Simplified approach for the reliability estimation of large transmission and sub-transmission systems

Includes bibliographical references.Various specialised power system reliability modelling software are commercially available to analyse the expected performance of a utility’s transmission and sub-transmission network. The software requires a physical network model to be constructed, representing all network components. A high level of accuracy is obtained using such software, but significant effort is required to create these models, especially when large utility-scale networks are modelled. Another limitation of the software is that specific design strategies can only be modelled by physically changing the network model, which again requires significant effort. A simplified approach is therefore required to enable utility engineers to analyse the reliability of different network configurations, reliability improvement strategies and planning criteria. The aim of this research is to provide a simplified reliability approach that will assist engineers in managing the reliability of their transmission and sub-transmission networks. The approach should be simplified to require minimum user inputs and it should be capable of quantifying the impact of different substation and line configurations on a system level. It is not expected that this approach will have the same level of accuracy as the detailed software models, but it should enable engineers to calculate system indices with much less effort, while still maintaining an acceptable level of accuracy. The scope of this research is limited to the transmission and sub-transmission networks (lines and substations). Power stations and MV distribution feeders are excluded from the analysis. Only technical, customer-based performance indicators are modelled, no load-based or economic performance indicators are calculated. An analytical approach is considered for the simplified reliability modelling, starting with a failure mode and effect analysis. The contribution of substation and sub-transmission events is decoupled and a detailed model of the substation is created, including all internal components. A reliability analysis is performed for each substation, to determine the unavailability experienced by customers connected to each busbar. An equivalent system model is then generated by replacing all substations with busbars, of which the outage frequency and outage duration are equal to that of the substation equivalent. The simplified substation reliability estimation is compared with detailed substation modelling using specialised software. The results obtained with the simplified reliability estimation show a good correlation with the detailed software models. The simplified reliability methodology was programmed into MS Excel and used to model the expected availability of the Ghana transmission network. Different scenarios were then modelled, analysing the impact of design and operational changes on the expected reliability of the network. The simplified reliability model developed through this research is capable of calculating system level technical performance indices for utility-scale networks, requiring much less effort than detailed software models, but still providing an acceptable level of accuracy. The technical system indices (SAIDI and SAIFI), calculated by means of the simplified reliability approach, provide an indication of the technical performance of the network, but they do not provide information on the economic impact of network outages. These technical indices have the potential to result in funding decisions that are not closely linked to economic interest. For this purpose economic indices are required, and it is recommended that the approach be extended to include the calculation of economic indices

“One moment of extreme irresponsibility”: notes and comments on Humphreys v S and the volitional component of dolus eventualis in the context of dangerous or irresponsible driving

The 2013 judgment of the Supreme Court of Appeal in Humphreys v The State has provided a measure of clarity as regards the application of the principles of dolus eventualis, particularly the volitional component thereof in the context of dangerous or irresponsible driving. The 2013 judgment of the Supreme Court of Appeal in Humphreys v The State has provided a measure of clarity as regards the application of the principles of dolus eventualis, particularly the volitional component thereof in the context of dangerous or irresponsible driving. The court held that references to “recklessness” on the part of the accused should be approached with caution so as not to conflate the test for dolus eventualis with that for aggravated (or “conscious”) negligence. In more general terms, the judgment also provides guidance as to what constitutes appropriate charges in response to dangerous or irresponsible driving that results in death or serious injury to innocent persons. It is submitted that, in general, the more aggressive prosecutorial strategy of the National Prosecuting Authority towards irresponsible and reckless driving, under which such drivers are now more likely to be charged with murder and/or attempted murder, remains justified (and necessary) notwithstanding the outcome of the Humphreys case. However, through the use of a hypothetical example substantially similar to the Humphreys case, it is argued that, in future, the NPA’s prosecutorial efforts in such cases must be guided by the interpretation of the legal principles of dolus eventualis in Humphreys and by the specific facts of the relevant case.Department of HE and Training approved lis

The polycystic ovarian syndrome

The original publication is available at http://www.samj.org.zaThe polycystic ovarian syndrome remains one of the enigmas of gynaecological endocrinology. A review of the literature is presented, with emphasis on practical aspects, as illustrated by the results of a study of 139 patients with this condition. In the majority of patients the diagnosis entails clinical judgement combined with minimal biochemical determinations. However, the differential diagnosis may depend on sophisticated investigations. Since the treatment of some of these patients is as yet unsatisfactory, early diagnosis with prevention of androgenic side-effects is desirable.Publishers' versio

Die gonadotropiene in amenoree

The original publication is available at http://www.samj.org.zaSerum gonadotrophin values were measured in 410 patients with amenorrhoea. These patients were grouped into five groups in order to determine diagnostic gonadotrophin values, since the latter are most often implicated in the diagnostic investigation of patients with amenorrhoea. Statistically significant differences were noted. To differentiate between hypergonadotrophic amenorrhoea and polycystic ovarian disease, determination of both gonadotrophins, namely follicle-stimulating hormone (FSH) and luteinizing hormone (LH), is necessary. Because of overlapping of values in the polycystic ovarian disease group and the normogonadotrophic group, the LH:FSH ratio is important.Publishers' versio

The prosecution of incitement to genocide in South Africa

The phenomenon of collective violence is complex and, as yet, not wholly understood. This notwithstanding, the incidence of collective violence is not entirely unpredictable. This is especially true of one particularly egregious form thereof, namely, genocide. Inflammatory speech, insidious propaganda and incitement to crime - all of which are directed at a specific group - are recurring hallmarks of the hatred that invariably precedes genocide. Just as sparks under certain conditions are more conducive to causing a fire, acts of communication that feed on, disseminate, and actively intensify pre-existing hatred towards a particular group often represent a precursor to as well as a powerful catalyst for genocide.International Bibliography of Social Science

Christelike Hoër onderwys en die Natuurwetenskappe

Dit is van belang dat met hierdie mylpaal in die geskiedenis van die P.U.K. vir C.H.O. teruggeblik word op die ontwikkelingsgang van die natuurwetenskappe aan genoemde inrigting en verantwoording in verband met toekomsideale gedoen word

Afrika die Onbekende: Die Federasie van Rhodesie Njassaland (I)

Die grondgebied van die Federasie van Rhodesië en Njassaland strek oor 14° 15’ in ’n N.-S.-rigting (vanaf22“ 30’ S. to t 8° 15’ S.) en ongeveervanaf 22° 0 to t 36° 0. Dit verteenwoordig afstande in albei gevalle van tussen 900 en 1000 myl

Commentary on the documents Nostra aetate and Lumen gentium7

No Abstract

Die Via Dolorosa

In die hartjie van Jerusalem, die heilige stad vir Jood, Mohammedaan en Christen staan daar ’n boog, die ,,Ecce Homoboog” genaamd, en 'n klein endjie daarvandaan, die Heilige Grafkerk