Performance Evaluation of IEC61850-90-5 Over a Non-Commercial4G LTE Network

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UPTEC IT 17 022

Examensarbete 30 hp Oktober 2017

Performance Evaluation of IEC

61850-90-5 Over a Non-Commercial 4G LTE Network

Linus Eriksson

Institutionen för informationsteknologi

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Teknisk- naturvetenskaplig fakultet UTH-enheten

Besöksadress:

Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0

Postadress:

Box 536 751 21 Uppsala

Telefon:

018 – 471 30 03

Telefax:

018 – 471 30 00

Hemsida:

http://www.teknat.uu.se/student

Abstract

Performance Evaluation of IEC 61850-90-5 Over a Non-Commercial 4G LTE Network

Linus Eriksson

Old electrical power grids with unidirectional power flow are transforming into enhanced smart grid systems with bidirectional power flow. Advancements in communication infrastructure can offer new ways on how communication can be utilized within the grid. The standardized communication protocol IEC 61850 defines data models and services designed for communication within a substation. Smart grid applications will require communication over wider areas and between substations.

The IEC 61850-90-5 addition to the standard defines how data can be sent over wider areas by utilizing Internet protocol, which is necessary if public communication networks such as 4G long term evolution is used.

This thesis evaluates the applicability of the IEC 61850-90-5 protocol when used over a non-commercial 4G LTE network. A prototype that emulates an intelligent

electronic device was derived from an IEC 61850-90-5 open source project and was used transmit and receive data over the network. To evaluate the applicability of the IEC 61850-90-5 stack and the performance of the non-commercial 4G LTE network different metrics such as reliability, availability, latency, and throughput was evaluated.

The overall result is promising and indicates that the IEC 61850-90-5 protocol in combination with 4G LTE would be suitable for most applications within the smart grid. It is concluded that cellular technologies such as 4G LTE will play an important role for smart grid applications, even though it does not fulfill the most stringent application requirements. The IEC 61850-90-5 protocol will be a key component in smart grids since it enables routing of standardized GOOSE and SV messages in IP packet format, which is needed when using commercial networks such as 4G LTE.

Examinator: Lars-Åke Nordén Ämnesgranskare: Tomas Olosson Handledare: Gargi Bag

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Acknowledgements

This report describes a master thesis project conducted at ABB Corporate Re- search in Västerås, Sweden.

I would like to begin this thesis report by thanking Mr. Rajendra Bogati who was a part of this project and whom I worked closely with.

I would also like to thank ABB Corporate Research for giving me the opportu- nity to work with an interesting project.

Many thanks to my supervisor Gargi Bag from ABB Corporate Research for the help, support, and feedback throughout this project.

Last but not least I want to thank my reviewer, Tomas Olofsson from Uppsala University, for your support and guidance throughout the project.

Linus Eriksson Uppsala, 2017

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Acronyms

AMI Advanced Metering Infrastructure APDU Application Protocol Data Unit

ACSI Abstract Communication Service Interface ASDU Application Service Data Unit

BAN Building Area Network BER Basic Encoding Rule CDC Common Data Class

CDF Cumulative Distribution Function DAS Data Acquisition Systems

DHCP Dynamic Host Configuration Protocol FAN Field Area Network

GOOSE Generic Object Oriented Substation Event GSE Generic Substation Event

GSSE Generic Substation State Event HAN Home Area Network

IAN Industrial Area Network

IEC International Electrotechnical Commission IED Intelligent Electronic Device

IP Internet Protocol LAN Local Area Network LTE Long Term Evolution MAC Medium Access Control

MMS Manufacturing Message Specification NAN Neighborhood Area Network

NTP Network Time Protocol PDC Phasor Data Concentrators PDU Protocol Data Units PMU Phasor Measurement Unit QoS Quality of Service

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ROCOF Rate Of Change Of Frequency SAS Substation Automation System

SCADA Supervisory Control And Data Acquisition SCL Substation Configuration Language

SCMS Specific Communication Service Mapping SPDU Session Protocol Data Unit

SV Sampled Value

SVCB Sampled Value Control Block TCP Transmission Control Protocol TLV Tag Length Value

UCS Utility Communication Architecture UDP User Datagram Protocol

UTC Coordinated Universal Time VPN Virtual Private Network WAN Wide Area Network

WAMPAC Wide Area Monitoring Protection and Control WLAN Wireless Local Area Network

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List of Figures

1 Traditional electric power grid [17] . . . . 6

2 Data rate and communication range [21] . . . . 8

3 IEC 61850 Data Modeling [10] . . . . 11

4 The IEC 61850 object transformed into a named MMS variable object with a unique reference for a element in the model [19] . . 12

5 The structure of the IEC 61850-90-5 Session Protocol From [9] . 16 6 Basic Encoding Rule . . . . 17

7 ANS.1 BER encoded SV APDU, from [8] . . . . 18

8 Mapping of phasor measurements [16] . . . . 19

9 Communication Requirements [9] . . . . 20

10 Environment test setup . . . . 21

11 Flow chart of the test process . . . . 23

12 Structure of the startup file for the application . . . . 24

13 Time Synchronization utilizing a NTP server . . . . 25

14 SV packet captured in Wireshark . . . . 26

15 The data representing three synchrophasors sent in a SV packet . 26 16 The network availability measurements graphed over a period of 24 hours . . . . 30

17 The throughput for different transmission intervals graphed against different packet sizes . . . . 31

18 The average latency for different packet sizes graphed against different transmission intervals . . . . 32

19 CDF graphed against latency for different transmission intervals 32 20 Reliability graphed against time . . . . 33

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1 Introduction

Traditional power grids with unidirectional power flow are transforming into smart grid systems with bidirectional power flow. Renewable sources of energy in the power grid such as wind and solar increase the need of having more control, monitoring, and protection applications that serve the needs for grid automation. At the same time as the power grid continues to evolve, communication infrastructure is evolving and can offer new ways on how communication can be utilized within the power grid. Increased connectivity makes it possible to connect more devices and applications to the grid. Wireless communication technology offers scalability and flexibility in a cost efficient way since it reduce the need of expensive wires and installation costs.

