2017 15th International Conference on Electrical Machines, Drives and

Power Systems (ELMA)

1-3 June 2017Sofia, Bulgaria

ELMA 2017

2017 15th International Conference on Electrical

Machines, Drives and Power Systems (ELMA)

ELMA 2017

Proceedings

1 - 3 June 2017, Technical University of Sofia, BULGARIA

ISBN 978-1-5090-6690-2 IEEE Catalog Number CFP17L07-PRT

Organised by:

Union of Electronics, Electrical Engineering and Telecommunications (CEEC)

IEEE Bulgaria Section

Friends of the ELMA 2017 are:

Technical Universities of Sofia, Varna and Gabrovo

University of Ruse “Angel Kantchev”

Federation of Scientific and Technical Unions

House of Science and Technology — Plovdiv

Faculty of Technical Sciences, “Prof. Assen Zlatarov” University – Bourgas

Bulgarian Association of Electrical Engineering and Electronics (BASSEL)

2017 15th International Conference on Electrical Machines, Drives and Power systems (ELMA)

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ISBN 978-1-5090-6690-2

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ISBN 978-1-5090-6690-2 Disclaimer: The authors are fully responsible for respecting the authors’ rights, industrial and patent properties.

iii

TABLE OF CONTENTS

Design & comparison of a conventional and permanent magnet based claw-pole machine for automotive application - Pranshu Upadhayay, Afef Kedous-Lebouc, Lauric Garbuio, Jean-Claude Mipo, Jean-Marc Dubus ...................................................................................... 1

Design and comparison of outer rotor bonded magnets halbach motor with different topologies - Amit Kumar Jha, Afef Kedous-Lebouc, Lauric Garbuio, Jean-Paul Yonnet, Jean-Marc Dubus .............................................................. 6

Output characteristics analysis of gensets for modeling of an expert system for fault detection purposes - Željko Hederić, Dejan Barešić, Venco Ćorluka ........................................................................ 11

Effects of cogging torque reduction techniques applied to surface mounted PMSMS with distributed windings – George Todorov, Bozhidar Stoev, George Savov, Petar Kyuchukov ...................................... 17

Development of a novel coaxial magnetic gear - Fuat Kucuk, Sadra Mousavi .................................................................................................... 22

The evolutionary optimization approach for voltage profile estimation in a radial distribution network with a decreased number of measurements - Marinko Barukčić, Marko Vukobratović, Dalibor Buljić, Dino Masle ........................................ 26

HV transmission line stringing operation. Usage of unmanned aerial vehicles for installation of conductor and OPGW - Karol Pawlak, Dorota Serek .................................................................................................... 32

Investigation of the capacitive interference of overhead multi-line power system - Atanas Chervenkov, Todorka Chervenkova ............................................................................ 38

Analysis of errors in distribution networks power losses calculations with relation to the time discretization intervals - Konstantin-Kiril Savov, Rad Stanev, Petko Stoyanov, Dimo Stoilov ....................................... 42

Loading curve optimization for electric networks efficiency improvement - Stanislav Eroshenko, Alexandra Khalyasmaa, Zhu Kaihui, Lin Zhixing, Yang Weixiu, Li Shunan ....................................................................................... 47

The short circuit currents calculations model for integral forecasting of the switching facilities residual life - Alexandra Khalyasmaa, Mihail Senyuk, Stanislav Eroshenko ................................................. 53

Simulation of air transformers with different sizes and geometry - Dimcho Hvarchilkov, Vladimir Dimitrov, Peter Goranov .......................................................... 58

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Modelling of an off-grid photovoltaic power supplying system for telecommunication equipment - Ivan Nedyalkov, Dimitar Arnaudov, Nikolay Hinov, Hristiyan Kanchev ................................... 64

Physical model of an electric vehicle for research of dynamic operating modes – Gergana Vacheva, Nikolay Hinov, Rad, Stanev ...................................................................... 70

Two-stage low-frequency square-wave electronic ballast with analog and digital control - V. C. Valchev, V. Chikov, V. Gyurov, and T. P. Todorova ....................................................... 74

Overview of heat transfer aspects for inductors and transformers for power electronics - Vencislav Valchev ................................................................................................................... 78

Bounded global irradiation prediction based on multilayer perceptron and time series formalism - Cyril Voyant, Gilles Notton, Marie Laure Nivet, Fabrice Motte, Alexis Fouilloy, Christophe Paoli ..................................................................... 82

