as well as the bio-organism and human body exposure to the electromagnetic radiation. 2.1 Electric motors. Star – delta starting All indirect starting methods are used to reduce the starting current. In the case of a star – delta starting the network voltage is applied directly to the star connected to a three phase winding coil.[4] When the motor reaches a rotation speed of 90 % of its nominal speed, the phase winding coils commute from star to delta with the help of a switch. The commutation can be made manually or automatic. Effective line current for a steady state on a star connection is described by the next expression: Because electricity is so much a part of our lives, there are electromagnetic fields around us most of the time. All electric flows have an associated electric field and magnetic field. The intensity of both electric and magnetic fields decreases with distance from the field source. Electric fields are more easily shielded or blocked than magnetic fields. The main purpose of this paper is to highlight the posibility of using the electromagnetic map of electrical equipment in the process of monitoring, diagnosing, controling and commanding them. By the achievment of advanced software/hardware structure intelligent devices can be realized, which represent important components in the structure of the electric power systems including both transportation and distribution systems. On the other side, these devices, equipment or system must not influence in a negative way the operating I lY I fY U fY / Z f U l / 3Z f (1) The effective current expression for a delta connection changes to: 38 Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12) ISSN 1843-6188 I l 3I f 3U f Zf 3U l Zf time – current characteristic t =f(I). t represent the melting time of the fuse element + the arcing time = the breaking time. The shape of the characteristic differs depending on fuse type. The main difference is due to the breaking time: there are slow fuses, fast fuses, mix fuses and ultra- fast fuses. (2) The absorbed current report for the two connections has the next value: I lY / I l 1 / 3 (3) Due to a 3 time mitigation of the phase voltage while in star connection, the starting torque is also 3 times lower than the direct starting case; the electromagnetic torque is proportional with the square stator phase voltage. This inconvenient is limiting the application of the star – delta starting only in the situation of an unloaded start of a motor or a low resistant static torque. The star – delta starting method is used for nonsynchronic short – circuit three phase motors, with a nominal power between 5.5 – 14 kW/ 400 V. [2] This method can be use only in the case of the motors that have the nominal phase voltage equal to the three phase network line voltage. The mechanical characteristic of the star – delta starting is shown in the figure below: Figure. 2. Time carachteristic For a current 15 times bigger that In the breaking time of the fuse is very short, the circuit being disconnected before the short circuit current reaches its maximum value. III. MODELLING AND SIMULATION ELECTRICAL EQUIPMENT OF Modelling and numeric simulation allows us to study and evaluate the electromecanic systems behaviour in the applications they were designed and realized for, but also for other application, fact that leads to the development of new types of systems and equipment. The electromagnet (figure 3) is one of the most important electromecanic systems. This quite simple device plays a significant role in the interconnections of two subsystems, where the first systems, with electric output signal, controls the second one which has mecanical input signal. Figure. 1. Electric characteristic of star-delta motor starting 1 The star- delta starting method is very efficient from the technical and economical point of view, that’s why it has a large application scale in power engineering. 2 2.2. Fuses The fuses are designed to protect the circuit against overload and short circuit. Depending on the current they are able to break (<1 kA to >1 kA) there are different types of fuses. The technical characteristic of a fuse are listed below: nominal current (In); nominal voltage (Un); breaking capacity – the maximum short circuit current that can be break according to standard normative; U U 4 3 x S Fa Ma i i Mr m x J Fr MS MS a b Figure.3. Air – gap zone: a-transition mobile armature; linear air- gap; x- motion; m-reduce weight; Fr-resistant force; MS-mechanic subsystem; b- titling mobile armature; -angular air - gap; J- inertia moment 39 Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12) In figure 3.a. the direct current electromagnet is designed with a transition mobile armature, while in figure 3.b. it has a mobile titling armature. Dependind on the amature type (transition or titling) its motion during the transient state is described by one of the following equations [3]: ISSN 1843-6188 circuit functioning. This is why for an electromagnet with translation armature (fig. 3.a), the model is based on the equations (41), (5) and (6), while for the electromagnet with the titling armature (Fig.3.b), the equation (41) is replaced with the equation (42). The electromagnetic field is characterised, in a certain point in space, by the superposition of an electric and magnetic field, variable in time, which are mutual generating. The state of the electric field is described by two vectors – E – the intensity of the electric field and D – the electric induction. The magnetic field state is described by B – magnetic induction and H – magnetic field intensity [1]. The numerical simulation is performed with the EMTP ATP software and the graphical results are shown with the help of the MC’s Plot XY, in figures 5 and 6. d 2 x dx at et x Fa ( x ) Fr ( x ), 2 dt dt (4) 2 d x dx dx J 2 ab eb x M a ( x ) M r ( x ),x( 0 ) x0 , 0 dt dt 0 dt m where at, ab şi et, eb are the damping and elastic constants of the electromagnet. The active force Fa and the active moment Ma, are described in relation (5): 0.20 0.15 2 Fa 2 F , M a rF , 0 S 0.10 (5) 0.05 0.00 F - active force reported to the air gap, r – force arm, - magnetic flow of the air gap, S- polar surface. The electric circuit single line diagram of the direct current electromagnet is shown in the figure 4. i -0.05 -0.10 -0.15 -0.20 0.00 L R 0.02 0.04 0.06 0.08 [s] 0.10 0.08 [s] 0.10 (f ile CA.pl4; x-v ar t) t: PSI Figure 5. Magnetic flow 3 U L 2 1 a is 0 Ls Rs -1 -2 ucs us Cs -3 0.00 0.02 (f ile CA.pl4; x-v ar t) c:CRT -CR factors: 1 1 offsets: 0 0 0.04 0.06 t: X 100 0 Figure 6. Current absortion of the coil and armature motion b Figure .4. Single line diagram: a-electromagnet: Rresistance; L-dispersion inductance, L-inductance of the magnetic flow; b-simulation mode Graphical results for an alternative electromagnet are shown in figures7 and 8. 