There are several wireless technologies for both short range and long range communication. Cellular technologies such as the Fourth Generation (4G) can play an important role in realizing fast and reliable communication for smart grid applications. 4G wireless systems were mainly developed for reasons such as that it is all-Internet Protocol (IP) based system, to reduce data latencies and signal loading and always-on user experience with flexible Quality of Service (QoS) support. The 4G systems can be accessed with different technologies such as Long Term Evolution (LTE) and LTE-Advanced [2].

For wireless communication to be accepted in the smart grid domain, it has to fulfill requirements related to parameters such as latency, reliability, availability, and throughput. The requirements for these parameters varies depending on the type of application. Some applications have very stringent requirements since failure or anomalies in data delivery can cause severe damages. LTE, which already is a technology in use, covers long distances and offers high throughput and it may therefore be suitable for smart grid applications if it meet the requirements.

The standardized communication protocol International Electrotechnical Com- mission (IEC) 61850 offers interoperability between devices from different ven- dors and defines data models and services designed for communication within a substation. Many of the applications in a smart grid system will require communication over wider areas and between substations. The IEC 61850-90-5 addition to the standard defines how data can be sent over wide areas utilizing IP, which is necessary if public communication networks such as 4G LTE is used.

1.1 Purpose and Goal

The purpose of this project is to benchmark and evaluate the performance of a non-commercial LTE network. Furthermore, to examine the readiness and applicability of the already available IEC 61850-90-5 stack to support phasor communication over a wireless network.

To evaluate the performance, different metrics need to be considered such as reliability, availability, latency, and throughput. The performance evaluation of the non-commercial LTE network, when using the IEC 61850-90-5 stack, will give insight on the applicability of the communication protocol when used over

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a LTE network. Furthermore will the evaluation of the metrics, show if and what improvements that are needed to meet the communication requirements given by different applications in the smart grid.

A prototype that emulates an Intelligent Electronic Device (IED) will be derived from an IEC 61850-90-5 open source project [12]. An IED is microprocessor- based controller used within power systems for protection, control, monitoring, metering, and communication [23]. The IEC 61850-90-5 stack will be used to transmit and receive data via the non-commercial 4G LTE network. Test cases will be derived to measure the above-mentioned metrics and the results will be presented as a benchmark of the non-commercial LTE network when using the IEC 61850-90-5 stack.

1.2 Scope

The scope of this thesis project is to prepare the IEC 61850-90-5 open source stack to exchange phasor data over the non-commercial 4G LTE network. This will give indications on the readiness and applicability of the IEC 61850-90-5 stack to support smart grid applications when wireless communication is used.

The following milestones have been considered in this project:

• To get an understanding of the IEC 61850 communication standard and how it works,

• To identify the key features of IEC 61850-90-5 such as:

– how data is structured and modeled,

– which parameters will be used to transmit and receive data, – what needs to be configured in order to exchange data,

• To transmit and receive IEC 61850-90-5 data over a non-commercial 4G LTE network,

• To benchmark the performance of the IEC 61850-90-5 stack when used over the network,

• To present and evaluate the results.

To be able to finish the project within the time span of a thesis project, the scope of the project had some delimitations. The main focus was on how the IEC 61850 and IEC 61850-90-5 standard are used for communication and to measure the performance when using the IEC 61850-90-5 stack in a wireless environment. Therefore aspects such as security was not considered.

The non-commercial 4G LTE infrastructure was provided by an external source and is hence not described in depth. This is a benchmark of the 4G LTE network and no profound analysis of the outcome of the tests is presented. A thorough analysis of the results would be time consuming and has therefore been left for future work.

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1.3 Related Work

It has been of interest to utilize wireless communication such as 4G LTE, Wi-Fi, ZigBee etc, for communication within the smart grid for a few years. Different studies have been made regarding if and how the wireless communication would be a feasible alternative to the wired communication.

1.3.1 Performance of LTE for Smart Grid Communications

The authors of [4] investigated whether LTE can be used in combination with IEC 61850 and Manufacturing Message Specification (MMS) to support smart metering and remote control communication and at the same time have a de- sirable QoS. Two sets of simulations were done to verify whether the latency and priority requirements are satisfied by their integrated LTE and IEC 61850 MMS solution, one set for remote control communication services and one set for smart metering services.

The remote control communication service experiment was based on a MMS client/server architecture combined with the LTE communication system. Fur- thermore is a Medium Access Control (MAC) scheduling mechanism used to prioritize the IEC 61850-based traffic over the generated LTE background traffic mix. The traffic mixes are used as the percentage of traffic such as 80/20 and 60/40 to imitate background traffic, i.e. 80/20 indicates 20 percent background traffic. Two MAC scheduling mechanisms are supported; Round Robin (RR) and Priority-aware Round Robin (PrioRR).

