SCADA – RTU Communications Using General Packet Radio Service (GPRS) – The New Era in Communication Technology

SCADA (Supervisory Control and Data Acquisition) systems used in industrial process control applications make monitoring and controlling of virtually any system possible. Conventional SCADA systems are, however, extremely complex and incredibly costly. However, with the use of wireless communication technologies, the ability to perform advanced monitoring and control of remote or mobile assets can be done deeper into the asset base of larger operators.

Wireless technology makes SCADA more affordable and reduces overall cost of the systems. Here in this paper the technical considerations and main operating and cost benefits achieved with SCADA system operating over GPRS-based communication is described. DNP3 Protocol is used for providing communication among devices.

INTRODUCTION

Supervisory Control and Data Acquisition (SCADA) is a process control system that enables a site operator to monitor and control processes that are distributed among various remote sites [3]. A properly designed SCADA system saves time and money by eliminating the need for service personnel to visit each site for inspection, data collection/logging or making adjustments [7].

In the present day, companies are under increasing pressure to reduce infrastructure operating costs. As such, new methods of communication are being explored to allow them to do so. A clear alternative is the use of GPRS based communication system. General Packet Radio Service (GPRS) is chosen as it provides an always on-line interconnection without any time based charges. GPRS based SCADA deals with the creation of an inexpensive, yet adaptable and easy-to-use SCADA device and infrastructure.

The hardware components making up the device are relatively unsophisticated, yet the custom written software makes it re-programmable over the air, and able to provide a given SCADA application with the ability to send and receive control and data signals at any non predetermined time.

However the following measures should be taken into consideration while selecting a communication platform for a SCADA system. The various devices that are going to be communicated (IEDs, RTUs, MTUs, etc) must be versatile, so that they can be used with the selected platform. The protocol to be used must reliably and efficiently transfer the field data to the master station. The characteristics of the physical medium, including its infrastructure, the information-packaging protocol, transmission speed and related costs. There must be telecom service in the locations where certain devices must be monitored and controlled. In this paper we have developed an integrated wireless SCADA system for monitoring and accessing the performance of remotely situated substations and distribution networks.

This paper will give an overview of the communications between the RTU’s and the MTU. It will explain why DNP 3.0 is considered the most reliable and comprehensive protocols for SCADA Systems operating over GPRS network. In the paper, it discusses the benefits of combining both protocols, which includes increasing efficiency and transmission speed while decreasing transmission speed.

GENERAL CONCEPTS

a - General Packet Radio Service (GPRS)

GPRS is the Internet/IP based data service of GSM (Global System for Mobile communications), the worldwide cellular phone network [1], [2]. Figure 1 below shows the network. In fact, GSM and GPRS networks are the same. They use the same infrastructure consisting of transmitter stations and controllers.

GPRS is intended to optimize data transmission services on a network that is currently used for voice transmission. In many countries, government typically does not allow the use of “voice networks” like GSM for M2M data communication applications [6]. The main reason is that the modem could not monopolize network bandwidth.

b - DNP 3.0

DNP was originally created by Westronic, Inc. (now GE Harris) in 1990. In 1993, the “DNP 3.0 Basic protocol specification document set was released into the public domain. Distributed Network Protocol Version 3 (DNP3) is used by SCADA systems to communicate between the Master host and the Slave units. This infrastructure is open and effective authentication or encryption mechanisms do not exist. DNP3 is an open, intelligent, robust, and efficient modern SCADA protocol.

c - Virtual Private Network

The security aspects of using the Internet as a corporate network are easy to solve, thus many organizations, including security-sensitive banks, adopt this technology. This technology is also known as Virtual Private Network (VPN) as a secure, private network is being built on the public Internet. VPN technology has been used in our project.

