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IMPLEMENTATION EXPERIENCE ON IEC 61850-BASED SUBSTATION AUTOMATION SYSTEMS
H.-J. HERRMANN C. HOGA N. SCHUSTER G. WONG Siemens AG, PTD Energy Automation
Germany
SUMMARY IEC 61850 enables control, protection and monitoring devices to communicate with each other without protocol convertors in substations. It also safeguards the investment of owners of substation automation systems in an environment in which communication technology changes rapidly. Since becoming international standard in 2005, it has increasingly gained acceptance from the utilities and industrial electricity consumers. The success of IEC 61850 owes much to the use of modern Ethernet and flexible communication technologies. The standard enables the fast communications between two or more control/protection devices, as well as more secure communications between a station controller and a control/protection device. Ethernet is the physical medium over which the operation, configuration and management data are exchanged. The physical network comprises switches, optical fibre cables and twisted-pair cables and is electromagnetically compatible with its environment. Experience has shown shorter system set-up time due to the standardised configuration process. User-friendly configuration tools simplify commissioning and data flow information is displayed on devices to assist trouble-shooting. The certification of devices by independent and approved test institutes for conformity to IEC 61850 helps ensure the interoperability of devices from different manufacturers. Manufacturers have witnessed the success of the earlier international standard IEC 60870-5-103 which created a uniform communication ground for protection devices. IEC 61850 is expected to be more widely applied as evident from the considerable number of installations with compliant equipment under constructions and in operation. Both utilities und industrial electricity consumers have full confidence on the standard and show no hesitation in adopting it in important substations and industrial plant demanding high reliability. Experience has also revealed that the compatibility of devices from different generations in an installation has not been adequately specified and the IEC working groups should address this issue as soon as possible to assure the continual success of the standard in the future. KEYWORDS Communication – Protocol – Substation – Automation – Protection - Interoperability
21, rue d’Artois, F-75008 PARIS CIGRE 2006 http : //www.cigre.org B5-104
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1 Introduction Control and protection of substations evolved from electromechanical devices to analogue electronic devices in the 1970s and further to microprocessor-based devices in the following decade. By the mid-1990s, substation automation systems with industrial personal computers were already available. The advantages of digital systems were tangible as inter-devices communication simplified the tasks of the operators. However, substation automation systems often comprised devices operating on different protocols, and the situation is not dissimilar to a party in which the guests all speak different languages. The efforts in carrying out the interpretation can be substantial enough to set back the fun. This embarrassment, to say the least, has been experienced by utilities and manufacturers of substation automation systems who employ protocol convertors to make the communication between devices possible. Eliminating protocol convertors, IEC 61850 was established and has allowed the potential of substation automation to be fully exploited. It specifies a small set of mainstream protocols and can also incorporate new communication technology in the future, if necessary. Since 2003, automation systems based on IEC 61850 have been under construction and some have been in operation. Utilities and industrial electricity consumers have been benefitting from the standard worldwide. This paper describes the implementation of the standard with focus on the components, network topology, electromagnetic compatibility and certification of conformity. The current projects and operating systems are surveyed and the statistics indicating the acceptance of this standard is illustrated.
2 Technologies behind and structure of IEC 61850
2.1 Ethernet Ethernet is the physical communication medium specified by IEC 61850. The data throughput of modern Ethernet is much higher than that of token ring or master-slave systems. It is highly forward and backward compatible and is the local area network in over 95% of offices. 100Mbit/s is now the commonly adopted base data rate. Ethernet components suitable for substation applications are readily available and have the following characteristics: − high electromagnetic immunity − wide operating temperature range − operating on substation AC/DC power supplies − provision of redundancy, prioritisation of telegrams, etc.
2.2 Separation of Data Models, Services and Communication Protocols
Recognising that communication technology changed rapidly, the IEC working groups have made IEC 61850 future-proof by specifying separately the three fundamental parts of communication in a substation automation system, namely − data models of the applications − services for transferring the data − real communication protocols. The data models and the services hardly change in the course of time. The real protocols for implementing the communication can in theory be anything and can change. In IEC 61850, the data models and the generic services for transferring the data have been standardised. The following real protocols have been specified:
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− Manufacturing Message Specification (MMS) − TCP/IP − Ethernet. These real protocols may be replaced by new ones in the future so that the standard keeps pace with technology.