The authors observed that the throughput results are approximately equal for the scenarios that use RR or PrioRR MAC scheduler. Furthermore, it can be observed that the average delay is almost the same for RR and PrioRR scheduler, which also is true for the packet loss ratio.

The main difference between the remote control communication service experiment and the smart meter service experiment is that in the latter, smart meter entity and MDMS Host entity is used instead of MMS client/server. Also, only the RR MAC scheduler was used for the experiment. The smart metering experiments showed that average delay increased when the total traffic load increased, which was expected.

The simulation results indicated that LTE can be integrated with IEC 61850 MMS to satisfy the performance requirements on smart metering and remote control communication services in smart grid distribution networks.

1.3.2 Performance Evaluation of IEC 61850 under Wireless Com- munication Networks

In the paper [20] the authors present the modeling and simulation of an IED in an IEC 61850 Substation Automation System (SAS) under wireless or hybrid networks for three type of messages, Generic Object Oriented Substation Event

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(GOOSE), Sampled Value (SV), and Interbay trip messages.

The SAS network was modeled using a network modeling tool called OPNET and different scenarios were simulated. The data messages are sent at various sampling rates which are 960 samples/sec, 1920 samples/sec and 4800 samples/sec. The wireless network consists of different IEDs such as IEDs for protection and control, measurement units, and circuit breakers.

To compare the wireless and hybrid network with a wired network, the same sce- nario was simulated with the same sampling rates. The authors conclude that when circuit breakers were connected wireless, trip messages had high delays.

Furthermore, it is concluded that the wireless network provides lower delays and high throughput for simulated scenarios having data rate of 54Mbps, which the authors recommend for wireless SAS networks.

1.3.3 Performance evaluation of smart grid communications via network simulation version 3

Other studies conducted in [18], investigated the performance of ZigBee under different setups. Moreover, the authors also investigate the performance of LTE and Wi-Fi. To measure the performance of data communication in a smart grid Neighborhood Area Network (NAN), a network simulation tool called network simulation version 3 were used.

The investigation of smart grid communication between Data Concentrator Units (DCU)s and Advanced Metering Infrastructure (AMI) separates the simulation results into two sections. Firstly, the maximum distance for data transmission between DCU and AMI devices is compared for three wireless technologies. Secondly, the performance of ZigBee in different smart grid situations.

Moreover, The authors describe smart grid technologies and communication frameworks such as DLMS/COSEM which is a protocol that can be utilized as an interface to gather power consumption data between DCUs and AMIs. Fur- ther the authors discuss ZigBee, Wi-Fi and LTE communication technologies in NAN networks.

The authors have added a DLMS/COSEM modules to the NS version 3.22 to suit their project. The results of the simulations, with DLMS/COSEM protocol, shows that the transmission length of LTE is greater than the transmission length of ZigBee and Wi-Fi. The remainder of the paper mainly focuses on experiments of various ZigBee simulations. The results from the ZigBee simulations shows that the appropriate distance between DCU and AMI is 100 meters and the maximum AMI density, when located nearly together, is 145 nodes.

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1.3.4 Opportunities and Challenges of Wireless Communication Tech- nologies for Smart Grid Applications

The authors of the paper [22] present various smart grid applications that utilize standardized communication technologies such as Wireless Local Area Network (WLAN), ZigBee and cellular 3G/4G. Furthermore are challenges related to various wireless technologies discussed.

It is stated that the advantage of cellular technologies is that, to some extent, the current cellular infrastructure can be used and that the evolution of 3G/4G cellular technology has improved the QoS as well as the data rates.

The Supervisory Control And Data Acquisition (SCADA) interface for remote distribution substation is a smart grid application that can utilize cellular technology such as 4G due to the availability of cellular coverage. It is concluded that wireless technology offers many advantages over wired technologies such as low installation cost, mobility, remote location coverage, and rapid installation.

1.4 Disposition

The rest of the report is organized as follows:

In section 2, a background to the subject is given and key features of the technology is described. This is followed by section 3 with a presentation of IEC 61850-90-5, the theory behind the technology and description of the data structure. Section 4 provides a description of the test methodology, the test setup, and the results are presented and evaluated. In section 5, future work is presented and the project as a whole is discussed, including the results and the quality of the results.

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2 Background

2.1 Power Systems

An electric power system is a network that consists of electrical machines, lines and ways to supply electricity to consumers. When such systems are intercon- nected and the transmission of energy can be done over longer distances it is known as a power network, or a grid [1]. The power system delivery grid have many times been referred to as the greatest and most complex machine built in the human civilization [3].

The grid operates the same way it did almost 100 years ago, where the energy is provided to the consumers from a centralized power plant [1]. At the same time as the grid is getting older and outdated, the consumption of electricity is steadily rising [24].

Figure 1: Traditional electric power grid [17]

Figure 1 illustrates a simplified traditional one-way power grid. As can be seen in the figure, the electric power is generated in power plants such as thermal or nuclear. The voltage levels are increased in the transmission substations to transport the electric power via high-voltage transmission lines over long distances closer to the consumers. In the distribution substations the voltage levels are reduced and is delivered to consumers via distribution lines [17].

