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Substation Automation


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Project Description

Substation Automation Communication Architecture

When the communication requirements of substation automation are considered, Internet can offer an alternative communication network to remotely control and monitor substations in a cost effective manner with its already existing communication infrastructure. However, Internet can not guarantee very strict QoS requirements that the applications of substations demand, since data communication in Internet is based on best effort service paradigm. In this context, Internet based Virtual Private Network (Internet VPN) technologies, that are transforming the Internet into a secure high speed communication network, constitute the cornerstone for providing strict QoS guarantees of substation automation applications. Internet VPN technologies offer a shared communication network backbone in which the cost of the network is spread over a large number of users while simultaneously getting the benefits of a dedicated private network. Therefore, the Internet VPN technology as a high speed communication core network can be utilized to enable minimum cost and highly reliable information sharing in substation automation applications.

Fig. 1. Substation Automation Communication Architecture.

Although Internet VPN technologies can provide the necessary real time communication for substations in urban areas, this may not be the case for substations in remote rural locations where the high speed communication core network, e.g., Internet, might not exist. Therefore, when the individual communication capabilities and locations of substations are taken into account, it is appropriate to consider the overall communication infrastructure as a hybrid network as shown in Fig. 1. This hybrid network consists of two separate parts:

High Speed Communication Core Network: It can be either private network or public network. Due to several technical advantages, Internet based Virtual Private Network can be considered as a cost effective high speed communication core network for substation automation.

Last Mile Connectivity: It represents the challenge of connecting the substations to the high speed communication core network. Each possible communication alternatives for Last Mile Connectivity introduces its own advantages and disadvantages.

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Communication Challenges

It is well known that power disturbances and outages in substations occur due to several reasons such as equipment failures, lightning strikes, accidents and natural catastrophes, and often result in long power service interruptions. In order to avoid these possible disruptions in substations, a highly reliable, scalable, secure and robust communication network between substations and a remote control center is vital. The communication requirements of substation automation applications are briefly described as follows:

High Bandwidth and Real Time Monitoring:The amount of data needed to remotely monitor and control the substations is large and expected to increase in the near future. Therefore, the monitoring and control system of the substations should support real time communication, and thus, the monitoring data should be transmitted without any additional delay.
Reliability:The communication network should be able to operate continuously over an extended period of time even in the presence of network element failure or network congestion. To achieve this, the communication network should be properly designed with the objective of no losses in all working conditions and able to deal with failure gracefully.
Scalability:Since the number of substations is large and rapidly grows, the communication system has to be able to deal with very large network topologies without increasing the number of operations exponentially for the communication network. A hierarchical or distributed approach are the natural solution to the scalability problem.
Robustness:Because the network traffic load can not be predicted accurately and timely, high performance communication even under different network traffic conditions is mandatory in substation automation. Therefore, the performance of communication network should not be deteriorated from changing network traffic conditions.
Security:Security is the ability of supporting secure communications between a remote control center and substations in order to make the communication safe from external attacks. Efficient authentication and encryption techniques should be applied to provide secure communication.
Communication Network Cost:While providing the communication requirements mentioned above, the network architecture must enable rapid implementation and possible modifications of communication network. In addition to all above communication requirements, the cost of the network should also be considered in order to make it feasible subject to budget constraints.

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Internet based Virtual Private Network

Internet based Virtual Private Network (Internet VPN) is considered as promising solution for the high speed communication core network. Internet VPN are based on the use of tunnelling. With the tunnelling mechanisms, e.g., Label Switch Paths (LSPs) in Multi Protocol Label Switching (MPLS) technology, virtual dedicated communication links having a certain bandwidth can be established on a certain path. In other words, the appropriate bandwidth and the best path on the physical network can be chosen and assigned to the tunnel in order to satisfy the communication requirements. In the following, we will describe how the communication requirements of substation automation applications can be provided with Internet VPN technology:

High Bandwidth and Real Time Monitoring in Internet VPN: The bandwidth demand matrix deducted from real time constraints, can be provided designing a network composed of virtual links which are properly dimensioned between substations and the remote control center.

Reliability in Internet VPN: In order to guarantee the protection from network failures, in addition to the working virtual tunnels, back-up virtual tunnels should be established with the minimum bandwidth consumption.

Scalability in Internet VPN: A hierarchical or distributed approach are the natural solution to the scalability problem in Internet VPN. According to the hierarchical approach, a set of substations can be clustered into domains each one having the smaller dimension compared to global network.

Robustness in Internet VPN: In order to avoid deteriorated communication performances due to changing network traffic conditions, the dimensioning process to assign the bandwidth to the virtual links of the Internet VPN should be based not only on the main bandwidth demand matrix, but also on other possible bandwidth demand matrices to provide a safe margin in network dimensioning to avoid congestion.

Security in Internet VPN: Internet VPN has to provide secure data transmission across an existing Internet backbone. To achieve this, two technologies, i.e., cryptography and tunnelling, can be applied.

Communication Network Cost in Internet VPN: In order to provide the above communication requirements, the traditional solution is based on dedicated leased communication lines. However, this solution is not cost effective and flexible enough. A Cost effective solution utilizing existing infrastructure can be offered by Internet VPN which guarantees QoS requirements like in leased communication lines.

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Communication Technologies for Last Mile Connectivity

Last Mile Connectivity represents the challenge of connecting the substations to the high speed communication core network. Each possible communication alternatives for last mile connectivity introduces its own advantages and disadvantages. The communication technologies evaluated for last mile connectivity are:

Power Line Communication: Power Line Communication (PLC) is transmission of data and electricity simultaneously over existing power lines as an alternative to constructing dedicated communications infrastructure. PLC has become more important in recent years due to developments in PLC technology. However, there are still several technical problems and regulatory issues that are unresolved. Moreover, a comprehensive theoretical and practical approach for PLC is still missing.

Satellite Communication: Satellite Communication can offer innovative solutions for remote control and monitoring of substations. It provides an extensive geographic coverage, and thus, it can be a good alternative communication infrastructure for substation automation in order to reach remote substations where other communication infrastructures such as telephone or cellular networks might not exist.

Wireless Communication: When compared to conventional wired communication networks, wireless communication technologies have potential benefits in order to remotely control and monitor substations, e.g., savings in cabling costs and rapid installation of the communication infrastructure. On the other hand, since radio waves in wireless communication spread in the air, eavesdropping can occur and it might be a threat for communication security.

Optical Fiber Communication: Optical fiber communication systems, which were first introduced in the 1960s, offer significant advantages over traditional copper-based communication systems. In substation automation, optical fiber communication system is one of the technically attractive communication infrastructures, providing extremely high data rates with its Electro Magnetic Interference (EMI) characteristics.