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Comparative Analysis of Shaft Voltage Harmonic Characteristics in Large-Scale Generators: OEM and Excitation System Comparisons.

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Title: Comparative Analysis of Shaft Voltage Harmonic Characteristics in Large-Scale Generators: OEM and Excitation System Comparisons.
Authors: Mailula, Katudi Oupa1 (AUTHOR), Saha, Akshay Kumar1 (AUTHOR) saha@ukzn.ac.za
Source: Energies (19961073). Dec2025, Vol. 18 Issue 23, p6128. 22p.
Subjects: Fast Fourier transforms, Electric generators, Electric power systems, Condition-based maintenance, Harmonic analysis (Mathematics)
Abstract: This study presents a comparative harmonic analysis of shaft voltage waveforms in large-scale steam turbine generators, emphasizing the influence of excitation system topology and generator design on spectral behavior. Using high-resolution Fast Fourier Transform (FFT) analysis of healthy-state data from five hydrogen-cooled turbo-generators (600–846 MW), this work identifies consistent harmonic patterns and their diagnostic value. Generators with brushless excitation systems exhibit dominant harmonics at 150 Hz (3rd), 250 Hz (5th), and 400 Hz (8th), whereas static-excited units show a 150 Hz (3rd) and 450 Hz (9th) pattern. These findings confirm that excitation architecture, rather than OEM design, governs the shaft voltage harmonic "fingerprint." The persistent 150 Hz component across all machines serves as a stable indicator of generator condition. The results provide a practical reference for establishing harmonic-based baselines to enhance early fault detection and predictive-maintenance strategies in power station generators. This work contributes new comparative insights linking excitation topology to harmonic behavior, enabling improved condition monitoring across diverse generator fleets. This study establishes harmonic profiles defined as the amplitude, frequency, and relative proportion of key harmonic components in the shaft voltage spectrum obtained via FFT analysis to serve as spectral fingerprints representing the generator's health condition. [ABSTRACT FROM AUTHOR]
Copyright of Energies (19961073) is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Comparative Analysis of Shaft Voltage Harmonic Characteristics in Large-Scale Generators: OEM and Excitation System Comparisons.
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  Data: <searchLink fieldCode="JN" term="%22Energies+%2819961073%29%22">Energies (19961073)</searchLink>. Dec2025, Vol. 18 Issue 23, p6128. 22p.
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  Data: <searchLink fieldCode="DE" term="%22Fast+Fourier+transforms%22">Fast Fourier transforms</searchLink><br /><searchLink fieldCode="DE" term="%22Electric+generators%22">Electric generators</searchLink><br /><searchLink fieldCode="DE" term="%22Electric+power+systems%22">Electric power systems</searchLink><br /><searchLink fieldCode="DE" term="%22Condition-based+maintenance%22">Condition-based maintenance</searchLink><br /><searchLink fieldCode="DE" term="%22Harmonic+analysis+%28Mathematics%29%22">Harmonic analysis (Mathematics)</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: This study presents a comparative harmonic analysis of shaft voltage waveforms in large-scale steam turbine generators, emphasizing the influence of excitation system topology and generator design on spectral behavior. Using high-resolution Fast Fourier Transform (FFT) analysis of healthy-state data from five hydrogen-cooled turbo-generators (600–846 MW), this work identifies consistent harmonic patterns and their diagnostic value. Generators with brushless excitation systems exhibit dominant harmonics at 150 Hz (3rd), 250 Hz (5th), and 400 Hz (8th), whereas static-excited units show a 150 Hz (3rd) and 450 Hz (9th) pattern. These findings confirm that excitation architecture, rather than OEM design, governs the shaft voltage harmonic "fingerprint." The persistent 150 Hz component across all machines serves as a stable indicator of generator condition. The results provide a practical reference for establishing harmonic-based baselines to enhance early fault detection and predictive-maintenance strategies in power station generators. This work contributes new comparative insights linking excitation topology to harmonic behavior, enabling improved condition monitoring across diverse generator fleets. This study establishes harmonic profiles defined as the amplitude, frequency, and relative proportion of key harmonic components in the shaft voltage spectrum obtained via FFT analysis to serve as spectral fingerprints representing the generator's health condition. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Energies (19961073) is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.3390/en18236128
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      – Code: eng
        Text: English
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        PageCount: 22
        StartPage: 6128
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      – SubjectFull: Fast Fourier transforms
        Type: general
      – SubjectFull: Electric generators
        Type: general
      – SubjectFull: Electric power systems
        Type: general
      – SubjectFull: Condition-based maintenance
        Type: general
      – SubjectFull: Harmonic analysis (Mathematics)
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      – TitleFull: Comparative Analysis of Shaft Voltage Harmonic Characteristics in Large-Scale Generators: OEM and Excitation System Comparisons.
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            – D: 01
              M: 12
              Text: Dec2025
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              Y: 2025
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