Solar potential for building integrated solar collectors: Application in Bulgaria, Romania & France - Elio Rebillout, Gilles Notton, Andrei Damian, Rodica Frunzulica, Vladimir Lazarov, Ludmil Stoyanov........................................................... 86

Modeling of PV panels – case study for Oryahovo, Bulgaria - Ludmil Stoyanov, Iva Draganovska, Zahari Zarkov, Vladimir Lazarov, Gilles Notton ............................................................................................... 91

Optimization of the solar thermal collectors integration in buildings for DHW preparation - Andrei Damian, Rodica Frunzulica, Razvan Stefan Popescu, Elio Rebillout, Gilles Notton ..................................................................................................... 96

Tilos, the first autonomous renewable green island in mediterranean: a horizon 2020 project - Gilles Notton, Marie Laure Nivet, Fabrice Motte, Cyril Voyant, Alexis Fouilloy, Dimitris Zafirakis, Christophe Paoli ............................................................... 102

Comparison between conventional wind measurement systems and SODAR systems for remote sensing including examination of real wind data - Dmitriy Dubov, Bohos Aprahamian, Meline Aprahamian ....................................................... 106

Forecasting software for hourly transmission losses - Stefan Sulakov ...................................................................................................................... 110

The cross-border trade impact on the transmission losses - Stefan Sulakov ...................................................................................................................... 115

The weather impact on the overhead line losses - Valentin Kolev, Stefan Sulakov ............................................................................................. 119

Influence of the tower construction of electrical power line 110 kV over the risk of electrical field exposure - Marinela Yordanova, Mediha Hamza .................................................................................... 124

v

A Monte Carlo algorithm for determining the point of collapse of power flow equations - Nikolay Nikolaev .................................................................................................................... 130

An algorithm for fast determining the point of collapse of power flow equations based on singular value decomposition - Nikolay Nikolaev .................................................................................................................... 135

The choice of optimal system composed of linear conductors for electrostatic space protection - Nebojsa Raicevic, Slavoljub Aleksic, Ana Vuckovic, Mirjana Peric ....................................... 140

The indicators system for the short circuit currents levels assessment in the power systems - S.A. Eroshenko, A.O. Egorov, M.R. Zagidullin, M. D. Senyuk ............................................... 144

Light electronic regulator based on open-source microcontroller platform - Hristo Antchev, Eltimir Stoimenov, Vlado Yankov ................................................................. 149

Design considerations of ZVS converter for charging of energy storage elements - Dimitar Arnaudov, Nikolay Hinov, Vencislav Valchev ............................................................ 154

Modelling of single transistor parallel ZVS DC-DC converter - Nikolay Hinov, Dimitar Arnaudov, George Kraev, Bogdan Gilev ........................................... 158

Modeling of the behavior of high pressure discharge lamps in circuits with ballast - Simona Petrakieva, Zahari Ivanov ......................................................................................... 162

Recognition of heat - conductive filling agents of a thermoelectric refrigeration system with focused time - delay neural network - Ivaylo Belovski, Sotir Sotirov, Anatoliy Aleksandrov, Nikolay Sotirov .................................... 166

Electroenergetical training laboratory with remote access to stands - Alexander Antipin, Vasiliy Frizen, Vladimir Udintcev, Sergei Nazarov .................................. 170

A real time street lighting control system - Seher Kadirova, Daniel Kajtsanov ......................................................................................... 175

Problems and trends in training of electrical engineers - Mariya Marinova, Marin Marinov ........................................................................................... 179

Some aspects of using real and virtual experiment in teaching electrical engineering - Ilonka Lilyanova, Marin Marinov, Radko Stoianov ................................................................. 186

Model-based virtual product development and data control with PLM - Dimitar Jetchev, George Todorov .......................................................................................... 191

Method of design public key infrastructure for secure audio information transmission in multimedia systems - Snezhana Pleshkova, Dimitar Kinanev ................................................................................. 195

Energy - efficient control of double inverter-fed induction motor - Gennady Tutaev, Maxim Bobrov, Igor Gulyaev ..................................................................... 199

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Development of an algorithm for modal control of SISO Linear Time-Invariant Discrete Systems - Nikola Nikolov, Mariela Alexandrova, Veselin Lukov ............................................................. 203

