IEC 61850 Substation Configuration Language as a basis for Automated Security and SDN Configuration PDF

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IEC 61850 Substation Configuration Language as a
basis for Automated Security and SDN Configuration...

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Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes

IEC 61850 based substation automation system: A survey Mohd. Asim Aftaba, S.M. Suhail Hussain b, , Ikbal Alic, Taha Selim Ustun b ⁎

a

Electrical and Instrumentation Engineering Department, Thapar Institute of Engineering and Technology, Patiala 147001, Punjab, India Fukushima Renewable Energy Institute, AIST (FREA), National Institute of Advanced Industrial Science and Technology (AIST), Koriyama 963-0298, Japan c Department of Electrical Engineering, Jamia Millia Islamia (A Central University), Jamia Nagar, New Delhi 110025, India b

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Keywords: Substation Automation System (SAS) Substation Communication Network (SCN) IEC 61850 Intelligent Electronic Devices (IEDs) Sampled Values (SVs) Generic Object-Oriented Substation Event (GOOSE)

Power systems are undergoing an evolution similar to what telecommunications sector went through several decades ago. Analog and hard-wired systems are replaced with automated digital ones. Infrastructure designs are not static anymore and are geared towards accepting new deployments as easily as possible. Limited data exchanges of the past are giving way to detailed data collection, reporting and analysis. When equipped with smart algorithms and techniques such as machine learning, these significantly enhance the capabilities of smart grids. Substations are core component of smart grid, where communication system is integrated. However, achieving a standard substation communication system that can operate with the principles of plug-and-play (PnP) is not a trivial task. Considering the cyber-physical nature of power system equipment, integration requires more diligence for safe operation. Furthermore, there are many different types of substation equipment which are manufactured by, again, countless many vendors. Achieving a common language and interoperability between them is a difficult task. IEC 61850 standard has been taking strides towards that goal. Its object-oriented structure makes its versatile while well-defined modeling blocks ensures compatibility. Recent work has focused on IEC 61850 based modeling of substation equipment, developing message exchange formats for substation functionalities as well as investigating the performance of different communication technologies when they are used to implement IEC 61850 based models. This paper reviews these efforts, their benefits to substation operation and possible future work, including cybersecurity considerations.

1. Introduction Substation plays a vital role in electricity transfer. It converts the voltage level from high to low level and vice versa using power transformers and performs switching and protection operations. With the emergence of global energy market, there is a growing competitive environment among different energy suppliers. Due to introduction of new players, more formally known as power players, and increasing market pressure, the motive of energy supplier is more towards customer satisfaction. Customer satisfaction is pivoted on transfer of right information to right entity. Thus, there are enormous information exchanges in the energy market. The challenge faced by utilities is managing the information and delivering the right information to the users who can analyze and use the information for specific applications. Thus, there is a pressing need to develop a standardized architecture to harness the information exchanges. This standardized architecture must be supplier independent and can interoperate with other applications. This paved the way for open system, which is a computer system that embodies supplier

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Corresponding author. E-mail address: [email protected] (S.M.S. Hussain).

https://doi.org/10.1016/j.ijepes.2020.106008 Received 7 February 2020; Accepted 11 March 2020

independent standard and is interoperable, uses non-proprietary software and supports easy future upgrades [1]. The advantages of open systems include longer system life, easy upgradeability and supplier independency. In order to sustain the open system, several standardization agencies came forward for developing a standard communication protocol which maps all features of open system and is industry adaptable. By a standard communication protocol, utilities may install devices from different manufacturers which can readily co-operate in the utility’s environment. After deliberate research and numerous meetings, the standardization agency IEC TC 57 came forward and proposed IEC 61850 standard for substation automation. The concept of IEC 61850 standard was applied to the substation, where enormous amount of data is exchanged among various Intelligent Electronic Devices (IEDs). These IEDs form the backbone of substation automation system. The substation communication was now governed with IEC 61850 which has functional use which was lacking in previous master slave standards such as Distributed Network Protocol (DNP), IEC 60870 etc. The IEC 61850 leverage several benefits from previous standards in terms of data speed, eXtensible Markup

