649
Abstract- With the advent of new technologies, the demand of
connecting IT systems to the Internet is increased. In modern electric power grid, to have improved operation, reliability and safety in distribution system through automated control , modern communication technologies are utilize. The use of communication architecture in distribution grid allows remote access to the facility through an IP network with high security, facilitating the operation and system diagnostics very quickly. The increased need for effective control turned the development of smart distribution grid. This paper proposes the comparative study of effective monitoring, diagnosis and supervisory control applied to distribution smart grid. The system is based on modern SCADA operation, the RMU are installed at key location on the feeder and interface with communication system for quick fault identification and control of operation. The paper highlight the network communication architect with the use of Ethernet TCP/IP and control of substation equipment and various communication standards use in the system for enhancing the grid performance.
Index Terms—Supervisory Control and Data
Acquisition-Smart grid.
I. INTRODUCTION
n modern electric power systems which include renewable energy resources, automated and intelligent management is a critical aspect that determines the usefulness of these power systems. The distribution automation offers a variety of advantages over the current systems in terms of digitalization, flexibility, intelligence, sustainability which facilitate the smart grid power system. In the smart grid, reliable and real time information becomes the key factor for reliable delivery of power from generating station to the end users [1].
The control centers are expected to monitor and interact the electric devices remotely in real time, the transmission infrastructures with communication network are expected to employ new technologies to enhance the system performance.
Sadhana A.Bhonde, Research Scholar, Dept. of Electrical Engg. G.H.Raisoni College of Engineering , Nagpur.
(E-mail: sadhanamohod123@gmail.com)
Dr.S.B.Bodkhe, Dept. of Electrical Engg, Ramdeobaba College of Engg. Nagpur.(sbbodkhe@gmail.com)
Sharad W. Mohod, Dept. of Electronics Engineering, Ram Meghe Institute of Technology & Research, Badnera. Amravati.
(E-mail: sharadmohod@rediffmail.com )
The communication network plays a vital role in the power system management. The network is required to connect the magnitude of electric devices in distributed locations and exchange their status information and control instructions. There is an increasing interest in applying technology to protect and control the electric utilities. At present conventional centralized control system has limitations, as they can degrade due to complexity with network events. Nowadays, intelligent electronic devices and robust communication processor contain large amount of data that is available for years. Initial efforts were on supervisory control and data acquisition [2]-[4].
In conventional SCADA , communications has been Point-to-Multipoint serial communications over lease line or private radio systems. With the introduction of Internet Protocol (IP), IP technology has seen increasing use in modern SCADA communications. The connectivity can give modern SCADA more scale which enables it to provide access to real-time data display, alarming and control by using different communication network such as Internet, satellite and remote modem. The distribution automation system includes signal sensing, control, human machine interface, management and networking [5].
Wireless sensor network will play a key role in the development of the smart grid and enables various demand and energy management, reducing the electricity expenses [6]-[7]. The objective of this study is to enhance the distribution system through the use of real time Ethernet, architecture of SCADA which is connected through the internet. Like a normal SCADA, it has remote terminal unit (RTU), power line communication (PLC), intelligent electronic control (IED) along with the Field remote terminal unit (FRTU). This also includes the user-access to SCADA which enables real time monitoring of the system under the developed/implemented supervision.
In this application, the challenges have to establish a communication system installed in the substation with individual control to resolve the problem [8].
The paper is organized as follows. Section II provides the communication architect. Section III modern substation communication and section IV gives the various standard used in communication. Section V discusses the comparison of modern SCADA for enhancing the distribution grid. Finally Section VI concludes the paper.
Enhancing Distribution System Through the
Use of Real Time Ethernet in Smart Grid
.
Sadhana A.Bhonde , S.B.Bodkhe
,S.W.Mohod
II. COMMUNICATION ARCHITECT
The communications within the grid are based on EPICS (Experimental Physics and Industrial Control System). It is a set of open source tools focused on the development of distributed control systems in real time using the Ethernet to communicate the different EPICS devices. The communication architecture allows remote access to the facility through an IP network with high security, facilitating the operation and system diagnostics. The fundamental data of the installation can be viewed in real time through a website; and locally, using the EPICS tools . For this purpose the system requires architecture to collect information of the smart grid, measuring devices across the net and in addition to connect the individual operator control (IOC) of the energy suppliers, which can be away from the control centre of the smart grid. Development of guideline for suitable IP protocol for smart grid application and identifying domain type is essential for reliability of power system.