Determination of control sensor position in a clapper type electromagnet using FEM - Ivan Kostov, Stefcho Guninski ............................................................................................... 207

Cogging torque effect on motor start-up in a sensorless motor drive for permanent magnet synchronous motors - Emil Rachev, Vladislav Petrov, Bozhidar Stoev .................................................................... 211

Application of recursive methods for parameter estimation in adaptive pole placement control of DC motor - Ivan Grigorov, Nasko Atanasov ............................................................................................. 215

Combined mobile robots motion control using information as voice and gesture commands from audio and thermal visual sensors - Snezhana Pleshkova, Zahari Zahariev .................................................................................. 219

Investigation of the dielectric permittivity of anodic aluminum oxide substrates for multi-chip modules - Svetozar Andreev, Nina Spasova .......................................................................................... 224

Features in the selection and operation of AC motors for electric propulsion system in ships - Lyubomir Dimitrov, Stefka Kanturska .................................................................................... 228

Electrical loads and profiles of public buildings - Nikolay Matanov, Ivan Angelov ............................................................................................. 233

Algorithm for selection of passive harmonics filters - Nikolay Matanov, Haralan Penev .......................................................................................... 238

Automated photovoltaic and lighting infrastructural system – APhoLIS - Valentin Gyurov, Vladimir Chikov .......................................................................................... 243

Application of automated photovoltaic and lighting infrastructural system APhoLIS-energy points - Valentin Gyurov, Plamen Kirovski ......................................................................................... 248

Mathematical and economic extrapolations on the model for optimal microgrid operation and its solution - Vesselina Trashlieva ............................................................................................................. 252

IP-based smart sensors for energy metering and efficient HVAC infrastructure in buildings - Basri Kul ................................................................................................................................ 258

Optimization of medium voltage backup power supply strategies for high power pump aggregates - Vultchan Gueorgiev, Plamen Rizov ....................................................................................... 262

vii

Influence of the excitation regime of turbo-generators on the own needs supply stability - Plamen Rizov, Vultchan Gueorgiev ....................................................................................... 267

Design of a low permanent magnet mass hybrid excited flux switching machine for a PHEV application - Noureddine Faltakh, Franck Vangraefschèpe, Raouf Benlamine, Sami Hlioui, Mohamed Gabsi ................................................................................................ 271

Torque ripple suppression in surface mounted PMSMs with distributed windings - Bozhidar Stoev, George Todorov .......................................................................................... 277

Evaluation and different control methods of the transformer noise (Literature survey) - Vili Boteva, Hristo Tsvetkov, Yordan Botev ........................................................................... 281

Harmonic impact testing on synchronous generator protection - Dimitar Bogdanov, Rosen Iliev .............................................................................................. 288

Power control of PMSG for wind turbine using maximum torque per ampere strategy - Zahari Zarkov, Boris Demirkov .............................................................................................. 292

Small wind generator system with non-inverting buck-boost converter and battery storage - Zahari Zarkov, Ivan Bachev, Vladimir Lazarov ...................................................................... 298

Experimental design of stand-alone field oriented control for WECS in variable speed DFIG-based on hysteresis current controller - Fayssal Amrane, Azeddine Chaiba, Bruno Francois, Badreddine Babes ............................. 304

Electrical energy wireless transfer: application to electric roads - Mehdi Rouissiya, Ikram El Abbassi, Bilal Amghar, Alain Jaafari, Moumen Darcherif ........................................................................................... 309

Critical meteorological conditions and the electrical power balance in Bulgaria - Nelly Harizanova ................................................................................................................... 314

Piezoelectric energy harvesting device with nanobranched ZnO on polymer/metal/polymer coated flexible substrate - Georgi Kolev, Mariya Aleksandrova, Georgi Dobrikov, Mileti Fartunkov, Krassimir Denishev, Habib Pathan ............................................................. 320

The study of bulk loading in high-temperature resistance furnaces - Alexander Antipin, Vasiliy Frizen, Fedor Tarasov, Fedor Sarapulov ..................................... 325

Magnetoelectric position sensors for automotive application – Nikolay Kolesnikov, Sergey Zhiglinsky, Roman Petrov, Mirza Bichurin, Slavcho Bozhkov, Ivan Milenov, Penko Bozhkov .................................................................. 329

