ENEL Smart Grid Projects - DER Management Applications

by Pietro Tumino, Giorgio Di Lembo and Gianpatrizio Bianco, Enel Distribuzione, Italy

Introduction

Historically the existing MV network was designed for mono-directional power flows, the line voltage profile was a monotone decreasing profile. Today this is not true anymore, furthermore DER causes uncertainty about the power generated, problems to protection, control and automation systems and network congestions.
Due to these problems there is a limited capacity to integrate Distributed Energy Resources (DER). Enel is working in a lot of projects aimed at finding the best way to integrate DERs in electrical networks and to use them as a resource for the network.


Enel Projects
The Figure on the first page shows Enel projects related to Smart Grids.

Functional and architectural developments
In all of these projects Enel has developed a lot of new functionalities in order to go towards the Smart Grids. The main of them can be seen in Table 1.

Voltage control
The massive introduction of distributed generators changes the constraints in hosting capacity calculation. In fact the hosting capacity of a MV network, with a high presence of DG, is not usually limited by conductors capability but by voltage increase caused by the distributed generators.
Historically and up to now, the voltage control was done by modulating the On Load Tap Changers (OLTC) of each HV/MV transformer by means of a method called “current compound.” The goal was assuring a good voltage level at both ends of the feeders. This method works until the voltage profile is monotone decreasing, but with the introduction of DG a different approach is required.

The new voltage control technique is based on two main points:

  • MV Bus bar voltage setting, based on electrical calculation made by a central DMS (Distribution Management System) and on the measurements coming from the network
  • Decentralized voltage control in corresponding of DG injection points, based on local measurement and reactive energy absorption of the generator

DMS evaluates the optimal voltage setting at the bus bar level each 10 minutes; in case of overvoltage due to a power injection from a distributed generator, a local control provides to ask the generator to absorb reactive power at a specific power factor.. If the local control may not be sufficient to restore the voltage levels, the control center could ask the closer generators to modulate the reactive power in order to “help” the voltage reduction. In extreme situations the control center could, also, ask the generator that causes the overvoltage to curtail the active power generation. (see Figure 1 and Figure 2)

Anti-Islanding + ∆f
The scope of the interface protection (IPR) installed in correspondence of the private power plant is to disconnect the generators from the network to avoid:

  • Unwanted Islanding supply conditions in case of the loss of the mains (DGs keep on supplying portions of network even if the main network is down)
  • Giving energy to a fault occurred on the MV or LV line where the client is connected
  • Damages of the generation equipment in case of automatic or manual reclosing of the distributor line breaker, with phase discordance between with the main network and the generator

IPR detects the tripping conditions measuring voltage and frequency variations due to islanding working situations. According to the Italian TSO Annex A70, the IPR is able to shift the range of frequency threshold between a restrictive range (49,7 - 50,3 Hz) and a permissive range (47,5 – 51,5 Hz), depending on local fault conditions that cause a relevant perturbation on the parameters.

Despite these countermeasures, in absence of faults, if the generated power is very close to the load, a balance condition may be present in a portion of the network. In this case an islanding condition may occur with negligible variations of voltage and/or frequency (they may remain inside the no trip area of the IPR).

This may happen at different levels:

  • On MV busbars of a HV/MV substation (no P/Q flows through the HV/MV TR)
  • In correspondence of a MV feeder

In a MV section of a feeder, automatically isolated by the automation system in case of a ground fault; Enel Remote Control System detects each potential situation of islanding and avoids possible problems sending explicit command of remote disconnection to all generators of the island, according to the recommendations stated in the annex A.70 of the Italian Grid code (issued by Italian TSO). (see Figure 3)

Fast Fault Selection

Fast Fault Selection
According to the Italian standards regulating the connection of customers to MV networks, (CEI 0-16), in case of a short circuit along a feeder, the circuit breaker at the line departure is opened after a time delay of 170- 250ms.
The scope of this delay is protection coordination between the distributor MV line breakers and also the customer fault-clearing devices.

Taking advantage of this time delay and of the short latency of message exchange of modern telecommunication networks, a new automatic fault clearing system can be implemented.
Special fault detectors can be installed in some automated secondary substations, connected together by a modern telecommunication system.

In case of a fault in a MV section, the detectors that sense the fault current send a “blind” signal to the other detectors located upstream along the feeder, preventing them from opening the related breaker; the only one not receiving the blind will clear the fault and open all the generation power plants located downstream its location. (see Figure 4 and Figure 7)

Monitoring and data collection
Thanks to sensing devices installed in secondary substations and inside the customer power plants, it is possible to monitor the production of distributed generators and collect many measurements along the feeder (voltage, current, active and reactive power, etc.).
These pieces of data can be used in daily operation of the MV network, stored in historical archives for back-office activities, aggregated per transformer or per substation.