SUPERVISORY CONTROL & DATA ACQUISITION (SCADA) SYSTEM

a - SCADA

Supervision consists of commanding a process and supervising its working [1]. SCADA is a process control system that enables a site operator to monitor and control processes that are spread among various remote sites [5]. A properly designed SCADA system saves time and money by eliminating the man intervention to visit each site for inspection, data collection/logging or making adjustments [3]. The SCADA at the same time generates a set of processed information, such as trend graphs, historical information, operating reports and event programming, among others. It allows the users to see information real time.

b - Communication Concentrators

Communication Concentrators allow users to handle the main communication protocols used in the power industry. They have a larger quantity of matter in the DNP 3.0 protocol than in the SCADA. They also issue reports as a single remote piece of equipment to minimize the amount of data entered into the system and avoid excess manipulation of the SCADA. They are same as Master Terminal Units (MTUs). The MTU is usually defined as the master of a SCADA system and is located at the operator’s central control facility. The MTU initiates virtually all communication with remote sites and interfaces with an operator. Data from remote field devices (pumps, valves, alarms, etc.) is sent to the MTU to be processed, stored and/or sent to other systems.

c - RTUs & IEDs

Each remote location of interest has an acquisition and control server, which, together with the communication device, constitutes either the Remote Terminal Unit (RTU) or the Intelligent Electronic Device (IED). RTUs are in constant communication with the operational stations (S1, S2, Sn) through the associated Communication Concentrator and/or the SCADA.

IMPLEMENTATION OF  SCADA ON GPRS PLATFORM

After verifying whether some of products of the GRPS are compatible with the interfaces in the SCADA System we decided to implement the system. Block diagram of the proposed system can be seen in Figure 1.

VPN has been used in our project to get good reliability, security and availability. It further reduces cost and does not require the installation of physical lines. There are several wireless Internet/VPN technologies available in the market:

  • UMTS (Universal Mobile Telecommunications Service) also known as the 3rd Generation (3G) follow-on of GSM/GPRS. It allows higher bandwidth but is available only in urban areas of a few countries. No industrial grade modems are available yet.
  • Wireless WAN hotspots: They are available in some areas and buildings, so the chance of getting Internet access this way at a distribution substation is low. So, the best choice for our application is GPRS.
  • DNP.3.0 Protocol has been used in our project to carry out transactions between the communication concentrators (Master terminal unit) and remote devices. Table I. shows the analysis of the technical features of the GPRS based SCADA system.

SCADA System which was implemented in the GPRS Platform

Speed High
Response Time 4 -  16
Life span of the Technology Long
Availability High
Coverage Very High

 Table I. Technical features of Proposed SCADA system under GPRS Platform

ADVANTAGES OF USING GPRS PLATFORM

  • Billing is based on the number of communication packets and is independent of connection time.
  • The GPRS provides broad coverage in all the areas (including rural areas).
  • Expenses related to man intervention/purchase of fittings and other devices are reduced.
  • The system is easy to implement.
  • Security is enhanced by creating the VPN and a direct link with the GPRS service provider.
  • Higher speed is recorded as whole system was connected to an IP connection.
  • Response time is reduced.

FAILOVER COMMUNICATION OF GPRS

GSM cellular phone networks can be affected by weather conditions or electrical interference, and in the worst case, communications can be lost. In the same way, a GPRS link over a GSM network connecting a SCADA system to RTUs can be cut at any time.

CONCLUSION

Using GPRS based SCADA system, any industrial plant can be monitored remotely. It improves reliability, response time, plant interface under continuous real time monitoring and under adverse environmental conditions for maximizing the industrial plant performance. This system can be used in oil/gas, environment monitoring, and water distribution application, covering a wide area and functioning under harsh conditions, and at the same time affordable and inexpensive to operate [4],[5]. By implementing such system, huge amount of savings can be obtained.

References

Sungmo Jung, Jae-gu Song, Seoksoo Kim, “Design on SCADA Test-bed and Security Device,” International Journal of Multimedia and Ubiquitous Engineering, Vol. 3, No. 4, October, 2008.

Surve, V, 2006, “A wireless Communication Device for Short Messages”, Masters Thesis, Available: www.certec.lth.se/doc/awireless.pdf.

Hildick-Smith, Andrew, “Security for Critical Infrastructure SCADA Systems,” (SANS Reading Room, GSEC Practical Assignment, Version 1.4c, Option 1, February 2005)

Dan Ehrenreich, “Wireless Data Communications for SCADA Systems,” BCWWA Conference, Vancouver, November 28-29, 2005.

Tahir Nizamuddin, Bilal Iqbal, “Design and Implementation of Locally Developed SCADA A Cost Effective Solution,” PCSIR, Institute of Industrial Electronics Engineering, (IIEE) Karachi.

http://en.wikipedia.org/wiki/General_Packet_Radio_Service

Tony Stafford, Taking Back – A SCADA case study, Camrosa Water District, California. July 2002. BIOGRAHIES).


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October 4, 2012
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