2.1.1 Communication in Power System

Communication in real-time systems, such as in power systems, have always been important since it is used to control the actual system. In the 1930’s, telephone lines were used in order to communicate between substations and the control center. The telephone lines were used to communicate if the dispatch operators should perform switch operations in the substation or to give readings of line loadings to the control center. Decades later, in the 1960’s, automated systems were used to collect data from substations. These systems was called Data Acquisition Systems (DAS) and had to be designed for low-bandwidth due to bandwidth limitations [19].

As technology evolved, bandwidth was no longer a major concern and new standards of how to communicate were needed. In 1988 the Utility Communi- cation Architecture (UCA) was developed, which aimed to suit the International

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Standards Organization (ISO) model for communication, named Open System Interconnect (OSI) [19].

Later, IEC presented the IEC 61850 standard, which is based on the concepts from UCA [19]. The standard is named IEC 61850 - Communication Networks and Systems in Substations. The goal of IEC 61850 is to be an international standard for communication within substations.

The introduction of enhanced SCADA systems offers new ways of controlling and monitoring the transmission substation equipment. The substation equipment could be controlled from operation centers which offered increased operational efficiency [17] and hence made the power grid more controllable, customizable, efficient, and smart.

2.2 Smart Grid

The smart grid relies on real-time exchange of measurements and control data between devices in homes and businesses, in the transmission and distribution grid, and in substations and control centers. This demands that the communication network is reliable, secure and high performing [17].

Bi-directional communication technology is utilized within the smart grid system with multiple functions such as automatic electrical management and renewable management, hence the smart grid is highly efficient and overall reduces the electrical loss during transmission [18].

The smart grid is evolving for reasons such as the need for clean energy, energy that can be deployed in large scale, renewable energy sources and environmen- tal reasons. As the smart grid technology continues to grow, new elements, functions, and application areas are introduced as presented in [17] and shown below:

• the deployment of renewable sources of energy throughout the grid,

• the deployment of AMI, also known as smart meters, at consumer loca- tions,

• the extended SCADA connectivity,

• the deployment of time stamped phasors, also known as synchrophasor, throughout the transmission grid.

A smart grid architecture generally consists of five layers; a power system layer, a control layer, a communication layer, a security layer and an application layer.

In a smart grid system, the communication layer consists of three types of networks separated by coverage range and data rate as illustrated in figure 2 [18]

[21].

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Figure 2: Data rate and communication range [21]

The Home Area Network (HAN), Building Area Network (BAN), and Industrial Area Network (IAN) are networks that have less coverage range and data rates and is typically used within customer premises. NAN and Field Area Network (FAN) is used when data is transmitted from a larger number of devices and long distances, thus require better coverage range and higher data rates. Appli- cations for Wide Area Network (WAN), such as wide-area control, monitoring, and protection typically requires transmission of more data over longer distances [21].

Depending on system requirements such as reliability, latency, bandwidth, and throughput, different communication technologies may be used to connect the networks [18]. Moreover, the different requirements for the communication networks depend on parameters such as data rate and communication range as shown in 2 [21].

The most stringent communication requirements are generally found in WAN compared to HAN/BAN/IAN and NAN networks. WAN typically supports real-time monitoring, control and protection applications and response times for these applications should be in the range of milliseconds to minutes. More- over should the WAN reliability for the communication system be high, e.g. >

99.9 % [21].

2.3 IEC 61850 Standard

The first publication of the IEC 61850 standards was released between 2002 and 2005. The standard was the result of nearly ten years of work done within IEEE/EPRI on UCA and within the working group called "Substation Control and Protection Interfaces" of IEC Technical Committee 57. The scope of the work was to standardize the communication in substation automation systems [10].

The first release mainly focused on protection, control, and monitoring and was divided into 10 parts as shown in table 1 [10]. New additions and updated ver- sions of the standard is continuously released but are not included in the table

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below.

The IEC 61850 standard provides models for power system devices on how to organize data, configure objects and map them to appropriate protocols to keep devices consistent and interoperable. Interoperability is obtained by having less or no restrictions in the hardware logic [15].

Part Title

IEC 61850-1 Introduction and overview IEC 61850-2 Glossary of terms

IEC 61850-3 General requirements

IEC 61850-4 System and project management

IEC 61850-5 Communication requirements for functions and device models

IEC 61850-6 Communication description language for communication in electrical substations related to IEDs

IEC 61850-7 Basic communication structure for substation and feeder equipment

IEC 61850- 7.1

Principles and models IEC 61850-

7.2

Abstract communication service interface (ACSI) IEC 61850-

7.3

System and project management IEC 61850-

7.4

Compatible logical node classes and data classes IEC 61850-8 Specific communication service mapping (SCSM) IEC 61850-

8.1

Mapping to MMS (ISO 95066-1 and ISO 9506-2) and to ISO/IEC 8802-3

IEC 61850-9 Specific communication service mapping (SCSM) IEC 61850-

9.1

Sampled values over serial unidirectional multidrop point to point link

IEC 61850- 9.2

Sampled values over ISO/IEC 8802-3 IEC 61850-

10

Conformance testing

Table 1: The 10 parts of the first release of the IEC 61850 standard Part 1 of the IEC 61850 standard gives an introduction and a general overview of the complete standard. The standard is based on data objects that are related to the needs of the electrical power industry. Furthermore is the communication profile is based on existing IEC/IEEE/ISO/OSI communication standards, if possible [10].

