Wireless sensor networks for SCADA Applications

1 Introduction

Industrialization and urbanization have led to a huge demand for energy and water in the world. The resources such as oil, gas, power, and water that are essential assets need to be distributed across the country. The pipelines are one of the most economical means of carrying petroleum products for thousands of kilometres across the country from production fields to the refineries and from refineries to the distribution system.  These pipelines are spread over large geographical areas across the country and installed overground, underground, or underwater. They form an integral part of any country’s energy economy. Similarly, power line carries electric energy from power stations to distribution centres and then to the consumers across the country.  Monitoring and protecting the health of these distributed infrastructure facilities of national importance is necessary. It is being done using Supervisory Control and Data Acquisition (SCADA) system for the last many decades. The SCADA systems have also been used to monitor and control mining, agriculture, and other utilities. Over a period, the technology has improved, and the SCADA system has been continuously upgraded using the latest hardware and software techniques apart from the sensors. Wireless Sensor Network (WSN), the basic element in the Internet of Things for collecting environmental data, is at the forefront of any technology upgrade in the industry. As per industry reports, the use of WSN can lead to infrastructure cost reduction by 80%, and consequently, their use is growing in the oil & gas sector, with revenue are likely to be $2.2 Billion by 2023.

This article explores wireless sensor networks for SCADA applications in the utility sector, especially pipelines.

2 SCADA System

The initial phase of SCADA system implementation used proprietary technologies, including mainframe computers, remote terminal units (RTU)s, and software for monitoring and controlling systems. The RTU collected data from sensors in the field and sent it to the master control centre over available telecommunication facilities to process and initiate controls. The systems were upgraded with the advances in computer systems and industrial control systems. The high-end workstation with graphical user interface and redundant computer network upgraded the SCADA system. The use of PLC used in process control applications for the past many years for data collection instead of RTUs further enhanced the SCADA system at the field level and introduced a distributed SCADA system. The RTU’s that used to be just data collection or control passing devices were replaced by PLCs, which could process the data at the source and take necessary control action at the local level without involving the master station. TCP/IP protocol and WAN protocols in communication with remote units brought some standardization in SCADA system communication protocols. SCADA applications are limited to industrial units and are traditionally used by Oil & Gas industry, power sector, railways, mining, and other utilities. Of late, SCADA systems have been integrated with the corporate network in a limited manner for management information. The integration with the corporate network allowed management direct access to key parameters of the process and enabled them to take quick and informed decisions.

3 Wireless Sensor Network

Wireless Sensor Network (WSN) consists of many small batteries powered sensing devices placed at strategic locations on the system to the monitored.  Each sensing device is capable of monitoring and/or displaying the information or actuating the controls.  The sensors may consist of measurement of temperature, pressure, vibration, flow, etc. The data collected by the sensor is periodically sent to the main computer system using radios embedded in the sensors

The WSN is a self-configured and infrastructure-less wireless network for monitoring physical environmental conditions in large dispersed areas. The sensors can organize themselves after deployment and use multi-hop communication for sending information collected. The environmental condition may include temperature, vibration, sound, pressure, pollutants, motion, etc., as per requirement. WSN acts cooperatively, and the data collected by the sensors are passed on to the main location called sink or base station in WSN terminology. The sink acts as an interface between users and the sensor. At the sink, these are observed and further analyzed.  The data from the sink can be obtained by injecting queries and observing results. A WSN may consist of hundreds and thousands of nodes or sensors dispersed over a large area.

A typical WSN node consists of a sensor module, a microcontroller, a radio unit, and a power supply system. The sensors and actuators are usually based on a micro-electromechanical system (MEMS). The microcontroller takes care of data acquisition, scheduling, communication protocols, data packets for transmission, battery/power supply status, and other management functions. The radio part consists of a short-range transceiver. To keep power consumption low, the sensors have minimal resources regarding storage capacity, computing power, and communication bandwidth.

After recent advances in technologies, the availability of reliable, miniaturized sensors with embedded microcontrollers and low bandwidth radios on a single chip have made them usable for large field deployment. These sensors require low power and have many power conservation features. The deployment and maintenance cost of the modern sensor is low enough for these to be deployed in large numbers with battery lasting for a couple of years. These sensors are being used in a wide variety of applications, including industrial applications, agriculture, large area environmental monitoring such as forest and agricultural fields, healthcare, monitoring civil structures and many more.