Language (XML) schema for configurations, peer to peer links and availability of communication conformance tests [2]. With the use of IEC 61850 for substation automation system, the performance testing and functional testing of the IEDs is also changed. Authors in [3] performed functional testing of IEC 61850 based systems. The principles of different IEC 61850 communication-based functions are discussed along with various factors which affect the system performance. A comparison between functional testing of conventional and IEC 61850 devices along with the testing methods have been presented in their work. Due to emergence of IEC 61850 as the leading protocol for substation automation systems (SAS), several studies were reported on the applicability and enhancement of usage of the standard for substation functionalities. In [2], the evolutions required during designing, configuring and testing an IEC 61850 based SAS has been presented. The transition from the physical architecture of a substation to a logical architecture based on IEC 61850 has also been addressed in [2]. The roadmap of IEC 61850, as a de facto standard for SAS, including the system configuration and interoperable design has also been presented. The SAS based on IEC 61850 was divided into three levels by author in [4]. The first level was the core function of a substation i.e. the operation of power system, the second being reliability and third being visibility. It also showed how the IEC 61850 protocol is to be employed for system design. The first real time implementation of an IEC 61850 based SAS was at the Tennessee Valley Authority’s (TVA) substation [5]. The researchers at TVA believed that the IEC 61850 based communication can streamline the substation application environment for advanced capabilities and can also result in resource savings in terms of construction, operation, maintenance and data management. Further in this direction, to develop industry ready engineers and practitioners, a substation automation laboratory was developed at Jamia Millia Islamia University, New Delhi [6]. IEC 61850 has gained popularity and has become a defacto standard for substation automation world over. Utilities world over upgraded or automated the substation according to IEC 61850 [7–12]. This paper presents a holistic review of different advancements in SAS through IEC 61850 standard.

2. IEC 61850 background The first edition of IEC 61850 standard series had 10 main parts. The Table 1 gives the brief description of different parts of IEC 61850 standard. The first four parts contain information about the standards concepts and ideology. The main strength of IEC 61850 standard is the common data model it uses for devices as well as its unique message protocols for

communicating power system information in a predefined fashion. The IEC 61850 standard advocates use of object-oriented approach for modeling of engineering tasks in a SAS. The advantage of having an abstract interface provides flexibility to the design engineer in adopting any underlying technology and protocol for a particular process in a substation. Abstract interface means that the standard is intended to provide guidelines for describing services rather than information on how these services are to be built. Also, the IEC 61850 standard defines a set of generic services for client/server interactions and transmission requirements for all sets of measurements in a substation in terms of latency, reliability and security. IEC 61850 defines all known functions in a substation and splits them into sub-functions known as Logical Nodes (LNs). Logical nodes are virtual representation of physical devices and exchanges information as per the standard. The term information modeling is way of exchanging standardized information and is realized by defining logical nodes. A group of logical nodes combine to form a Logical Device (LD). The implementation details and application view of the IEC 61850 standard is discussed by authors in [13]. 2.1. Object oriented modeling of IEC 61850 The IEC 61850 standard adopts object-oriented methodology and technique for modeling the data and data sets in a SAS. Authors in [18] provided a holistic overview of the IEC 61850 standard and the process of standardizing the substation data using object-oriented approach. IEC 61850 standard supports all functions of the substation and its engineering by employing a object-oriented data models which are used to describe the processes to be implemented and controlled in a substation. An outline and application view of IEC 61850, describing the information model, logical nodes and data objects that are used to represent a physical device in IEC 61850 standard is discussed in detail in [18]. Further in this direction, the impact of edition 2 of the IEC 61850 standard on the object modeling of IEDs has been covered by author in [19]. As per Edition 2 of IEC 61850 standard, complex devices can be modeled as servers containing multiple logical nodes to realize various substation functions such as protection, measurement etc. The functional hierarchy in the nested model is an important parameter to improve the overall efficiency of the device. The changes in the multifunctional distribution IEDs due to adoption of Edition 2 of IEC 61850 has been discussed in their work. 2.2. Information modeling Information modeling is a well-established and effective method for managing information exchanges. Its main purpose is to provide standardized syntax, semantics and hierarchical structures for the data that

