Maintenance strategies to get the best performance from your generator

Hydrogen-cooled generators can experience hydrogen losses and reduced purity due to several factors, primarily related to the wear and tear of seals and other components. Over time, mechanical stresses can cause seals, such as hydrogen seals, to degrade, leading to leaks. Additionally, terminal studs are subject to constant mechanical forces, which can also lead to failure as the unit ages. High voltage bushings are another area where leaks commonly occur, and they should be thoroughly inspected during any planned maintenance activities. Regular inspections and timely replacement of worn components are critical in maintaining hydrogen purity and preventing efficiency losses. Addressing these issues promptly helps ensure the generator continues to operate safely and effectively. 

The seven F fleet is closely monitored for various reliability trends, particularly given its significant role in power generation. Common failure modes tracked include degradation in stator and rotor installations, shorted turns, main terminal stud failures, and issues related to contamination and collector ring flashovers. GE Vernova utilizes this data to develop comprehensive reliability models that inform maintenance strategies and production levels. By analyzing these trends, GE can better anticipate maintenance needs and adjust production of critical components like stator bars and exchange rotors to meet demand. This proactive approach ensures that resources are available to address these issues, minimizing downtime and maintaining operational performance.

Online stray flux monitoring is an invaluable tool for forecasting the health of generators. By employing flux probe sensors, plants can collect data on the generator's magnetic field ahead of scheduled outages. This data is critical for identifying potential issues such as turn shorts, which allows maintenance teams to plan for necessary repairs and procure replacement materials in advance. Timely data collection and analysis help ensure that maintenance activities are conducted efficiently, reducing the risk of unexpected failures. Furthermore, as demand for maintenance services increases, effective planning using stray flux monitoring data helps manage shop capacity and staffing needs, ensuring timely and effective repairs. 

The life expectancy of a generator before a rewind is necessary can vary significantly based on factors such as model type and operational conditions. On average, generators may require a rewind after approximately 20-25 years of service, although base-loaded units often last longer than those operating under more cyclic conditions. Operational stress, environmental factors, and maintenance practices all contribute to the wear and tear of generator components. It's essential to conduct regular assessments and consultations with GE Vernova to determine the best timing for a rewind. Proactively addressing potential issues before they lead to failures can extend the life of the generator and enhance overall reliability. 

We recommend that newer generator components, including rotor retaining rings, undergo non-destructive testing before reaching 30 years of service or accumulating 10,000 starts. Older units, particularly those over 25 years old, may have different design parameters requiring tailored inspection recommendations. It's advisable to consult GE product engineering for specific guidance on these units, especially if there has been a shift in operational profile from baseload to cyclic or peaking operations. The GEK 103566M document provides detailed recommendations on the necessary non-destructive tests to ensure the continued reliability of these components. Regular inspections and adherence to these guidelines help mitigate the risk of unexpected failures and extend the operational life of the generator. 

While technically feasible, rewinding generator rotors in the field for large turbine generators is generally impractical due to the complexity and cost involved. Onsite rotor rewinds require significant labor, specialized tooling, and a controlled environment, often making them several times more expensive than shop-based rewinds. Additionally, onsite work presents challenges in handling unexpected repairs, such as machining needs or crack removal, which are more efficiently managed in a shop setting. As a result, GE Vernova has not conducted onsite rotor rewinds in many years, favoring the efficiency and cost-effectiveness of shop-based solutions. Transporting the rotor to a dedicated facility ensures a higher quality of repair and reduces the overall risk of complications. 

The ongoing energy transition significantly influences generator maintenance strategies, primarily due to changes in operational profiles. Many generators are shifting from steady base-load operations to more cyclic patterns with frequent starts and stops, increasing thermal and mechanical stress. This transition necessitates enhanced maintenance strategies to manage the additional wear and tear on generator components. Units approaching the 20-year mark, in particular, require careful monitoring and maintenance planning to ensure continued reliability. A proactive approach to maintenance, including regular inspections and the implementation of upgrades where necessary, is crucial in adapting to these operational changes and maintaining generator performance. 

A rotor earth fault is a serious issue that should never be ignored, as it poses a significant risk to generator operation. While a generator can technically operate with a single ground fault, the development of a second fault can lead to catastrophic failure. Such a failure would likely necessitate extensive repairs, including potential rotor and stator rewinds, alongside other costly repairs. Therefore, operating with a known ground fault is not recommended. Immediate attention and corrective action are essential to prevent further damage and ensure the safety and reliability of the generator. Regular monitoring and maintenance can help detect and address potential faults before they escalate.

Preparing for either a generator rotor or stator rewind during an inspection involves a thorough understanding of the generator's current condition and maintenance history. The extent of the remaining inspection and testing will depend on the type of outage planned, with more comprehensive inspections possible when the rotor is removed. Collecting data from previous outage reports, coupled with the generator's age and operational profile, helps guide future maintenance planning. Even if a rewind is not immediately planned, understanding the unit's condition allows for better preparation for future outages. Proactively planning for potential rewinds and allocating resources accordingly can lead to more efficient maintenance and reduced downtime. 

