Optimal Real-time Activated Sludge Regulation

Proceedings of the 1991 Georgia Water Resources Conference, March 19-20, 1991, Athens, Georgia.An application of optimal control techniques in regulating a conventional activated sludge process (Figure 1) is presented. In this process, organics in the influent wastewater (substrate) serve as energy source for the aerobic growth of microorganisms (biomass or activated sludge) in the biological reactor. The resulting mixed liquor is purified (clarification) by settling of the microbial floes in a following tank (settler). The thickened sludge is recycled to the biological reactor to sustain the biomass amount. To maintain a constant amount of biomass in the system, excess biomass is regularly removed (wastage). The process can be regulated by varying certain inputs such as the wastewater feed point, sludge recycle and wastage rates, aeration rate, and on-line sludge storage and resupply rates. The scope of this paper is to present an application of an optimal control method to a detailed activated sludge model, consisting of a multicomponent biological reactor and a dynamic multilayer settler. A real-world implementation for the Yellow River/ Sweetwater Creek wastewater treatment plant in Gwinnett county is presently being conducted.Sponsored by U.S. Geological Survey, Georgia Department of Natural Resources, the University of Georgia, Georgia State University, and Georgia Institute of Technology.This book was published by the Institute of Natural Resources, The University of Georgia, Athens, Georgia 30602 with partial funding provided by the U.S. Department of the Interior, Geological Survey, through the Georgia Water Research Institute as authorized by the Water Resources Research Act of 1984 (P.L. 98242). The views and statements advanced in this publication are solely those of the authors and do not represent official views or policies of The University of Georgia or the U.S. Geological Survey or the conference sponsors

Power system static and dynamic security studies for the 1st phase of Crete Island Interconnection

The island of Crete is currently served by an autonomous electrical system being fed by oil-fired (Heavy fuel or light Diesel oil) thermal power plants and renewables (wind and PVs). The peak load and annual electric energy consumption are approximately 600 MW and 3 TWh respectively; wind and photovoltaic parks contribute approximately 20% of the electricity needs of the island. Due to the expensive fuel used, the Cretan power system has very high electric energy generation cost compared to the Greek mainland. On the other side the limited size of the system poses severe limitations to the penetration of renewable energy sources, not allowing to further exploit the high wind and solar potential of the island. According to the Ten Year Network Development Plan (TYNDP) of the Greek TSO (Independent Power Transmission Operator S.A. IPTO S.A.), the interconnection of Crete to the mainland Transmission System of Greece will be realized through two links: A 150 kV HVAC link between the Peloponnese and the Crete (Phase I) and a HVDC link connecting the metropolitan area of Athens with Crete (Phase II). The total length of submarine and underground cable of the HVAC link will be approximately 174km; it is at the limits of the AC technology and the longest and deepest worldwide at 150 kV level. A number of studies have been conducted by a joint group of IPTO and Hellenic Electricity Distribution Network Operator (HEDNO) for the design of this interconnection. This paper presents briefly the power system static and dynamic studies conducted for the design of the AC link and its operation. Firstly, the paper presents the main results of the static security study regarding the calculation of the maximum power transfer capability of the link and the selection of the reactive power compensation scheme of the cable. Results from dynamic security analysis studies are also presented. The small-signal stability analysis concludes that a new (intra-area) electromechanical oscillation is introduced to the National System after the interconnection. The damping of the electromechanical oscillations is sufficient; however the operation of power system stabilizers at power plants located both at the mainland and at Crete power system can increase significantly the damping of important oscillation modes. Finally with respect to the risk of loss of synchronism after a significant disturbance in the system of Crete, such as a three-phase fault (“transient stability”)- enough safety margin is estimated by means of Critical Clearing Time calculations

Power system static and dynamic security studies for the 1st phase of Crete Island Interconnection

