With so many communication protocols costing transmission grid companies time and money, a new IEC standard aims to streamline resources by speaking everyone’s language.
C. Hoga, G. Wong, Siemens AG, Germany
Since protection and control were automated in sub-stations, the large number of communication protocols involved has undermined the joint operations of devices from different manufacturers. The introduction of IEC 61850, a single communication standard for the world, allows substation automation systems (SASs) to be streamlined by permitting the interoperability of devices from different manufacturers without the use of protocol converters. It does so by considering data models of the applications, services for transferring these data, and real communication protocols.
The data models and the services hardly change over time, whereas the real protocols for implementing the communication can change and in theory, can be anything. The new standard, IEC 61850, standardizes the data models and the generic services for transferring the data, and specifies the real protocols of Manufacturing Message Specification (MMS), TCP/IP and Ethernet. These real protocols may be replaced by updated versions so that the standard keeps pace with technological advances
Three projects in which Siemens has supplied the SASs, and which have been completed or are close to completion, are Garzweiler, Salzgitter and Winznauschachen.
The German power generating company RWE Power has equipped the Garzweiler substation with equipment compliant with the IEC standard. Three substations of 110kV, 25kV and 6kV supply electricity to an open cast mine that serves four power stations. The order was placed in summer 2003 and the SAS will be in service in April 2005.
At Salzgitter, the substations required by the engine factory owned by Volkswagen comprise an intake 110/20kV substation, four 20kV distribution substations for the assembly halls and one substation for site heating facilities. The order was placed in December 2003 and the SAS will be in service before the third quarter of 2005.
At Winznauschachen, the Swiss distribution network operator AVAG, a company of the Atel Group, requested a 16kV substation be fitted with an IEC 61850-compliant automation system. The order was placed in April 2004 and the SAS has been in service since November 2004.
IEC 61850 benefits
IEC 61850 standardizes the names of all the anticipated substation automation functions. Both generic services and the real protocols are standardized. A typical specification based on these standardized features would cover:
- Network configuration
- Communication stack
- Application functions
- Required services
- Engineering process
For example, the communication stack would contain MMS, TCP/IP and Ethernet. The application functions would list the desired standardized data models. No ambiguity or misinterpretation would arise between the bidders for the SAS and the customers. The bidders offered these standardized features for Garzweiler, Salzgitter and Winznauschachen. The customers in these three projects have recognised this as the trend of future specification.
The lifetime of the Garzweiler and Salzgitter substations is expected to be 25-30 years, during which time expansion of the primary equipment is foreseen. RWE Power and Volkswagen chose IEC 61850 as the standard for the substations because of the scalability of Ethernet. The Ethernet bus can easily incorporate more nodes to deal with the corresponding expansion of the SAS and will incur minimum interruption to substation operation.
Ethernet is highly flexible and gives bidders freedom in meeting the customers’ specific requirements. For instance, in Garzweiler, transformers required monitoring as well. Siemens integrated seamlessly onto the Ethernet station bus a voltage regulator from a tap-changer manufacturer who used IEC 61850 standardized transformer data.
In all three projects, Siemens offered a 100Mbit/s optical fibre Ethernet ring with ring redundancy for each substation. When a project involved several substations, the individual rings were tied to a main ring on which the human machine interface (HMI) and other local or remote monitoring and control equipment found themselves.
With the new standard in place, utilities and consultants can adjudicate bids fairly because it is no longer necessary to compare different protocols, for example DNP3.0, Modbus or a proprietary bus. Without the burden of numerous different protocols, Siemens focused on optimising the SAS and making the overall system cost effective, and on engineering the interfaces between the IEC 61850 system and external systems, such as the IEC 60870-5-101 connection required in Garzweiler and Winznauschachen.
The standardized data models of IEC 61850 can be carried over directly from the specification to the design stage, saving time and leading to a lower chance of errors.
In general, an existing Ethernet structure in a substation can be re-used with little extra design work. However, in the case of these three projects, the customers were experiencing both IEC 61850 and Ethernet at the substation level for the first time, and the communication platform was established from new. Nevertheless, from the point of view of Siemens, hardwire design of the SAS was simplified, because no protocol converters were required among the devices, and fewer components in the SAS meant less time spent on co-ordination and review meetings. Also, the Ethernet components suitable for high-voltage substations were readily available, leaving only the minor setting up of the required Ethernet switches on-site.
A laptop can be used anywhere in the station, speeding up commissioning.
The Substation Configuration Description Language of IEC 61850 allows the primary and secondary equipment in the bays to be specified in standardized electronic format. In most cases, the design staff can establish templates of basic protection and control schemes for typical bays, for example incomer bays and transformer bays. These templates can be modified to suit other similar bays, saving time and reducing errors.
In conventional parallel wiring, preparing the schedules for the multicore cables, the supporting trays, terminal blocks and marshalling boxes is time-consuming. With IEC 61850, a single Ethernet cable can carry all the data exchanged in the SAS. In most substations, the numbers of multicore cables, accessories, as well as the associated design efforts, are significantly reduced. This benefit is more evident at the process level close to the primary equipment. For the three projects, although IEC 61850 has been applied at the station and bay levels, the customers have benefited from the reduction in equipment variety.
Right first time
The Substation Configuration Description Language simplifies the configuration of SASs. There is no need to exchange information on paper, therefore less time is needed for co-ordination. Because the chance of errors was lower, Siemens conducted less rework and retest, and consequently shortened project execution time. The Substation Configuration Description Language underpins the notion of ‘right-first-time’. Ethernet is the medium for the transfer of SAS data as well as configuration data. No extra communication links or specific ports on the devices are needed to transfer the configuration data.
For the three projects, the SAS was set up at Siemens test facilities in Nuremberg, Germany, and tested with full Ethernet cabling. Not needing to deal with numerous unfamiliar protocols, Siemens staff focused on fault-finding and fault-rectification. Only the parts with conventional parallel wiring linked to primary equipment were tested on site.
The simpler cabling of Ethernet and the absence of protocol converters reduce installation time, decreasing the chance of connection or termination errors.
The accessibility of the new standard simplifies day-to-day operation still further. Running on TCP/IP, a portable computer such as a laptop may be moved around in the substation and plugged into any Ethernet switch during commissioning to display the information about the whole substation. In the three projects, the work of the commissioning staff was substantially lightened.
The customers of all the three projects will notice several benefits. The data flow experiences no delay, which can otherwise caused by protocol converters. Ethernet multicasting allows messages to be sent simultaneously to many receivers and at a faster pace. Bottlenecks, commonly found in master-slave communication, are not present. And the 100 Mbit/s data rate of Ethernet in substation communication is pushing technology barriers.
System availability was important to Volkswagen because there were practically no warehouses for storing the completed engines and the units were manufactured ‘just-in-time’. IEC 61850 yields SASs of high availability because firstly, distributed intelligence is used, e.g. interlocking without a central coordinating device, and secondly, in the absence of collisions of telegrams, Ethernet switches speed data throughput.
In the Garzweiler and Salzgitter projects, the SICAM PAS CC on the station bus offers a full graphic service platform to the operation personnel on site. All these data can also be accessed by maintenance staff in the offices of Volkswagen via the corporate network.
The three customers will find maintenance easier because there is less equipment and their training efforts have now been reduced because the staff need not learn so many protocols.
The benefits of the standard IEC 61850 on substation automation have been experienced by utilities and industries. The substation automation communities in the world are putting the final touches on the procedures for conformance testing. The extension of the IEC 61850 data models up to the control centre is in progress and manufacturers are helping utilities and industries migrate towards IEC 61850 in order to make the most out of seamless communication in their enterprises.