Processing efficiency of plasma-aided porous media finishing - Peter Dineff, Dilyana Gospodinova, Ivaylo Ivanov................................................................. 334

Comparison of the conductors’ mechanical mode calculations using different mathematical models - Nikola Nikolov, Dimo Stoilov .................................................................................................. 339

viii

Comparative study of electric car traction motors – Emil Sokolov .......................................................................................................................... 348

Application of infrared thermography technique in transformers maintenance in distribution network – Emil Mechkov ........................................................................................................................ 354

Ferroresonance modes determination of single-phase toroidal transformers - Emil Cazacu, Lucian Petrescu, Valentin Ioniţă ...................................................................... 358

Losses and temperature rise within power transformers subjected to distorted currents - Emil Cazacu, Lucian Petrescu, Valentin Ioniţă ...................................................................... 362

Monitoring system for sensorless energy characteristics identification of inverter-fed single-phase collector motor drive - Dimitar Spirov, Milko Dochev................................................................................................. 366

Coupled electric – thermal model for SR-drives - Sorin Cosman, Claudia Martis, Radu Martis .......................................................................... 370

Analysis of permanent magnet synchronous machines used for hybrid vehicles – Plamen Rizov, Tsvetomir Stoyanov, Radoslav Spasov, Vasil Spasov .................................. 374

Decision making in transformer manufacturing companies with help of ERP business software – Josip Nađ, Mario Vražić ......................................................................................................... 379

Effect of static or dynamic eccentricities on the unbalanced magnetic pull in doubly-fed induction machines - Nicolas Moisson-Franckhauser, Thomas Lugand, Alexander Schwery, Lauric Garbuio ...................................................................................... 383

Harmonic analysis of the magnetic field of a coaxial magnetic gear - Iliana Marinova, Miglenna Todorova, Valentin Mateev .......................................................... 389

Filtration of deteriorated signals used in the control systems by orthogonal wavelets - Mariyana Todorova, Reneta Parvanova ................................................................................ 395

Design of digital PI regulators from experimental frequency response of electrohydraulic steering system - Alexander Mitov, Jordan Kralev, Ilcho Angelov ..................................................................... 400

Power and energy parameters of the inductor with an electromagnetic shield - Alexander Antipin, Vasiliy Frizen, Fedor Sarapulov, Maksim Kondratev ............................... 406

Investigation of a new technology of controlling electrical apparatus via a smart phone – Pavel Andreev, Bohos Aprahamian ....................................................................................... 410

Dynamic study of thermal characteristics of linear induction motors - F.Sarapulov, V. Frizen, I.Smolyanov, E. Shmakov ................................................................ 414

ix

The importance of standardization for risk management on Seveso site - Maja Ljubić, Božidar Raković, Ljubomir Dimitrov, Slavoljub Aleksić, Ivan Garvanov .......................................................................................... 419

Induction crucible furnace with dual frequency power supply - Vasiliy Frizen, Vladislav Luzgin, Alexander Koptyakov, Kirill Bolotin, Nikolay Tarchutkin ............................................................................................ 423

Research on the temperature field of a combined device for cooking Zanussi - Yanita Slavova, Maria Marinova, Tatyana Dimova ................................................................ 427

Influence of cold air plasma treatment on thermobonded PET nonwoven textile - Dilyana Gospodinova, Margarita Neznakomova, Peter Dineff .............................................. 431

Influence of the pole shapes on the force characteristics of a DC solenoid actuator - Dian Malamov, Ivan Hadzhiev, Ivan Yatchev ........................................................................ 435

Studying the magnetic field of three-phase induction device with split-phase - Georgi Zhelev, Marin Marinov, Maik Streblau ....................................................................... 439

Investigation of the exploitation modes of a special type magnetic separator - Tatyana Dimova, Mariya Marinova, Bohos Aprahamian, Marin Marinov ............................... 444

Simulation of the shading in photovoltaic systems - Ludmil Stoyanov, Nelly Cholakova ........................................................................................ 448

Modelling of magnetic concentrators in induction heating systems - Iosko Balabozov, Hartmut Brauer, Ivan Yatchev ................................................................... 453

Modelling of current sensor based on hall effect - Mehmet Sen, Iosko Balabozov, Ivan Yatchev, Ratcho Ivanov .............................................. 457

GPSS language as tool for reliability simulations - George Popov ....................................................................................................................... 461

