Electricity distribution networks are a critical infrastructure of the modern society. The continuity of the electricity distribution service is therefore a key topic. Network automation is aimed at improving service continuity. Among the several possible automation schemes, logic selectivity of protection relays is one of the most effective approach because it allows minimizing the extent of the area affected by the fault with a short clearing time. IEC 61850 provides a standard way to implement automation. This paper describes a laboratory setup where the logic selectivity—based on the IEC 61850 standard—was tested before moving protection relays to a real operating environment for field demonstration. An analysis of system configuration and performance is reported when phase-to-ground and phase-to-phase faults were tested. Failure of the communication infrastructure enabling the coordination among relays and a failure of the breaker were also simulated to determine how the system was fault tolerant. The results show that the logic implemented is fast enough to send the trip command to the breaker in less than 170 ms in the case of phase-to-ground fault and in less than 130 ms in the case of phase-to-phase fault, even considering the time needed for the coordination of relays.

Smart Grid Automation Based on IEC 61850: An Experimental Characterization

Power quality in distribution grids is already a concern in many European Countries where there is a strong presence of renewable energy generation. There is therefore a growing interest in new technologies able to improve the power quality level, among them the Open Uninterruptible Power Quality Conditioner (Open UPQC). Despite several proposals have been analyzed in literature, there are still few examples of experimentation in real environments. The paper discusses the design and the simulation of the Open UPQC, focusing on its series component. This analysis is the result of the preliminary investigation lead before the physical installation of the system in a real operating distribution grid.

Open UPQC: A possible solution for power quality. Series unit analysis

Distributed generation (DG) has gained popularity among electricity end users who are determined to contribute to a cleaner environment by conforming to green and sustainable energy sources for various daily needs. The power system impact of such trends (e.g. roof-top solar-PV) need thorough investigation, such as impact on fault current levels on the distribution network. Varying fault current levels could adversely affect the operation of protection relays, which may lead to localized blackouts. Therefore, it is imperative to avoid localised blackouts due to mal-operation of protective relays under high penetration of DGs in distribution network. The focus of this research is to study the importance and implications of protective relays and over-current protection in the presence of distributed generation; where the impact of distributed generation on distribution network is identified. Relay coordination is observed to determine their operation characteristics to avoid mal-operation with the presence of DGs (e.g. solar-PV). This paper uses the UK generic distribution network model to simulate different scenarios in DIgSILENT Power Factory. The resulting power quality measures, such as voltage levels, short-circuit current levels and frequency are presented and discussed in the paper. The research highlights that small-scale DG penetration allows for existing protection infrastructure to continue operation and expensive upgrades for overall network are not required as fault levels remain the same.

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Impact of Distributed PV Generation on Relay Coordination and Power Quality

This paper addresses the meshing of distribution networks through MVDC (Medium Voltage Direct Current) links, based on VSCs (Voltage Source Converters), as a viable solution to manage critical network conditions, i.e. overloads or the connection of large loads to the existing distribution system. In this paper the impact of MVDC links on distribution networks was evaluated with OPF (Optimal Power Flow) analyses either for a test distribution network and a real case study provided by Unareti SpA (an Italian Distribution System Operator - DSO). For the real case study, fault studies to check the adequateness of the existing protection systems to the proposed meshed network configuration were performed.

The impact of MVDC links on distribution networks

Distributed Energy Resources (DER) connected to distribution grids through static power converters may have major impacts on Power Quality (PQ). For this reason, power converters used as Universal Compensators (UC) are gaining more and more interest. This paper describes the design, modeling and study of a shunt static compensator for Low Voltage distribution grids. The proposed device can be used for interfacing Distributed Generators (DG) or Energy Storage Systems (ESS) to the grid and can be connected close to disturbing loads. This device can compensate harmonic currents, reactive power and unbalances of disturbing loads, and it can also supply sensitive loads in island operation. Performances of the proposed device, with different control schemes and with different harmonic compensation strategies, are assessed through Control Hardware in the Loop (CHIL) Real Time simulations.

