Standard-based Secondary Substation Automation ...

Standard-based Secondary Substation Automation Unit–the ICT Perspective Shengye Lu and Sami Repo Department of Electrical Engineering Tampere University of Technology 33720 Tampere, Finland [email protected]

Abstract—To improve automation level at LV network in a costeffective way, a “secondary substation automation unit” solution has been developed. Its main idea is to integrate smart metering data and MV/LV grid measurement, using them to realize LV network management functions at secondary substation. This automation unit can be implemented in an open and standardbased manner. A proof-of-concept prototype system has been implemented, and it achieves LV network monitoring in near real-time. A second release of this automation unit extends it by adding a new set of features for Demand-Response applications. This paper focuses on the ICT perspective, explain how this secondary substation automation unit have been implemented in the first and the second releases, and how IEC 61850 and CIM standards have been used in its design and implementation. Index Terms—secondary substation automation, IEC 61850, CIM, low voltage network, Demand-Response

I. I NTRODUCTION

Davide Della Giustina A2A Reti Elettriche SpA Via Lamarmora 230 25124 Brescia, Italy [email protected]

Italian Ministry of Economic Development co-funded project Smart Domo Grid[3], a second release of this automation unit is now under development. It adds a new set of features dedicated for Demand-Response applications. This paper explains the implementation details of this secondary substation automation unit, focusing on its ICT perspective. The implementation details of the first prototype system (achieved in INTEGRIS project), including its hardware/software components, are presented in section II; while the details of the second release (in Smart Domo Grid project) are described in section III. Because this automation unit heavily relies on standards, section IV explains how IEC 61850 and CIM standards have been used in its design and implementation. Section V and section VI briefly present the results and draw a conclusion.

II. SSAU WITH LV N ETWORK M ONITORING F UNCTIONS Traditionally, distribution automation mainly focused on high The Secondary Substation Automation Unit, or SSAU, aims voltage (HV) and medium voltage (MV) level. The decisionmaking point is at control centre, where Supervisory Control to improve the automation level at LV grid in an affordable And Data Acquisition (SCADA) system continuously monitors manner. Similar as the idea in [4], the very essence of and controls devices at primary substations and MV feeders. SSAU is to shift distribution management from traditionally Low voltage (LV) grid and secondary substation, on the other the control centre room-based centralized architecture to the hand, have very limited level of automation. However, with “decentralized” architecture. Its basic idea is to gather smart-metering data and LV grid increasingly widespread deployment of distributed generation and distributed energy resources (DER) in the future LV measurement data at secondary substation. These data are stored network, there is a clear trend that more intelligent will be and analysed locally at secondary substation, only alarms and requested or analysed information need to be sent to control needed at LV level[1]. To improve automation level at LV network and to pursue centre. In the meanwhile, with these locally stored measurement a balanced trade-off between Distribution System Operators’ data, secondary substation may conduct some autonomous (DSO) investments and benefits, a “secondary substation decision-making and perform some LV management functionalautomation unit” solution has been developed. Its main idea is ities. In this way, distribution management architecture becomes to merge smart meter data together with distribution automa- “decentralized”. Because measurements are transferred only to tion, and adopt standard-based interfaces. A proof-of-concept the level where it is needed, and the decision-making is done as prototype system has been implemented and tested during the close to measurement units as possible, the whole distribution European 7th Framework Program project INTEGRIS[2]. It management has better scalability and efficiency. realizes LV network monitoring in near real-time. A prototype system of this Secondary Substation Automation This prototype system can be further extended by adding Unit has been implemented and tested in INTEGRIS project. more functionalities and applications on top of it. Within the This SSAU realizes LV network monitoring in near realtime. It consists of several hardware/software components, The research has received funding from the European Unions Seventh deployed at secondary substation. Fig. 1 describes its internal Framework Program project INTEGRIS and Italian Ministry of Economic Development co-funded project Smart Domo Grid. components, which are highlighted in brown dash circle, with

