201109-285the real-time relay protection communication systen

http://www.paper.edu.cn

- 1 -

中国科技论文在线

The Real-Time Relay Protection Communication Systen based on GOOSE#

LIU Qunying1, Liu Qifang2* (1. Energy source science and engineering school, uniersity of electronic science and techlonogy, 5

ChengDu 611731; 2. China GUODIAN ashine company)

Foundations: national neture science foundation(No.51007006), Education department doctoral New teacher foundation(No.20090185120023) Brief author introduction:LIU Qunying, (1977-）,female,asociated professor,research intersting:power system stability and control. E-mail: [email protected]

Abstract: GOOSE (GOOSE: generic object oriented substation events) is a type of communication mode established in IEC 61850 standards to facilitate efficient and reliable communication in substation system. The protocol stack mapping method and retransmission mechanism enable the 10 GOOSE based communication system to have good real-time performance and high reliability. This paper reports the design and implementation of a communication system, which transmits data from the source to the receiver with GOOSE protocol, for relay protection device. The design of communication system software process, the configuration approach of the message publisher, and the design and implementation of the thread refreshing and decoding in subscription equipment, are described in detail. 15 At the end of the paper, a test system in which a GE Multiline general-purpose relay protection device is used as the message publisher, is built. The performance of the designed system is tested and analyzed on the test setup, and the test results show that the designed communication system satisfies the requirements of the protective device communication in reliability and real-time performance. Keywords: The relay protection device; communication system; GOOSE; IEC 61850; real-time; 20 reliability

0 Introduction

The traditional relay protection devices have single function. Cabling and ancillary equipment are more complex, which lead high cost and low efficiency. With the promotion of 25 digital substation technologies, more and more digital relay protection devices began to use in substation protection. Compared with the traditional protection devices, digital protection devices can take advantage of existing mature communications technologies, such as Ethernet communications, which transfer real-time data to control equipment and man-machine interface[1]. This feature of digital protection devices will improve substation reliability and efficiency 30 significantly.

Among the digital protection devices, communication equipment is the core of the information exchange between devices and substation control center. Communication based on IEC 60870 protocol, modbus and DNP (Distributed Network Protocol) are used at present[2].

With the development of communication technology, the timing and accuracy of data 35 communication have becoming more and more important[3]. GOOSE is a communication mode based on IEC 61850, which can transfer data fast and reliable in the system. The core messages of GOOSE can be flexible developed by the user, and the improved structure of publisher / subscriber make the GOOSE message has high priority and high real-time. This communication mode has obvious advantages. Therefore, GOOSE has been initially applied to substation 40 communications, such as substation remote video monitoring system based on GOOSE[4], GOOSE test of digital relays[5] and so on.

A protection devices communications system is designed based on GOOSE communication protocol stack model in the paper, which is validate through self-built experimental platform. On the experimental platform[6], GE Multiline general’s purpose relay products are used as the release 45


- 2 -


of GOOSE message, and the subscribe is a receiving program via VC 6.0. GOOSE message is configured and packed at the release side, and a specific multicast address is assigned. Through the hardware addresses, the message is directly mapped to the data link layer, in order to ensure real-time of GOOSE communication and results and analysis of the communication system are provided. 50

The results show that the relay communication system based on GOOSE can transfer the data from the source to the receiving fast and reliable.

1 GOOSE communication protocol stack model GOOSE communication uses a publisher / subscriber structure, which is event driven and can

support the point to point communication among multiple nodes. This structure is fit for 55 communication situations that has large data flow and require high real-time, which is the best structure transferring data from multiple data publishers to multiple subscribers.

IEC 61850 provides a data communication process through abstract communication service interface (ACSI). ACSI simply provides communications service used by specific model elements, which is a conceptual abstract interface and does not define a specific protocol stack mapping 60 method. It should be mapped as the specific real-time communication protocol using specific communication service mapping (SCSM) method. This method ensures the scalability of the protocol stack and solves the contradictions between stability of the standard and development of the future network technology. With the development of communication protocols, SCSM are simply modified, when the protocol stack changes, in order to achieve the decoupling between 65 functional and communication. Mapping process is shown in Fig.1.