Part 3, 4 and 5 describes the general requirements for using IEC 61850 for communication within substations. These requirements are the foundation of the identification of what services and data models that are needed, such as physical layers, data link, and network [19].

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Part 6 of the standard gives an overview of the system engineering process and specify the System Configuration Language (SCL). SCL is a way of describing communication that is related to IED configuration and parameters among other things [10].

Part 7 of the IEC 61850 standard is divided into four subparts. The first part describes the basic architecture for the communication structure between different devices [7]. Part 7-2 of the IEC 61850 standard defines the Abstract Communication Service Interface (ACSI) [6]. The abstraction makes it possible to map the standardized data object and services to protocols that meet the requirements [19].

Part 8-1 defines a method on how to exchange data by mapping ACSI to MMS for data that is both time-critical and non-time-critical [5].

Part 9-2 defines Specific Communication Service Mapping (SCSM) for the transmission of SV between sensors and IEDs as specified by the ACSI in IEC 61850- 7-2 [8].

Part 10 describes how to test the conformance of the protocol definitions and constraints that are defined in the standard [19].

2.3.1 IEC 61850 Data Modeling

The IEC 61850 standard models the common information from real devices by using abstract models. Figure 3 illustrates the hierarchical structure of the data model. The functions of the application are decomposed to smaller entities which are used for the information exchange within the system. As can be seen from figure 3, the hierarchical model consist of five layers from the physical device to the smallest object, which is the data attribute.

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Figure 3: IEC 61850 Data Modeling [10]

• Physical Device

The first layer of the data model is a real device or a physical device, for example an IED. The physical device is connected to the network and is typically defined by its network address. Within the physical device, there are one or more entries of logical devices [19][10].

• Logical Device

The second layer of the data model is the logical devices, which usually is a group of functions to support some power system function such as measurement or protection [10]. Within each logical device, there can be one or more logical nodes.

• Logical Node

A logical node is the smallest entity of the application and represents specific functions. The naming convention is for example that all logical nodes for metering and measurement begin with the letter M. Further- more, if there are two measurements from two different sources, they need to be differentiated. The logical nodes for these measurement units would typically be named MMXU1 and MMXU2 respectively. Each logical node contains one or more elements of data [19].

• Data Object

Within the logical nodes, the data is contained. The data object is based on the information and functionality of the logical node, the data may contain information such as the position of the device.

• Data Attribute

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Each data attribute is a Common Data Class (CDC) that describes the type and structure of that data, there is CDCs for a variety of data, such as status information and measured information. The CDCs is grouped into categories, a set of Functional Constraints (FC) such as status (ST) as shown in figure 4 [19].

Figure 4: The IEC 61850 object transformed into a named MMS variable object with a unique reference for a element in the model [19]

2.3.2 Abstract Communication Service Interface

The ACSI defined in IEC 61850-7-2 is a standardized way of describing devices in a power system. This service interface makes it possible for IEDs to use identical structures to represent data that is related to functions of the power system [19].

The ACSI service provides a virtual interface that gives access to real devices and real data and the interface can be used to describe the behavior of devices.

Furthermore, the devices can be accessed from other devices such as SCADA or other maintenance systems [6].

The IEC 61850 standard provides the following types of communication models for compatible information exchange among components of a power utility automation system, Client/Server communication service model, GOOSE, SV, and Generic Substation State Event (GSSE) [10].

The abstract services and objects are mapped within a SCSM, which is defined in part 8-1 and 9-2 of the IEC 61850 standard for GOOSE and SV respectively [10].

2.3.3 Generic Substation Event

The Generic Substation Event (GSE) model, described in [6], is a model that makes it possible to distribute input and output values in a SAS in a fast and reliable manner. The model defines two control classes and also the structure of two message formates

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• Generic Object Oriented Substation Event (GOOSE) - Supports the exchange of common data organized by a data-set,

• Generic Substation State Event (GSSE) - Capable to transfer state change information.

In order to exchange information, a publisher and subscriber mechanism is used.

Basically the publisher writes the values to a transmission buffer. The values are sent to the receivers reception buffer and the receiver reads the values from the reception buffer.

The reception buffer at the subscriber side is updated by the communication system. The procedure of the corresponding buffer, the transmission buffer at the publisher side, is controlled by a generic substation event control class [6].

2.3.4 Sampled Values

The model for transmission of SV described in [6], is a model which makes it possible to transmit SV in a time controlled way. To exchange SV information, a publisher and subscriber mechanism is used.

A publisher writes data in a local buffer, the transmission buffer. The data in the transmission buffer is sent to the local buffer at the receiving side, the reception buffer, then the receiver reads the values from the local buffer at the receiving side.

There is a need to add a time stamp so that the receiver can examine the timeliness of the values. Furthermore, there is a need for a Sampled Value Con- trol Block (SVCB) on the publisher side to control this procedure. There are two different methods for exchange of SV depending on the number of receivers.

If it is one receiver unicast are used and for more receivers multicast are used [6].

2.4 IEEE C37.118.1

The standard C37.118.1 presented by IEEE defines the concept of synchronized phasors, also known as synchrophasors. The standard also defines frequency and Rate of Change of Frequency (ROCOF) measurements, and methods and requirements for how the measurements can be verified. In an AC power systems analysis, phasors that represent the sinusoidal signals can be used [13].