A. Hardware Components The hardware components of the SSAU implementation are indicated as blue boxes in Fig. 1, including: Meter Data Concentrator, for aggregating data from multiple smart meters; secondary substation monitoring unit (RTU), for measuring transformer and LV feeders; and EGX 3200 gateway, for protocol mapping. In INTEGRIS project, two types of smart meters are in use. The first type is single-phase fiscal meter. They are installed at customers premises, measuring phase voltages, currents, active and reactive power, as well as energy values. The second type is three-phase power quality meter. They can measure values such as voltage level, rapid voltage changes and harmonics. In the field trial conducted by A2A Reti Elettriche SpA (A2A), power quality meters are placed in LV street cabinets. Data from these smart meters are collected by Meter Data Concentrator (MDC). MDC communicate with these smart meters via Broadband over Power Line (BPL) technology, using DLMS/COSEM standards. In A2A field trial, MDC polls single-phase fiscal meters every minute and polls power quality meters every 10 minutes. Secondary substation monitoring unit (i.e., RTU) provides measurement such as phase voltage, current and power quality values from MV and LV side of transformer, and from LV feeders. These measurement values are encoded in Modbus format. EGX3200 gateway transforms them into IEC 61850 format. Figure 1. Major components in the first release of SSAU implementation

B. Software Components

On secondary substation’s computer system, host some software components. They are indicated as yellow boxes blue boxes representing hardware components and yellow boxes in Fig. 1. They realize data collecting and SCADA reporting functions, as well as some intelligent computations such as as software components. state estimation and fault location. As indicated in Fig. 1, smart meter data from customers, “Customer Data Collector” software reads smart meter data as well as secondary substation measurements provided by from MDC and stores them into database. It also conducts Remote Terminal Unit (RTU), are aggregated and stored in protocol mapping, to transform meter data from DLMS format the database at secondary substation. From there, data are to IEC 61850 format. “Substation Data Collector” software colreported directly to SCADA system in control centre. In the lects secondary substation measurement values from EGX3200 meanwhile, some LV network management functions, such as gateway and keep them in database. The communication uses state estimation and fault management, are carried out locally IEC 61850/MMS protocol[7], with Substation Data Collector at secondary substation. as the IEC 61850 client and EGX3200 gateway as the server. This SSAU is built on top of IEC 61850 standards. It With real-time measurement data aggregated in secondary uses IEC 61850 data model to organize measurement data substation database, LV network monitoring now becomes and uses IEC 61850 communication service interface[5] to possible. This is realized by a software called “SCADA realize communications. As will be shortly explained, SSAU Reporting Gateway”. SCADA Reporting Gateway periodically utilizes this standard to report data from secondary substation reads measurement values from database and reports to control to SCADA in control centre. centre. The reporting procedure operates in an innovative way: It should be noted that the SSAU relies on an extensive com- it uses IEC 61850 reporting service[5]. SCADA Reporting munication infrastructure. This communication infrastructure Gateway is implemented as an IEC 61850 server application. has been accomplished in INTEGRIS project by combining At control centre, a lightweight SCADA system called iControl multiple communication technologies such as Wi-Fi and SCADA functions as an IEC 61850 client application. It broadband power line communication[6]. With this “INTEGRIS “subscribes” desired datasets and then receives reports from communication infrastructure”, this SSAU is able to report data SCADA Reporting Gateway. The detail is presented in [8]. towards control centre via a direct access to the Wide Area Using these locally stored measurement data, some intelligent Network. decision-making can be realized autonomously at secondary

substation. “State Estimation” software estimates currents, voltages and power flows in all phases and all parts of the LV network. It improves the accuracy and reliability of the LV network state when real-time measurement information is unavailable from some of the customers – for instance, in A2A field trial, only some of customers have smart meters installed. The detail of this software is explained in [9]. “Fault management” software uses smart metering data to detect some LV network faults, such as missing phase and neutral conductor faults[2].