In particular data regarding the power (active and reactive) injected into MV network by dispersed generation, aggregated per each HV/MV transformer and subdivided into groups according to the energy source (solar. wind, bio-fuel, etc) can be transmitted to Transmission System Operator (TSO), to be used in dispatching activity.

New control infrastructure
Figure 6 shows the new IEDs developed and installed in the network, Below there is a short description of them.

TPT represents the Remote Terminal Unit (RTU) of the HV/MV substations and it is the interface between central system and protection devices. It collects and sorts the events coming from the field and it can, also, manage the IEDs in terms of configuration.
UP is the RTU of secondary substation, it manages autonomously the automation cycle of the breakers on the MV lines and/or commands from the central system.

RGDM is an advanced Fault Passage indicator: It provides local intelligence for fault detection, fast fault isolation, voltage control and V, P, Q, f measurements.

IRE is the energy controller, installed inside the private power plant. By means of this device the distributors can regulate the energy (active and reactive) exchanged with the network and it provides V, P, Q, f, measured on the user side both for generators and loads.

DV7300 is an IEC61850-Wires converter: This device interfaces the Interface protection (if a generator is present) and the General protection (if a pure load is present) of the user. It can provide the state of these protections to other relevant IEDs of the Enel system.
Enel, in its Smart Grid projects, adopts IEC 61850 standard for each kind of communication (Commands, controls etc.) between all network devices (including the devices installed inside the customer power plant ) and suitable LAN and WAN networks allow GOOSE and MMS message to be exchanged (see Figure 5.) Furthermore, Enel has developed a Data Model compliant with IEC 61850 for each device.

Regarding the solutions for WAN communications within “POI” project, Enel is testing two different solutions:

  • The first one (developed in Calabria) is based on the optical fibers installed on the same poles used for energy lines
  • The second one (developed in Sicilia, Puglia and Campania) is based on wireless connections using WiMax and LTE(G4) technologies..

Conclusions: After the experimentation phase and pilot projects, it is very likely that Enel MV networks will be equipped with the new devices and the new functionalities will become operative.
Also the user power plants will be equipped with the devices and in particular with a control system implementing IRE functions. In fact all the customer devices should not be provided by the distributor but they should become unified interfaces built-in all commercial power plant control and protection systems. This is why Enel is working hardly to implement in practice the smart grids functionalities to propose a new regulatory framework to operate the network with the new technologies, on a daily basis.

Biographies

Pietro Tumino received the M.S. degree in Electrical Engineering from University of Catania, Italy. He has worked in Enel Distribuzione S.p.A, Roma, Italy on devices and algorithms for remote control and automation of the distribution networks since May 2012. He is involved in the experimentation regarding the installation of Energy Storage Systems in Enel Distribuzione network and he has worked on the communication model of the ESS based on IEC 61850. He collaborated to the development of a new communication architecture, for the Enel Distribuzione networks, based on IEC 61850, between SCADA and the several IED’s of the network and to the development of a customer controller plant IED and to develop its data model compliant with IEC 61850 and with DSO requirements. Since 2013 he has worked in the new “Smart Cities Research Centre” of Enel Distribuzione in Bari, as senior researcher.

Giorgio Di Lembo joined ENEL after graduating in Electronic Engineering in 1989. He initially dealt with the practical problems of electricity distribution networks, working in an operative unit of the company, then joined the engineering department of ENEL Distribution Division. Since 1991 he is working in the field of Distribution Automation and electrical protection systems. He supervised most of the technical activities to develop Central systems and peripheral units for remote control of ENEL Primary and secondary substations. Therefore he can be considered one of the fathers of telecontrol and network automation systems presently adopted in ENEL. Today he is responsible for “Telecontrol and Automation systems” in ENEL DISTRIBUZIONE and his main activity is focused on Smart Grids

Gianpatrizio Bianco received the M.S. degree in Electronic Engineer from Politecnico di Bari, Italy. He works in Enel Distribuzione, Central Office, at Network Technologies function. He is involved, regarding remote control and automation systems, in many research projects and experimentations for Smart Grid, in particular POI-P3 project founded by the government and Isernia project (supported by the Italian Energy Autorithy). Since 1st January he is involved in Res Novae, a project focused on Smart Cities issues, as responsible for the Smart Grid research group. Before working for the Central office, he coordinated and supported activities for the territorial division of Enel Distribuzione. In particular he worked in the operation of the remote control system and in the device for the remote control in HV/MV and MV/LV stations.

Power. Flexible. Easergy.
Let?s start with organization in protection testing