Now showing 1 - 8 of 8
  • Publication
    Analysis of the voltage control capability of energy harvesting networks
    (Energynautics, 2010-10) ; ;
    At times of high generation levels from distributed generators (DGs), there may be a paucity of conventional generators still synchronised to the transmission system. These synchronous machines have traditionally been the power system's principal source of controllable reactive power. If DGs are operated at inductive power factors, total reactive power absorption at distribution system bulk supply points may be highest at times when the transmission system is least equipped to supply it. On the Irish power system, new DGs (typically windfarms) may be connected in a clustered fashion to a new transmission node. This paper will show how the aggregate reactive power capabilities of these clustered DGs may be characterised. Of particular importance is how the cluster can respect distribution system operating limits while also providing reactive power support to the transmission system.
  • Publication
    Understanding the interactive role of the rumen microbiome with diet and enteric emissions in cattle
    (University College Dublin. School of Agriculture and Food Science, 2022) ;
    Enteric methane (CH4), produced by members of the microbial population residing in the rumen of domesticated livestock, is accountable for ~6% of global greenhouse gas (GHG) emissions. In a bid to develop cost effect dietary and breeding based mitigation strategies for the livestock industry, a series of studies that utilised 16S ribosomal RNA (rRNA) amplicon sequencing to investigate the relationship of the rumen microbiota with diet and enteric CH4 emissions in cattle, were investigated as part of this thesis. In addition, this thesis aimed to optimise the bioinformatics analysis of rumen microbial amplicon sequencing data. With the use of a rumen specific amplicon sequencing standard, the taxonomic classification of rumen microbial amplicon sequence data amongst the main 16S rRNA databases was evaluated in Chapter 3. In Chapter 4, 16S rRNA amplicon sequencing was utilised to investigate the impacts of including white clover in the grazing sward on the rumen bacterial and archaeal populations of dairy cows. The CH4 abatement potential of supplementing concentrates, solely formulated from industrial plant based by-products (BP), to a pastoral based diet, was explored in Chapter 5. The benefits of utilising the residual CH4 emissions (RME) concept to determine the methanogenic output of ruminant livestock, independent of animal productivity, and the impacts ranking animals in terms of RME on the rumen microbiota, was investigated in Chapter 6 and 7. In Chapter 3, the benefits of utilising a rumen specific amplicon sequencing standard to optimise 16s rRNA amplicon analysis was illustrated, with the results obtained implemented during the rumen microbial analysis conducted in Chapters 4, 5 and 7. Results from Chapter 4 highlighted a subtle change to the composition of the grazing sward, associated with the inclusion of white clover, resulted in an increased ruminal abundance of the pectin degrading bacteria Lachnospira and methylotrophic archaea Methanosphaera. A reduced abundance of the Firmicutes phyla, yet lack of an effect on the rumen methanogen community, and a ~20% lower CH4 output, was observed with the supplementation of a pastoral based diet with a high fat and fibre BP concentrate formulation, in comparison to a cereal based ration, in vitro. Comparable levels of animal performance but a ~30% difference in all measures of enteric CH4 emissions, and alteration to the rumen fermentation profile, was observed in beef cattle ranked as high and low for RME, in Chapter 6. In Chapter 7, a small cohort of bacterial genera involved in the acrylate pathway and methanogens indicative of a reduced synthesis of dihydrogen (H2) in the rumen, were identified as potential rumen microbial biomarkers for a low RME phenotype. In conclusion, data generated as part of this thesis emphasised the mitigation potential of novel dietary and animal breeding based strategies and provides a baseline assessment of the relationship of the rumen microbiota with diet and enteric CH4 emissions in cattle. This information will guide the future metagenomics and metatranscriptomic attempts to better understand the influence of the ruminant host on prevailing conditions within the rumen and methanogenesis.
  • Publication
    Effect of energy harvesting network reactive support on transmission system voltage performance
    It is common to operate distributed generators (DGs) at fixed inductive power factors to overcome voltage rise constraints on distribution networks. This approach increases distribution system reactive power demand, which may strain transmission system reactive power resources at times of system-wide high DG output, particularly if such output displaces synchronous generators. If a number of adjacent DGs are connected to a transmission node in a clustered fashion via a dedicated energy harvesting network (EHN), it is possible to characterise their aggregated reactive power capability as a form of virtual power plant. Such a characterisation will be provided in this paper. The aggregated capability may readily be included in transmission system models. This work will explicitly compare the transmission system voltage-control performance of EHN reactive capability with that of traditional synchronous plant.
