Measuring the efficiency in Spanish municipal refuse collection services

The objective of this study is to analyse the technical or productive efficiency of the refuse collection services in 75 municipalities located in the Spanish region of Catalonia. The analysis has been carried out using various techniques. Firstly we have calculated a deterministic parametric frontier, then a stochastic parametric frontier, and finally, various non-parametric approaches (DEA and FDH). Concerning the results, these naturally differ according to the technique used to approach the frontier. Nevertheless, they have an appearance of solidity, at least with regard to the ordinal concordance among the indices of efficiency obtained by the different approaches, as is demonstrated by the statistical tests used. Finally, we have attempted to search for any relation existing between efficiency and the method (public or private) of managing the services. No significant relation was found between the type of management and efficiency indices- L'objectiu d'aquest estudi és analitzar l'eficiència tècnica o productiva dels serveis de recollida d'escombraries a 75 municipis de Catalunya. L'anàlisi s'ha portat a terme utilitzant varies tècniques. En primer lloc, hem calculat una frontera paramètrica determinística, després una frontera paramètrica estocàstica, i finalment, varies aproximacions no-paramètriques (DEA i FDH). Pel que fa als resultats, aquests naturalment difereixen en funció de la tècnica utilitzada per aproximar la frontera. No obstant això, guarden una aparença de solidesa, al menys pel que fa referència a la concordança ordinal entre els índexs d'eficiència obtinguts per les diferents aproximacions, com mostren els tests estadístics utilitzats. Finalment, hem intentat buscar si existeix alguna relació entre l'eficiència i el mètode (públic o privat) de gestionar els serveis, no trobant-se cap relació significativa entre el tipus de gestió i els índexs d'eficiència

Ensuring public safety through proper earthing in low-voltage networks

\u3cp\u3eElectrical network should have proper earthing (grounding) system for its reliable operation and for the safety of operating personnel and connected customers. Good earthing provides a suitable return path for the fault current when a short circuit occurs in the network. In a low-voltage (LV) network mainly terra-terra (TT) and terra-neutral (TN) type network configurations are commonly used. Depending on the agreement between the network operator and the customer, earthing at a customer's point of connection (POC) is provided by a dedicated earth conductor, combined network cable (PEN conductor), or via a separate earth electrode. When an earth retour path is broken or interrupted, it will not be able to provide earth retour circuit and can cause dangerous fault voltage at various exposed parts of the conducting circuit. In this paper, various LV network configurations are discussed. Further, a practical monitoring based case study is presented to analyze the diversity of earth resistance values for different LV network configurations. Also, guiding rules are given to define safe value of circuit impedance and earth resistance path for various configurations. Finally, a proposal is given to optimize the safety needs at a customer's POC.\u3c/p\u3

A Bayesian approach for fault location in medium voltage grids with underground cables

This paper proposes a statistical approach for section-based fault location in medium voltage (MV) grids with underground cables, using Bayesian inference. The proposed approach considers several important uncertainties in the MV grid, including measurement errors, fault breakdown resistance, and the inaccuracies of zero-sequence parameters. The approach first obtains the prior distribution of the fault position from the component failure database, the readings of the transmitted fault indicators, and the relevant digging activity record. With the estimated prefault grid status and the measured transient voltages/currents, the posterior distribution is then calculated based on Bayes' theorem. To solve the problem numerically, the Monte Carlo integration is applied and a two-step calculation procedure is proposed. Simulations are performed on a typical European MV feeder to demonstrate the feasibility of the approach. The distribution grid operators can use the calculated posterior distribution to rank the possible faulted sections and to facilitate the restoration process, which can reduce the interruption duration of power supply

Dealing with customer's complaints regarding PQ issues - from DNO perspective

\u3cp\u3eDuring the last two decades the customers have become more aware about the voltage quality that they receive from the grid and its possible (negative) impacts on their household apparatus and on the living environment. The modern customers use sophisticated devices in their day to day life and do not want to comprise on their comfort level. Therefore, any inconvenience that might be caused by the electricity utility service is immediately reported as a 'complaint' to the network operators. When the operational people are convinced that it is voltage-quality related complaint, a week-long power quality monitoring (PQM) is generally done at the customer's point of connection (POC). If the measured power quality (PQ) parameters violate the standard limits of the EN50160 and the Dutch Netcode, an appropriate measure is taken/advised at that installation or in the network to improve voltage quality at the POC. In this study, customer's complaints related to some specific PQ problems are discussed. Furthermore, a PQ complaint handling methodology is discussed briefly, which gives guidelines to tackle customer complaints efficiently. Some national level activities are highlighted at the end of this study.\u3c/p\u3

