Application of synchronous compensators in the GB transmission network to address protection challenges from increasing renewable generation

The GB transmission network is experiencing significant changes in its generation mix, with increasing volume of renewables and the decommissioning of large-scale thermal power plants. One of the main challenges resulting from these changes in the generation portfolio is the potential impact on the reliable operation of the existing protection schemes. Specifically, the likely decrease in the fault level may result in conventional protection schemes being slow/failing in detection faults, and the decrease of the system inertia would lead to a power system being more sensitive to disturbances, which may subsequently lead to undesired operation of Rate of Change of Frequency (RoCoF) – based Loss-of-Main (LOM) relays. Synchronous compensators are considered to have the potential to offer, among other benefits, a boost to system inertia and an increase of system fault level, which could facilitate the operation of protection systems in future energy scenarios. This paper presents the initial studies conducted under a project that has been initiated by a number of utility companies in the UK, focusing on the demonstration and deployment of the first synchronous compensator at a strategic point in the GB transmission system. The studies investigate the potential impacts of a GB transmission system with high penetration of non-synchronous generation on fault levels and system inertia, while contrasting the results with that of a system reinforced by synchronous compensation. The results of the inertia studies show that synchronous compensation could be used as a potential solution to limit system RoCoF following a disturbance, thereby reducing the risk of a cascading event as a result of the tripping of RoCoF relays. In the fault level studies, it was observed that while increasing the synchronous compensator rating, fault current and short circuit ratio increased, with a faster rate of increase the closer the synchronous compensator is to the fault. This observation suggests that synchronous compensators can also be used to minimise the risk of commutation failure of HVDC links, with the added likelihood of ensuring that the network protection operates correctly in low fault level scenarios

Potential solutions to the challenges of low inertia power systems with a case study concerning synchronous condensers

This paper will review the recent and on-going changes to the power system in Great Britain (GB). One of the main challenges resulting from these changes in generation mix is the assurance of frequency stability in a low inertia system, and the provision of adequate dynamic responses to frequency changes, while meeting the requirements of the energy trilemma. Specifically, the increase in penetration of non-synchronous generation increases the risk of undesired operation of protection devices and contributes to a shortage of dynamic immediate response to frequency changes. A range of potential solutions will be briefly reviewed in this paper including, demand side response (DSR), energy storage, synthetic inertia, and synchronous condensers. A case study concerned with evaluating the impact that synchronous compensation may have in a low inertia power system will be described in the paper. The paper will conclude with an outline of the avenues for further study towards addressing the challenge of frequency stability and system inertia in a future power system

Long-term efficacy and safety of migalastat treatment in Fabry disease: 30-month results from the open-label extension of the randomized, phase 3 ATTRACT study

Results from the 18-month randomized treatment period of the phase 3 ATTRACT study demonstrated the efficacy and safety of oral migalastat compared with enzyme replacement therapy (ERT) in patients with Fabry disease who previously received ERT. Here, we report data from the subsequent 12-month, migalastat-only, open-label extension (OLE) period. ATTRACT (Study AT1001–012; NCT01218659) was a randomized, open-label, active-controlled study in patients aged 16–74 years with Fabry disease, an amenable GLA variant, and an estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2. During the OLE, patients who received migalastat 150 mg every other day (QOD) during the randomized period continued receiving migalastat (Group 1 [MM]); patients who received ERT every other week discontinued ERT and started migalastat treatment (Group 2 [EM]). Outcome measures included eGFR, left ventricular mass index (LVMi), composite clinical outcome (renal, cardiac or cerebrovascular events), and safety. Forty-six patients who completed the randomized treatment period continued into the OLE (Group 1 [MM], n = 31; Group 2 [EM], n = 15). eGFR remained stable in both treatment groups. LVMi decreased from baseline at month 30 in Group 1 (MM) in patients with left ventricular hypertrophy at baseline. Only 10% of patients experienced a new composite clinical event with migalastat treatment during the OLE. No new safety concerns were reported. In conclusion, in patients with Fabry disease and amenable GLA variants, migalastat 150 mg QOD was well tolerated and demonstrated durable, long-term stability of renal function and reduction in LVMi

Solvent-Induced Reversal of Activities between Two Closely Related Heterogeneous Catalysts in the Aldol Reaction

The relative rates of the aldol reaction catalyzed by supported primary and secondary amines can be inverted by 2 orders of magnitude, depending on the use of hexane or water as a solvent. Our analyses suggest that this dramatic shift in the catalytic behavior of the supported amines does not involve differences in reaction mechanism, but is caused by activation of imine to enamine equilibria and stabilization of iminium species. The effects of solvent polarity and acidity were found to be important to the performance of the catalytic reaction. This study highlights the critical role of solvent in multicomponent heterogeneous catalytic processes

Computational Treatment of Metalloproteins

Metalloproteins present a considerable challenge for modeling, especially when the starting point is far from thermodynamic equilibrium. Examples include formidable problems such as metalloprotein folding and structure prediction upon metal addition, removal, or even just replacement; metalloenzyme design, where stabilization of a transition state of the catalyzed reaction in the specific binding pocket around the metal needs to be achieved; docking to metal-containing sites and design of metalloenzyme inhibitors. Even more conservative computations, such as elucidations of the mechanisms and energetics of the reaction catalyzed by natural metalloenzymes, are often nontrivial. The reason is the vast span of time and length scales over which these proteins operate, and thus the resultant difficulties in estimating their energies and free energies. It is required to perform extensive sampling, properly treat the electronic structure of the bound metal or metals, and seamlessly merge the required techniques to assess energies and entropies, or their changes, for the entire system. Additionally, the machinery needs to be computationally affordable. Although a great advancement has been made over the years, including some of the seminal works resulting in the 2013 Nobel Prize in chemistry, many aforementioned exciting applications remain far from reach. We review the methodology on the forefront of the field, including several promising methods developed in our lab that bring us closer to the desired modern goals. We further highlight their performance by a few examples of applications

