MIXED-MODE SCADA NETWORK FOR HYDRO ELECTRIC POWER PLANT

Abstract

The hydro power generation is one of the efficient and economic forms of all the renewable energy sources. Hydro power stations are located at remote places and require an automation system which would continuously monitor various plant parameters and remotely control operations of the plant. SCADA (Supervisory Control and Data Acquisition system) performs the function of data acquisition, for providing an unattended, efficient and reliable supervision and control. SCADA network includes interconnection with the station computers and device level networks. At the device level, SCADA employs standard protocols for communication with the field devices and several clients connect to the work station server to access the parameters for display and processing. In the past few years, industry has developed at the level of the field-devices at its own range of digital communication protocols with the increasing involvement of intelligent instrumentation. When these networks are used in a plant it requires access to the plant parameters for the remote control and centralized supervision. The applications had to develop drivers for their own packages to access the data. Hence there was an urgent need to develop standard schemes for communicating with multiple protocol networks. A mixed-mode SCADA network is one which can connect the work station to a number of device level networks and provide data to multiple client applications simultaneously. In the present work a mixed-mode SCADA network, integrating a FOUNDATION FIELDBUS (FF) and two RS485/MODBUS networks, is implemented for a model hydro power station of 2* 1.5 MW capacity. The network has a central server node connected to the Fieldbus network through a bridge (Ethernet to FF) and to two Modbus networks through RS232 to 485 convertor. Each device level network has its individual OPC server (Object Linking and Embedding for Process Control) and acts as an interface between hardware providers and software developers. It provides a mechanism to provide data from a data source and to communicate the data to any client application in a standard way. The OPC servers installed on the server node are Dfi OLE server, NAPOPC server and NDS OPC server. Dfi Ole Server acquires the real-time data tl from the Fieldbus devices where as NAPOPC and NDSOPC servers have been used to configure and acquire the data from the Modbus networks. Fieldbus devices have been used to measure the pressure heads at the forebay and tailrace, water level, inlet nozzle position, various generator temperature and current. The Modbus devices monitor generator and transformer voltages, currents, temperatures, frequency and the breaker and isolator positions. GraphworX, AlarmworX, TrendworX, LabVIEW and Visual Basic have been used as the OPC clients. GraphWorX is an OPC compliant human-machine interface (HMI) software package for process control. AlarmWorX is OPC-compliant alarming software, performs alarm detection and reporting based on the OPC Alarm and Events Standard. TrendWorX is similar to GraphWorx but is equipped with more advanced options such as different kinds of plots etc. Smar WebHMI has been used as a thin client Web solution that enables standard Web browsers, such as Microsoft Internet Explorer, for use as real-time operator interfaces. In the present work two remote clients are connected to the plant server on local area network (LAN). The clients have been configured with DCOM (Distributed Component Object Model) and windows registry settings to communicate the installed OPC clients with the servers on the central server node so that any client can monitor and control. Thus a mixed-mode SCADA network involving Foundation Fieldbus, Modbus and Ethernet protocols has been successfully implemented in the laboratory with the above functionalities. Iv