3 Implementation
3.1 Common Data Highway Two main kinds of dialogue are present in an IEC 61850 automation system, namely − Dialogue between a station controller and a bay/protection device
A bay/protection device may talk to a station controller via ‘reporting’. The messages may contain measured values, fault records and control signals. The data throughput over TCP/IP is much higher than that over other protocols such as IEC 60870-5-103.
− Dialogue between two or more bay/protection devices The Generic Object Oriented Substation Event (GOOSE) is a fast data transfer over Ethernet between two or more bay/protection devices. Its configuration and mapping are described in Parts 6 and 8 of the standard. GOOSE can deliver information such as status of switchgear and protection signals [1]. GOOSE telegrams are prioritised and transferred over switches with minimal delay.
The Ethernet network is the data highway of a substation automation system, as shown in Figure 1, because it is the medium for the transport of not only the IEC 61850 data but also all other supporting data. The use of a single data highway means less cabling, simpler installation and fewer spares.
Figure 1: Ethernet as IEC 61850 data highway
Datahighway:100 Mbit/sEthernet
Info – Report
DIGSI
GOOSE 1)
SNMP 3)
Services working inparallel :
1) 1) Generic Object Oriented Substation Event2) Simple Network Time Protocol3) Simple Network Management Protocol
SNTP2
Port B
Electrical module Optical module
Port B
Common substation-control and maintenance port
Port B
Datahighway:100 Mbit/sEthernet
Info – Report
DIGSI
GOOSE 1)
SNMP 3)
Services working inparallel :
1) 1) Generic Object Oriented Substation Event2) Simple Network Time Protocol3) Simple Network Management Protocol
SNTP2
Port B
Electrical module Optical module
Port B
Common substation-control and maintenance port
Port B
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3.2 Hardware implementation Bay/protection devices have long been designed for high electromagnetic disturbances in substations. To ensure that IEC 61850 telegrams are also transmitted securely between devices, Ethernet switches, convertors and cabling must meet the requirements of Chapter 3 of the standard. Figure 2 shows the arrangement of a complete system under test, and the electromagnetic immunity has been demonstrated. The cores of screened twisted-pair cables of Category 5 and up to 20 m long have also been shown to be adequately shielded from external disturbances. The Ethernet switches should be able to operate without cooling fans and can be powered by the batteries of the substation.
Figure 2: A test set-up for electromagnetic compatibility of Ethernet components and cabling
3.3 Network Topologies The reliability of a network depends much on its topology. In Figure 3, the switches and the multimode optical fibres form a ring, carrying light signals of wavelength of 1.3 µm. The switches support the prioritisation of GOOSE telegrams. Up to six bay/protection devices may be connected to an Ethernet switch via a twisted-pair cables. Each device has two electrical Ethernet ports providing redundancy as shown in Figure 1. Each port is connected to different Ethernet switches. If one port fails, the other port would take over within a few milliseconds and communication is restored. The entire network is monitored at the station controller by means of Simple Network Management Protocol (SNMP). The controller knows the status of all the components in the network as the devices are constantly monitored. As soon as a network fault is identified, for example a broken fibre, the network is immediately re-configured by means of the rapid spanning tree algorithm. Such a fault, as well as a port failure, raises an alarm at the station controller. The twisted-pair cables in Figure 3 could be replaced with optical fibres to form a fully optical network is desired. However, because the component costs of such a network are high, a more cost-effective fully optical arrangement shown in Figure 4 is preferred. The Ethernet switch is integrated into the network module of the device and this reduces the number of components. The integrated switches support equally telegram prioritisation and network monitoring through SNMP. Up to 30 devices can operate on a ring. Should more devices be required, several rings may be created and connected to the same or different Ethernet switches.