Incorporating a completely renormalized coupled cluster approach into a composite method for thermodynamic properties and reaction paths

The correlation consistent composite approach (ccCA), using the S4 complete basis set two-point extrapolation scheme (ccCA-S4), has been modified to incorporate the left-eigenstate completely renormalized coupled cluster method, including singles, doubles, and non-iterative triples (CR-CC(2,3)) as the highest level component. The new ccCA-CC(2,3) method predicts thermodynamic properties with an accuracy that is similar to that of the original ccCA-S4 method. At the same time, the inclusion of the single-reference CR-CC(2,3) approach provides a ccCA scheme that can correctly treat reaction pathways that contain certain classes of multi-reference species such as diradicals, which would normally need to be treated by more computationally demanding multi-reference methods. The new ccCA-CC(2,3) method produces a mean absolute deviation of 1.7 kcal/mol for predicted heats of formation at 298 K, based on calibration with the G2/97 set of 148 molecules, which is comparable to that of 1.0 kcal/mol obtained using the ccCA-S4 method, while significantly improving the performance of the ccCA-S4 approach in calculations involving more demanding radical and diradical species. Both the ccCA-CC(2,3) and ccCA-S4 composite methods are used to characterize the conrotatory and disrotatory isomerization pathways of bicyclo[1.1.0]butane to trans-1,3-butadiene, for which conventional coupled cluster methods, such as the CCSD(T) approach used in the ccCA-S4 model and, in consequence, the ccCA-S4 method itself might fail by incorrectly placing the disrotatory pathway below the conrotatory one. The ccCA-CC(2,3) scheme provides correct pathway ordering while providing an accurate description of the activation and reaction energies characterizing the lowest-energy conrotatory pathway. The ccCA-CC(2,3) method is thus a viable method for the analyses of reaction mechanisms that have significant multi-reference character, and presents a generally less computationally intensive alternative to true multi-reference methods, with computer costs and ease of use that are similar to those that characterize the more established, CCSD(T)-based, ccCA-S4 methodology

Incorporating a completely renormalized coupled cluster approach into a composite method for thermodynamic properties and reaction paths

The correlation consistent composite approach (ccCA), using the S4 complete basis set two-point extrapolation scheme (ccCA-S4), has been modified to incorporate the left-eigenstate completely renormalized coupled cluster method, including singles, doubles, and non-iterative triples (CR-CC(2,3)) as the highest level component. The new ccCA-CC(2,3) method predicts thermodynamic properties with an accuracy that is similar to that of the original ccCA-S4 method. At the same time, the inclusion of the single-reference CR-CC(2,3) approach provides a ccCA scheme that can correctly treat reaction pathways that contain certain classes of multi-reference species such as diradicals, which would normally need to be treated by more computationally demanding multi-reference methods. The new ccCA-CC(2,3) method produces a mean absolute deviation of 1.7 kcal/mol for predicted heats of formation at 298 K, based on calibration with the G2/97 set of 148 molecules, which is comparable to that of 1.0 kcal/mol obtained using the ccCA-S4 method, while significantly improving the performance of the ccCA-S4 approach in calculations involving more demanding radical and diradical species. Both the ccCA-CC(2,3) and ccCA-S4 composite methods are used to characterize the conrotatory and disrotatory isomerization pathways of bicyclo[1.1.0]butane to trans-1,3-butadiene, for which conventional coupled cluster methods, such as the CCSD(T) approach used in the ccCA-S4 model and, in consequence, the ccCA-S4 method itself might fail by incorrectly placing the disrotatory pathway below the conrotatory one. The ccCA-CC(2,3) scheme provides correct pathway ordering while providing an accurate description of the activation and reaction energies characterizing the lowest-energy conrotatory pathway. The ccCA-CC(2,3) method is thus a viable method for the analyses of reaction mechanisms that have significant multi-reference character, and presents a generally less computationally intensive alternative to true multi-reference methods, with computer costs and ease of use that are similar to those that characterize the more established, CCSD(T)-based, ccCA-S4 methodology. © 2012 American Institute of Physics

An expert database technique applied to an aphasia classification system

Medical expert systems or clinical decision support systems (CDSS) are computer applications that emulate the diagnostic techniques of medical experts. An advanced concept in CDSS is the integrated CDSS, which begins with the diagnostic capability of the CDSS and adds the abilities to generate signals or warnings about patient conditions and to store patient data in such a way that it can be retrieved and used efficiently. A new technique in the computer subfield known as database management systems (DBMS), is the object-oriented DBMS (OODBMS). This paper will discuss an innovative technique that uses an OODBMS to develop an integrated CDSS for individuals with aphasia. The diagnostic basis for the integrated CDSS is the Aphasia Diagnostic Profile (ADP). The paper will briefly describe the ADP classification scheme, the OODBMS concept, and the technique developed to create the aphasia integrated CDSS. © 1994, Taylor & Francis Group, LLC. All rights reserved

Unmasking a patent foramen ovale during recurrent paradoxical cerebral embolism

A patient with an acute ischemic stroke had an interatrial septal aneurysm shown by transesophageal echocardiography. Interatrial shunting, compatible with a patent foramen ovale, was observed on a follow-up study after a second stroke. This was seen in association with a right atrial thrombus. This case illustrates that an interatrial septal aneurysm serves as a marker for potential interatrial shunting, which can lead to paradoxical cerebral embolism