The island of Crete is currently served by an autonomous electrical system being fed by oil-fired (Heavy fuel or light Diesel oil) thermal power plants and renewables (wind and PVs). The peak load and annual electric energy consumption are approximately 600 MW and 3 TWh respectively; wind and photovoltaic parks contribute approximately 20% of the electricity needs of the island. Due to the expensive fuel used, the Cretan power system has very high electric energy generation cost compared to the Greek mainland. On the other side the limited size of the system poses severe limitations to the penetration of renewable energy sources, not allowing to further exploit the high wind and solar potential of the island. According to the Ten Year Network Development Plan (TYNDP) of the Greek TSO (Independent Power Transmission Operator S.A. IPTO S.A.), the interconnection of Crete to the mainland Transmission System of Greece will be realized through two links: A 150 kV HVAC link between the Peloponnese and the Crete (Phase I) and a HVDC link connecting the metropolitan area of Athens with Crete (Phase II). The total length of submarine and underground cable of the HVAC link will be approximately 174km; it is at the limits of the AC technology and the longest and deepest worldwide at 150 kV level. A number of studies have been conducted by a joint group of IPTO and Hellenic Electricity Distribution Network Operator (HEDNO) for the design of this interconnection. This paper presents briefly the power system static and dynamic studies conducted for the design of the AC link and its operation. Firstly, the paper presents the main results of the static security study regarding the calculation of the maximum power transfer capability of the link and the selection of the reactive power compensation scheme of the cable. Results from dynamic security analysis studies are also presented. The small-signal stability analysis concludes that a new (intra-area) electromechanical oscillation is introduced to the National System after the interconnection. The damping of the electromechanical oscillations is sufficient; however the operation of power system stabilizers at power plants located both at the mainland and at Crete power system can increase significantly the damping of important oscillation modes. Finally with respect to the risk of loss of synchronism after a significant disturbance in the system of Crete, such as a three-phase fault (“transient stability”)- enough safety margin is estimated by means of Critical Clearing Time calculations

Power system regulation planning and control with the support of an energy market simulator

Energy market simulation has a role to play in regulation, planning and control of liberalised electricity markets. The development and evolution of such markets internationally has focused the needs of different stakeholders within these markets over a variety of time scales. This paper describes the main objectives and principal assumptions for development and implementation of energy market simulators. The authors describe the background requirements and needs from the perspective of different user groups for this kind of tool. Examples of possible applications are presented for the use of a market simulator and data requirements and indications for a practical realisation of models have also been included

A new frontier approach to model the eco-efficiency in European countries

This study aims to evaluate the resource and environment efficiency problem of European countries. We specify a new stochastic frontier model where Gross Domestic Product (GDP) is considered as the desirable output and Greenhouse Gases (GHG) emissions as the undesirable output. Capital, Labour, Fossil fuels and Renewable Energy consumption are regarded as inputs. GDP/GHG ratio is maximized given the values of the other four variables. The study is divided into two distinct periods: 2000-2004 and 2005-2011. This division is related to the implementation of the Kyoto Protocol in 2005, and will allow us to evaluate the difference between the levels of efficiency before and after the establishment of environmental targets. Since stochastic frontier models are typically ill-posed, a new maximum entropy approach to assess technical efficiency, which combines information from the data envelopment analysis and the structure of composed error from the stochastic frontier approach without requiring distributional assumptions, is presented in this work

A geomorphologic instantaneous unit hydrograph streamflow model

M.S.Aristidis Georgakako

Impacts of Large Scale Wind Penetration on Energy Supply Industry

Large penetration of Renewable Energy Sources (RES) impacts Energy Supply Industry (ESI) in many aspects leading to a fundamental change in electric power systems. It raises a number of technical challenges to the Transmission System Operators (TSOs), Distribution System Operators (DSOs) and Wind Turbine Generators (WTG) constructors. This paper aims to present in a thorough and coherent way the redrawn picture for Energy Systems under these conditions. Topics related to emergent technical challenges, technical solutions required and finally the impact on ESI due to large wind power penetration, are analyzed. Finally, general conclusions are extracted about the ESI current and future state and general directions are recommended

INVESTIGATION OF PARAMETERS AFFECTING VOLTAGE SECURITY OF THE HELLENIC INTERCONNECTED SYSTEM

peer reviewedThe Hellenic Interconnected System pre-sents a structural geographical imbalance between generation sites and load centers. This imbalance leads to bulk power transfers on long electrical distances leading to voltage stability problems. In order to improve the opera-tional practices aiming at improving the voltage security, an on-line Voltage Security Assessment tool has been installed at the National Control Center of the Hellenic Transmission System Operator that operates and controls the interconnected power system of Greece. This paper presents some indicative results obtained by the use of this tool. The analysis includes the investigation of the main parameters that affect the voltage stability of the system, such as the position of non-automatic taps of autotrans-formers, the network topology, and the spatial distribution of generation