The definition of a sinusoidal waveform is given by:

x(t) = Xmcos(ωt + φ) (1)

which can be represented as a phasor:

X = (Xm/√ 2)e^jφ

= (Xm/√

2)(cosφ + jsinφ)

= Xr+ jXi

(2)

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In equation (2), the magnitude of the phasor is the root-mean-square value, X_m/√

2, and the values of X_rand X_i are the real and imaginary parts of a complex value in rectangular components. The phasor is defined for the angular frequency ω and when compared to other phasors, the time scale and frequency must be the same.

The definition of a synchrophasor representation of x(t) in equation (1) is the value X in (2). The value of φ is the instantaneous phase angle relative to a cosine function when the system frequency is synchronized to UTC [13].

A Phasor Measurement Unit (PMU) can be a function within an IED and is described in the IEEE C37.118.1 standard as a device that is used to produce synchrophasors and also frequency and ROCOF estimates. The estimations are done from the voltage and/or current signals and a time synchronized signal [13].

2.5 IEEE C37.118.2

The standard C.37.118.2 describes how synchrophasor measurement data can be exchanged between power system equipment. The standard also describes data formats for communication in real-time. Communication can be between PMUs, Phasor Data Concentrators (PDCs) and other applications [14].

The UTC time, that corresponds to the time when the synchrophasor measurement was done shall be tagged to the actual measurement, the tag shall consist of three numbers [14]:

• the second of century, seconds since UTC midnight of January 1, 1970,

• the fraction of a second,

• the time quality.

The PDC defined in IEEE C37.118.2 is a part of the communication network.

The PDC is fed with synchrophasors from PMUs or other PDCs and the data is sorted by the time tag [14]. The PMU can be a stand alone function or a function within an IED.

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3 IEC 61850-90-5

The IEC 61850-90-5 protocol defines how IP can be utilized to send data over WAN in a way that is compliant with the IEC 61850 standard. The use of IP is necessary if the data is transmitted over a public communication network such as 4G LTE.

3.1 Overview

The synchrophasor measurements and calculations done by the PMUs that are defined in IEEE C37.118.1 is considered useful to estimate the condition of an electrical power network. Therefore, it is desired to have a communication mechanism that is compliant with the IEC 61850 concept.

The scope of the IEC 61850-90-5 part of the IEC 61850 standard is to provide a way of sending and receiving synchrophasors information between PMUs, PDCs, Wide Area Monitoring Protection and Control (WAMPAC) and between control center application in a way that is compatible with IEC 61850. The IEC 61850-90-5 standard also provides a way to route the IEC 61850-8-1 GOOSE and IEC 61850-9-2 SV packets. These packets can be used to transport synchrophasor information as well as general IEC 61850 data [9].

Applications that utilize synchrophasors are often separated by large distances.

When the applications need to send data over long distances, IP can be utilized.

The use of IP gives the ability to route the data between different networks over any arbitrary distance. Both Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) can be used for streaming the data [9].

3.2 Data modeling

When describing a system as an IEC 61850 system, both the client and server need to be modeled as logical nodes within an IED [9]. The data model and decoding/encoding of the data gives insight on how the data is structured and used.

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Figure 5: The structure of the IEC 61850-90-5 Session Protocol From [9]

The structure of the IEC 61850-90-5 session protocol is shown in figure 5 and is structured to accommodate GOOSE and SV messages in an IP packet. As can be seen in 5, the general format consists of 3 major parts, the Session Identifier (SI), the session header, and the session user information. The hexadecimal values in the SI is used for encoding and decoding, which is explained and ex- emplified in section 3.3.

SI is a one byte length which covers the length of the parameter for the session header.

• Session Identifier

– The hexadecimal SI value A0 is used for Tunneled GOOSE and SV packets

– The hexadecimal SI value A1 is used for Session Protocol Data Units (SPDU)s that contain non-tunnelled GOOSE Application Protocol Data Units (APDU)s

– The hexadecimal SI value A2 is used for SPDUs that contain non- tunnelled SV APDUs

– The hexadecimal SI value A3 is used for SPDUs that contain non- tunneled management APDUs

• Session Header – SPDU length – SPDU Number

– SPDU Version Number – Security Information

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∗ TimeofCurrentKey, time for first usage of current signature and encryption key

∗ TimetoNextKey, time before a new key is assigned for signature and encryption

∗ SecurityAlgorithms, indicated which cipher suit and algorithms that are used

∗ Key ID, reference to the key currently in use

• Session User Information – Length of the User Payload

– User Payload, representing a sequence of Tunnelled, GOOSE or SV packets

– Signature, calculated based on values of the SecurityAlgorithm field Within the user payload, multiple user data Protocol Data Units (PDU)s can be sent in the same SPDU. The sequence of the values begins with a tag, as for the SI that indicates what type of payload the session protocol is transporting [9].

• GOOSE, hexadecimal tag of value 81

• SV, hexadecimal tag of value 82

• Tunnel, hexadecimal tag of value 83

• MNGT, hexadecimal tag of value 84

3.3 Data Encoding

For decoding of GOOSE and SV, ANS.1 Basic Encoding Rules (BER) is used.

The principle of the BER transfer syntax is that it is a triplet of the format Tag, Length Value (TLV) as shown in figure 6, the TLV triplet is a series of octets [8].

