Roberto Caldon

Distribution Line Carrier: Analysis Procedure and Applications to DG

The paper deals with analysis of carrier signals transmission in MV distribution networks. A multiconductor matrix procedure based on bus admittance matrix, which accounts for the earth return currents, allows predicting the high frequency behaviour of distribution networks and hence the effectiveness of transmitted signals. To this aim suitable models have been implemented based of the Carsons theory for overhead lines with ground return and Wedephols theory for cable lines. A comparison with the modal analysis demonstrates the advantages of multiconductor matrix algorithm with respect to modal analysis. In order to validate the theoretical results two measurement campaigns have been carried out on real MV networks. A good agreement between measured and computed values has been verified. Since distribution networks are generally unlike each other, the procedure becomes a valuable tool, which makes it easy to assess the feasibility of distribution line carrier (DLC) applications in any given system. In particular a protection system to prevent islanding of dispersed generators is proposed. In addition, in a foreseeable hypothesis of allowed islanding operation of portions of distribution networks (microgrids), DLC are proposed as communication control of the interface device at the point of common coupling

Reactive power control in distribution networks with dispersed generators: a cost based method

Abstract The reactive power service is one of the control area ancillary services that must be in place to make the electric energy delivery possible. It may be of interest to examine the advantage of providing the necessary reactive power support by local devices, namely shunt capacitors or Dispersed Generators (DG) where available. To this purpose the paper first defines costs for the service performed by these devices, then it proposes an optimal co-ordination method which allows distributors to select, for every operating condition, the more profitable combination of reactive sources in order to maintain the network voltage levels within a desired range and to minimise the regulation action global cost.

The Voltage Control on MV Distribution Networks with Aggregated DG Units (VPP)

In this paper a procedure that allows distributed generation plants (DGs) to be operated as a virtual power plant (VPP), maintaining meanwhile the voltage profiles on medium voltage (MV) feeders within the permissible interval, is presented. To this aim a co-ordinated controller is proposed. It acts both on the on line tap changer (OLTC) and on the reactive power production of specific plants so that voltage regulation is performed whatever the working condition (generation units disconnected or partially loaded or working at maximum power). In particular this controller can influence a VPP economic criteria dispatch by bounding, for example, the maximum active power generated by each unit in order to obtain the DG reactive generations required by the management of the distribution system. Thus, as a consequence some lower variable cost productions might have to limit their active outputs which represent a possible cost increase in VPP management. These automatic limitations, imposed by the controller, allow the distribution system operator (DSO) to control voltage on the whole distribution system and the DG plants to guarantee their connection to the network. Simulations on a realistic network case study are carried out to compare the VPP management impact on voltage profiles with a traditional voltage regulation (only OLTC action) and with a coordinated control system. Results demonstrate that the proposed procedure is able to preserve distribution network from dangerous under and over voltages with limited interferences with the VPP optimisation algorithm.

Application of distribution line carrier-based protection to prevent DG islanding: an investigating procedure

The paper deals with the possibility of using the distribution line carrier (DLC) in order to prevent dispersed generation islanding. The feasibility of this technology applied to MV networks has been investigated from a theoretical as well as experimental point of view. A multiconductor matrix procedure based on bus admittance matrix allows us to predict the high frequency behaviour of MV lines (overhead and cable): the signal strength can be verified at any section of MV networks. Moreover two measurement campaigns have been performed on real MV networks in order to validate the theoretical results.

Application of PLC for the Control and the Protection of Future Distribution Networks

The paper shows the great possibilities offered by PLC applied to the medium voltage power networks. The paper focuses the attention on the need for new strategies of control and protection of future distribution networks with high penetration of distributed generator (DG) and points out how PLC could have a key role among the technologies that are expected to be applied. In the paper, three chief proposals of application of PLC will be illustrated: the co-ordinated voltage control, a protection system to prevent dispersed generation islanding and the control of the interface device at the point of common coupling for a micro-grids distribution structure. By means of multiconductor matrix procedure already presented by the authors in previous researches, the feasibility of power line carrier applications will be demonstrated.

Analysis of the Italian distribution system evolution through reference networks

This paper presents initial results of a three-year research project entitled ATLANTIDE, which is aimed at developing a comprehensive digital archive of reference models of Italian distribution networks, including forecasted load and generation development evolving towards future smart grid scenarios. Such reference network models and evolutionary scenarios should provide a useful benchmark for testing and comparing different control methodologies, distribution schemes and operation strategies for dealing with the new challenges caused by the envisaged widespread diffusion and integration of distributed generation, renewable generation and distribution storage devices. The paper focuses on the criteria adopted for defining a set of evolutionary scenarios for the reference networks, accounting for current drives and future trends, valuable to a wide range of the stakeholders of the distribution business.

Coordinated voltage control in MV and LV distribution networks with inverter-interfaced users

In the last years there has been a progressive growing of distributed generators connected to the LV distribution networks, leading to possible depletion of power quality levels. For this reason, standards and grid codes are under revision and several studies have been conducted investigating the possibilities offered by grid connected inverter-interfaced generators to participate to network voltage regulation and unbalance correction. In this paper a control strategy is proposed applicable to a DMS coordinating the MV network regulation, applied through a novel adaptive regulation area criterion, with local LV network controllers which, in turn, coordinate the downstream inverter-interfaced generators. The aim is to demonstrate the benefits coming from a correct coordination of the distributed LV resources with the DMS located at the primary substation.

Application of modal analysis for the enhancement of the performances of a UPFC controller in power oscillation damping

The aim of this work is to investigate and evaluate the performance of UPFC (unified power flow controller) devices operating in a transmission system in order to control inter-area power oscillations originated by small disturbances. Particular emphasis is given in using the participation factor matrix in order to identify the state variables which mostly affect the modes of inter-area oscillations and to intervene on those state variables directly related to the FACTS action. The efficiency of the method is subsequently assessed by means of detailed dynamic simulations.

Resonance phenomena on line-to-ground fault current harmonics in MV networks

High levels of harmonic components measured on MV line fault currents have prompted a detailed investigation of the phenomena in order to develop models to accurately reproduce the observed harmonic currents and clarify the resonance characteristics of the system under line-to-ground fault conditions. A procedure which can predict the fault current wave-form of a whatsoever complex distribution system supplying a variety of loads, enabling identification of potentially harmonic resonance conditions, is presented. It may be applied, for instance, to verify the performance of networks adopting suppressing coil (which is normally tuned on the fundamental frequency) or zero-sequence protection relays. A parametric analysis on typical MV distribution systems shows how it is possible to identify critical fault locations which may give rise to very high harmonic currents.

Impact of distributed generation on network security: Effects on loss-of-main protection reliability

The growing penetration of GD in distribution networks determines a complete redeployment of power flows along distribution feeders, thus causing altered voltage profiles and new issues in protection reliability. This paper addresses the issue of island opening operation, by using detailed models of GD sources and analyzing the frequency and voltage oscillations induced by islanding in different condition of power flow on the interrupted branch. The aim is to identify which network conditions should be considered as possible causes of loss-of-main protection bad operation.