However, due to their low design complexity, limited storage, low bandwidth, and low power, these have limitations in their use. It requires a delicate balance between their communication and processing capabilities. Scientists are looking for unconventional paradigms for suitable protocol and processing design to make these more useful.

The WSN uses short-range communications standards such as IEEE 802.15.4, Zigbee, Bluetooth, and Ultra-wide Band (UWB) for communicating in the network and to the base or sink node.

WSN is one of the critical components of IoT systems as they have low power and allow precise placement. The use of  WSN in the oil & gas sector is in areas such as process control, asset locating and tracking, asset monitoring, safety, and environment. The WSN sensor can be deployed without shutting down the system, such as for rotating equipment monitoring.  For example, ABB WiMon provides a complete solution for rotating equipment vibration monitoring using WSN and operates at Gudrun oil and gas field located in the North Sea.

The WSN in a mesh network can provide redundancy and high availability due to alternate communication paths in the network.

4 WSN for Pipeline/power line Applications

The traditional SCADA system uses cables connected to the PLC or RTU using cables, and power to these are also supplied using cables. These sensors, once installed, usually are never changed unless these go bad but recalibrated as per their schedule. On the other hand, the WSN sensor can be placed in the field without cumbersome cabling requirements. These can also be powered by solar panels or power available at the facility in a small setup.  However, for remote locations with limited power availability, they can be powered using batteries. The sensor output can be aggregated using the base station and then transferred to the SCADA master station over normal communication links. WSN sensors can reduce the cost of installation, reduce the maintenance required, and make the system flexible. The WSN sensor has no issues of cable cut due to wild animal damage, physical wear, corrosion, etc. These sensors can be replaced quickly in case of problems without any cumbersome procedure required in the case of wired sensors. The WSN sensor can be easily relocated, and new sensors can be quickly installed without bothering about cable trays and cable installation issues.

Mexican state-owned PEMEX used 1450 wireless sensors for monitoring wellhead pressure and temperature of scattered onshore oil fields along with long-range Ethernet modems for getting information in their control room.

BP at their production centre in Geel, Belgium, used smart wireless technology from St. Louis-based Emerson Process Management for monitoring leaks of xylene or benzene from the large plant. The system used Pentair (Tyco)- Fast Fuel sensors and Emerson’s Rosemount 702 wireless discrete transmitters to get information quickly to the control room. It saved them 50% cost that they would have incurred using wired systems.

The use of a sensor for monitoring water pipeline by allowing nodes to flow with water and then get attached to the pipe has been investigated. The advantage is automatic deployment, easy configuration, and removal of nodes when they go faulty, or their battery gets depleted by detaching them and collecting at the end. A field trial of a pipeline monitoring system called PIPENET was done in collaboration with Boston Water and Sewer Commission (BWSC). The system used to pressure, level, vibration, temperature monitoring of the pipeline using Intel Mote Sensor nodes and platform. The system provides valuable insight into the deployment issues and solutions.

International Oil and Gas Companies (IOCs) have deployed thousands of WSN nodes in oil and gas installations in the Nigeria Niger Delta region. The installation covered included oil rigs, pipelines, oil wells, and flow stations. The WSN sensors used were battery operated and had a bidirectional communication range of 4-5 miles using ZigBee/IEEE 802.15.4 based radios.

The deployment of WSN in a pipeline or power line network can be using infrastructure network mode with a back-end network being used for data transmission from the base node to the central station. The deployment model for pipeline network and utility monitoring will be deterministic rather than ad hoc. The sensor needs to be placed at fixed locations for monitoring the system. The power supply for base station nodes is not a major issue for this sector as the power available for cathodic protection of pipeline can be used. The normal communication back end such as fibre optic system or satellite or Cellular system can get all the data to master control room.

5 Challenges in using WSN for industrial applications

The WSN system is not without challenges in implementation. The challenges include using power efficient management, efficient protocols, network security, and quality of radio links. This section deals with challenges specific to the linear pipeline network.