Diversity in nature and technology – Tool for Increase the Reliability of Systems - George Popov, Kamelia Raynova ......................................................................................... 464

Indoor propagation of signals between wireless sensor nodes - Zlatan Ganev ......................................................................................................................... 467

Challenges for Bulgarian industrial small and medium sized enterprises to manage change effectively - Kiril Anguelov, Miglena Angelova .......................................................................................... 471

Criteria at selection of method for job implementation evaluation in high-tech enterprises - Kiril Anguelov, Alexanadar Ferdov ........................................................................................ 476

IoT Implementation for digital transformation of modern high-tech organizations - Roumiana Ilieva, Kiril Anguelov, Violeta Goleshevska .......................................................... 480

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Real-time model of switched reluctance drive based on a LUT magnetization curve for educational purposes - Dmitriy Savkin, Alecksey Anuchin, Vasiliy Kulmanov, Igor Gulyaev, Yuriy Vagapov ................................................................................................ 486

Concept for development of 2D virtual reality laboratory in electrical circuits: basic equipment - Boris Evstatiev, Katerina Gabrovska-Evstatieva ................................................................... 490

Development of model for automatic tutor in e-learning environment based on student reactions extraction using facial recognition - Salma Boumiza, Dalila Souilem, Alexander Bekiarski, Snejana Pleshkova .......................... 494

The methodology of risk evaluation for power equipment technical state assessment - Alexandra Khalyasmaa, Rustam Valiev, Viktor Bolgov ......................................................... 499

Processing Efficiency of Plasma-Aided Porous Media Finishing

Peter Dineff , Dilyana Gospodinova, and Ivaylo Ivanov

Department of Electrical apparatus, Faculty of Electrical engineering, TU-Sofia e-mail: dineff_pd@abv.bg, dilianand@abv.bg, ivo_pmg@abv.bg

Abstract— The efficiency of a plasma-aided finishing process e.g., surface impregnation can be predicted only by setting twobasic parameters of the real wood porous surface and the actual impregnating solution – surface free energy and surface tension. Successful finishing can be expected if the process efficiency pa-rameter take a positive value after a specified aging time of the plasma-chemical surface activation – 2 or 24 hours.

Keywords—processing efficiency, plasma-aided finishing; porous media, surface free energy, surface tension

I. INTRODUCTION

Plasma-aided technique can be used to facilitated the sur-face finishing rather the surface impregnation of porous media such as wood, wooden and cellulosic materials [1, 2, 3 and 4].

Porous materials with low surface free energy (SFE, σS) were subjected to plasma-chemical surface activation (functionaliza-tion) for increasing its SFE. So, this plasma-aided process can-not be applied out of the production line because SFE decreases quickly after an aging in ambient air [1].

a)

b)

Fig. 1. Schematic illustration of two model of wetting phenomena: a – the wetting phenomena on an ideal surface when a liquid drop is placed on a smooth, non-porous and rigid solid, both exposed to a gas/vapor, the system will be not in equilibrium and the liquid “wets out” the solid then the liquid exhibits a contact angle of zero against the solid i.e. so if σS > σSL + γL cos θ, then cos θ = 1 and sin θ = 0 (θ = 0°), and γL sin θ = 0 (Good, 1993); b - the wetting phenomena on a real surface can be involved by: i - the spreading of liquid over a solid surface; ii - the penetration or wicking of an impregnating liquid into a porous solid (Berg, 1993).

II. PARAMETER OF PLASMA ACTIVATION PROCESS

EFFICIENCY

Both SFE and liquid(-solid) surface tension (LST, γL) are es-sential in porous media finishing phenomena [1]. Plasma-chem-ical surface functionalization technique can be used to enhance surface finishing: materials with low SFE were subjected to ox-idative plasma pre-activation for increasing it, fig. 2.

Surfactants are compounds that can be used to lower the in-terfacial tension (IFE, σSL) between a liquid and a solid, fig. 1.

The higher the SFE of the solid (wood) substrate, the better the finishing including surface impregnation. The lower the LST, the better the result of finishing. In sum the difference between SFE and LST should be as large and positive: σS – γL > 0, (or σS > γL), the effective shall be the surface impregnation [1, 2 and 3].

