P. Caramia

• Parthenope University of Naples

The analysis of power quality disturbances in distribution systems has gained significance with the diffusion of electric vehicles (EVs). Waveform distortions are interesting since EV currents introduce distortions with spectral components in both low and high-frequency bands. This paper develops specific indices to assess cumulative emissions from...

The transformation of electrical networks in the context of the new smart grid paradigm unavoidably involves new challenges regarding Power Quality (PQ) disturbances not only for customers but also for all the other involved stakeholders. Among PQ disturbances, waveform distortions have recently gained growing interest due to the massive presence o...

Microbial fuel cells (MFCs) represent a key solution in the context of sustainable energy development from organic material. Their implementation for real applications is still limited because of economic issues and low power densities. Several efforts have been done both to improve the economic performance byselecting low-cost materials and to inc...

Due to the growing diffusion of single-phase Photovoltaic Systems (PVSs), the analysis of active unbalanced three-phase 4-wire distribution networks in short-circuit operating conditions is nowadays of great interest. However, this analysis is not trivial due to various factors (e.g., environmental conditions, inverter control system, limits of the...

Photovoltaic systems (PVSs) are among the most diffuse Distributed Generators based on renewable energy sources. PVSs contribute to the short-circuit currents during a fault, modifying the short-circuit capacity of the distribution systems. Then, the contribution of PVSs to the fault current must be adequately modeled to extend the traditional shor...

Distributed generation (DG) produces many benefits for the distribution systems, which, although traditionally designed under the assumption of passive networks, have become however active distribution systems. Then, new technical issues must be addressed, involving both normal and abnormal operating conditions such as short circuits. Photovoltaic...

A high penetration of Photovoltaic (PV) systems into power networks can alter the fault currents and negatively impacts on the operation of the protection systems. In this paper, a new analytical model of the fault contribution of a three-phase PV system equipped with a voltage source converter is proposed. Such a model extends the classical steady...

The management of micro grids requires the dynamic harmonic state estimation of the system in order to perform control strategies that optimize waveform distortions. In industrial context, AC and DC devices and sources coexist and, therefore, micro grids can be a hybrid combination of AC and DC power sections. Also for such hybrid AC/DC micro grids...

This paper proposes a model to the optimal management of a complex DC microgrid with advanced forecasting method for photovoltaic generation. The strategy is aimed at minimizing the daily total energy cost using a very short-time predictive control procedure. At first, the predicted power of the renewable generation unit is obtained by using an inn...

There is an increasing interest in standards and technical literature to the probabilistic characterization of voltage and current harmonics in multi-convertor power systems. The characterization requires to express the input data of the harmonic penetration modelling by random variables and to apply probabilistic techniques of analysis. Among prob...

The method of fault position is useful for characterizing power-system performance in the presence of voltage dips due to faults. It is based on short-circuit simulations repeated for all the system nodes and for many points along the system lines: fault voltages that are below a preset threshold are the required voltage dips. These dips are stored...

Future distribution networks are undergoing radical changes, due to the high level of penetration of dispersed generation and information/communication technologies, evolving into the new concept of the Smart Grid. Dispersed generation systems, such as wind farms and photovoltaic power plants, require particular attention due to their incorporation...

This is a companion paper to a paper of the same title, Part I, in which the theoretical aspects of some spectrum estimation methods for the analysis of non-stationary waveform distortions in power systems due to Wind Turbine Systems (WTSs) are analysed. In particular, Part I dealt with sliding window (SW) DFT, some parametric methods (SW Prony and...

Discrete Fourier Transform (DFT) and high-performance signal-analysis techniques (i.e., Prony, ESPRIT, root-MUSIC methods) have been proposed to calculate Power Quality indices that characterize waveform distortions in power systems. DFT can be affected by spectral leakage problems that cause inaccuracies in the spectral component calculation while...