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Figure 3: IEC 61850 network in a ring with switches and optical fibres
Figure 4: Optical Ethernet ring with integrated switches
62,5µ or 50µ multimode fibreswitch
DIGSI 4
Optical Optical interface interface with with integrated integrated switchswitch
Wireless accessWireless access
WirelessWirelessLANLAN
STSTconnectorsconnectors
Station unit withtime synchronisation
max. 30 devices per ring
100Mbit/s Ethernet with ring management
opticalopticaltwisted pairtwisted pair62,5µ or 50µ multimode fibre
switch
DIGSI 4
Optical Optical interface interface with with integrated integrated switchswitch
Wireless accessWireless access
WirelessWirelessLANLAN
STSTconnectorsconnectors
Station unit withtime synchronisation
max. 30 devices per ring
100Mbit/s Ethernet with ring management
opticalopticaltwisted pairtwisted pair
100Mbit/s Ethernet with ring management
62,5µ or 50µ multimode fibre
switch
DIGSI 4 Station unit withtime synchronisation
6 devices per switch redundant
path
opticalopticaltwisted pairtwisted pair
100Mbit/s Ethernet with ring management
62,5µ or 50µ multimode fibre
switch
DIGSI 4 Station unit withtime synchronisation
6 devices per switch redundant
path
opticalopticaltwisted pairtwisted pairopticalopticaltwisted pairtwisted pair
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3.4 Configuration and Commissioning To configure an automation system, a unique IP-address is firstly assigned to each network device. These devices are typically the protection devices, bay devices, station controller and the time server. A subnet mask is usually employed for a small substation network. By means of the system configurator of the engineering tool, the logical communications between devices are established according to the IED Configuration Description (ICD) files, where IED stands for Intelligent Electronic Device. Double assignment of IP-addresses must be avoided. The Ethernet switches from another manufacturer are configured separately by means of their own configuration tool, with which the ring management and the telegram prioritisation are set up. The system configurator of the engineering tool links the data objects of the devices and creates a System Configuration Description (SCD) file. The information of this file is written into the devices to complete the configuration. As the configuration process is standardised and all the information is in electronic form, mistakes are unlikely to occur. ‘Right-first-time’ was indeed the experience of manufacturers such SIEMENS, ABB and Areva who participated in the earlier interoperability tests. After the network has been configured, devices can exchange messages. During commissioing, the health status and the data flow of the network interface can be monitored and displayed to assist trouble-shooting. For protection, the time delays between successive events such as fault inception, relay response, breaker opening are important. All the events, including the sending and receiving of GOOSE messages, are time-stamped to an accuracy of 1 ms by the Simple Network Time Protocol and can reveal the required delays information. During commissioning, the Ethernet network is usually lightly loaded. Manufacturers can generally advise on the transfer delays under heavy data-traffic conditions.
3.5 Certification from KEMA and UCA International Users Group The certification of devices compliant with IEC 61850 is an important milestone towards the creation of an environment in which equipment from different manufacturers work smoothly together. The certification practice already began for earlier standards such as IEC 60870-5-103. The conformity tests specified in IEC 61850 were carried out on one representative device of the manufacturer. KEMA, an independent test institute approved by the UCA International Users Group, was responsible for the first set of tests in March 2005. The certification process involves checking the documents of manufacturers and confirming that actual implementation matches what is written in the standard-document. For example, in Protocol Implementation Conformance Statement (PICS), the communication services which the device offers are described. The Model Implementation Conformance Statement (MICS) lists the supported data models. The Protocol Implementation eXtra Information for Testing (PIXIT) document describes the mapping between the device specific parameters and the IEC 61850 logical nodes. If desired, the actual mapping information of each device can be exported from the ICD file of the device and stored in PDF form in the MICS document. The PICS and PIXIT documents shall be available on the website of the manufacturer, for example http://siemens.siprotec.de. The MICS document is supplied together with the engineering tool of the device. Experience has revealed that the standard has not adequately specified the need for backward compatibility of configuration tools and such compatibility is important in substations comprising devices from different generations.
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4 Experience on life cycles of communication technologies In the mid-1990s, IEC 60870-5-103 became an international standard and products shortly followed. Users, particularly those who took part in the standardisation work, were delighted with this standard as it allowed protection devices and station controllers to communicate in an internationally agreed way. The popularity of this standard was further assured by the use of existing serial communication methods. In spite of the overwhelming preference for IEC 60870-5-103, proprietary protocols continued to have their share in substation communication because manufacturers took time to make all the products compliant with the IEC standard. Some old devices took approximately five years to be phased out, and these are still now occasionally ordered by customers. The inadequacy of IEC 60870-5-103 to cover control data in substations transpired as combined control and protection devices became popular. The substation automation community started to focus on IEC 61850 which would cover all kinds of data flows in substations. With this as the single standard in the world, the manufacturers would not need to cater for different communication modules on a device, when each module would correspond to one protocol and require a dedicated processor. IEC 61850 has now been completed. In the first year of the market launch, a manufacturer already delivered approximately 5% of its devices as IEC 61850-compliant devices. It is estimated that because of IEC 61850, all the other communication protocols such as Modbus and DNP3 will gradually disappear in the next ten years. Figure 5 illustrates the number of devices based on the different communication standards.
1985 1990 1995 2000 2005 2010 2015 2020
Year
rela
tive
num
ber o
f de
vice
s
proprietary protcocol IEC60870-5-103 IEC61850
Figure 5: Lifecycles of products based of different standards
5 Projects and Installations By December 2005, approximately 110 substation automation systems based on IEC 61850 have been delivered worldwide. A seventh of these systems are already in service, of which the Winznauschachen system [2] in Switzerland is the world’s first. Figure 6 shows the distribution of these installations worldwide. Approximately three quarters of these installations belong to utilities and the rest to the industrial sector. 36% are in Germany, the
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country currently with the largest number of applications, and the Garzweiler II system [3] came into operation in December 2005. This statistics indicates that the customers have recognised the benefits due to IEC 61850 such as higher system-performance, simplified maintenance and lower overall life-cycle costs. In the substations concerned, over 2000 bay devices and protection devices with the IEC 61850 network interface have been installed.
Figure 6: Installations based on IEC 61850 The highest voltage level on which IEC 61850 has been applied is 765kV. Table 1 illustrates the extent of applying IEC 61850 at different voltage levels and reveals that 64% of the installations are above 100kV. This suggests that transmission network operators desire to gain first-hand experience and show no hesitation in applying this relatively new standard in important transmission substations. Table 1: Application of IEC 61850 at different voltage levels
Voltage level (kV) Percentage of substations (%) up to 20 15
above 20 and up to100 21 above 100 64
6 Conclusions IEC 61850 is becoming the single standard for substation communication in the world. The substation information is exchanged over modern Ethernet. Manufacturers offer industrial-grade components and networks with management which assures secure and reliable operations of the automation systems. Standardised configuration shortens system set-up time and simplifies commissioning. As IEC 61850 becomes increasingly adopted, other communication protocols will gradually disappear. The popularity of IEC 61850 is reflected by the number of installations under construction and in operation.
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Experience has shown that if IEC 61850 is to remain successful, present devices without any upgrade should be able to operate together with future devices in an installation. These requirements have not been adequately stated in the standard and should be addressed as soon as possible by the IEC working groups. Process bus is the next step towards fully automated substations, offering more benefits to utilities and industrial electricity consumers. Voltage and current samples are continuously transmitted and loss of telegrams can lead to protection malfunctioning. The implementation would require the latest technologies such as 1Gbit/s data rate and intelligent structured networks. BIBLIOGRAPHY [1] N. Schuster “Reverse Interlocking implemented by means of IEC 61850 GOOSE” (Basics and
user-oriented project-examples for the IEC 61850 series for substation automation, Praxis Profiline, July 2005, pages 44-46)
[2] G. Wong, F. Koschanin, C. Hoga “World’s first IEC 61850 substation commissioned” (Modern Power Systems, May 2005, pages 51-54)
[3] G. Wong, W. Krudewig “Garzweiler II – die Norm IEC 61850 hält hohe Anforderungen ein” (EW, Ausgabe 23, 31.Oktober 2005, Seiten 41-44)