Retailer

DSO Control Centre

... iControl SCADA

Retailer Intelligence

DSO Intelligence

RTU

Meter Date Concentrator

Secondary Substation O-UPQC∑

III. SSAU WITH D EMAND -R ESPONSE F UNCTIONS The second release extends the implementation in Section II Power Quality Customer’s DEMS Meter premises by adding a new set of features for Demand Response appliSmart cations. It utilizes state estimation algorithm to foresee some Meter O-UPQC// LV network congestion issue, then carries out some DemandSmart (and energy Applicances Response transactions, and performs some DER controls to storage) mitigate the network issue. It is now under development in Smart Domo Grid project[3]. Data flow The development of this SSAU is driven by the fact Additional hardware Hardware reused from first release that with increasing number of DERs (e.g., Photo Voltaic productions, heat pumps and electric vehicles) connected to Additional software Software reused from first release distribution network, DSOs have to deal with ensuing LV network congestion problems, such as “overloading” and Figure 2. Main components in the second SSAU release, including some “voltage drift” issues. relevant components at customers premises Overloading is a condition where the current/power flowing through an asset is higher than the rated current/power of the asset itself. This issue can be solved by peak shaving (curtailing To implement aforementioned Demand-Response functions, customers consumption or production), by peak shifting (shift- some additional hardware/software components need to be ing consumption or controllable production to off-peak periods), installed at customers’ premises and at secondary substation. or by production following principle (strategically increasing The structure of the second SSAU release is illustrated in Fig. shiftable consumption during high production periods). Voltage 2, with additional hardware and software indicated as orange drift is a condition where the voltage in a node is outside and green boxes. the range specified by, for example, the EN 50160 standard (+/ − 10% of the nominal value). In Smart Domo Grid project, A. Hardware/Software Components at Customer’s Premises voltage drift issue is solved via a sink/injection of reactive Firstly, the customer who joins the Demand-Response power by customers’ DERs. program has to own some controllable home appliances, known The methodology to implement Demand-Response, as as Smart Appliances (SAs). proposed by Smart Domo Grid, is as follows: firstly, DSO In addition, he needs to install a Domestic Energy Manageforesees overloading and voltage drift issues by using the State ment System (DEMS). The DEMS can be either owned by Estimation algorithm. Secondly, it creates Demand-Response the Retailer, or provided by a Service Provider. It could be requests intended to mitigate the network issues, and sends either deployed in a home gateway, or centralized in a cloudthese requests to the Retailer. The Retailer is, today in Italy, based architecture. It communicates with SAs and secondary the party that holds the contract with the customer. Thirdly, substation via Internet connection. The DEMS monitors and the Retailer adds to the request some incentive or bonus controls the domestic energy consumption, distributed generinformation, then dispatches Demand-Response requests to ation and/or storage. It receives Demand-Response requests corresponding customers. Finally, these Demand-Response with incentive information, and optimizes the best schedule requests are evaluated by the customer with the help of for Smart Appliances according to some boundary conditions Domestic Energy Management System (DEMS), and fulfilled set by the customer. if the customer chooses so. If the customer fulfils DemandSecondly, to solve voltage drift issue, an innovative disResponse requests, he will receive a bonus. tributed power electronics system, called O-UPQC (Open The new SSAU release allows DSO foresee LV network Unified Power Quality Conditioner), is deployed both at congestion issues, and it provides control logics for both customers’ homes and at secondary substation [10]. DSO and the Retailer. In this way, DSO and the Retailer The O-UPQC component installed at customer’s home can collaborate and interact at secondary substations, realizing is called O-UPQC// unit. It consists of an AC/DC power Demand-Response efficiently. converter, connected to a Domestic Distributed Energy Storage,

as well as a set of static switches. The O-UPQC// is owned by the customer and is controlled by the DEMS via Internet. Its main function is to improve the power quality at the customers connection point in a cost-effective way. The details of OUPQC implementation are presented in [11].