The decision to undertake a stator rewind versus returning to service when partial discharge is observed depends on several factors, including the extent of the damage and the availability of materials. Partial discharges can indicate insulation breakdown, which may necessitate immediate attention if severe. In some cases, temporary repairs or patches can be implemented to maintain operation until a more convenient time for a full rewind. The availability of replacement materials and the potential impact on operational schedules are critical considerations. Effective planning and regular maintenance are essential to minimize disruptions and optimize generator performance. Consulting with GE experts can provide valuable insights into the best course of action based on the specific circumstances.

To address the anticipated increase in generator maintenance needs, we are actively expanding our inventory and support programs. This includes increasing the production of critical components such as stator bars, exchange rotors, and rotor and stator rewind parts. By maintaining robust inventory levels, GE aims to meet the growing demand for generator upgrades and maintenance services. These efforts are designed to support both planned and unplanned maintenance activities, ensuring that resources are readily available when needed. Additionally, GE's strategic inventory management helps mitigate potential delays and enhances the ability to respond promptly to customer needs.

Proactive stator rewinds are generally recommended for units identified as high-risk based on reliability data and operational history. Conducting a rewind before a failure occurs is typically less expensive and disruptive than addressing an unexpected outage. Planning for a proactive rewind allows for better resource allocation and potentially spreading costs by pre-purchasing components or exchange fields in advance. This approach also provides the flexibility to schedule maintenance activities during less critical operational periods, minimizing the impact on production.   
 
A cost-effective time to perform proactive rewinds is when there is an already scheduled major outage on the turbine-gen train.  This maximizes the labor and tooling costs and minimizes the overall downtime compared to separate outage events.

Collaboration with GE Vernova representatives can help identify the optimal timing for a proactive rewind, ensuring continued generator reliability and performance. 

The Generator Health Monitoring (GHM) system plays a crucial role in maintaining generator performance by providing comprehensive insights into the generator's condition. GHM systems collect and analyze data from various sensors, offering a detailed assessment of the generator's health. By identifying potential issues early, the GHM system enables more informed maintenance planning and decision-making. The system's flexibility allows for continuous or periodic monitoring, depending on the generator's age and operational profile. Regular data review and analysis, in collaboration with engineering teams, help ensure timely maintenance interventions, reducing the risk of unexpected failures and optimizing operational efficiency. 

Yes, GE Vernova's rotor exchange program includes 324 generator rotors, offering significant advantages for both planned and unplanned outages. Several generator models, both legacy GE and Alstom, are available for each outage season.  The program is designed to facilitate shorter outage durations by providing readily available replacement rotors, minimizing downtime and associated costs. As demand for rotary windings increases, GE continues to expand its rotor exchange inventory to meet customer needs effectively. Participating in the exchange program ensures access to high-quality, pre-tested rotors, enhancing generator reliability and performance. This proactive approach to maintenance and resource management supports the efficient operation of power generation facilities.

Retaining rings, particularly those made from older 18-5 material, are prone to cracking and should be proactively replaced to prevent potential failures. Generators with these older rings may face restrictions on high-speed balancing and other operational limitations. For rings made from 18-18 material, periodic assessments are recommended to ensure they remain free from indications such as cracking or arcing. Regular inspections and maintenance activities help identify potential issues early, allowing for timely replacement and avoiding costly downtime. GE's maintenance guidelines provide detailed recommendations on retaining ring assessments and replacements, ensuring continued generator reliability.

Blowing compressed air into generator rotors, especially when they are outside the stator, is generally not recommended as a cleaning practice. While it might seem like a straightforward way to remove loose contaminants, there is a significant risk of driving foreign materials deeper into winding slots and cooling passages. Such actions can exacerbate contamination issues and potentially lead to further operational problems. Controlled cleaning methods, informed by thorough inspections and conducted in specific circumstances, are preferable. Proper maintenance practices, including hand cleaning and inspection, ensure effective cleaning without introducing additional risks to the generator's performance.

Transitioning from baseload to peaking operation introduces several reliability challenges due to increased thermal and mechanical stress on generator components. Common issues observed include rotor shorted turns, main lead cracking, and migration of slot contents, all of which can impact generator performance and reliability. Additionally, the increased frequency of starts and stops associated with cyclic operation can lead to accelerated wear and tear. GE provides solutions to address these conditions, often implemented during rotor rewinds or through the use of exchange rotors. Proactive maintenance and upgrades help mitigate the impact of these operational changes and ensure continued reliability. 

Older generators may be recommended for rewind even if they pass standard tests due to their position on reliability curves, which indicate increasing risk over time. While some units, especially those operated in baseload conditions, can exceed the average lifespan, proactive planning for rewinds is advisable. Regular maintenance activities, such as stator re-wedging and rotor inspections help maintain performance, but planning for potential rewinds ensures readiness for future needs. GE's reliability data and expertise provide valuable insights into the optimal timing for rewinds, balancing operational needs with long-term maintenance strategies. 
 
It’s also worth noting that many of our older models do not have the same level of strategic inventory, so downtime may be significant.

During generator maintenance, a comprehensive suite of tests is conducted to assess the condition of both stator and field components. For the stator, tests include insulation resistance, polarization index, copper resistance, wedge tightness mapping, and stator core assessments. Field tests often involve winding insulation resistance, copper winding resistance, AC impedance tests, and collector stud inspections, particularly for hydrogen-cooled units. These tests provide critical data on the generator's health, guiding maintenance planning and decision-making. Detailed recommendations for these tests are available in GE's maintenance documentation, ensuring that maintenance activities are thorough and effective.