In general, the following processing efficiency parameter (PSP) was found as [1]:

Fig. 2. Penetration-spreading parameter (PSP = σS - γL) of an effective plasma-aided surface impregnation processing at liquid surface free tension γL: PSP = σS - γL > 0 (σS > γL). A non-effective plasma-aided surface impregnation has PSP < 0. Relationship between the “solid-liquid” interfacial energy (IFE) σSL and the static contact angle θeq measured by Sessile Drop Technique. SFE (σS) – surface free energy, mJ/m2; LST (γL) – liquid surface tension, mN/m; Line of boundary equilibrium (in green) – a boundary line at PSP = σS - γL = 0 or σS = γL.

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γ LG.si

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Spreading Spreading

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2017 15-th International Conference on Electrical Machines, Drives and Power Systems (ELMA)

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Fig. 3. The use of distilled water (DW) as a test liquid does not carry adequate information on the effectiveness of the process of surface impregnation of European white pine (Pinus Sylvestris, Bulgaria) wood with an aqueous solution of a phosphorus flame retardant (FR). The effective mode (LF-XX-: APP-activation at 11, 13, 15, and 17 kV rms; 50 Hz) selection of plasma-aided wood impregnation can be determined by testing only with the used impregnating solution or the relationship between the “solid-liquid” interfacial free energy (IFE) σSL and static contact angle θeq measured by Sessile Drop Technique: σSL = PSP (θeq = 0). The all SFE values were determined for aging 2 hours in the theory of Wu.

FR- basic water impregnation liquid containing phosphor- and nitrogen flame retardant PhFR; SFE (σS) – surface free energy, mJ/m2; SFT (γL) – liquid surface free tension, mN/m; IFE (σSL) – interface “solid-liquid” free energy, mJ/m2. PSP – penetration-spreading parameter, mJ/m2.

“Plasma-aided wood finishing of a porous material will be more successful and this material will be more susceptible as the difference between its SFE σS and the LST γL or the so-called penetration-spreading parameter is positive: PSP = (σS - γL) > 0. If not, wetting and finishing (impregnating or penetration, drain-ing and spreading) problems will be occur.”

Plasma-aided surface impregnation process will be more successful and the material will be more susceptible as the PSP > 0 and better – PSP >> 0. This is the essence of the rule for obtaining effective plasma-enhanced impregnation process.

Fig. 4. The use of distilled water (DW) as a test liquid does not carry adequate information on the effectiveness of the process of surface impregnation of investigated bare (-K) and plasma-chemical, activated (-LF-XX) woods by an aqueous solution of a phosphorus flame retardant (PhFR). The surface impregnation and the plasma-aided surface impregnation are not effective: min σSL (θeq = 0°) = PSP and PSP < 0.

The maximum value of the IFE, at θeq = 90°, is equal to the value of wood SFE, σSL = σS, fig. 2 and 3. The minimum value of the “solid-liquid” interfacial energy (IFE, σSL) at θeq = 00 is equal to the value of PSP: σSL = PSP:

PSP= σS - γL = σSL + γL (cos θ – 1) > 0 (1)

Therefore, the requirement for effective finishing process

σS > σSL > PSP > 0 (2)

can be transformed into a new requirement for effectiveness, which already refers directly to IFE: “it is necessary for the en-tire range of variation of the static contact angle (00 ≤ θeq ≤ 900) the value of the IFE be greater than zero: σSL > 0” [1].

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Pin- : European white pineTza- : TzalamCed-: Mexican white cedarMah-: Mahogany caoba

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This means that the PSP accepts a value of IFE at θeq = 00 or in this way, the PSP has the physical nature of the IFE.

Fig. 5. Effective mode selection of APP- activation for an effective plasma-aided impregnation processing was found only for European white pine (Pin-LF-15), Mexican white cedar (Ced-LF-18), and Tzalam (Tza-LF-18): PSP > 0. No operative APP-activation mode for Mahogany caoba (Mah-LF-18) was found.

THE OBJECTIVE of this paper was to study the effect of APP- activation at industrial frequency (50 Hz) and critical volt-age of 15 (or 18) kV rms, after 2 and 24 hours of aging, on the wood surface impregnability monitored by PSP and the pro-cessing efficiency rule: PSP > 0.

The plasma-chemical surface functionalization ages rapidly on ambient air after APP-activation. For this reason, plasma-aided surface impregnation can not be used effectively “out of production line” е.g. after 2 or 24 hours of aging.