Microgrids 1 are electrical subsystems which include small generation units, storage devices and loads, which can operate either in grid connected or islanding mode. This paper deals with a DC microgrid that will be realized in an Italian industrial facility of GETRA Group. In particular, in this paper an optimization model is formulated to solve t...

Wind farms have several impacts on the steady-state behavior of an electrical distribution system, and these impacts must be taken into consideration. This chapter dealt with deterministic approaches for the steady-state analysis of distribution systems with wind farms, considering both balanced and unbalanced systems. The steady-state analysis was...

In recent years, modern distribution networks are rapidly evolving toward the new concept of Smart Grid (SG) due to the increasing level of penetration of distributed generation (DG) units, storage systems and information and communication technologies. In the framework of low voltage distribution systems, SGs based on either AC or DC grids have be...

Smart grid behaviour is characterized by significant uncertainties due to the time-varying nature of powers generated by random energy sources and of load demands. These uncertainties introduce several technical problems in smart grid planning and operation and new issues have to be addressed. In this context, an important role is played by probabi...

The paper presents a probabilistic approach based on a Monte Carlo technique for the evaluation of the probability density function of three phase short-circuit currents in a distribution network with distributed generations. The proposed approach takes into account all the major uncertainties affecting the magnitude of the fault currents: power lo...

In this paper, we propose a new method for the accurate estimation of frequencies and magnitudes of harmonics and interharmonics caused on the supply-side currents by an adjustable-speed drive. The proposed method consists of a three-step procedure in which Estimation of Signal Parameters by Rotational Invariance Technique (ESPRIT) and Prony high-r...

Distribution networks are undergoing radical changes due to the presence of an increasing level of penetration of Distributed Energy Resources (DER); mainly for the increasing installations of Dispersed Generation (DG) units and Energy Storage Systems. Energy saving, reducing environmental impacts, Power Quality improvements are the main driving fo...

The problem of developing a definition that adequately assesses power-quality (PQ) levels in the presence of distributed generation (DG) is addressed by using proper probabilistic indices for distribution networks. In the planning of new DG installations, these indices take the variation of PQ level into account and use weighting functions properly...

The paper deals with the optimal operation of a Smart Grid (SG) including distributed resources based on dispersed generation (DG) units and plug-in vehicle fleets with the aim of furnishing some services both inside the SG and outside to the interconnected electrical system. The distributed resources are connected through power electronic interfac...

The paper deals with Smart Grids including renewable generation units, in particular concentrated photovoltaic systems and plug-in vehicles fleets. DG units and fleets are interfaced to the grid through static converters. Several services are performed thanks to the converters presence, with objectives aimed at meeting needs either internal or exte...

In this paper, the point estimate method is applied to account for the uncertainties that affect the evaluation of the steady state operating conditions of an unbalanced three-phase power system in the presence of wind farms. The accuracy of the proposed technique is tested on the three-phase unbalanced IEEE 34-bus test system adequately modified t...

Electrical power system robustness is defined as the intrinsic capacity of an electrical power system to maintain assigned disturbance levels when external conditions change. In this paper the concept of robustness against is applied to the voltage dips, one of the most severe disturbances in power quality. Using graphical color schemes as immediat...

Power quality (PQ) regulation is of great importance due to the economical consequences associated with the presence of the disturbances in power systems. Regulations should provide interventions at the system level (transmission and distribution networks) and the local level at the point of common coupling between utilities and customers. This pap...

IntroductionSingle-site indicesSystem indicesConclusions References

In this chapter, some models for the probabilistic network analysis of transmission and distribution power systems in the presence of harmonics are dealt with. The models considered derive from the classical models for deterministic analysis: direct method, harmonic power flow and iterative harmonic analysis. The chapter is organized so that for ea...

The presence of the new liberalized markets has increased the interest in power-quality (PQ) disturbances due to their economic effect. In particular, in the case of disturbances caused by a single event (such as a capacitor switching or voltage sag), the waveform assessment can be difficult due to the rapid variations in waveform spectral componen...

