Years Of System Operation Research Articles

A review of grid code technical requirements for wind farms

This paper provides an overview of grid code technical requirements regarding the connection of large wind farms to the electric power systems. The grid codes examined are generally compiled by transmission system operators (TSOs) of countries or regions with high wind penetration and therefore incorporate the accumulated experience after several years of system operation at significant wind penetration levels. The paper focuses on the most important technical requirements for wind farms, included in most grid codes, such as active and reactive power regulation, voltage and frequency operating limits and wind farm behaviour during grid disturbances. The paper also includes a review of modern wind turbine technologies, regarding their capability of satisfying the requirements set by the codes, demonstrating that recent developments in wind turbine technology provide wind farms with stability and regulation capabilities directly comparable to those of conventional generating plants.

Performance of wastewater sludge ecological stabilization

In this article, wastewater sludge ecological stabilization (WWSES) was presented for sludge dewatering, mineralization, and stabilization, as well as for percolate treatment. Two years of pilot scale experimental results indicated that sludge volatile solid, triphenyltetrazolium chloride (TTC)-dehydrogenase activity (DHA), and moisture content as indicators showed the process and degree of sludge stabilization. The observation on dewatering process showed that dried sludge reached a content of 20%-50% total solid after two years of system operation. Sludge TTC-DHA in the first year was obviously lower than that of the second year, and TTC-DHA tended to decrease with an increase in the drying time of the sludge. Total nitrogen, total phosphorus, and organic contents of sludge decreased gradually from the top to the bottom of dried sludge layer. In comparison with natural stands on stands treated with sewage sludge, individual shoot was significantly higher, and coarse protein, coarse fat, and coarse fiber contents in reed roots, stems, and leaves in the system were higher than that of wild reed, especially coarse protein contents of reed roots in the system (7.38%) were obviously higher than that of wild reeds (3.29%).

Evaluation of full‐scale biofilter media performance

AbstractThe objective of this study was to characterize the key physical, chemical and biological properties of compost media from a full‐scale biofiltration system used to control VOC emissions. Results of media characterization we re used to assess the need for operational changes and media replacement. Biofilter media properties evaluated included: moisture content, pH, total organic carbon (TOC) and nitrogen content in water extracts and solid matrix, oxygen uptake rates, and microbial plate counts including total heterotrophs, oligotrophs, actinomycetes and fungi. Samples we re taken from various locations and depths in the biofilter after three and five years of system operation. Media moisture content was highly variable, with samples from deeper in the bed dryer than surface samples. Low moisture contents we re associated with low pH values and low oxygen uptake rates. Total organic carbon contents in water extracts we re higher than typical biosolids compost in samples near the inlet to the biofilter, possibly due to extracellular polysaccharides. After five years of use, total nitrogen and organic carbon contents in the solid matrix did not significantly differ from initial levels or those in typical biosolids compost.

ASSESSING POPULATION DYNAMICS IN A RURAL AFRICAN SOCIETY: THE NAVRONGO DEMOGRAPHIC SURVEILLANCE SYSTEM

In 1993, the Navrongo Health Research Centre launched a new demographic research system for monitoring the impact of health service interventions in a rural district of northern Ghana. The Navrongo Demographic Surveillance System uses automated software generation procedures that greatly simplify the preparation of complex database management systems. This paper reviews the Navrongo model for data collection, as well as features of the Navrongo system that have led to its replication in other health research projects requiring individual-level longitudinal demographic data. Demographic research results for the first 2 years of system operation are indicative of a pretransitional rural society with high fertility, exceedingly high mortality risks, and pronounced seasonal out-migration.