Fig.1 Mapping Process of GOOSE

In order to ensure the rapid transmission of message, IEC 61850 provides that GOOSE 70

messages will be directly mapped to the corresponding Ethernet type. GOOSE communication protocol stack use only four layers in the OSI seven-layer-network-model. The message is encoded in presentation layer by the ASN.1 through application layer, and then directly mapping to the data link layer. In order to improve the transmission speed, priority tag packets header structure in IEEE 802.1Q are used in the data link layer. GOOSE message transmission 75 communication protocol stack is shown in Fig.2.


- 3 -


Fig.2 GOOSE message transmission communication protocol stack

A communication mode with priority tag structure is conducive to the rapid transmission of 80

packets when requirement of real-time is high. In addition, IEC 61850 provides the core content can be user-specific set, which makes GOOSE wide use and flexible.

2 Design of relay protection device communication system The protection devices communication system using IEC 61850 GOOSE as the

implementation method, and GOOSE message is realize by GOOSE communication control block. 85 Control block class includes control block name, GOOSE control block path, GOOSE enabled, application identity, reference data set, version number and logo for whether need to be re-configured or not. Input device receive analog signals and then relay protection device isolate the signals, which will be encapsulated as control block class model.

Relay protection device is the release side. The encoded message mapping by the hardware 90 MAC addresses, and will be received and resolved by the subscription. System structure is shown in fig. 3.

Fig.3 System structure

95

2.1 Design of software process of communication system Relay protection device is the released side of the communication system. Other software

will be developed as a subscriber terminal, which can be run on the control center server or installed on the portable computer device used for tests. At the same time, the system can connect


- 4 -


multiple protection devices. Device name can be realized by the GOOSE Control Block. Decoding 100 thread will be called to analyze and display. To ensure real-time, GOOSE messages can not be available by TCP / IP, SOCKET interfaces.

WINPCAP is used in this design. WINPCAP is a Win32-based platform for capture network data packets to analyze, which is a open source library. It can capture the original packet, filter them, count network traffic and remote capture[8]. This design uses a pcap_loop function to 105 captures packets, which called callback function. The overall process is shown in Fig.4.

Fig.4. Overall process of GOOSE communication

2.2 Release end 110

Before sending GOOSE data, the release end should complete the appropriate configuration, including GOOSE control block name, application ID and MAC address. GOOSE Control Block name in the LD should be guaranteed to be unique. MAC address that is multicast MAC address will be selected in in IEC 61850 multicast MAC address range by release end management module. In addition, GOOSE packet priority, and Ethernet-based applications such as header 115 structure identifier can be configured by the user directly.

To ensure the reliability of GOOSE communications, IEC 61850 provides a special retransmission mechanism to meet the reliable requirements of GOOSE message. Firstly, a send request is generated by the release end, and then the message such as the value of the data set is encoded. The release end trigger a event that there’s a GOOSE message need to be sent, and then 120 resend the same data by increasing transmission time and sqNum. Thus the reliability of GOOSE communication is ensured. Each GOOSE message is allowed to bring a survival time parameters called time allowed to live, which is used to determine the longest wait time at subscribe end. The connection realized to be lost when there’s no retransmission message and new event in the allowed time. The retransmission mechanism is shown in fig.5. 125


- 5 -


Fig.5. retransmission mechanism

T0 is the retransmission time when there’s no event occurred in a long time. When an event

occurs, T1 is a minimum retransmission time. After the new event transferred, retransmission time 130 is increase gradually from T2, T3 back to T0.

2.3 Subscribe end In accordance with the IEC 61850, TPID is 0X8100, and the default priority is 4. The

provisions of the Ethernet type code is 0X88B8 for GOOSE message. Application layer is responsible for connecting a number of application service data unit (ASDU) into an application 135 protocol data unit (APDU), and submitting APDU to the send buffer. APDU is encoded by Basic Encoding Rules (BER) in ASN.1. BER uses 8Bit as a basic transmission unit. For each transmission value, there are three fields called TLV, which refers to the data identifier (TAG), data length (LENGTH) and the data content (VALUE). In which data type tag accounted a byte, and the 8-bit and 7-bit is the label type that divided into four categories. The 6-bit refers to the 140 format of abstract data types which is basic type and structure type. BER coding structure is shown in fig.6.

Fig.6. BER coding structure

145

2.3.1 Decode thread

Decoding thread is designed in the Subscribe end of the communication system, which can improve the decoding efficiency of the system.