Electrical power system robustness is defined as th e intrinsic capacity of an electrical power system to maintain assigned disturbance levels when external conditions change. In this paper the concept of robustness against is applied to the voltage dips, one of the most severe disturbances in power quality. Usin g graphical color schemes as immedi...

Electrical power system robustness is defined as the intrinsic capacity of an electrical power system to maintain assigned disturbance levels when external conditions change. This paper compares two methods for estimating voltage dip severity: the critical distance method and the fault position method. Their differences are not linked to the type o...

The voltage continuity and quality are two different aspects of the quality on the electrical supply. Their regulation is of great importance due to the economical consequences associated with the presence of the disturbances in the electrical power systems. While voltage continuity has been regulated in several countries for his undouble importanc...

The presence of the new liberalized markets has increased interest in power quality disturbances due to their economic value. Customers have more choices; then disturbances are becoming bigger issues and suppliers and customers should regulate them in the frame of power quality contracts. A single global power quality index can be very useful for c...

A probabilistic method is proposed to take into account the uncertainties of loads and wind production in electrical unbalanced distribution systems. The proposed method is based on Monte-Carlo simulation applied to the nonlinear three-phase load flow equations including wind farms, thereby taking into account all load and line unbalances that can...

The paper deals with the power converter to be used in realising small scale generation units of electric and thermal energy. Polymeric fuel cells supplied with hydrogen obtained with natural gas reforming are considered as the most adequate fuel cell type for low and medium size applications. The complete structure of multistage converters is pres...

Actual Standards require specific tests on the generator sets to be overcome before introducing them into the market. During these tests, synchronous machines produce electrical energy that, in traditional test facilities, is dissipated on resistors. In this paper the realization of a no dissipative test facility able to recover this produced elect...

IEC Standards characterize the waveform distortions in power systems with the amplitudes of harmonic and interharmonic groupings (subgroups and groups) calculated by using the waveform spectral components obtained with a 5 Hz frequency resolution DFT. In some cases the power system waveforms are characterized by means of spectral signal components...

Passive and active filters have traditionally been used to reduce harmonics in power systems. Only recently combined systems of shunt passive and active filters have been proposed in order to overcome the technical problems of passive filters and to reduce the costs of active ones. The paper tries to overcome some drawbacks of a combined filtering...

The method of fault position is useful for characterising power-system performance in the presence of voltage dips due to faults. It is based on short-circuit simulations repeated for all the system nodes and for many points along the system lines: fault voltages that are below a preset threshold are the required voltage dips. These dips are stored...

Representation of signals in time and frequency domain has been of interest in power systems for many years, especially in the case of nonstationary signals. Standard tools of waveform distortion analysis are based on the Fourier transform while only recently the Prony and rootMusic methods were tested for this purpose. However, these methods show...

The present paper deals with the relevant aspects related to EG and its influence on the quality of supply of the distribution networks, focusing on the impact of EG on harmonic distortion, voltage variations and dips. It is shown that assessment of the network power quality levels can be efficiently performed by means of suitable indices defined f...

The stochastic prediction of voltage dips due to faults in transmission and distribution systems can be effected applying the fault position method. Also assuming deterministic operating condition before the faults and pre-assigned failure rates of the faulted components, this method may require severe computational efforts in case of high dimensio...

The concept of the system robustness against voltage dips is firstly analysed evidencing the main parameters it depends on. Then, the link between short circuit power and robustness is dealt with using also some numerical results obtained on a medium voltage distribution test system. Finally some considerations are offered with the aim to contribut...

The paper deals with the problem of assessing the impact on the service power quality (PQ) of new installations of embedded generation. To face with this problem, two types of indices are proposed: variation and benefit index. Their definition is irrespective to the specific disturbance to be considered so that it is possible to indicate them as ge...

