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research-article

Measurement and evaluation of shaft torsional vibrations using shaft instantaneous angular velocity

[+] Author and Article Information
Jindrich Liska

University of West Bohemia, NTIS - European Centre of Excellence, Pilsen, Czechia
jinliska@ntis.zcu.cz

Jan Jakl

University of West Bohemia, NTIS - European Centre of Excellence, Pilsen, Czechia
jjakl@ntis.zcu.cz

Sven Kunkel

University of West Bohemia, NTIS - European Centre of Excellence, Pilsen, Czechia
kunkel@ntis.zcu.cz

1Corresponding author.

ASME doi:10.1115/1.4041006 History: Received June 26, 2018; Revised July 09, 2018

Abstract

Online evaluation of possible failures of a turbine is a key factor for a successful long-term turbine operation. Fluctuations of generator air-gap torque, caused for example by non-stationary conditions of electrical power grid, influence shaft torsional vibrations as well as rotating blades vibrations. Symptoms of shaft torsional vibrations are not measurable by normally used relative shaft vibrations sensors, so special measurement must be used. The direct consequence of shaft torsional vibrations is local acceleration or deceleration of shaft circumference when it is measured by a stationary sensor. This article deals with a measurement method using an optical probe measuring the passage of black and white stripes of a zebra tape which is stuck on the rotor. The shaft torsional vibrations manifest themselves as a phase modulation of the optical probe output signal, so the sampling rate influence the achievable resolution of the calculated shaft vibrations. The presented method for the calculation of the shaft torsional vibrations is based on the evaluation of shaft instantaneous angular velocity. The advantage of this method is a direct compensation of possible non-regular geometry of the zebra tape. The analysis of shaft torsional vibrations evaluation using this method is supplemented by two case studies from the authors' current work.

Copyright (c) 2018 by ASME
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