Figure 6: Basic Encoding Rule

A TLV triplet can contain more triplets within the value of the current triplet, making it a hierarchical structure. Figure 7 shows the functionality of ANS.1 BER encoding of a SV APDU, and as can be seen the SV APDU frame contains 4 concatenated Application Service Data Units (ASDU)s [8].

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Figure 7: ANS.1 BER encoded SV APDU, from [8]

3.4 R-GOOSE and R-SV

The communication described in [9] shall satisfy WAMPAC applications that use synchrophasors according to IEEE C37.118.1. Communication within a substation is typically based on SV. Other communication such as communication for event data can, depending on the time constraints, be communicated via GOOSE or reporting.

The IEC 61850-90-5 standard defines two methods for communication to receivers outside a substation. When the communication is aimed for receivers outside a substation, either tunneling across high speed networks like Syn- chronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH), or across IP networks [9].

When the communication is done via IP networks, the messages need to be mapped to an IP based protocol. In the IEC 61850-90-5 standards, UDP is used with multicast addressing. Therefore the SV service and GOOSE is mapped to the routable UDP protocol and is hence called R-SV and R-GOOSE [9].

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Figure 8: Mapping of phasor measurements [16]

As can be seen from 8, the IEC 61850 real time communication services, SV and GOOSE, are directly mapped to the Ethernet layer and can hence not be sent over IP whereas the IEC 61850-90-5 is mapped to IP [16].

3.5 Communication Requirements

The requirements of a communication system are highly dependable on what type of system the communication serves [1]. Network reliability is fundamental for smart grid applications. High end-to-end reliability demands that equipment such as routers, base stations, and the network links independently are reliable [17].

Other important aspects are low latency and high throughput. The communication requirements for synchrophasor data depends on what type of application the data is used for.

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Figure 9: Communication Requirements [9]

The use cases for synchrophasors described in [9] have different communication requirements as can be seen in figure 9. The SV service could in principle be used for all the applications but since it is directly mapped to Ethernet it is not usable over wide area communication systems. Instead, the R-SV defined in IEC 61850-90-5 can be used even though it does not cover the most stringent requirements needed for usual protection [9].

The transfer time presented in [11] is the time it takes for the complete transmission of a message including handling, both for the receiver and sender, i.e.

from the time that the sender codes the data and sends it until the message is received and decoded. Furthermore [11] defines message types and performance classes which basically depends on what type of message it is and what functionality is serves. The different type of messages are listed below:

• type 1 - fast messages,

• type 2 - medium speed messages,

• type 3 - low speed messages,

• type 4 - raw Speed messages,

• type 5 - file Transfer functions,

• type 6 - command messages and file transfer with access control.

Each message type can have different performance classes depending on the required transfer time. The requirements for the transfer time varies between

≤ 3ms and ≤ 10000ms depending on the message type and performance class.

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4 Implementation and Result

To evaluate and benchmark the performance of the non-commercial 4G LTE network when using a modified IEC 61850-90-5 stack, different metrics need to be considered such as availability, reliability, latency, and throughput. The following section describes the modifications done to the IEC 61850-90-5 stack, the setup, and the above mentioned metrics.

4.1 Test Methodology

4.1.1 Test Environment Setup

In order to test and benchmark the non-commercial 4G LTE network, a modified IEC 61850-90-5 stack was used to exchange GOOSE and SV messages between two machines. The IEC 61850-90-5 stack was running on both machines, em- ulating two IEDs. The machines were connected via Ethernet directly to two separate 4G LTE modems that had 100 Mbit/s downlink and 50 Mbit/s uplink capacity.

When the test was conducted, both machines were configured to have static IP in order to avoid change of IP addresses. Dynamic Host Configuration Protocol (DHCP) could have been used but would require more configuration changes during the test runs. Since the machines were connected to different modems, they were on different Local Area Networks (LAN)s and thus no communication could be directly between the machines without enabling port forward functionality in the modems. With port forwarding enabled, UDP packets were exchanged between the machines over the port number defined by the IEC 61850-90-5 stack, for the test port 102 was used.

Figure 10: Environment test setup

The UDP packets, containing GOOSE or SV data, was sent from the machines via the modems to the base station as illustrated in figure 10. To reach the core network infrastructure, a Virtual Private Network (VPN) tunnel was used through the public network to connect the base station to the core network.

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4.1.2 Modification of the IEC 61850-90-5 Open Source

The performance of the non-commercial 4G LTE network was tested through experiments using the open source IEC 61850-90-5 protocol stack from [12].

Modifications were done to the original source code in order to achieve desired functionality as described below:

• Packet size was a parameter that defines the size of each packet that was sent and was updated frequently during testing. Dynamic update of packet size was implemented to facilitate fewer adjustments between different test cases.

• To represent a synchrophasor, the data representing a phasor needs to be timestamped during encoding for both GOOSE and SV. Therefore functionality for stamping the data with the current time was implemented.

This was achieved through the use of a Windows built-in function.

• Each packet sent contained three synchrophasors and each synchrophasor has an angle, magnitude, time, and time quality. To send this data in every packet, functionality to represent the above mentioned parameters was implemented. The magnitude and angle for the phase were float values that were randomly generated for each packet, to represent a change of phasor values.

• The original IEC 61850-90-5 open source project supports encoding and decoding for SV, but no such functionality for GOOSE. This was implemented during the course of the project. The encoding and decoding is based on ANS.1 Basic Encoding Rule as described in section 3.3.