Performance test of a PQ universal compensator through Control Hardware in the Loop simulation

The growing trend of installed power from Distributed Generators (DG) in distribution networks is giving rise to new issues in grid operations. In particular, the interaction between DG and grid protections can cause nuisance trips, unwanted island operations and, in general, worsening of power quality. The paper discusses a possible protection scheme suited for active networks and implementing logic selectivity. The proposed approach is based on directional protections coordinated through communications. Simulation models of an urban Medium Voltage (MV) distribution grid, of distributed generators and of the employed types of protections have been developed in the DIgSILENT Power Factory environment. Digital simulations confirms the effectiveness of the proposed approach.

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Simulation model of a protection scheme for active distribution networks

A Universal Compensator (UC) for Power Quality improvement is presented in the paper. It can compensate harmonic currents, reactive power and unbalances of disturbing loads and supply in island mode sensitive loads. In case of grid disturbances, a static switch is open and the UC restores the voltages before disturbance occurrence at the load connection point. A 50 kVA UC model has been designed and a digital simulation model is used to assess its performances. Simulation results of compensation of different type of loads are reported both for grid connected and island operations.

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A universal compensator for power quality improvement in lv distribution grids

The joint use of the two IEC core standards CIM and IEC 61850 requires the handling of both data models in an integrated way. This paper illustrates a software tool which can automatically derive IEC 61850 device configurations from the topological analysis of CIM networks, for the implementation of logic selectivity between line protection devices. Moreover, the topological analysis is performed by directly manipulating the graph-based knowledge representation format used by CIM, called RDF, using a dedicated query language. This approach can be extended to any CIM-based algorithm. Finally, two complementary simulation environments have been setup in order to test the device configurations.

IEC CIM-61850 harmonization — The logic selectivity case

The growing amount of information produced by automatic systems is often associated with the paradigm of Big Data. Next to this approach it remains the interest in integrating information of different origin within a shared framework, conceptually able to be formalized by an ontology. The IEC Common Information Model (CIM) is a natural candidate to take on the role of reference ontology in the electrical context being able to describe different types of electrical domain information (eg. topologies of electrical networks, market information, metering, etc.) in an integrated way. The activities described here have adopted the CIM standard as a reference semantic model for the representation of information gathered from Power Quality (PQ) monitoring of medium voltage distribution networks, in order to demonstrate the possible synergies with the types of information already provided in that model, namely those associated with topological and cartographic information. The result of this integration could also be in perspective leveraged in the context of the deployment of the 2° generation of Italian meters that will include Power Quality data.

Integration of power quality information in the framework of a standard semantic model

The paper presents a demonstrator tool, designed as an architecture of microservices, to visualize and correlate Power Quality (PQ) data with topological, cartographic and meteorological information. Starting from a single web access point, the tool allows a network operator to “cast a glance” to different kind of data, involved in the management of its network or coming from open data sets, to investigate possible correlations among them. The adopted approach in data management make use of both the ontological and big data paradigma. This choice allows the operator to manage and correlate large volume of data of different kind (structured and unstructured data). The adopted ontology is the IEC Common Information Model (CIM), which allows the integration of PQ information recorded by the QuEEN monitoring system, at the HV/MV stations of the DSO Unareti S.p.A., with the associated distribution network topology. Services offered regard: (i) the visualization of PQ indices in association with topological and cartographic information; (ii) a classifier, based on a Software Vector Machine (SVM) algorithm, to define the origin of voltage dips; (iii) a web application, developed in the Spark framework, to correlate in space and time QuEEN voltage dips times series with storm cells.

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Salvatore Pugliese

Papers

Simulation model of a protection scheme for active distribution networks

A universal compensator for power quality improvement in lv distribution grids

IEC CIM-61850 harmonization — The logic selectivity case

Integration of power quality information in the framework of a standard semantic model

A demonstrator tool to provide the network operator with microservices based on big data and semantic web technologies