III. EXPERIMENTAL REZULTS AND DISCUSION

The development of an effective process of plasma-en-hanced surface impregnation passes through three stages:

• The first stage or selection of a plasma-chemical mode of surface activation (functionalization) that provide the necessary high SFE after an aging of 2 hours, fig. 2;

• The second stage or selection of an anionic micelle-form-ing water surfactant concentration to ensure the required minimum of LST (30 mJ/m2 > γL > 20 mJ/m2), fig 4.

• Third stage or selection of an effective APP- activation that provide the necessary high SFE after an aging of 24 hours and an adequate surfactant concentration, fig. 5;

Fig. 6. Effective mode selection of water impregnation solution of phosphoric flame retardant modified with anionic micelle-forming or water surfactant at concentration of 5 vol. % (FR-A5). The rule of processing efficiency was met for all applications of plasma-aided impregnation.

This experimental study was carried out on four kind of wood samples according the well known method, [1, 2, 3, and 4]; the plasma- chemical surface activation was carried out with atmospheric-pressure dielectric barrier discharge in a working gap of 6 mm and time of 60 sec.

On the first stage the PSP- testing (PSP = 8.2 mJ/m2 > 0) indicates that the voltage of the APPT of European white pine

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samples should be higher than 15 kV rms (σS = 54.2 kJ/m2) for an effective impregnation processing, PSP > 0, fig. 5.

Fig. 7. Effective mode of plasma-aided surface impregnation for all investigated wood samples – APP- activation at critical voltage of 18 (15) kV rms and surface impregnation by modified FR-impregnation solution (γL = 22.4 mJ/m2) with anionic micelle-forming surfactant at concentration of 5 vol. % (-FR-A5). The rule of processing efficiency was met only for all applications of plasma-aided impregnation with the modified FR-impregnation solution: PSP > 0.

The critical tension which fulfill the requirement PSP > 0 for other wood samples – Tzalam, Mexican white cedar and Ma-hogany caoba, was determined using the same procedure and it is 18 kV rms.

On the second stage the PSP-testing of European white pine indicates that the basic FR-impregnation solution (γL = 46.4 mJ/m2) and the modified FR-solution with less LST (γL = 22.4 mJ/m2) perform the rule of processing efficiency after 2 and 24 hours of aging, PSP > 0, fig. 6 and 7.

But this is not so for the other studied wood samples. The processing efficiency rule was performed for all application of plasma-aided surface impregnation, after 2 hours of aging, and

the use of modified impregnating FR-solution, γL = 22.4 mJ/m2: PSP > 0, fig. 6.

On the third stage the PSP-testing of all studied wood sam-ples indicates that the APP- activation at critical voltage and sur-face impregnation with the modified impregnating FR-solution (γL = 22.4 mJ/m2) satisfy the rule of processing effectiveness: PSP > 0, fig. 6.

This study proves our claim that the plasma-aided surface impregnation can be applied “out of the process line” after aging of one day or 24 hours between APP-activation and surface impregnation.

This study meets another issue which can be formulated so: “is it possible a simple drop test with destilled water to adequately replace the entire study conducted with the real im-pregnating FR-water solution”. The answer can be found in the information submitted to the two figures – fig. 1 and 2.

Distilled water has too high surface tension: γL = 72.3 >> 46.4 > 22.4 mJ/m2. Atmospheric pressure plasma activation cannot compensate it by increasing surface free energy σS, so be enforced rule process efficiency: σS < γL; PSP < 0, fig. 4.

The study of the APP-activation by distilled water carries quite different information about the outcome of plasma-aided surface impregnation with modified (γL = 22.4 mJ/m2) or not modified (γL = 46.4 mJ/m2) FR-solution. Normally it fails to predict effective plasma-aided impregnation, fig. 1 and 2.

Fig. 8. Atmospheric pressure plasma activation of wood samples by non-equi-librium DBD in asymmetric coplanar electrode system with one glass barrier (a), technological discharge characteristic “specific surface active power pa – voltage U”, and cathode-directed streamer mode (A) of plasma-chemical sur-face activation at industrial frequency (b). HVE - high-voltage electrode; GE – grounded electrode; DB – dielectric alka-line barrier.