  • Publication
    Studying the maximum instantaneous non-synchronous generation in an Island system-frequency stability challenges in Ireland
    Synchronous island power systems, such as the combined Ireland and Northern Ireland power system, are facing increasing penetrations of renewable generation. As part of a wider suite of studies, performed in conjunction with the transmission system operators (TSOs) of the All-Island system (AIS), the frequency stability challenges at high and ultra-high wind penetrations were examined. The impact of both largest infeed loss and network fault induced wind turbine active power dips was examined: the latter contingency potentially representing a fundamental change in frequency stability risk. A system non-synchronous penetration (SNSP) ratio was defined to help identify system operational limits. A wide range of system conditions were studied, with results showing that measures such as altering ROCOF protection and enabling emulated inertia measures were most effective in reducing the frequency stability risk of a future Ireland system. © 2014 IEEE.
      1898Scopus© Citations 209
  • Publication
    Capability Chart for Distributed Reactive Power Resources
    (Institute of Electrical and Electronics Engineers, 2013-09-11) ; ;
    The ubiquity of synchronous generation should not be assumed in highly renewable power systems. Various problems may consequently arise, not least of which are the difficulties entailed in maintaining regional reactive power balance. Offering a potential solution to such problems, modern renewable generator technologies offer controllable reactive power resources. As many of these generators will be embedded in distribution networks, their incorporation into transmission system operational and planning activities appears challenging. An extension of the capability chart concept offers insight here: for a given active power exchange between the transmission system and a distribution network section, the range of controllable reactive power typically available is of interest. This aggregate capability depends on the innate machine capabilities of the distributed generators and on the prevailing conditions within the distribution network. Novel optimisation techniques are useful in addressing the latter point, offering a means to identify the combination of power flow profiles within the distribution system most restrictive to reactive power provision. The capability chart thus derived gives the dependable range of reactive power available, under the assumption that each generator is operated to locally maximize its own reactive power contribution. Such a description can be applied in transmission system planning or to quantify the effects of modifications to the distribution system.
      1139Scopus© Citations 40
  • Publication
    Characterisation of the reactive power capability of diverse distributed generators: Toward an optimisation approach
    (Institute of Electrical and Electronics Engineers, 2012-07) ; ;
    The highly renewable power system cannot assume the ubiquity and constant availability of synchronous plant. For this reason, the provision of ancillary services must shift to renewable generators, concomitant with their rising penetration levels. This work will focus on one aspect of this challenge: the provision of reactive power from distributed generation. As such resources become increasingly important, their incorporation into transmission system operation and planning activities becomes vital. To that end, a capability characterisation appears useful, delineating the range of controllable reactive power available for a given power flow onto a section of distribution network. Work to date has used time series techniques to provide a proxy to this type of capability chart. Distribution system optimisation techniques offer the potential for a more rigorous and general-purpose characterisation methodology. This work will set out how such an optimisation problem may be formulated, and will provide some initial results and validations.
      795Scopus© Citations 8
  • Publication
    Ireland's approach for the connection of large amounts of renewable generation
    This paper discusses the connection policies adopted to facilitate the large number of wind farms seeking access to the Irish power system. A key feature is a grouped connection offer process that provides certainty for wind project developers and optimises the development of the network. A further interesting feature is the development of a “wind cluster” concept which permits semi-dedicated MV networks for the connection of a group of adjacent wind farms, together with equitable arrangements for sharing the financial burden of construction between developers.
      907Scopus© Citations 10
  • Publication
    Transmission System Impact of Wind Energy Harvesting Networks
    (Institute of Electrical and Electronics Engineers, 2012-10) ; ;
    The increasing emphasis placed upon renewable sources of energy requires that power systems accommodate a roll out of variable, asynchronous generators throughout transmission and distribution networks. High penetration levels of such generation will displace synchronous plant and may cause a challenging scarcity of ancillary service providers, notably in the area of reactive power provision. Consequently, the onus must increasingly be laid upon renewable generators to provide the ancillary services necessary to operate the power system. An emerging practice is to connect adjacent distributed generators in a clustered fashion to a dedicated transmission node, an arrangement that offers rich possibilities for participation in transmission-level control. Performance characterizations of such networks will be helpful in planning transmission system development for reduced synchronous plant availability. This work will examine the effect of increasing penetration of wind generators on transmission system voltage levels and voltage security.
      558Scopus© Citations 24