First, load the data decoding thread and call pcap_loop to capture GOOSE message issued by release side, and if the capture is not successful, the thread will be damaged. Second, identify 150


- 6 -


device name by decoding, which means the name of GOOSE message control block. If the device detects a new name, a new device directory will be created by calling BuildTree. Finally, when the user activates the tree node click event, SetItemText will be called to displays the control block path, the data set name and data set values of the corresponding GOOSE message in the list box. If a instruction that to end the progress of subscription is received, the thread will be closed to 155 release resources.

2.3.2 Subscribe to decode

According to the IEC 61850, GOOSE messages map directly to the Ethernet protocol stack without protocol headers such as TCP, UDP. The virtual LAN identification and priority structures are added to the message. The field that independent to the APDU unit will be skip when 160 decoding.

The second step of decoding is process the predefined control block in the APDU, including GoCBRef, timeAllowedtoLive, DatSet, goID, Time, stNum, sqNum, Test and NumDatSetEntries and so on. Whether it is a test message is determined by Test. If the current value of stNum is different as the previous, the event is determined new. In addition, the sqNum of new event is 165 necessarily 1, while the sqNum of retransmission is increase recycling.

According to the TLV encoding rules of ASN.1, the subscription-side structure body GOOSEData is used to save data set values. The definition of GooseData as follows:

struct GOOSEAllData { 170 int Index; CString Type; unsigned char Length; CString Value; }; 175 GOOSEFrame_Header and GOOSEApdu are designed to save the data link layer header and

the sqNum and stNum of the GOOSE control block. Data member information of GOOSE includes a wealth of data types such as BOOL, String, INT and so on. Different decoding options should be choose according to the value of index. The detailed definition of the type of coding structure see paper[11], this paper will not repeat them. 180

switch(GooseData.Index) { case 0x83: GooseData.Type = "BOOLEAN"; //BOOL type … 185 break; case 0x8a: GooseData.Type =“STRING”； //string type …

break; 190 case 0x85: //INT type GooseData.Type =“INT”； …

break; } 195


- 7 -


3 System testing and analysis To evaluate the system performance and make the corresponding analysis, the test platform is

built to test the GOOSE-based relay protection devices communication system. The hardware platform is Intel Celeron [email protected]; 1G DDR2 800MHz, while the software platform is Visual C + + 6.0. In order to better evaluate the system performance, wireshark is used to monitor 200 and record for the message at real-time.

IEC 61850 provides that the time delay should be less than 4ms for GOOSE message. The message monitored by wireshark has a time stamp, which accurate to μs level. Thus system performance can be evaluated effectively. The portable computer is used as a subscription client. All other non-related procedures are turned off in order to reducing the number of processes and 205 keep the network load is less than 25%. The test platform is shown in fig.7.

Fig.7 Test platform

3.1 Running result 210

When the publishing side completes deploying, it filled information in buffer. The release side subscribes the message and read information from the receive buffer. Whether the message is discarded or not is determined by the value of stNum and sqNum. Directory tree is designed to display device name that receive GOOSE message, the path name of each message and the data set value. The list is used to display the serial number, stNum and sqNum of control block. 215 Running result is shown in fig.8.


- 8 -


Fig.8. Directory tree and display list 220

3.2 Performance Analysis

3.2.1 Real-time Analysis

IEC 61850 provided that GOOSE communication should have a high real-time and reliability. When evaluating the system, real time and reliability are the most important indicators. 225

GOOSE communication uses a special achieve way and retransmission mechanisms. Protocol data unit is specifically defined in the application layer. After coding in the presentation layer, the message direct mapping to the data link layer and physical layer, which means transport layer and network layer are empty. This special transmission mode can avoid the traffic delay caused by the stack, thus ensuring the transfer and process fast. 230

In this paper, a portable computer is used to simulate the control center of the substation. The subscription client software is started, and the GOOSE message is sent from the Release side. At the same time, the message is monitored by wireshark and the system is evaluated by time stamp. The comparison between GOOSE-based relay protection device communication system and MMS-based IEC 61850 communication system for the same device is shown in fig.9. 235


- 9 -


Fig.9. Performance Testing of communication system

The results show that the average time that the subscription side communicates with the 240 published side via Ethernet 40 times is 0.35ms in the GOOSE mode, much smaller than the upper limit of 4ms. The average delay is more than 1.3ms in the MMS-based client / server communication mode. The GOOSE communication system is efficient and stable. When the communication system is actually used in substation system, the detention will increase because there are more network load. American Electric Power had a special study on the issue that the 245 Ethernet can meet the power system’s real-time requirement. The results show that even in the "worst" case, the requirement of 4ms can be meet whether connected via 100Mb/s Ethernet through shared HUB or Switching HUB.