Ground‐Water Contamination from Two Small Septic Systems on Sand Aquifers

AbstractDistinct plumes of septic system‐impacted ground water at two single‐family homes located on shallow unconfined sand aquifers in Ontario showed elevated levels of Cl−, NO3−, Na+, Ca2+, K+, alkalinity, and dissolved organic carbon and depressed levels of pH and dissolved oxygen. At the Cambridge site, in use 12 years, the plume had sharp lateral and vertical boundaries and was more than 130 m in length with a uniform width of about 10 m. As a result of low transverse dispersion in the aquifer, mobile plume solutes such as NO3− and Na+ occurred at more than 50 percent of the source concentrations 130 m downgradient from the septic system. At the Muskoka site, in use three years, the plume also had discrete boundaries reflecting low transverse dispersion. After 1.5 years of system operation, the Muskoka plume began discharging to a river located 20 m from the tile field. Almost complete NOs attenuation was observed within the last 2 m of the plume flowpath before discharge to the river. This was attributed to denitrification occurring within organic matter‐enriched riverbed sediments.The very weakly dispersive nature of the two aquifers was consistent with the results of recently reported natural‐gradient tracer tests in sands. Therefore, for many unconfined sand aquifers, the minimum distance‐to‐well regulations for permitting septic systems in most parts of North America should not be expected to be adequately protective of well‐water quality in situations where mobile contaminants such as NOs are not attenuated by chemical or microbiological processes.

Transport modelling of biological tracers from septic systems

The potential of contamination of individual ground water supplies from septic systems was investigated. Chloride (Cl) and electrical conductivity ( C e ) as tracers of chemicals and indicator bacteria—total coliforms (TC), fecal coliforms (FC) and fecal streptococci (FS)—were determined for 7 months in septic tank effluent and ground water samples collected downgradient from 17 new or replacement septic systems. Indicator bacteria were also determined occasionally in ground water samples from wells near the systems for a continuing period of 2 years. Following 5 years of system operation a last round of analyses was conducted. Water table fluctuations in the vicinity of the septic systems were monitored for 2 years. As a model for viruses, poliovirus in feces from babies who had received the trivalent Sabin oral poliovirus vaccine was introduced into one septic system as a single dose by flushing stools down the toilet. Effluent and ground water were assayed for poliovirus over a period of approx. 6 months. The data were evaluated statistically and a biological contaminant transport model was tested to simulate ground water contamination by the tracers of pathogens. No tracer bacteria reached ground water from any of the 17 septic systems. Presumably, the bacteria were removed by the soil under the seepage bed; mean transport was < 1 count/100 ml for each bacterial type, in keeping with U.S. drinking water regulations. Poliovirus entered and spread in ground water from the one septic system tested, even though this system was functioning properly. Of 3.3 × 10 8 PFU of poliovirus inoculated into the septic tank, a mean of 70 PFU/100 ml escaped from the tank with the effluent and an overall mean of 62 PFU/100 ml were transported to ground water. Septic systems had little influence on water table fluctuations in their vicinity, compared to the seasonal climatic factors.

Operating experience of the Fair Isle wind turbine

The paper describes the combined wind-turbine and diesel generation scheme installed on Fair Isle in June 1982. The reasons for the choice of the system in use and the preferred mode of operation are given. The main features of the wind turbine and its control system are described in some detail. Some of the problems encountered in service are described as well as the solutions adopted. Three years of system operation are reported and the contribution of community participation in the successful operation of the scheme is emphasised. In addition to extended hours of supply at lower cost, by producing some 90% of the energy requirement from the wind turbine, diesel fuel consumption has been reduced by two thirds and extra savings for the community are reflected in a reduction of coal and heating oil imports by 40% and 34%, respectively.

Effective Allocation of Sales Resources

Beginning in 1976 the Bell Telephone System's national sales effort was supported by a computer-based system. This system identified specific business enterprises to be contacted directly by the Bell System account representatives as well as those businesses with appropriate potential sales levels to be included in the corporate national direct marketing program. In addition to increases in the sales rate and average revenue per sale, this systematic approach to account qualification has allowed a formal tracking program to be implemented. In the initial two years of system operation, a conservative estimate of the revenue generated is 15 million dollars. The method is quite general and could be applied to the sale of many industrial products.

Cost Effectiveness Modeling Applied to Integrated Circuits

A computer logic model has been used to anticipate the functioning of an electronic system over its complete life span. Performance, cost, and availability comparisons were made between an existing equipment, Conalog, and redesigns using advanced microcircuit techniques. Results from the model indicated reductions in: cost of ownership by one-third, number of failures to one-tenth, and skill level of maintenance. Ten years of system operation were simulated using the IBM GPSS language in two minutes of IBM 7094 II time.