Using Intrinsic 3rd Harmonics for Large Synchronous Generator Insulation Fault Condition Monitoring

As the most expensive electrical equipment in the power industry, the operational health of large synchronous generators is a primary concern for generator owners. This concern has become more pressing as many owners seek to extend the lifespan of their aging generation facilities. With the construction of numerous data centers and the subsequent rise in electricity demand, some generator owners are even considering restarting retired units. As a result, effectively monitoring the condition of large synchronous generators with minimal effort is a significant challenge. Despite the development and application of numerous testing and monitoring techniques over the past century, unexpected generator failures continue to occur. Detecting insulation failures in large machines remains a complex issue and an area of active research. The primary objective of this project is to propose a simple and effective method for detecting compromised insulation in large synchronous generators. While Partial Discharge (PD) monitoring has garnered significant research interest, it is well understood that synchronous machines may experience PD activity throughout their lifespan without catastrophic failure. A review of conventional testing methods highlights conductivity as the most critical and reliable indicator of insulation degradation. This research discusses the classic insulation model and its degradation mechanisms. Test data collected from numerous units during outages support the importance of conductivity in identifying degraded insulation systems. This project proposes a novel technique for detecting generator stator insulation faults using intrinsic third harmonics. Based on two-port network theory, a mathematical model is derived and presented in this thesis. Data from offline experiments has been analyzed to verify the technique’s effectiveness. Additionally, online data collected from several generator units has been reviewed and analyzed. Both offline experimental data and online operating data confirm the proposed technique’s efficacy. Online PD test data and offline inspection findings further validate the technique's predictions. To evaluate the technique’s sensitivity to inter-turn faults in salient field poles, third harmonic current was injected into suspected poles, which showed significant overheating and potential inter-turn short circuits. Conventional voltage drop methods were compared with recurrent surge oscillograph results, as well as the new approach involving the injection of higher-frequency currents (3rd and 6th harmonics). Analysis of the test results revealed the challenge of pinpointing the exact location of field winding faults, even when they are clearly present. The findings demonstrate that injecting a 180 Hz current into the field winding yields superior performance in identifying faulty poles. For monitoring stator insulation systems, the proposed method can be easily integrated into a standard digital relay without the need for additional external hardware. Although this research has shown the potential of using intrinsic third harmonic signals for online monitoring of generator winding faults and for offline detection of insulation faults in salient pole windings, there are still several opportunities to further develop and enhance the technique’s applicability and reliability. Building on the findings and limitations of this study, the future work and recommendations are outlined.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Discipline thesis:degree_discipline

Engineering – Electrical & Computer

Grantor

Schulich School of Engineering

Year dc:date.issued

2025

Author dc:creator

• Lu, Yongdong

Advisors dc:contributor.advisor

• Knight, Andy
• Malik, Om P.

Committee members dc:contributor.committeemember

• Knight, Andy
• Malik, Om P.
• Gray, Philippe
• Nowicki, Edwin Peter
• Belostoski, Leonid
• Al-Haddad, Kamal

• Generator
• Insulation degradation
• Ground fault
• Inter-turn fault
• Split-phase fault
• Third harmonics
• Partial discharge
• Power factor
• Capacitance
• Two-port network
• Nesting
• Online monitoring
• Degradation mechanism
• TEAM
• Thermal
• Elextrical
• Ambient
• Mechanical
• Offline testing
• Innovative technique
• Salient pole

Statement dc:rights

• Unless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

en

DOI

https://dx.doi.org/10.11575/PRISM/50683

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:1880/123141