Table 1 Description of IEC 61850 standard Parts for SAS. Parts

Description

IEC 61850-1 IEC 61850-2 IEC 61850-3 IEC 61850-4 IEC 61850-5 [14] IEC 61850-6 IEC 61850-7-1 IEC 61850-7-2 IEC 61850-7-3 IEC 61850-7-4 [15] IEC 61850-8-1 [16] IEC 61850-8-2 IEC 61850-9-2 [17] IEC 61850-9-3 IEC 61850-10

Introduction and overview Glossary General requirements Specifies the system and project management for power utility automation systems with communication between IEDs. Specifies information on communication requirements of substation automation functions. specifies a description language for the configuration of IEDs in SAS called System Configuration description Language (SCL) give an overview of Abstract Communication Service Interface (ACSI), different Logical Nodes (LNs), Data Objects (DOs), Common Data Classes (CDCs) and how to achieve interoperability using these building blocks.

parts specify the protocol structure and mapping of different ACSI services to MMS, XML messages transported over XMPP and ISO/IEC 8802–3 (Ethernet).

Specifies a precision time protocol (PTP) profile of IEEE 1588–2008 in compliance with IEC 61850. Specifies standard techniques for testing of conformance of client, server and sampled value devices and engineering tools.

is exchanged among different devices and systems. To achieve interoperability, all Data Objects (DOs) in the data model need a strong definition with regard to syntax and semantics. In IEC 61850, the group of DOs that serve specific functions are defined as LNs. Composition of relevant LNs for providing information needed for a particular device is defined as LD. An IED may contain a number of LDs and even one LD device may be part of different IEDs. A LN consists of a set of DOs, and these DOs can be of any one of following type: Transient (T), Mandatory (M), Optional (O) and Conditional (C). The status of DO with (T) or (M) or (O) or (C) designation specifies whether the DO in the LN is momentary or mandatory or optional or conditional respectively. Interoperability becomes much easier to achieve, when more DOs are defined as mandatory. IEC 61850 standard defines a large number of LNs corresponding to different components of power utility systems. Furthermore, IEC 61850 standard defines the DOs with full semantics which further make the interoperability with the LNs even more convenient. To avoid exclusive extensions that are developed by separate entities in an incompatible way, IEC 61850 specifies normative naming rules for LN classes and data object names. The LNs have 4 letter names where the first letter corresponds to the group that LN belongs to. Different groups of LNs are defined in IEC 61850-7-4 standard. For example, the LN MMXU belongs to the measurement group. The data model of the MMXU LN is shown in Fig. 1. The MMXU data model is composed of the instance of the data object phase voltage (PhV) instantiated from the Common Data Class (CDC) WYE, which is composed of phase A voltage (phsA) instantiated from CDC CMV, which is also composed of complex value cVal (of type Vector), which is, further, composed of voltage mag (of type AnalogueValue), which is, finally, composed of floating-point value f (of type FLOAT32). Initially IEC 61850 standard was developed for substation automation and it contained the information models (i.e. logical nodes defined) for different components of substations. Later, with publication of new parts of IEC 61850 such as IEC 61850-7-420 for DERs [20], IEC

61850-90-5 for PMU [21], IEC 61850-90-8 for electric vehicles [22], IEC 61850-90-7 for power converters [23], IEC 61850-90-1 for intersubstation communication [24], IEC 61850 was extended to entire power utility automation systems. Further, based on these standards the information models for different components such as smart meters [25], DERs [26–28], EV and charging stations [29 –31], PMU [32,33], fault current limiters [34] etc., were developed and reported in literature. The information models contain the data objects and attributes that are required by a particular component. In order to exchange this information for realizing different functions and services, this information model has to be mapped to different protocols. The next section details about different functions, messages and protocols defined in IEC 61850 for exchanging this information that is modeled in a standardized fashion.