2) “Retailer Intelligence” Software Components: “Retailer Intelligence” software mainly take care of Demand-Response functions. Firstly, a software called “Exception Detector” analyses the network state forecast based on State Estimation result, identifies possible network issues such as overloading or voltage B. Hardware/Software Components at Secondary Substation drift. The O-UPQC component deployed at secondary substation Then, software “Exception Handler” translates the detected P is called O-UPQC unit. It consists of a coupling transformer, network issue into a new Demand-Response Request. In the with the primary circuit connected in series with the mains line case of voltage drift issue, it may also sends a new voltage P and a secondary one supplying the reversible AC/DC power reference to O-UPQC Controller. P converter. The O-UPQC is owned by the DSO and controlled In Smart Domo Grid project, there are two types of Demandby SSAU software, and its main function is to compensate Response Requests (or DR Requests, for short). The first type voltage dips and regulate the voltage level to a specific reference is “peak-shaving” request, which focuses on active power. The value at the secondary side of the MV/LV transformer. Its detail DSO uses this request asking those customers who have a is presented in [11]. DEMS to reduce their consumption within a specified time The software components of this SSAU release can be frame. The customer can acknowledge this request by shifting divided into two groups. The first group is related with his load, using a local storage if it is present, or using local DSO real-time network management functionalities. They are production if present. The second type is “voltage regulation” collectively indicated as “DSO Intelligence” in Fig. 2. Many request, which is targeted at reactive power. The DSO uses “DSO Intelligence” components have been implemented in this request asking those customers who have O-UPQC// and the previous SSAU release. The second group is related with energy storage to sink or inject reactive power. The customer Demand-Response functionalities. They are collectively de- can acknowledge this request by controlling the reactive power noted as “Retailer Intelligence” in Fig. 2. “Retailer Intelligence” of inverters of a local storage, or a local production. components interface with Retailer and make decision for Before a DR Request is dispatched to a customer, a piece Demand-Response request. of “bonus” information need to be attached to it. This bonus 1) “DSO Intelligence” Software Components: “DSO In- information tells how much reward the customer can receive telligence” software reuses some components from the first by acknowledging this DR Request. release, including Customer Data Collector, Substation Data For the customer who fulfils the DR Request, his reward is Collector and SCADA Reporting Gateway. In addition, the decided by “Request Status Checker” software. This software original State Estimation software has been extended. A new verifies whether the customer has fulfilled the DR Request by P software, called “O-UPQC Controller”, is added in order to analysing real-time measurement tables, and monitoring the P control O-UPQC unit at secondary substation. customer’s active/reactive power profile. If the DR Request is State Estimation estimates the state of the LV grid at fulfilled, then it confirms the bonus to the Retailer. certain time by using the LV topology, assets information, Besides, “Retailer Intelligence” contains some software measurements on the LV network, and customer’s load profiles. allowing the three parties – Retailer, DSO and customers Load profiles have been defined for each customer group based (via DEMS) – to exchange information with each other. For on smart meter measurements[12]. In the second SSAU release, example, State Estimation calculates both the current state and a future • DEMS Data Reporting–It sends the customers real-time state (e.g. 1-12 h later than the execution time). The former consumption information to the DEMS, which uses it to provides the present snapshot of the LV grid. The latter gives a determine the current consumption with respect to the short-term forecast for the state of the network, which will be contractual power of the customer. used as the base point to manage some LV network issues. The • Request Router–It forwards a Demand Response Request future state is calculated based on information such as load to a corresponding DEMS. profiles, solar irradiation forecasts and temperature forecasts. IV. U TILIZING IEC 61850 AND CIM STANDARDS The state estimation results are stored in database tables. P O-UPQC Controller is used to communicate with the To improve the interoperability, the SSAU utilises standards P O-UPQC unit. It basically provides a voltage set point, such as IEC 61850 and CIM standards. The SSAU uses IEC asking to regulate a new voltage reference by applying a 61850 to describe and organize electrical measurement data. It P voltage value in series to the secondary side of the MV/LV also uses this standard to control electronic device O-UPQC . transformer. The communication usesP IEC 61850 standards. The SSAU uses CIM model to describe static features of the If the compensation done by O-UPQC is not enough, then LV network. “Retailer Intelligence” software will communicate with DEMSs, asking for the assistance of those customers who have joined A. IEC 61850 modeling the Demand Response program and have O-UPQC// (and distributed energy storage) installed.

Those real-time measurement values stored in SSAU database, whether from customers or from substation, are

all organized and named according to an IEC 61850 data model. The IEC 61850 data model is modeled based on the following strategy: First, for each customer or LV feeder, there is one dedicated Logical Device that encapsulates all of his/its measurement data; Second, each Logical Device contains several Logical Nodes, including MMXU (for measurement like voltage, current, etc.), MSTA (for statistical values), MMTR (for energy values), etc.; Third, every Logical Device defines several Datasets, each of which is used for reporting different group of data – e.g., alarms, statistical values, energy values, or real-time measurements. More details about this IEC 61850 data modelling can be found in [8]. The same data model is described in a Substation Configuration Language (SCL) file, located in the working directory of SCADA Reporting Gateway. SCADA Reporting Gateway is implemented as an IEC 61850 server application, which essentially creates an IEC 61850-enabled “IED”, and this “IED” represents the entire LV grid from real-time measurement perspective. This “IED” sends interesting data, such as alarms and statistical values, to iControl SCADA (an IEC 61850 client application) via IEC 61850 ACSI Reporting service. P In the second SSAU release, software P “O-UPQC Controller” communicates with O-UPQC unit by using IEC 61850 standards as well.PBut it uses a different data model: the interface to O-UPQC is modelled as one single Logical Device; this Logical Device contains several Logical Nodes, including MMXN (for describing the capacitor state), AVCO (for voltage control), etc. The software, functioning as an IEC 61850 client, issues Pvoltage set point and Switch-On commands towards O-UPQC unit (the IEC 61850 server) by using IEC 61850 ACSI Control service[5]. B. CIM modelling In the second SSAU release, static features of the LV network, such as topology, asset information and customer information, are modelled by using a subset (or profile) of the CIM model. The versions of CIM standards considered in our design are iec61970cim16v04, iec61968cim12v01 and iec62325cim01v07. This data model is implemented as a series of database tables. Some of them are explained as follows: • LV topology tables –They describe the structure of the LV grid, starting from the secondary substation until the point of energy delivery, at the customer premises. They cover details including: MV/LV transformers, busbars, LV breakers/fuses, LV lines (single and three-phases), junctions between lines, loads and productions. They also provide the information about connections among those elements, for tracing back and forward along the topology. In addition, they give a formal definition of the measurements placed over the LV topology. • Asset information tables –They contain relevant parameters for those assets present on the LV grid topology. The typical example is the length and the electrical model of LV cables such as resistance and reactance, which are used to estimate the network state. Asset information is also strictly related to measurement ranges. For instance,