5.1 Security in WSN

The resource limitations of WSN nodes limit the implementation of security protocols, leaving them vulnerable to attacks with implications on privacy, safety, and availability. Cisco has come out with a unique set of security devices and software for the oil & gas industry.

The wireless nature of WSN makes it prone to attacks similar to other wireless networks apart from vulnerabilities in wired networks. The broadcast nature of WSN allows anyone with proper equipment to eavesdrop on the network. The security of WSN is different from other wireless networks due to limitations of the sensor’s computational capacity, memory, battery power, random deployment, etc. The sensors can be physically removed or relocated, and their failures may not be noticed.

Some specific attacks and their mitigation against sensor networks are given below:

Denial of Service (DoS) can be launched simply by making the node exhaust their limited resources, making them unavailable for any work or at the physical layer by jamming the signal or at the link layer by creating collisions or at the network layer using misdirection, block holes and at transport layer using desynchronization and malicious flooding. The DoS due to jamming can be prevented to a certain extent using the spread spectrum technique for transmission and region mapping. The use of authentication and encryption can remove DoS attacks due to desynchronization and other threats.

The Wormhole attack: In this attack, the attacker records the packet at one place and then sends it to the network from another location. The nodes receiving the message tries to send it to their neighbours, and the neighbours try to send it to the originator whose location is camouflaged, and the message keeps on moving in the network. The wormhole attacks can be prevented by using a proactive routing protocol such as DAWWSEN.

The Sybil attack: In this attack, the node sends incorrect information such as signal strength, nodes position about itself, or making up a nonexistent node to other nodes. This attack can be prevented by using proper encryption and authentication techniques. The identity certificates can be used to prevent Sybil attacks.

Black/Sinkhole attacks: In this attack, a node tries to attract all the traffic towards itself by making it attractive for routing the information. A node with high power transmitter can act as a black hole node as it will provide a good quality route for other sensors. The use of geographic routing protocols can limit these attacks by using localized interactions without involving the base station.

Passive Information Gathering: The attacker with a good quality receiver can eavesdrop on network traffic and do traffic analysis to find the required information. The attacker can also insert its node in the network to misdirect the packets or attract the packets. The passive attacks can be prevented using proper encryption and authentication techniques.

Selective Forwarding: The attacker can use a rogue node to selectively drop few selected packets to confuse the network or refuse to forward the packets. The selective forwarding attacks can be prevented by using multiple routing techniques.

Hello flood attacks: The malicious node sends Hello packets using high power, making itself a parent node so that most messages are sent to it, causing a delay in the network. The Hello flood attacks can be prevented by checking the bidirectional link so that all nodes can reach the parent’s node in just single-hop.

5.2 Energy Management for Pipeline Network

The pipeline network is a linear network where all the nodes are located along the pipeline. Since nodes have a small battery, replacing the batteries or recharging them is an arduous task and requires efficient energy management.  This requires the use of energy-efficient protocols that need minimal communication effort. The protocol needs to work on activation of nodes transmission based on a minimum energy principle so that the life of batteries can be enhanced and minimize the overall deployment cost.

5.3 Routing Challenges

Routing in a linear network is a big challenge in the face of strict energy consumption requirements. Nodes in this scenario have to transfer data from an adjacent node as well. However, no route discovery is required as the route is already known. The protocol needs to use special schemes to overcome node failures and reduce power consumption.

5.4 Localization

Some applications require that the WSN nodes are aware of their physical location in relative or absolute terms. Two approaches can be used for localization. One is the direct approach, where a system such as GPS is used to provide location information. The other is the indirect approach, where the relative position to a fixed location allows estimation of location.

6 Conclusion

The SCADA system is being continuously upgraded with up-gradation in technology. The wireless sensor network is one such technology that is being embraced for the up-gradation of monitoring and control systems of oil & gas, power, agricultural, water, and other utilities. The cost reduction of up to 80% by using WSN nodes instead of the traditional wired sensor has prompted the utility sector to embrace this technology. The technology can be used by pipeline by replacing wired sensors in the field with WSN nodes. With necessary security measures, including encryption, safety protocols, and authentication, these can replace wired sensors to provide quick installation, easy configuration, and maintenance, as well as quick up-gradation when required. Thus, the use of WSN along with the traditional SCADA system can be very beneficial for the industry in saving deployment and maintenance costs.