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Wear and tear on hydro power turbines: influence from primary frequency control
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)ORCID iD: 0000-0003-1638-0792
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
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2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 87, 88-95 p.Article in journal (Refereed) Published
Abstract [en]

Nowadays the importance and need of primary frequency control of hydro power units are significantly increasing, because of the greater proportion of intermittent renewable energy sources and more complex structure of power systems. It brings a problem of increasing wear and tear of turbines. This paper studies this problem by applying numerical simulation and concise theoretical derivation, from the point view of regulation and control. Governor models under opening and power feedback mode are built and validated by measurement data. The core index, guide vane movement, is analyzed based on ideal sinusoidal frequency input and real frequency records. The results show the influences on wear and tear of different factors, e.g. governor parameters, power feedback mode and nonlinear governor factors.

Place, publisher, year, edition, pages
2016. Vol. 87, 88-95 p.
National Category
Ocean and River Engineering
Identifiers
URN: urn:nbn:se:uu:diva-262747DOI: 10.1016/j.renene.2015.10.009ISI: 000367759500008OAI: oai:DiVA.org:uu-262747DiVA: diva2:855160
Available from: 2015-09-18 Created: 2015-09-18 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Dynamic Processes and Active Power Control of Hydropower Plants
Open this publication in new window or tab >>Dynamic Processes and Active Power Control of Hydropower Plants
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Hydro-electricity plays an important role in the safe, stable and efficient operation of electric power systems. Frequency stability of power systems refers to the ability to maintain steady frequency following a severe system upset resulting in a significant imbalance between generation and load. In order to suppress power grid frequency fluctuations, generating units change their power output automatically according to the change of grid frequency, to make the active power balanced again. This is the primary frequency control (PFC). PFC of electrical power grids is commonly performed by units in hydropower plants (HPPs), because of the great rapidity and amplitude of their power regulation.

A hydropower generation system is a complex nonlinear power system including hydraulic, mechanical, electrical and magnetic subsystems. Nowadays, the size of HPPs and the structure complexity of systems have been increasing, especially in China. The proportion of electricity generated by intermittent renewable energy sources have also been growing. Therefore, the performance of HPPs in terms of frequency control is more and more important. The research on control strategies and dynamic processes of HPPs is of great importance. The frequency stability of hydropower units is a critical factor of power system security and power quality. The power response time for evaluating the frequency regulation quality, is also a key indicator.

In recent years, there is a tendency that the new turbines experience fatigue to a greater extent than what seem to be the case for new runners decades ago, due to more regulation movements caused by increasingly more integration of intermittent renewable energy sources. In some countries, as in Sweden, PFC is a service that the transmission system operator buys from the power producers. In other countries, as in Norway and China, there is also an obligation for the producers to deliver this service, free of charge. However, there are costs related to this, e.g. due to design constraints and auxiliary equipment when purchasing a new unit or system, and due to wear and tear which affects the expected life time and maintenance intervals. Hence the specific research on wear and tear of hydro units due to PFC is exceedingly necessary. 

Place, publisher, year, edition, pages
Uppsala: Institutionen för teknikvetenskaper; Elektricitetslära, 2015. 53 p.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-262768 (URN)
Presentation
2015-10-19, Polhemsalen, Ångströmlaboratoriet (Ång/10134), Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2015-10-14 Created: 2015-09-20 Last updated: 2015-10-14Bibliographically approved
2. The Frequency of the Frequency: On Hydropower and Grid Frequency Control
Open this publication in new window or tab >>The Frequency of the Frequency: On Hydropower and Grid Frequency Control
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Variations in the electricity consumption and production connected to the power system have to be balanced by active control. Hydropower is the most important balancing resource in the Nordic system, and will become even more important as the share of variable renewable energy sources increases. This thesis concerns balancing of active power, especially the real-time balancing called frequency control. The thesis starts in a description of the situation today, setting up models for the behaviour of hydropower units and the power system relevant to frequency control, and comparing the models with experiments on several hydropower units and on the response of the Nordic grid. It is found that backlash in the regulating mechanisms in hydropower units have a strong impact on the quality of the delivered frequency control. Then, an analysis of what can be done right now to improve frequency control and decrease its costs is made, discussing governor tuning, filters and strategies for allocation of frequency control reserves. The results show that grid frequency quality could be improved considerably by retuning of hydropower governors. However, clear technical requirements and incentives for good frequency control performance are needed. The last part of the thesis concerns the impact from increased electricity production from variable renewable energy sources. The induced balancing need in terms of energy storage volume and balancing power is quantified, and it is found that with large shares of wind power in the system, the energy storage need over the intra-week time horizon is drastically increased. Reduced system inertia due to higher shares of inverter connected production is identified as a problem for the frequency control of the system. A new, linear synthetic inertia concept is suggested to replace the lost inertia and damping. It is shown that continuously active, linear synthetic inertia can improve the frequency quality in normal operation and decrease wear and tear of hydropower units delivering frequency control.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 105 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1460
Keyword
hydropower, frequency control, governors, power system stability, inertia, primary control
National Category
Engineering and Technology Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-308441 (URN)978-91-554-9769-9 (ISBN)
Public defence
2017-02-07, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2017-01-13 Created: 2016-11-25 Last updated: 2017-01-17
3. Hydropower plants and power systems: Dynamic processes and control for stable and efficient operation
Open this publication in new window or tab >>Hydropower plants and power systems: Dynamic processes and control for stable and efficient operation
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As the largest global renewable source, hydropower shoulders a large portion of the regulation duty in many power systems. New challenges are emerging from variable renewable energy (VRE) sources, the increasing scale and complexity of hydropower plants (HPPs) and power grid. Stable and efficient operation of HPPs and their interaction with power systems is of great importance.

Theoretical analysis, numerical simulation and on-site measurement are adopted as main study methods in this thesis. Various numerical models of HPPs are established, with different degrees of complexity for different purposes. The majority of the analysis and results are based on eight HPPs in Sweden and China.

Stable operation (frequency stability and rotor angle stability) and efficient operation are two important goals. Regarding the stable operation, various operating conditions are analysed; the response time of primary frequency control (PFC) and the system stability of isolated operation are investigated. A fundamental study on hydraulic-mechanical-electrical coupling mechanisms for small signal stability of HPPs is conducted. A methodology is proposed to quantify the contribution to the damping of low frequency oscillations from hydraulic turbines. The oscillations, with periods ranging from less than one up to hundreds of seconds, are analysed.

Regarding the efficient operation, a description and an initial analysis of wear and tear of turbines are presented; a controller filter is proposed as a solution for wear reduction of turbines and maintaining the frequency quality of power systems; then the study is further extended by proposing a framework that combines technical plant operation with economic indicators, to obtain relative values of regulation burden and performance of PFC.

The results show that the coupling between the hydraulic-mechanical subsystem and the electrical subsystem can be considerable and should be considered with higher attention. Effectiveness and applicability of different numerical models are shown, supplying suggestions for further model optimization. For the influence from power systems on HPPs, the dynamic processes and corresponding control strategies of HPPs under diverse disturbances and requirements from power systems are addressed. For the influence from HPPs on power systems, quantifications of frequency quality and the hydraulic damping are conducted utilising proposed methodologies.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 140 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1494
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-318470 (URN)978-91-554-9871-9 (ISBN)
Public defence
2017-05-19, Polhemsalen, Ångtröm 10134, Lägerhyddsvägen 1, Ångströmlaboratoriet, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2017-04-28 Created: 2017-03-24 Last updated: 2017-05-05

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Yang, WeijiaNorrlund, PerSaarinen, Linn

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