Self-extinguishing faults in MV cable networks-feasibility study of fault prediction

\u3cp\u3eThe Dutch grid operator Alliander started an ongoing substation refurbishment in 2006 with SASensor, a measurement, protection and control system, including fault localization of persistent faults. Around 20 percent of the recorded measurements comprise the phenomena of 1-phase self-extinguishing faults. In order to assess the usability of these events to predict faults, the phenomena and their behaviour in time are described in MV networks with isolated neutral and low-impedance earthing. Furthermore the feasibility of fault localization using the information included in those events is discussed.\u3c/p\u3

Basis-adaptive sparse polynomial chaos expansion for probabilistic power flow

This paper introduces the basis-adaptive sparse polynomial chaos (BASPC) expansion to perform the probabilistic power flow (PPF) analysis in power systems. The proposed method takes advantage of three state-of-the-art uncertainty quantification methodologies reasonably: the hyperbolic scheme to truncate the infinite polynomial chaos (PC) series; the least angle regression (LARS) technique to select the optimal degree of each univariate PC series; and the Copula to deal with nonlinear correlations among random input variables. Consequently, the proposed method brings appealing features to PPF, including the ability to handle the large-scale uncertainty sources; to tackle the nonlinear correlation among the random inputs; to analytically calculate representative statistics of the desired outputs; and to dramatically alleviate the computational burden as of traditional methods. The accuracy and efficiency of the proposed method are verified through either quantitative indicators or graphical results of PPF on both the IEEE European Low Voltage Test Feeder and the IEEE 123 Node Test Feeder, in presence of more than one hundred correlated uncertain input variables

Analysis of reflectivity & predictability of electricity network tariff structures for household consumers

\u3cp\u3eDistribution network operators charge household consumers with a network tariff, so they can recover their network investment and operational costs. With the transition; towards a sustainable energy system, the household load is changing, through the introduction of photovoltaics and electric vehicles. The tariff structures which are currently employed in the EU are either capacity and/or energy consumption based. In light of the changes in the household load the question whether these tariff structures are the most suitable merits renewed attention. In this work, the cost-reflectivity of various tariff structures has been computed based on a distribution network planning approach. Next to this, the predictability of a network tariff, i.e. how much change would a household experience in network charges in two consecutive years has also been computed to gain insight into how well users will be able to react to the tariff. The results show that a peak load based network tariffs score best on the reflectivity while having an acceptable level of predictability. The switch from an energy consumption based network tariff, which is now most often applied, towards a peak load based network tariff should therefore, be considered.\u3c/p\u3

A proposal on voltage dip regulation for the Dutch MV distribution networks

\u3cp\u3eVoltage quality regulation has been an ongoing discussion in many countries in the world to set up a regulatory framework where also voltage dips are included in the national grid codes. Regarding voltage dips, the regulatory framework is useful for establishing the coordination between the network operators, the equipment manufacturers, and the customers. The voltage dip regulation can provide benefits for the involved parties. By defining the responsibilities for the network operators and the customers, it can help distribution system operators to evaluate the quality of supply voltage and to take possible measures when the number of dips exceed the reference values defined in the regulation. The regulatory framework can also help customers to make an economic analysis for choosing appropriate mitigation methods to reduce the expected economic damages caused by voltage dips. This article presents two approaches for classifying different types of voltage dips into various clusters. Using datasets of voltage dips from the Dutch MV networks, the paper also describes the methodology for setting limits on the number of voltage dips for the regulatory purpose.\u3c/p\u3

Assessment of errors in the measurement chain of distribution grids for feasibility study of a PMU application

\u3cp\u3eThis paper presents the results of tests done to review and discuss required levels of accuracy in the entire instrumentation and measurement chain of PMU-applications for distribution grids. Specific grid monitoring and estimation applications could have different requirements in terms of accuracy and resolution of the PMU estimates. Apart from the PMU's own accuracy, the overall accuracy of PMU estimates are dependent on accuracy level of the entire instrumentation channel and the grid's physical parameters. The results and discussions presented in this paper are in the context of a PMU-based line parameter estimation and Dynamic Line Rating (DLR) algorithm for medium voltage lines. These tests could be used to check feasibility of the DLR application on existing instrumentation infrastructure as well as to select the instrumentation equipment for futuristic applications in grids. The same methodology could be utilized to investigate the feasibility of other PMU-based applications for distribution grids.\u3c/p\u3