Energy-efficient control strategies for variable speed driven parallel pumping systems based on pump operation point monitoring with frequency converters

The pumping processes requiring wide range of flow are often equipped with parallelconnected centrifugal pumps. In parallel pumping systems, the use of variable speed control allows that the required output for the process can be delivered with a varying number of operated pump units and selected rotational speed references. However, the optimization of the parallel-connected rotational speed controlled pump units often requires adaptive modelling of both parallel pump characteristics and the surrounding system in varying operation conditions. The available information required for the system modelling in typical parallel pumping applications such as waste water treatment and various cooling and water delivery pumping tasks can be limited, and the lack of real-time operation point monitoring often sets limits for accurate energy efficiency optimization. Hence, alternatives for easily implementable control strategies which can be adopted with minimum system data are necessary. This doctoral thesis concentrates on the methods that allow the energy efficient use of variable speed controlled parallel pumps in system scenarios in which the parallel pump units consist of a centrifugal pump, an electric motor, and a frequency converter. Firstly, the suitable operation conditions for variable speed controlled parallel pumps are studied. Secondly, methods for determining the output of each parallel pump unit using characteristic curve-based operation point estimation with frequency converter are discussed. Thirdly, the implementation of the control strategy based on real-time pump operation point estimation and sub-optimization of each parallel pump unit is studied. The findings of the thesis support the idea that the energy efficiency of the pumping can be increased without the installation of new, more efficient components in the systems by simply adopting suitable control strategies. An easily implementable and adaptive control strategy for variable speed controlled parallel pumping systems can be created by utilizing the pump operation point estimation available in modern frequency converters. Hence, additional real-time flow metering, start-up measurements, and detailed system model are unnecessary, and the pumping task can be fulfilled by determining a speed reference for each parallel-pump unit which suggests the energy efficient operation of the pumping system.

Foreign Operation Mode Strategies of Finnish Companies in Russia

The object of this study was to examine foreign operation mode strategies used by Finnish companies in Russia. Thus, it was necessary to understand how Finnish companies have used foreign operation modes and which factors have influenced on their foreign operation mode strategies in Russia. Moreover, the purpose was also to find out that have Finnish companies switched, stretched or combined their foreign operation modes. The study's empirical part was conducted as a semi structured qualitative within-case and cross-case analysis of seven case companies that are selected to represent different industries. There are five Finnish LSEs and two Finnish SMEs as case companies. The results of this study indicated that Finnish companies have mainly used exporting as their initial entry mode to the Russian market. After they had gained understanding and experience of the Russian market, they switched from non-equity and simple foreign operation modes to more challenging and equity demanding foreign operation modes, and established wholly owned operations.

Intensification of Operation of Inclined Plate Settler at Fertilizer Plant

Fertilizer plant’s process waters contain high concentrations of nitrogen compounds, such as ammonium and nitrate. Phosphorus and fluorine, which originate from phosphoric acid and rock phosphate (apatite) used in fertilizer production, are also present. Phosphorus and nitrogen are the primary nutrients causing eutrophication of surface waters. At fertilizer plant process waters are held in closed internal circulation. In a scrubber system process waters are used for washing exhaust gases from fertilizer reactors and dry gases from granulation drums as well as for cooling down the fertilizer slurry in neutralization reactor. Solids in process waters are separated in an inclined plate settler by gravitational sedimentation. However, the operation of inclined plate settler has been inadequate. The aim of this thesis was to intensify the operation of inclined plate settler and thus the solids separation e.g. through coagulation and/or flocculation process. Chemical precipitation was studied to reduce the amount of dissolved species in process waters. Specific interest was in precipitation of nitrogen, phosphorus, and fluorine containing specimens. Amounts of phosphorus and fluorine were reduced significantly by chemical precipitation. When compared to earlier studies, annual chemical costs were almost eight times lower. Instead, nitrogen compounds are readily dissolved in water, thus being difficult to remove by precipitation. Possible alternative techniques for nitrogen removal are adsorption, ion exchange, and reverse osmosis. Settling velocities of pH adjusted and flocculated process waters were sufficient for the operation of inclined plate settler. Design principles of inclined plate settler are also presented. In continuation studies, flow conditions in inclined plate settler should be modelled with computational fluid dynamics and suitability of adsorbents, ion exchange resins, and membranes should be studied in laboratory scale tests.

