This article deals with results from analysis of acoustic signal obtained from experiments realized in nonhomogeneous
electric field. These signals exist in the form unwanted noise which can be used also for diagnostic
purpose. In power engineering this case occure in high voltage power station and transmission lines. We
analyse acoustic signal from acoustic sensor in audible band from 1 kHz to 20 kHz. The acoustic signal
transmitted from object is unique for specific conditions. Exploitation of audible band for discharge detection is
difficult in outdoor bias level. Advantage of this method consist in simple results prepare

Dolník, Bystrik

Kurimský, Juraj

Tkáč, Ján

Vilček, Miroslav

University of West Bohemia Digital Library

Acoustic detection of noise emission from discharge activity in power engineering

DSpace at University of West Bohemia

51707-IC-3-2004-1-CZ-ERASMUS-IPUC-260 ACOUSTIC DETECTION OF NOISE  EMISSION FROM  DISCHARGEACTIVITY IN POWER ENGINEERINGJán Tkáč, Bystrík, Dolník, Juraj Kurimský, Miroslav Vilček ABSTRACTThis article deals with results from analysis of acoustic signal obtained from experiments realized in non-homogeneous electric field. These signals exist in the form unwanted noise which can be used also for diagnosticpurpose. In power engineering this case occure in high voltage power station and transmission lines.  Weanalyse acoustic signal from acoustic sensor in audible band from 1 kHz to 20 kHz. The acoustic signaltransmitted from object is unique for specific conditions. Exploitation of audible band for discharge detection isdifficult in outdoor bias level. Advantage of this method consist in simple results prepare. KEYWORDSacoustic noise, discharge, acoustic sensor 1. INTRODUCTIONElectric equipments are in the form of different electrode systems produced. Between these electrodes existsdifferent shapes of electric field. In the area of the high voltage technique electric fields are classified accordingto electrical field homogenity into:- homogeneous,- slightly non-homogeneous and- strong non-homogeneous.This clasification result from geometrical point of view and material properties of  electrode system andappropriate distribution of electric field. Homogeneous electric field has constant electric field intensity in eachpoint. Typical example of discharge originated in homogeneous electric field is so-called Townsend dischargeand Reather-Meek discharge.Slightly non-homogeneous electric field is very small different from homogeneous field. Non-homogeneouselectric field originate mainly between electrodes with high difference of curve radius. Significant influence ondischarge processes has space charge. During discharge processes in non-homogeneous electric field existionizing and de-ionizing processes. These have main influence on formation of discharge path and also onproperties of discharge.Ionization occur in the form of elastic or non-elastic collision of particles, photoionization andthermoionization. Deionizating processes are: recombination of particles, absorption of electrons and difuzion ofions.51707-IC-3-2004-1-CZ-ERASMUS-IPUC-261 2. CLASSIFICATION AND ANALYSIS OF DISCHARGE PHENOMENA IN NON-HOMOGENEOUS FIELDDischarge processes are classified according to duration on temporary and steady. Steady discharges aredivided into independent and non-independent. Sort criterion result from the condition which lead to generationand sustain of discharge path. Category of independent discharges include: silent discharge, corona discharge,spark discharge and arc discharge. Non-independent discharges require the source of charge carrier or source ofenergy for ionization of atoms.Corona discharge exists surround electrodes with small curve radius which create non-homogeneou electricfield in discharge path. Corona discharge existing only on one electrode  we call unipolar. Corona dischargecreate by specific voltage which is called corona inception level. Under corona inception level exist only non-independent silent discharge in consequence of secondary discharging processes e.g. space, ultraviolet radiation.If voltage on the electrodes is higher then corona inception level plasma enlarges to oposite electrode andbreakdown of discharge path occur. Corona discharge changes to spark discharge or arc discharge. Under DCvoltage positive or negative corona discharge is created. Under AC voltage AC corona discharge is createdwhich properties are dependend to time.On the interface solid-gas material creeping discharge in non-homogeneous electric field is developed. Thisdischarge act on the surface of insulation between electrodes. For these processes the best representation isToepler model. Creeping discharges are undesirable because these discharges quickly degrades insulation andshutdown high voltage devices from operation. The advantage is that we have possibilities to eliminate forexample by using different surface layers especially semiconducting layers.Sparc discharge is temporary form of electric discharge in gas. This discharge manifest in the form of shinedchanel which has high temperature and high level of thermal ionization. 3. MEASUREMENT IN NON-HOMOGENEOUS HV FIELDMost of measurement method originate from the following discharge activity phenomena:- electromagnetic,- optic,- acoustic.Technical insulation materials which are used in the area of high voltage technique are realised from thesolid, liquid and gas combination e.g. liquid-solid, gas-liquid, eventually gas-solid. On the interfaces ofparticular materials under specific condition surface discharges occures which produce noise.ATASPC OTVNT ESFig. 