2.0 This circuit is described by the equation (6): 1.6 di d N , dt dt (6) d Ni F , F K , dt where F the solenation that coresponds to Foucault currents, N-number of coil coilings and K- constant coeficient. U Ri L 1.2 0.8 0.4 0.0 0.00 0.04 0.08 0.12 (f ile CC.pl4; x-v ar t) t: PSI Figure 7. Magnetic flow 3.1. Numerical simulation in EMTP - ATP The mathematic model of the direct current electromagnet functioning is based on a differential equations system, from which one corespond to the mobile armature motion and the others to the electric 40 0.16 [s] 0.20 current Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12) ISSN 1843-6188 0.10 0.08 0.06 0.04 0.02 0.00 0.00 0.04 (f ile CC.pl4; x-v ar t) c:CRT -CR factors: 1 1 offsets: 0 0 0.08 0.12 0.16 [s] 0.20 t: X 10 0 Figure 8. Current absortion of the coil and armature motion Figure 11. Magnetic induction – fuse of 60 A 4. NUMERICAL RESULTS 4.1. Electromagnetic radiation field for different fuses For this study we have used two fuses of 40 and 60 A. Graphical results are shown in figures 9 – 12. The data was captured with the help of an aquisition board and process in a LabView application. [5] In order to distinguish the way the electromagnetic field is influencing the good functiong of the electrical equipment and to see the impact that it has on the staff and the environment, the monitoring and diagnose techniques were applied for fuses and electric motors. Figure 12. Magnetic induction captured at the starting of the instalation SF 60 A Figure 9. Magnetic induction – fuse of 40 A For the 40 A fuse we observe that the functioning time of the instalation is 0.588 ms and in case of the 60 A fuse, the time the instalation is in use is reduce to 0.382 ms, as we can see from the table below: Table 1. Signal amplitude – Service time SF 40 A SF 60 A Time[s] Amplitude [V] 0,588 0,382 14,6 16,2 4.2. Electromagnetic radiation field at the motor star – delta starting The front panel of the instalation is shown in figure 13. Figure 10. Magnetic induction captured at the starting of the instalation SF 40 A 41 Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12) ISSN 1843-6188 Table 2. Signal amplitude – Service time Star – delta starting Contactor starting Contactor stop Time[s] Amplitude [V] 4,989 0,261 0,283 15 15,8 7 All the data presented above was captured using diferent electric and magnetic sensors (magnetic coil, electric and magnetic sensor from MetraHit 28 s device) connected to an aquisition board, National Instruments 6024 E. Figure 13. Front panel – star – delta starting The grafical results are presented in the figures 14, 15 and 16. 5. CONCLUSIONS In this paper we have tried to study new possibilities in the monitoring and diagnose of the electrical equipment and instalations making use of the information contained in their own electromagnetic radiation field. In order to obtain a very good accuracy of the registered data a National Instruments 6024 E acquisition board was used. All the information thus obtained was send on- line to an application specially made in LabView software. For the equipment and devices that were studied a mathematic model was build in order to run a numerical simulation with the help of EMTP– ATP software. A special attention has been given to the electric and magnetic radiation field of each equipment that has been part of our study and on how its values are influencing the equipment or the surrounding equipment behavior while in service. The present study was based especially on a successive functioning of the studied equipment obtaining this way a very good accuracy of the registered data. An example of successive functioning that has been studied is the star – delta starting of an electric motor. Knowing the values of the electromagnetic field is very important for the exploring staff of the power systems, from human body and environment exposure point of view. That is why we consider analyzing the information contained in the electromagnetic map of the electrical equipment and devices an important step in the monitoring and diagnose techniques. Figure 14. Star – delta motor starting Figure 15. Contactor starting 6. REFERENCES [1] Valeriu David, Mihai Creţu – Measuring the magnetic field intensity (Măsurarea intensităţii câmpului electromagnetic – Teorie şi aplicaţii), Casa de Editură Venis, Iaşi, 2006 [2] G. Hortopan – Electric Aparatus (Aparate Electrice), Editura Didactică şi Pedagogică, Bucureşti 1967 [3] A. Baraboi, M. Adam, I. Ciutea, E. Hnatiuc – Tehnici moderne în comutaţia de putere, Editura A 92, Iaşi 1996 [4] Basics for practical operation, Motor starting, Traditional motor starting, Soft starters, frequency inverters, Publication WP Start, EN, January 1998 [5] Monica Rotariu - Experimental and theoretic basis of electromagnetic radiation field used in monitoring and diagnose electrical equipment and installation, PhD Thessis Report, December 2009 Figure 16. Contactor stop The time that coresponds for the star – delta starting, the opening and closing of the contactor and also the amplitude signal for each of these operations are shown in the next table: 42 ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12) 43