All experimental studies relate to plasma-chemical surface activating the wood specimens in a specific burning mode of the

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dielectric barrier air discharge (DBD) at a maximum of the sur-face density of real power pa = 26 W/m2 (18 kV rms) and 8 W/m2 (15 kV rms) in asymmetric coplanar electrode system with 6 mm air gap. The effective operating modes of DBD at voltages above 13 kV rms (18.3 kV peak value) determine a surface density of real power above 4 W/m2, fig.8.

In a well known impregnation FR-solution with measured surface tension and depleted possibilities for its reduction, the only possibility for effective surface impregnation remains to be sought to increase the surface free energy by selecting a suitable plasma-chemical surface activation technology, fig. 9.

Fig. 9. The response of wood surface on plasma-chemical surface activation was complex but appears to be governed by its changed surface composition, especially by the introduced oxygen containing functionalities that increased the surface free energy and polarity.

The created new plasma-aided surface impregnation pro-cesses can find its wide application only if it can be predicted and managed so as to be executed the process efficiency rule: PSP > 0. The condition for this is the possibility of surface free energy measurement “in situ” out of the lab.

We believe that this approach can be successful, as the mar-ket now has the technical device for measuring the surface free

energy “in situ”. There is an innovative “mobile surface ana-lyzer” for measuring surface free energy with two liquids using new dispenser with two parallel drops with “one click” for direct analysis of the contact angle and the derived results of the sur-face free energy [1].

IV. CONCLUSION

The efficiency of a plasma-aided process of impregnation can be predicted only by setting the two basic parameters of the real porous wood surface and the actual FR-impregnating solu-tion – surface free energy and liquid surface tension. Successful finishing process, including effective surface impregnation, can be expected if the process efficiency parameter take a positive value (PSP > 0) after a prescribed aging time – 2 or 24 hours.

The evaluation of the finishing process effectiveness by in-strumentally determining first, the reduced by surfactants im-pregnation liquid surface tension, and second, the increased sur-face free energy after plasma-chemical surface activation, is able to predict the result of a plasma enhanced finishing process.

REFERENCES [1] P. Dineff, D. Gospodinova, and I. Ivanov, “Study on processing efficiency

of plasma-aided capillary impregnation of porous media through a penetration-spreading parametes,” X-th International Conference Advanced Manufacturing Technologies & 11th International Conference Advanced Materials and Operations “AMT&AMO 2016”, Sozopol, Bulgaria, Prossidings, pp. 54÷65, 26÷29 July, 2016.

[2] P. Dineff, I. Ivanov, and D. Gospodinova. “Efficiency processing parameter for plasma-aided surface impregnation: I. Penetration-spreading parameter”. XIX-th International Symposium on Electrical Apparatus and Technologies “SIELA 2016”, Bourgas, Bulgaria, 29 May÷01 June 2016. Electronic ISBN: 978-1-4673-9522-9, Print on Demand (PoD), ISBN: 978-1-4673-9523-6, DOI: 10.1109/SIELA.2016. 7542991

[3] P. Dineff, I. Ivanov, and D. Gospodinova. “Efficiency Processing Parameter for Plasma-Aided Surface Impregnation: II. Interfacial Energy, Adhesion and Capillary Pressure”. XIX-th International Symposium on Electrical Apparatus and Technologies “SIELA 2016”, Bourgas, Bulgaria, 29 May÷01 June 2016; Electronic ISBN: 978-1-4673-9522-9, Print on Demand (PoD), ISBN: 978-1-4673-9523-6, DOI: 10.1109/SIELA.2016.7542992.

[4] P. Dineff, I. Ivanov and D. Gospodinova. “Efficiency Processing Parameter for Plasma-Aided Surface Impregnation: III. Plasma Surface Activation”. XIX-th International Symposium on Electrical Apparatus and Technologies “SIELA 2016”, Bourgas, Bulgaria, 29 May÷01 June 2016; Electronic ISBN: 978-1-4673-9522-9, Print on Demand (PoD), ISBN: 978-1-4673-9523-6, DOI: 10.1109/SIELA.2016.7542993.

Low-Energy Surface (Low Surface Free Energy)

Better Spreading on Surface and Wicking into Porous Medium

Improved Surface Impregnation

Increased Polarity (Introduced by PST)

Increased Polar Component of Surface Free Energy

Decreased Contact Angle

Increased Surface Free Energy

Plasma Surface Activation (PSA)

Changed Wood Surface Composition

High-Energy Surface

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