Wide area networks (WAN) form the communication backbone to connect the highly distributed smaller area networks that serve the power systems at different locations. When the control centers are located far from the substations or the end consumers, the real-time measurements taken at the electric devices are transported to the control centers through the wide area networks
The communication architecture is shown as in Fig. 1.
Fig.1. Grid Communication Architecture
III. CONTROL SCHEME OF THE SYSTEM
The electrical substation is an important component in power systems. It changes the voltages on the electrical transmission lines and controls the power flow in the transmission system. A substation is a complex system composed of many elements such as transformers, capacitors, voltage regulators, and circuit breakers. Automated substation
control will be implemented extensively in the smart grid systems to provide real-time monitoring and control through local area networks. The possible network technologies to be used in a substation include Ethernet.
The functions of substation are to control and monitoring of the switch yard, protection of the power equipment, revenue metering and automation functions for energy management. The conventional substation is composed with interlocking logic, RTU (Remote Terminal Unit), Relays, conventional switchgear and CT/PT (current/potential transformers). Each component is hardwired connected with wires.
Modern substation is structured in three basic levels. The station level provides an overview across the whole station and is located in a shielded control room. Station level includes Human Machine Interface (HMI) Workstation, Master Station Computer, Backup Station Computer and GPS (Global Positioning System) receiver, etc. The bay level conducts maintenance work only within one bay and it is usually close to the switchgear. Bay level includes protection and control IEDs (intelligent electrical devices) of different bays such as circuit breakers, transformers, and capacitor banks. Equipment in bay level and station level are called secondary equipment. Process level provides the interface between the substation automation system and the switchgear. Process level includes switchyard equipment such as CTs/PTs, remote I/O, actuators etc.[9]-[10].
The Substation data communication system plays a critical role in the real time mission, critical operation of substation automation system. All secondary equipment within a substation is interlinked with communication buses. In conventional substation, communication devices typically rely on one-way communication. Serial communication buses or proprietary communication media with associated protocols are used for local HMI, as well as for remote SCADA (Supervisory Control and Data Acquisition) communication
651 Fig.2. Communication Network in substation
The network technologies to be used in a substation include Ethernet TCP/IP. To connect the various equipments in a substation, dedicated sensors are attached to the equipments to take their status. The control equipment in a substation is shown in Fig.3.
Fig.3. Control Equipments in substation
The external and real time data requests are served through the Server. The operator stations and other internal data users communicate through server. The control executes through I/O port. Input port gives the information of input signal such as breaker ON/OFF position , Isolator ON/OFF position , also analog input cards analog signal such as Voltage , I/O card consist of analog input card and digital input card which gives analog and digital signal from substation through RTU. The digital Output card control the equipment in substation. Digital input signal from RTU are transmitted through Router and Modem towards Multi-packet label switching cloud and send to control center. For controlling substation equipments signals are transmitted from control center to MPLS cloud towards Modem at substation and forwarded to RTU. The arrangement of control center for operating the equipments through the communication network are shown Fig.4.
Fig.4. Control Centre Equipments through communication network The operation for Feeder Remote Terminal Unit (FRTU) in SCADA system is shown in Fig.5. Input signals from FRTU are transmitted through Modem towards CDMA/GPRS cloud and then send to control center. For controlling purpose the output signals are transmitted from control centre to GPRS Modem through cloud towards FRTU.
Fig.5. Feeder remote terminal unit operation through communication network
Modern SCADA Software are developed and designed for the specific hardware .It can be proprietary type or open type software. Open software systems are designed to communicate and control different types of hardware.
IV. COMMUNICATION ASPECT
A. Distributed Network Protocol
The distributed network protocol (DNP3) is specifically designed for various applications in SCADA. It is highly standardized, with relatively high compatibility and inter-operability between devices from different manufacturers. It support the analog and digital data type. DNP3 also supports a variety functions commonly used on control applications, such as pulsed and paired outputs. The end user can monitor the network and take the required action.