3. IEC 61850 substation automation systems functions and requirements The functions of a SAS are the tasks which are performed inside a substation. These are functions to control, monitor and protect the equipment of the substation and its feeders [14]. In addition, there exist functions, which are needed to maintain the SAS, i.e. for system configuration, communication management or software management. These functions of a SAS are logically divided into three levels such as process, bay and station levels as shown in Fig. 2. The process level functions are all functions interfacing to the process. The sensors or actuators are interfaced to the SAS functions through the process level. The bay level functions are functions which uses data of one bay and act mainly on primary equipment of one bay. The protection and control functions of bay which require data or information from other bays are known as inter bay protection and control functions. The bay level communicates with the process level as shown in Fig. 2. The station level functions are divided into two categories, process related station level function and interface related process level

Fig. 1. Data model of MMXU LN [15] .

Fig. 2. Functional levels of a SAS [14] .

functions. The process related station level functions are functions which uses the data of more than one bay or of the complete substation and acting on the primary equipment of more than one bay or of the complete substation. The interface related station level functions represent interfacing of the substation to local station operator (such as Human Machine Interface (HMI)) or to a remote control center or to remote engineering for monitoring and maintenance purposes. The devices of a SAS are implemented physically on the process, bay and station levels. The process and bay level functions are usually performed inside a same device. This does not change the logical interpretation but only changes the physical operation. The process level devices include I/O devices, sensors and actuators connected by a process bus. The station level devices include IEDs which are used for monitoring, control and protection functions. The station level devices are station level computers, operator’s workplace, remote communication interface. To fulfill the requirements of a SAS, the functions are decomposed in form of LNs which may reside logically in a physical device. The discussion on LNs has been presented in next subsection. For proper running of functions in a SAS, it is essential and crucial to meet the performance requirements of the supporting communication interface. This includes the total latency, i.e. the total transfer time between two functions in a SAS. The total transfer time is defined as the sum of communication processing delay at sending and receiving end and the propagation delay as shown in Fig. 3. The transfer time is applicable for the complete transmission chain as indicated in Fig. 3. In physical device 1, a function f1 sends data to another function f2, located in physical device 2. The transfer time is sum of processing times at communication processors and the network transfer time, including queueing and processing time at routers and other devices in the network. The testing and verification of transfer times for the communication network is performed before deployment to ensure reliable operation. The data between different functions of a physical device is transferred in form of messages. 3.1. Message types and structures According to IEC 61850, the different messages are classified into

seven types which are further subdivided in to two independent groups of performance classes. 3.1.1. Type 1 - Fast messages This category of messages contains a single point status data or command such as “trip”, “close”, “start ”, “stop” or “block ”. The messages carrying the “trip” command is further named as Type 1A, while other fast messages are named as Type 1B. The Type 1A message have stringent timing requirements and are most important than other fast type of messages. Whenever a fault occurs it is detected by protection devices which respond to it by generating burst of Type 1A Generic Object-Oriented Substation Event (GOOSE) messages. During fault conditions, the periodic heartbeat nature of GOOSE message is changed to burst mode. In burst mode, the transmission interval of GOOSE messages increases sequentially. As an event occurs (such as a fault) the retransmission time of GOOSE message is changed from To to T 1, T 2, T 3, ……T n such that T1 < T2 < T3 < …. < T n. The sequential increase in retransmission time ends until Tn reaches to T o. After some period of time, the retransmission time changes back to normal periodic nature as shown in Fig. 4. The gradual increase in retransmission time in bursts is adopted in order to increase reliability of the network, since the Type 1A GOOSE message conveys critical commands. 3.1.2. Type 2- Medium speed messages This category of me...