Operation Attilas första skede : De turkiska operationerna på Cypern i juli 1974.

Avhandlingen berör de turkiska operationerna på Cypern, som inleddes den 20 juli 1974 till följd av att den cypriotiska presidenten Makarios avsatts i en statskupp. Avhandlingen behandlar de turkiska förbandens stridsverksamhet under tiden 20.- 31.7.1974 med tyngdpunkt vid de tre första dagarna. Operation Attila genomfördes med trupper från alla försvarsgrenar, men huvudansvaret låg hos armén. Den turkiska fredsstyrkan, som utgjordes av den 6. armékåren hade en total styrka på ungefär 16000 man under operationens första skede. Den huvudsakliga forskningsfrågan lyder, hur genomförde Turkiet Operation Attilas första skede? Övriga forskningsfrågor som stöder huvudfrågan är: Av vilka förband var den turkiska fredsstyrkan sammansatt och hur såg dessa förband ut? Vilken roll spelade den turkiska marinen och det turkiska flygvapnet i operationen? Vilka var de turkiska truppernas största taktiska och stridstekniska problem under operationen? Vilka faktorer bidrog till att Turkiet lyckades med Operation Attila? Forskningen baserar sig på skriven litteratur i form av böcker, skriftliga utkast och artiklar. Som forskningsmetod används en kvalitativ litteraturanalys där ovan nämnda forskningsfrågor besvaras. De turkiska förbanden lyckades genomföra Operation Attilas första skede, men de nådde inte sina uppsatta militära mål förrän flera dagar senare än planerat. Turkarnas försening berodde mera på egen inkompetens än kraftigt motstånd från den grekcypriotiska krigsmakten, CNG.

The influence of high cable penetration in distribution networks on earth fault currents and the operation of relay protection.

Recent Storms in Nordic countries were a reason of long power outages in huge territories. After these disasters distribution networks' operators faced with a problem how to provide adequate quality of supply in such situation. The decision of utilization cable lines rather than overhead lines were made, which brings new features to distribution networks. The main idea of this work is a complex analysis of medium voltage distribution networks with long cable lines. High value of cable’s specific capacitance and length of lines determine such problems as: high values of earth fault currents, excessive amount of reactive power flow from distribution to transmission network, possibility of a high voltage level at the receiving end of cable feeders. However the core tasks was to estimate functional ability of the earth fault protection and the possibility to utilize simplified formulas for operating setting calculations in this network. In order to provide justify solution or evaluation of mentioned above problems corresponding calculations were made and in order to analyze behavior of relay protection principles PSCAD model of the examined network have been created. Evaluation of the voltage rise in the end of a cable line have educed absence of a dangerous increase in a voltage level, while excessive value of reactive power can be a reason of final penalty according to the Finish regulations. It was proved and calculated that for this networks compensation of earth fault currents should be implemented. In PSCAD models of the electrical grid with isolated neutral, central compensation and hybrid compensation were created. For the network with hybrid compensation methodology which allows to select number and rated power of distributed arc suppression coils have been offered. Based on the obtained results from experiments it was determined that in order to guarantee selective and reliable operation of the relay protection should be utilized hybrid compensation with connection of high-ohmic resistor. Directional and admittance based relay protection were tested under these conditions and advantageous of the novel protection were revealed. However, for electrical grids with extensive cabling necessity of a complex approach to the relay protection were explained and illustrated. Thus, in order to organize reliable earth fault protection is recommended to utilize both intermittent and conventional relay protection with operational settings calculated by the use of simplified formulas.

Map - Plan of Operation against Cantigny

A map titled "Plan of Operation against Cantigny" and dated 17 December 1918.

Pointers on Design and Operation of Cattle Restrainer Systems

The article discusses the importance of design and the people who run handling systems.