B. IEEE Standard
IEEE has proposed a number of standards related to the communications in power systems, including C37.1, IEE 1379 ( Recommended practice for interconnection between IED and RTU), IEEE 1547 (Standard for interconnecting distributed energy resources with electric power system) and IEEE 1646.( Standard for communication performance)[11].
C. IEC Standard
The International Electro-technical Commission (IEC) has proposed a number of standards on the communication and control of electric power systems. The standard 60870 and IEC 61850 defines the communication systems used for power system control.
IEC 61850 is a standard for communication networks and systems for power utility automation and is being produced by IEC Technical Committee 57 Working Groups 10. It is developed based on Utility Communications Architecture 2.0 which is based on the Manufacturing Message Specification (MMS). IEC 61850 is a lower-layer object-oriented protocol being implemented over TCP/IP and Ethernet networks. It defines a vendor independent communication infrastructure allowing seamless IEDs integration. Compare to DNP3 or IEC 60870-5-104, IEC 61850 is not only another way of providing the same functions as a traditional SCADA protocol, it also provides information modes, configuration languages and abstract services in substation communication.
Main features of IEC 61850 are as follows:
• It translates all in the information in the real substation into information models in the form of standard naming conventions structures and formats for easy information management.
• It provides Abstract Communication Service Interface (ACSI) and makes it possible for applications and databases to be unchanged with changes in the communication protocols and media. provides communication protocols of TCP/IP based SCADA, real time Generic Object Oriented Substation Event (GOOSE) and Generic Substation Status Event (GSSE) and real time sample measured value (SMV). GOOSEs support system protection applications and run directly over Ethernet. It defines process bus which is supported by GOOSE and can minimize substation wiring requirements in the yard by converting data of CTs/PTs to digital information [12]-[14]. The National Institute of Standards and Technology (NIST) also published standards to provide guidance to the smart grid
construction. It states the importance and vision of the smart grid, defines the conceptual reference model, identifies the implementation standards, suggests the priority action plans, and specifies the security assessment procedures.
V. MODERN SCADA SYSTEM
A case study of conventional SCADA in the distribution grid is compared with the incorporation of modern facilities in the grid.
The present SCADA operations used in 33/11KVsubstation in distribution system for fault identification and restoration are shown in Fig . 6 a) .The feeder has incoming supply from both the side and it is associated with the circuit breaker and distribution transformer and midway cut point which is normally open point used in old system so that complete system get supply from two feeder. In case of fault in the system, the circuit breaker trips and portion of feeder will get disconnected, shown with red mark in Fig.6 b). The operators manually open the isolator and restore the part of supply portion within 30-45 min after inspection as shown in Fig.6 c). After the further inspection up to the fault line the operator opens the isolators between the faulty sections shown in Fig.6d).
Fig.6a. Fault location Fig.6b.Circuit breaker open
Fig.6c Isolator open Fig.6d. Faulty section open
653 receiving the signal from FRTU. The partial restoration of supply can be done within very short time shown in Fig.7c. The faulty portion will get isolated by field staff after identification of location
Fig.7a. System with RMU installed Fig.7b.System with Fault passage indicator
Fig.7c. partial Restoration Fig.7d.Faulty portion isolation
The modern SCADA operation in the distribution system enables the real time monitoring, diagnosis and control of the system effectively.
VI. CONCLUSION
In Modern substation , Human Machine Interface, Master Station Computer, and GPS are included for the control IEDs and protection of different equipments such as circuit breakers, transformers etc. It gives the interface for substation automation. The substation equipment monitoring and controlling is very effective with the use of communication technology.
The different standards and protocols have to be followed for the development of smart distribution grid . In order to ensure high communication reliability the Ethernet switch is used for the control and protection with IEDs
The studies of modern SCADA are compared with conventional system in fault identification in the distribution system. Thus modern grid operation control the distribution system and improves the system problems through monitoring using sensors and intelligent electronic devices which enhances the system performance and down time. The paper
presents the study to enhance the distribution network , which must be planned carefully in order to meet the system performance and requirement in today’s energy management.
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