•

the rated current of a cable is used to detect overloading on that line. Customer information tables –They contain details about customers such as the phase where the customer is connected to, the contractual power and load profile.

C. Bridging IEC 61850 data model with CIM model One important software component in the SSAU is State Estimation. It needs input such as real-time measurement values, network topology, asset information and customer information. By design, all these input data can be obtained from database. However, these data are organized according to different data models: real-time measurement values are based on an IEC 61850 data model; topology, asset and customer information are based on a CIM profile. The challenging issue here is how to correctly connect a measurement value (from IEC 61850 model) to its corresponding measurement point on the LV topology (from CIM model). To solve this issue, we model the LV topology in a way that bridging these two models can be straightforward: 1) State Estimation software extracts from LV topology tables a list of “buses” (also called nodes) and “branches”. “Buses” include busbars in a substation or in a street cabinet, and junctions between two segments of cable that compose a line. “Branches” include segments of cables, breakers, disconnectors and fuses. 2) Each “bus” is associated with multiple instances of CIM Measurement class (via ConductingEquipment - Terminal - Measurement relationships). The Measurement instance provides information such as measurement type (analog or discrete) and boundary (e.g., 0-100 A for a cable). 3) Each “bus” also has a corresponding IEC 61850 Logical Device. The Logical Device comprises a list of Logical Nodes, Data Objects and Attributes. They contain realtime measurement values received from field devices such as the RTU and smart meters. 4) The real-time measurement in step 3 and the CIM Measurement instances in step 2, have one-to-one mapping relationship. The mapping is realized by simply using a mapping-table. Note that measurement modelling is done in an innovative way: instead of using CIM classes AnalogValue and DiscreteValue to represent measurement values as suggested in CIM standard, we directly use IEC 61850 data model to organize measurement values, and place them to relevant locations in the CIM network topology. These measurements are all placed near “bus” areas. The reason for this placement is that it matches exactly how physical devices are installed in the field. Figure 3 illustrates the details of measurement placement. In Fig. 3, there are four types of measurement units: RTU, at secondary substation; smart meter, at customer connection point; measurement unit of PV generation unit; power quality (PQ) meter, in street cabinet. RTU measures LV busbar voltage (V1 ), as well as the current, power flows of transformer (I1 , P1 , Q1 ) and LV feeder

Figure 3. In our CIM modelling, measurements are placed near “bus”.

(I2 , P2 , Q2 ). All these measurement values are attached to neighbouring CIM Terminals of Bus 1. Values from power quality meter in street cabinet are associated with neighbouring Terminals of Bus 2, including voltage measurement (V2 ) attached to the Terminal of Junction, and current and power flow measurements (I3 , P3 , Q3 ) attached to the Terminal of ACLineSegment (branch4). The net measurement of customer connection point is realized with a smart meter associated with the Terminal of ACLineSegment (branch5, I4 , P4 , Q4 ) and the Terminal of Junction (bus3, V3 ). The measurements of production unit (I5 , P5 , Q5 ) are associated with the Terminal of EnergySource. In short, both customer consumption and production measurements are placed at neighbouring CIM Terminals of Bus 3. V. R ESULTS The first release of SSAU implementation has been tested in field trials and in RTDS (Real Time Digital Simulator) environment. In the field trial conducted by A2A, the SSAU allows DSO to real-time monitor a LV network that includes 2 feeders coming from a MV/LV substation. By aggregating measurements from 20 smart meters, 2 power quality meters and 2 RTUs, and utilizing state estimation, the SSAU provides accurate information about the state of the whole LV grid. It can show, for instance, the clear picture of phase voltage changes due to load and PV production. In RTDS tests, the overall accuracy of LV network monitoring influenced by averaging of quantities and measurement reading frequencies has been studied. Simulation results show that using less than 10 minutes reading frequencies and less than 20 minutes averaging can have reasonable monitoring accuracy[13]. The detailed testing results of the first SSAU release are presented in [2][6]. The second release is now under development in Smart Domo Grid project. Its result will be tested during 2014 in a real DSO environment in the city of Brescia, Italy. VI. C ONCLUSION This paper presents the implementation details of the secondary substation automation unit, focusing on the ICT