1 Block diagram  of schemeAT – autotransformer, VNT – hv transformer, ES – electrode system, AS –acoustic sensor, PC – personal computer, OT – separate winding transformer51707-IC-3-2004-1-CZ-ERASMUS-IPUC-262The utilisation of non-renewable energy sources is doubtful also from economical point of view, because oftheir high external costs, i.e. social, political, environmental and nuclear costs. These forgotten costs are notincluded in selling price and they are by much higher than actual electricity price (Fig. 2).In the praxis following types of interfaces exists:a) homogeneous electric field with explicitly tangential action of field on interface,b) homogeneous electric field rectangular affect on interface of two insulant,c) non-homogeneous electric field with tangential action of field and small normal part,d) non-homogeneous electric field with tangential action with strong normal part.For the operation the most dangerous is case (d). This case we applicated for measurement and acousticsignal analysis. On the figure 1 is block diagram of scheme and applicated electrode arrangement on figure. 2.Electrode arrangement applied in our experiment represent interfaces between solid and gas material. In themeasurement according to Toepler different types of electrodes were applied, see figure 3. Electrodes A and Bhave cylindric design and were in contact with dielectric, electrode C has point shape with curve radius of0,5 mm. Electrodes D–F are created from needles and their mutual distance (case E and F) is 5 mm.                                                            BA1 2 3213Fig. 2   Electrode system for non-homogeneous electric field creation1 – earthed electrode, 2 – dielectric, 3 – electrode connected to high voltage; A – measurement ofcreeping discharges,  B – measurement according to ToeplerAC voltage on the electrode system was applied with variable amplitude from 5 kV to 50 kV. Distancebetween acoustic sensor and electrode system was 30 cm. The signal from acoustic sensor was recorded on datamedium and postprecessed.A B C D E FFig. 3   Types  of electrodes in measurement according to Toepler 4. CONCLUSIONSFor evaluation of measured acoustic signal frequency analysis with FFT was applicated. The amplitude ofsignal is relatively equally distributed over acoustic band. However, contains several extremes which vary inaccordance with the shape of electrode, its distance from grounded electrode and amplitude of applied voltage.Measured characteristics are nearly directly proportional with applied voltage.51707-IC-3-2004-1-CZ-ERASMUS-IPUC-2630 2 4 6 8 10 12 14 16 18 20 220-1070102030405060A  (dB)f (kHz)40 kV35 kV25 kV30 kV20 kV15 kV10 kVFig. 4   Frequency characteristic of signal from acoustic sensor for all measured voltage levelsOn the figure 4 an increase in amplitudes of particular frequencies for given voltages and electrode systemon figure 2B with electrode A according to figure 3 is shown. On the figure 5 comparison of amplitude growthfor frequencies 1 kHz, 5 kHz, 10 kHz, 15 kHz and 20 kHz and electrode system according figure 2Bwith electrode E and distance of 2 cm from grounded electrode is shown. On figures we can see that frequencies5 kHz a 10 kHz dominate. 1 kHz frequency was compared with another frequencies because represent ambientacoustic noise. Similar characteristics with other electrode systems and appropriate distances were measured.-50510152025303520 25 30 35 40 451 kHz10 kHz5 kHz20 kHz15 kHzA  (dB)u (kV)Fig. 5   Increase in amplitudes of particular frequencies for given voltages and electrode system on figure 2Bwith elektrode E and distance 2 cm from grounded electrodeHowever measurement of discharge activity in acoustic band is strongly affected with acoustic backgroundof surrounding environment and therefore its practical application is delimited on objects with low ambientacoustic noise. In the case of high ambient acoustic noise exist reason for solution of this problem fromenvironmental point of view. Advantage of this method consist in simplicity of quantitative as well as ability ofimmediate qualitative evaluation. In environments with strong noise it is better to orient on measurement ofsignals in ultrasonic band. 5. REFERENCES[1] Creyghton, Y. L. M. – Rutgers, W. R. – Van Veldhuizen, E. M.: In-Situ Investigation of pulsed coronadischarge, University of technology Netherlands, 1993. ISBN 90-6144-289-651707-IC-3-2004-1-CZ-ERASMUS-IPUC-264[2] Vilček, M. Výbojové javy v nehomogénnom poli. In: Master thesis on FEI TU in Košice on KEE. Chief ofdiploma thesis Ing. Ján Tkáč, CSc. Košice, 2004. 45 s., 6 s. appendixes.This work was supported by APVV, number of research project APVV-20-006005. Authors:Ing. Ján Tkáč, CSc – Dr. Ing. Bystrík Dolník – Ing. Juraj Kurimský, PhD.Department of Electric Power EngineeringFaculty of Electrical Engineering and InformaticsTechnical University of KošiceMäsiarska 74040 01 KOŠICE, Slovak RepublicE-mail: Jan.Tkac@tuke.sk, Bystrik.Dolnik@tuke.sk, Juraj.Kurimský@tuke.skTel.: +421 55 6023551Fax: +421 55 6023552

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Acoustic detection of noise emission from discharge activity in power engineering

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