EXPERIMENTAL STUDY OF THE EFFECTS OF A CONSTANT AND VARIABLE ELECTRIC FIELDS ON THE STRENGTH PROPERTIES OF THE BLADE STEEL SURFACE LAYER

Author

Andrey V. Nechaev, A. Podgorny Institute of Mechanical Engineering Problems of NASU (2/10, Pozharsky St., Kharkiv, 61046, Ukraine), e-mail: nechaev.an98@gmail.com , ORCID: 0000-0001-6586-4713

Abstract

It is known that in wet steam turbines the wet steam flow is electrified when passing through the turbine flow path. In this, the mutual electrification of the condensed moisture flow and flow path surfaces occurs. Until now, experts in the field of steam turbine operation have been aware of the problem of electrical phenomena in flow paths in terms of electroerosion phenomena associated with the accumulation of electric charges on the rotors. Similar phenomena in the working fluid flow are less known. As a result of the research conducted at IPMash NAS of Ukraine, it has been established that the electrification of the wet steam flow leads to the formation of a volume charge in the flow path, which can have a significant value (up to 10^–3 C/m³) and exert a significant effect on the working processes in the turbine and condenser. The volume charge of the steam flow in the flow path also generates electric fields with constant and variable components. As a result, parts and assemblies of the flow path may be under the action of an electric field. In particular, turbine blades may be in the electric field of the volume charge of the working fluid. As is known, the impact of an electric field can reduce the strength of the metal surface layer. Therefore, an experimental study of the effect of electric fields, similar to those occurring in the turbine flow path, on the strength properties of blade steel is an important task. The article presents the results of the experimental determination of the microhardness of the 15H11MF blade steel surface layer exposed to a constant or variable electric field. It is shown that its effect significantly reduces the microhardness of the blade steel surface layer. Since the strength of the surface layers of the working blades is one of the most important characteristics of their erosion resistance, the effect of the electric field of the steam flow volume charge can be one of the negative factors that reduce the erosion resistance of turbine blade surfaces. Based on the obtained results, it can be concluded that it is necessary to further improve the system for neutralizing the accumulation of electric charges in the flow path, which currently mainly performs the function of turbine rotor grounding.

Keywords: microhardness, electric field, blade steel.

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References

1. Tarelin, A. A., Sklyarov, V. P., Veres, O., & Surdu, N. V. (1999). Elektrofizicheskiye yavleniya v parovykh turbinakh [Electrophysical phenomena in steam turbines]. teplotekhnika − Industrial Heat Engineering, no. 4–5, pp. 98–102 (in Russian).
2. Tarelin, A. A., Sklyarov, V. P., & Kryzhenko V. P. (2000). Osobennosti izmereniya obyemnoy plotnosti zaryadov vo vlazhnom parovom potoke turbiny [Features of measurement of the bulk density of charges in a wet turbine steam flow]. Problemy mashinostroyeniya − Journal of Mechanical Engineering, vol. 3, no. 1, pp. 11–16 (in Russian).
3. (1998). Electrostatic charge measurements in the turbine – condenser connection of Salt River Project’s Navajo Generating Station Unit 3, Electric Power Research Institute, Palo Alto, CA, 1998. EPRI WO3849-01.
4. Tarelin, A. A. & Sklyarov, V. P. (2012). Parovyye turbiny: elektrofizicheskiye yavleniya i neravnovesnyye protsessy [Steam turbines: Electrophysical phenomena and non-equilibrium processes]. Petersburg: Energotekh, 292 p. (in Russian).
5. Tarelin, A. A., Nechayev, A. V., & Khinevich, A. Ye. (2017). Elektromagnitnyye izlucheniya v vykhlopnoy chasti parovoy turbiny [Electromagnetic radiations in the exhaust part of a steam turbine]. Problemy mashinostroyeniya − Journal of Mechanical Engineering, vol. 20, no. 2, pp. 18–21 (in Russian).
6. Zima, I., Nechayev, A. V., & Bogdanov, G. F. (1999). Rotornaya spektroskopiya potokov bolshikh energiy [Rotor spectroscopy of high-energy flows]. Vestn. Khark. politekhn. un-ta – Bulletin of the National Technical University “KhPI”, no. 75, pp. 93–97 (in Russian).
7. Orlova, D. V., Filipyev, R. A., & Danilov, V. (2012). O vozmozhnykh prichinakh vliyaniya elektricheskogo potentsiala na soprotivleniye metallov mikroindentirovaniyu [Possible causes of the influence of the electric potential on the resistance of metals to microindentation]. Izv. vuzov. Chernaya metallurgiya – Izvestiya Vuzov. Black Metallurgy, no. 10, pp. 66–67 (in Russian).
8. Orlova, D. V., Danilov, V. I., Zuyev, L. B., Kolesnik, A. S., & Dulbeyeva, O. N. (2012). O vliyanii elektrostaticheskogo polya na mikrotverdost monokristallov tsinka [Effect of the electrostatic field on the microhardness of zinc single crystals]. Obrabotka metallov – Metal Finishing, no. 4 (57), pp. 98–102 (in Russian).
9. Zuyev, L. B, Danilov, V. , & Orlova, D. V. (2013). Kharakter izmeneniya mikrotverdosti ploskosti (0001) monokristallov Zn pod deystviyem elektrostaticheskogo polya i vozmozhnaya prichina etogo effekta [The nature of the microhardness of the (0001) plane of Zn single crystals under the action of an electrostatic field and a possible cause of this effect]. Fizika tverdogo tela − Physics of the Solid State, vol. 55, no. 2, pp. 313–317 (in Russian).
10. Zuyev, L. B., Danilov, V. I., & Konovalov, S. V. (2009). O vliyanii kontaktnoy raznosti potentsialov i elektricheskogo potentsiala na mikrotverdost metallov [Effect of contact potential difference and electric potential on the microhardness of metals]. Fizika tverdogo tela − Physics of the Solid State, vol. 51, iss. 6, pp. 1077–1080 (in Russian).
11. Markovets, M. P. (1979). Opredeleniye mekhanicheskikh svoystv metallov po tverdosti [Determination of the mechanical properties of metals by hardness]. Moscow: Mashinostroyeniye, 191 p. (in Russian).

Received 29 November 2018

Published 30 March 2019