Nowadays the need for more flexible electric systems, the changing in the regulatory and economic scenarios, the importance of harnessing energy savings and minimising environmental impact have been providing the impetus for the development of a new distribution system into which embedded generation with wind farms is predicted to play a key role....

The widespread use of advanced technologies and automation in AC and DC railway systems requires an accurate investigation of the Power Quality disturbances they suffer. In some cases, both railway systems operate in the same transmission network area, so that voltage unbalances and waveform distortions can be complicated by the interactions betwee...

In this paper the problem of the low voltage cables thermal sizing in nonsinusoidal steady-state operating conditions is considered. In particular, the case of four conductors low voltage cables feeding groups of single-phase nonlinear loads such as desktop computers, TV, light-dimmers and so on is taken into account. Particular attention is paid t...

Distribution system engineers have frequently to choose among different solutions under problem data uncertainty; in most cases related to modern distribution system components sizing, among the uncertainties, the ones deriving from the presence of static converters must be included. In these conditions, decision theory can offer efficient and valu...

This paper deals with the harmonic indices and gives considerations about their random behavior; the indices taken into account refer to the entire electrical distribution system. System indices are useful metrics to qualify distribution systems (or a part of it) and are able to take into account different quality service aspects. Indices not yet i...

The growing complexity of the AC and DC traction systems in terms of both new technologies and automation requires a careful control of the power quality disturbances they cause. In some cases-as in Italy-both traction systems operate in the same transmission network area, so that the power quality problems have become much more complex because of...

Some evaluation methods to obtain the probability density functions of voltage and current harmonics in multi-convertor power systems are presented. The approaches are based on Monte Carlo simulation applied to the non linear and linear harmonic power flow equations, on convolution process and on Pearson distributions. These methods are compared in...

This paper looks at the harmonic indices and gives considerations about their random behavior. The indices taken into account refer to both the single customer point-of-common coupling and the entire electrical distribution system. The analysis of on-site measurements and numerical simulations on medium voltage distribution systems allow us to evid...

Some techniques are presented to obtain the probability density functions of phase-voltages in an unbalanced three-phase power system. The techniques are based on the Monte Carlo simulation applied to the non-linear and linear three-phase load flow equations, on convolution process and on the Pearson distributions. These methods are compared in ter...

The problem of the evaluation of the buried cable thermal useful life in presence of harmonic distortion and taking into account the moisture migration is analysed. The evaluation is effected in nondeterministic scenario with a probabilistic approach. Numerical applications referred to medium voltage cables are presented and discussed in order to s...

The paper proposes procedures which allow to know, for assigned harmonic profile of nonlinear loads, the cable cyclic and emergency ratings in nonsinusoidal operating conditions. The proposed procedures refer to distribution cables and employ simplified expressions very similar to those adopted by IEC Standard 853 for the sinusoidal conditions; the...

Selection of cable size in the nonsinusoidal conditions is only based on ampacity considerations without any attention to the cost of the losses that will be suffered in the cable life. Since the cost of these losses (fundamental plus harmonics) can assume significant values, the selection of a cross section higher than required for ampacity consid...

Both amplitude and argument of voltage harmonics can affect the electrical component behavior. In the paper an integrated index taking into account both of them is proposed for inclusion in harmonic standards. This index, which refers to the well known peak value of distorted voltage, allows taking into account the main effect of distorted voltages...

Modern AC traction locomotives use PWM controlled converters on the line-side which produce harmonics on the supply system. Configurations with multiple interlaced PWM converters reduce the harmonic emission to levels for which the input current of the locomotive is close to a sine wave. The paper analyzes the interaction between the 15 kV-162/3 Hz...

Selection of cable size in nonsinusoidal conditions is based only on ampacity considerations without any attention to the cost of the losses that will be suffered in the cable life. Since the cost of these losses (fundamental plus harmonics) can be high, the selection of a cross-section higher than required for ampacity considerations can result in...