3.2.2 Reliability analysis

GOOSE communication uses a special retransmission mechanism. In order to ensure GOOSE 250 reliability, the same data retransfer through the sqNum incremental and increasing transmission time. At the same time, sqNum and stNum sign in GOOSE message can be used as a basis for judging failure.

The initial value of sqNum and stNum are both 1. When an event occurs, stNum plus 1 while sqNum change to 0, and then sqNum order plus 1. When stNum do not change, sqNum jump and 255 stNum jump or plus 1 based on the stNum of the last frame. Message may be lost when the stNum does not equal to 1. If the stNum do not change, the sqNum and the message are the same as the last frame, which means the GOOSE is repeated. If the sqNum is less than the previous and do not equal to 1 or the state count stNum is less than the previous and do not equal to 1, which indicates the message is reversed. The message is error if stNum change but the data set did not change. 260 While time allowed to live, if there’s no new GOOSE message that means the GOOSE link disconnect, you need to reconnect.

4 Conclusion On the basics of IEC 61850 in this paper, communication system of relay protection devices

are designed based on GOOSE. Take GE F35 Multiple Feeder Management Relay Protection for 265 example, The experimental platform is built to verify GOOSE message transmission. The results show that GOOSE can meet the real-time and reliable communication requirements of relay protection devices. It’s an efficient transmission method that will become the mainstream of the substation development. This communication system is relatively independent. Although GOOSE


- 10 -


communication protocol stack can greatly increase the subscription to real-time decode, some 270 measures should be take to end the subscription to make the GOOSE more priority than other packets.

Acknowledgements This project is supported by Special Fund of the National Priority Basic Research of China

(51007006) ,Doctoral New Teacher Fund of Ministry of Education of China (N0.20090185120023) 275 and University of Electronic Science and Technology Science Foundation for the Excellent Youth Scholars.

References

[1] LI H,XU J Y,LIU H.Research and application on high performance synchrophasor measurement unit[J].Power 280 system protection and control,2010,38(7):81-85 [2] WANG Y J,REN X W.Synchronous phasor measurement unit and error analysis[J].Automation of electric Power systems,2004,24(1):66-71 [3] WANG ZL.Summary of application in power system based on synchronously sampled date of PMU[J].Journal of electric power,2005,20(1):8-10 285 [4] JI K,WANG KY,CAI ZX.Communication scheme of phasor measurement unit in WAMS[J].Automation of electric power systems,2005,29(3):77-80 [5] ZHANG J C,ZHANG C X,WU F J.Feasibility study of PMU based on the Beidou satellite navigation and position system[J].Automation of electric Power Systems,2005,29(15):86-88 [6] LIU Y L,CHEN Y,HUANG X.Study and design of distributed PMU using both GPS and Beidou satellite 290 position system mutually backup based on ARM[J].Application of Electronic Technique,2008,6:29-34

基于 GOOSE 网的继电保护实时通信系统刘群英1，刘起方2

（1. 电子科技大学，成都 611731； 295 2. 中国国电阿水电力开发有限公司）

摘要：GOOSE（面向通用对象的变电站事件）是 IEC 61850 标准为保证变电站系统高效可靠

通信而提出的一种通信方式，其特殊的协议栈映射方式以及重传机制使得基于该方式构建的

通信系统具有良好的实时性和可靠性。本文设计并实现了一种采用 GOOSE通信方式完成发布

端到订阅端数据传输的继电保护装置通信系统。论文主要介绍通信系统软件流程设计、GOOSE300 报文发布端配置方法以及订阅端设备刷新线程和解码方式的设计及其实现。最后以 GE

Multilin 的通用型继电保护产品作为 GOOSE 报文的发布端，对系统的整体性能进行了测试

与分析，经测试，所设计的通信系统满足保护装置通信的可靠性和实时性要求。关键词：关继电保护装置；通信系统；GOOSE；IEC 61850；实时；可靠中图分类号：TM774 文献标识码：A 305

201109-285the real-time relay protection communication systen

Documents