perspective. The very essence of this automation unit is the “decentralized” distribution management architecture. It adds decision-making points at secondary substation, by aggregating smart metering data and MV/LV grid measurement at secondary substation, processing them locally and conducting some LV network management functions autonomously. This makes it possible to improve LV network management without overloading communication infrastructure and control centre systems. This automation unit can be implemented in an open and standard-based manner by utilizing, e.g., IEC 61850 and CIM standards. This can maximize the interoperability and make it easier to integrate with other applications. The first prototype implementation has realized real-time LV network monitoring. Furthermore, by utilizing the measurement values aggregated by this automation unit, it is also possible to realize more advanced LV management functions and applications at secondary substation – the second implementation, for instance, realizes some Demand-Response functions at secondary substation. R EFERENCES [1] M. H. J. Bollen, Synthesis Lectures on Power Electronics: The Smart Grid – Adapting the Power System to New Challenges. Morgan & Claypool Publishers, 2011, pp. 55–56. [2] S. Repo, S. Lu, T. P¨oh¨o, D. D. Giustina, G. Ravera, F. A.-C. Figuerola, and J. M. Selga, “Active distribution network concept for distributed management of low voltage network,” in Proc. 2013 IEEE/PES Innovative Smart Grid Technologies Europe Conf., pp. 1–5. [3] G. Accetta, D. D. Giustina, S. Zanini, G. D’Antona, and R. Faranda, “Smartdomogrid: Reference architecture and use case analyses for a gridcustomer interaction,” in Proc. 2013 IEEE/PES Innovative Smart Grid Technologies Europe Conf., pp. 1–5. [4] C.-H. Lo and N. Ansari, “Decentralized controls and communications for autonomous distribution networks in smart grid,” IEEE Trans. Smart Grid, vol. 4, pp. 66–77, Mar. 2013. [5] IEC 61850:Communication networks and systems in substations, Part 7-2: Basic communication structure for substation and feeder equipment - Abstract communication service interface (ACSI), IEC Std. 61 850-7-2, Rev. 2.0, 2010. [6] D. D. Giustina, L. Andersson, and G. Ravera, “Experimental performance characterization of a meshed network for the smart grid,” in Proc. 2013 IEEE/PES Innovative Smart Grid Technologies Europe Conf., pp. 1–5. [7] IEC 61850:Communication networks and systems in substations, Part 8-1: Specific Communication Service Mapping (SCSM) – Mappings to MMS (ISO 9506-1 and ISO 9506-2) and to ISO/IEC 8802-3, IEC Std. 61 850-8-1, Rev. 1.0, 2004. [8] S. Lu, M. Pikkarainen, S. Repo, and F. A.-C. Figuerola, “Utilizing scada and iec 61850 for real-time mv/lv network monitoring,” in Proc. 2013 IEEE/PES Innovative Smart Grid Technologies Europe Conf., pp. 1–5. [9] A. Mutanen, S. Repo, P. J¨arventausta, A. L¨of, and D. D. Giustina, “Testing low voltage network state estimation in rtds environment,” in Proc. 2013 IEEE/PES Innovative Smart Grid Technologies Europe Conf., pp. 1–5. [10] R. Faranda, M. Brenna, and E. Tironi, “A new proposal for power quality and custom power: Open upqc,” IEEE Trans. Power Delivery, vol. 24, pp. 2107–2116, Oct. 2009. [11] G. Accetta, G. D’Antona, D. D. Giustina, and R. Faranda, “Power quality improvement in lv smart grid by using the open upqc device,” in Proc. 2013 International Conference on Renewable Energy and Power Quality. [12] A. Mutanen, M. Ruska, S. Repo, and P. J¨arventausta, “Customer classification and load profiling method for distribution systems,” IEEE Trans. Power Delivery, vol. 26, pp. 1755–1763, Jul. 2011. [13] A. L¨of, M. Pikkarainen, S. Lu, T. P¨oh¨o, and S. Repo, “Low voltage network monitoring in rtds environment,” in Proc. 2013 IEEE/PES Innovative Smart Grid Technologies Europe Conf., pp. 1–5.