• Modifications were done on how the statistics output was logged. This to ensure that the extracted output data was meaningful and could be used to graph and evaluate the results.

• The code was overall adjusted in minor ways to suit the project but the basic functionality of the application remained the same.

4.1.3 Setup Overview

The general flow of the process is shown in figure 11. When the application starts, it reads the configuration values from the configuration file as described in 4.1.4. Once the configuration is done the application starts to transmit and receive data. The data is exchanged between the application in server mode and the application in client mode.

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Figure 11: Flow chart of the test process

When the application runs, data is exchanged between the client and server.

Wireshark is running simultaneously to capture raw data that is used to analyze and verify packet delivery. Furthermore, a statistics output log is generated from both applications which also is used to analyze the communication. The statistics log file is a text file generated by the application. It contains statistics and other information such as missing packets, transmitted packets, and received packets.

4.1.4 Configuration Parameters

When running an application that emulates an IED, configuration parameters need to be set. This is done with the use of a startup file which holds the given configuration. When starting the application, it read the values from the startup file and sets the configuration accordingly. The startup file is a .cfg file and holds one value on each line as seen in figure 12.

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Figure 12: Structure of the startup file for the application

In the list below, some of the important configuration parameters is explained.

• InterfaceID - Is the Globally Unique IDentifier (GUID) for the interface used to transmit/receive data over, e.g. Ethernet,

• SMVIP4Pub - Is the IP address that the PDU should be published to,

• StatResetMinutes - Time in minutes on when the internal statistics of the software will be reset,

• LogIntMin - The interval for when the statistics should be logged to a log file,

• TransIntMsec - Timer in milliseconds that sets the transmission interval,

• Ulong - Sets the size of the packet.

4.1.5 Time Synchronization

Applications utilizing IEC 61850-90-5 is often time critical, hence time synchronization in the system is important. Synchronization between the two machines that had the IEC 61850-90-5 stack running was achieved through the use of Network Time Protocol (NTP) as seen in figure 13.

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Figure 13: Time Synchronization utilizing a NTP server

NTP is a client/server IP used to synchronize the clock between computers to some reference. As seen in figure 13, the NTP client on machine 1 is synchronized to a network time server, in this case, 0.se.pool.ntp.org. To get synchronization between the machines, machine 2 is synchronized to get the time from machine 1 by embedding its IP address as a server address.

Before each test, the offset and drift were measured in order to know the difference between the machines. The difference between the machines was com- pensated when the results were compared. Time synchronization is especially important when calculating the latency since the latency often is only a few milliseconds (ms).

4.1.6 Wireshark Captures

During the tests, all of the traffic was captured using a packet sniffing tool called Wireshark. To capture the IEC 61850-90-5 GOOSE and SV packets Wireshark with an IEC 61850-90-5 extension were used, as can be seen from figure 14 and 15.

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Figure 14: SV packet captured in Wireshark

Figure 14 shows the IEC 61850-90-5 SV packet that was captured during a test run. The tabs of the capture have been expanded to show the headers and data of the packet. The phasor data is stored within the ASDU under the samples tab.

Figure 15: The data representing three synchrophasors sent in a SV packet Within the SV packet the data can be found, that represents synchrophasors, i.e. a phasor with a timestamp. As can be seen from figure 15, the sequence of data (samples) is of the structure BER (TLV) with tag 87 and hexadecimal length 3C, followed by the value, which is the actual data. The value in this example is 3 synchrophasors sent within the SV packet and are 20 bytes each:

• 2 bytes - indicates which phase (e.g. 1,2 or 3),

• 5 bytes - the angle value in float,

• 5 bytes - the magnitude value in float,

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• 8 bytes - the timestamp for the measurement.

4.1.7 Data Extraction and Plotting

For data extraction, different scripts were implemented. The tests were conducted in a Windows environment and hence batch files with .bat filename extension was used.

Two different scripts were created for data collection, one script to collect data for the availability measurements and one script to collect data for the other measurements, i.e. latency, throughput, and reliability. To plot the different graphs, Matlab scripts were created to read the output file generated from the .bat scripts and plot accordingly.

4.2 Test Cases

Test cases that were derived to test the availability, reliability, throughput, and latency. This to benchmark and verify if it is feasible to use IEC 61850-90-5 over a wireless communication link such as 4G LTE. Tests were conducted for both GOOSE and SV but this report only covers the results for SV due to time limitation.

The results from the GOOSE tests indicated that GOOSE and SV behaved similarly over the network and had no remarkable deviations in the results even though GOOSE typically were smaller in size.

The size of the raw data from the test is approximately 45 Gigabyte. The raw data consists of Wireshark captures and statistic files that were generated during the test runs and are for future analysis.

4.2.1 Availability

To verify the availability of the non-commercial 4G LTE network, i.e. how sta- ble the network is over a longer period of time, a test was conducted for 24 hours. The transmission interval was set to 1000 ms, i.e. one packet is sent every one second and the packet size used was 1235 bytes.

To calculate the availability of the network over a 24 hour period, the statistics were logged every 5 minutes. During the test, the logged values from the pre- vious log 5 minutes, were subtracted from the value that was currently logged, continuously.

After 24 hours, when the test was done, the results for each 5 minutes period were concatenated and this gives the availability for the network. All the calculated values were put together in a graph representing the availability of the network.

The availability was calculated as: