By Sorin-Ioan Lupa
This article has been evaluated and edited in accordance with reviews conducted by two or more professionals who have relevant expertise. These peer reviewers judge manuscripts for technical accuracy, usefulness, and overall importance within the hydroelectric industry.
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| The 17-unit 103-MW Les Cedres hydrolectric facility in Quebec, Canada, which rests on bedrock outcrops, was designed as a function of the site’s low head and high flow rate. |
This article describes recent developments in managing the delicate balance between traditional hydraulic governor systems and new requirements. Owners’ decisions regarding operation, maintenance and security are affected by these new requirements. In addition, the new ways owners often must operate generating units, with many more unit starts and stops per day and many power plants being controlled remotely, influences the need to maintain this balance.
Challenges related to existing equipment
As Figures 1 and 2 (on page 37) indicate, Hydro-Quebec’s oldest hydropower plants or plant components are close to 100 years old, with the average about 35 years old.
Little of the hydraulic equipment is modular. In addition, the design criteria are obsolete and not optimal for use with electronic speed governors or electrical interfaces. This will be even more problematic should speed governor standardization be extended to validation of the hydraulic equipment criteria and performance as well.
With older equipment, typically normal wear results in internal hydraulic leakage, friction forces increase and pump flow decreases.
Challenges related to new requirements
Today, units are operated with more startups and shutdowns than in the past. Units used to be cycled about once a month before 1990, but since 2000 they could be cycled several times a day. The frequent start/stop operation causes oil foaming and equipment damage, resulting in premature component wear. (Note: Some studies indicate newer governors require more maintenance, due to aggressive operating scenarios, than older governors. However, at Hydro-Quebec we have not found that older units are always necessarily “better” in this aspect.)
One often-used practice is to increase unit power output by over-wide opening of wicket gates, which increases servomotor stroke and consequently oil-receiver volumes required to achieve the same margins.
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| Hydro-Quebec saw its largest amount of units commissioned between 1965 and 1995. |
New functions often have to be integrated into existing hydraulic systems and although the amount of facilities is proprietary information, since 2000, an increasing amount of power plants are remotely operated. In the case of a governor failure, sending technicians to remotely operated facilities, depending on their geographical location, could mean considerable delay before a person reaches the plant.
Modern project management that is heavily objective-based, related to efficiency and production, reduces maintenance windows. Additionally, government regulations require greater levels of security and safety for operating teams, the public and the equipment. For example, agencies similar to the Nuclear Energy Regulatory Commission, IEEE (Institute of Electrical and Electronics Engineers), and IEC (International Electrotechnical Commission) require:
– Emergency shutdowns be better- controlled;
– The grid be more reliable; and
– The grid be more stable, with steady parameters, no oscillation and constant frequency.
Intelligent monitoring
The method Hydro-Quebec experts recommend to address the issue of adapting existing older equipment to oncoming requirements is the result of collaboration with other hydro project owners, as well as equipment suppliers.
In the past, hydraulic speed regulation was analyzed periodically, as shown in Figure 3, and design evolution was not necessarily considered. Traditional maintenance programs include some collection of data for subsequent analysis by specialists.
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| Hydro-Quebec’s installed capacity experienced its greatest growth between 1952 and 2008. |
The proposed method takes advantage of the tremendous recording and analysis capabilities of today’s computer systems. Figure 4 (on page 40) shows in red the key elements of the new strategy.
The key steps of this strategy are described below.
Generic model
A generic model is developed that takes into account the usual design parameters for a hydraulic governor, as well as new requirements arising from current operating criteria.
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| This figure indicates hydraulic speed regulation periodic analyzation methodology for Hydro-Quebec’s traditional maintenance program. |
The generic model is deterministic, based on common design criteria, the laws of thermodynamics and fluid dynamics, international standards and internal guidelines and regulations. The main purpose of the model is to guide design and decision-making, allowing criteria to be modified and adapted to current needs.
Customized model
Next, the generic model is customized for each installation, depending on specific operating requirements, the particularities of the unit and operational limitations.
The result is the starting point and reference for all units with the same characteristics. Once validated, this customized model provides a realistic signature for unit behavior under current constraints and performance forecasting.
Validation tests
On-site tests are performed to validate the customized model and confirm that the equipment operates properly.
The main features of the customized model are validated, checking system performance and predicted values for the following:
– Instrument settings and operating ranges – normal operation limits;
– Security margin for protections; and
– Residual margin for fail-safe behavior.
Regular inspections
Regular inspections of equipment are recommended to monitor predicted parameters, so the model can be updated and forecasts can be adjusted accordingly. This can also be done during technical audits or regular maintenance.
Intelligent monitoring
Finally, the signature obtained is formalized and the information is transferred to an intelligent monitoring system. The software is sustained by appropriate hardware, which ensures acquisition and continuous data processing for comparison with measured values so current equipment status can be determined.
A list of the main monitoring parameters was drafted for each major hydraulic component and each generating unit operating mode: startup; normal operation; and normal or emergency shutdown – not in use.
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| Shown in red, elements in this figure detail the proposed method to take advantage of the recording and analysis capabilities of current computer systems, which are key elements of the new strategy. |
Instrument measurement values are thus compared with reference values based on the formalized equipment signature.
The difference between expected and real values provides degradation status of equipment and indicates required proactive maintenance. Figure 4 indicates this also gives owners guidance for measures to be taken and helps prevent unexpected failures.
Financial spinoffs
There are positive financial spinoffs of the recommended strategy. The main benefits of the new strategy are:
– Facilitates collaboration among internal and external stakeholders;
– Ensures successful knowledge transfer;
– Facilitates integration of future requirements;
– Facilitates tracking the effects changing operating requirements have on equipment life and degradation;
– Optimizes maintenance and corrective measures; and
– Extends equipment life, reduces risks and increases security/safety.
We also see a business opportunity stemming from the following:
– Stepped-up speed regulation efficiency and blade synchronization for Kaplan turbines, resulting in greater overall efficiency of unit operation;
– Shorter periods of unavailability by preventing unscheduled shutdowns and unsuccessful start-ups; and
– Improved planning of related activities (cost savings).
Sorin-Ioan Lupa is senior engineer at Hydro-Québec in charge of turbine mechanical expertise for governors and hydraulic systems.
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