In designing a distribution system, engineers have to choose optimal solutions under environmental uncertainty; in most cases, among the uncertainties the ones deriving from the presence of nonlinear loads must be included. Under these conditions, the Decision Theory appears to be a valuable tool for solving distribution design problems. This paper...

The paper analyzes the interaction between the EMU locomotives and the 15 kV-16 2/3 Hz AC supply system. To this aim the power converters on board of the EMU locomotive have been modeled and then included into the model of the whole traction system. In particular the power converters have been simulated by ATP implementing two models with different...

The Inherent Structure Theory of Network is a valuable tool to solve power quality problems. In fact, in the frame of this theory, the direct or inverse sequence impedance matrix at the fundamental frequency or the harmonic impedance matrices can be formulated in terms of their eigenvalues and eigenvectors; these expansions are useful to create a f...

The paper deals with the costs due to the harmonics. The introduction of costs evaluation in the harmonic analysis allows quantification of the real effects of different pollution levels on the equipment and components. Moreover, it can be the basis to define “quality price” of energy suitable to be introduced in a de-regulated market. The consider...

The paper proposes a procedure which allows to known, for assigned harmonic profile of nonlinear loads, the cable cyclic ratings in non sinusoidal operating conditions. The proposed procedure employs simplified expressions very similar to those adopted by IEC Standard in sinusoidal conditions, being the harmonic presence taken into account by a new...

The adjustable speed drives are now designed for so high power usage to be employed without restrictions for the power plant auxiliary services. Unfortunately, they employ power electronic devices to generate the variable frequency power supply for AC motor speed control with the consequent generation of harmonics and interharmonics which add to di...

Harmonic distortion can affect significantly the reliability of electrical plant components by increasing the degradation rate of electrical insulation. This paper presents life models which enable estimation of failure times of the electrical insulation of the main components of industrial electrical plants, i.e. capacitors, cables, motors and tra...

The paper presents and analyzes the results of harmonic and interharmonic measurements performed at the vehicle test room of CRIS Ansaldo on the new high-speed locomotive ETR500. The adjustable speed drives of this locomotive utilize PWM-controlled converters to both rectify the voltage of the AC supply system and feed AC motors. These converters s...

The paper describes the effects of power quality degradation on the AC input current response of three-phase PWM-VSI adjustable speed drive with diode bridge rectifier. The study accounts for different voltage nonideal conditions, showing the results obtained in presence of single and multiple disturbances, like harmonics, fluctuation and unbalance...

In actual systems unavoidable uncertainties affect the steady-state operating conditions of a power system: these uncertainties are mainly due to changes of load demands and of generation system. Taking into account the uncertainties, it is most useful to introduce random variable and to apply probabilistic techniques of analysis. Up to now probabi...

In this paper the economical damage due to the harmonic losses is quantified by means of the expected values of the operating costs and of the aging costs. To evaluate the above quantities a simplified approach based on closed form relations is proposed. It can be applied when only one group of nonlinear loads is the main cause of the harmonic poll...

The most adequate way to take into account the uncertainties which affect the modelling of unbalanced three-phase power systems including HVDC interconnections is to express the input data by random variables and to apply probabilistic techniques of analysis. In this paper, a probabilistic three-phase AC/DC power flow is proposed able to take into...

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The problem of evaluating the losses in unbalanced three-phase power systems is considered. To take into account the uncertainties which can affect the losses, the evaluation is effected by applying probabilistic techniques of analysis; both closed form solutions and Monte Carlo procedures including correlation among the loads are presented. The pr...

The problem of harmonic loss evaluation is of growing interest among power system engineers, both for the increase of operating costs and the decrease of the useful life of the system components. The paper addresses this problem with a probabilistic approach to take into account the randomness of current and voltage harmonics; a method for evaluati...

The most adequate way to take into account the uncertainties which affect the modelling of harmonic penetration is to express the input data by random variables and to apply probabilistic techniques of analysis. In this paper a probabilistic method is proposed for assessing harmonic distortion levels in power systems. This method transfers to the f...