Designing IEC 61850 systems for maintenance, retrofit and extension

Author: Dr. Wolfgang Wimmer, ABB, Switzerland

Designing IEC 61850 systems for maintenance, retrofit and extension

Usage of names

Names are used at system engineering time to establish relations between the different parts of the system: Relations between the switch yard (primary system) and the IED signals (secondary system), and data flow between IEDs for communication engineering respective online communication association establishment. A name change at a data source therefore leads to reengineering of all IEDs connected to the changed one respective replaced one. In former master slave architectures all data flowed between the bay level IEDs and one single central place, only the IED to be replaced and the central IED were concerned. For IEC 61850 however already for availability reasons several station level IEDs might be connected to the same bay level IEDs, and the new communication services GOOSE and SMV (Sampled Values) allow new substation functionality or existing functionality with less engineering effort and higher reliability, however introduce multiple sinks for certain signals, which might be concerned by a change at the signal source, as illustrated in Figure 1.

IEC 61850 object types and data identification

IEC 61850-7 introduces IED and communication modelling concepts, and standardized data semantics by standardized names. However, the concrete instance names are additionally dependent on the physical and logical structuring of the data and therefore not a priori stable when replacing IEDs or changing the architecture. What is long term stable (as least as long as the switch yard itself), is the functional meaning of the data in relation to the switch yard respective the power delivery process. Further the substation automation functionality related to the switchyard is normally long term stable, although extensions are not excluded. Therefore IEC 61850-6 introduces a second way of identifying the same data, namely by functional designations as defined in IEC 61346.

IED related objects and their identifications

IEC 61850 as a communication standard in first line addresses data identification at communication level, i.e. at interface level between a server or publisher IED and the data receivers (clients, subscribers). To make this naming independent from the physical structure, the concept of a logical device (LD) is introduced as a management unit for functional parts. Figure 2 shows the resulting internal structure of an IED.

The communication function uses IED access points to connect clients with servers. In principle each logical node can be a client to other logical nodes on some server. IEDs which only receive data, like the OPC server AA1KA1 in Figure 1, can also be pure clients without a server.

To reach the goal of having standardized semantics, the DATA names as well as the names of DATA attributes are completely standardized. Also the semantic of the logical nodes is standardized by means of a logical node class, which is part of the logical node instance name. A real system needs instances of logical node classes, which are associated to different parts of the switch gear; therefore the LN instance identification has non standardized parts. The logical device name as a manufacturer / organization related structuring is completely free within some syntactical limits. This is illustrated in table 1 with an example designation for a switch position value within the switch control function:

MyControl LD1/Q0CSWI3.Pos.stVal

A product manufacturer typically provides IEDs as products with some predefined functionality, however with no context to the project specific usage. Therefore the LD relative name and some parts of the LN instance identification need to be given by the manufacturer independent of the unknown project, and might be needed after project engineering to associate the project specific data to the project independent preconfiguration of the IED. Therefore it is manufacturer dependent, which parts of the LN instance identification can be adapted specifically for a project.

Although this designation is mainly used for communication establishment, we might call it a 'product related' designation in the sense of IEC 61346-1, especially if the IED designation is used as part of the LD name.

From this discussion we see how the physical architecture influences the communication level naming. Table 2 illustrates this with two logical nodes for the control function: the CSWI handling control commands from the operators and the XCBR executing these commands at the circuit breaker. The architectures referenced in the table are illustrated in Figure 5.

Consequence: different physical architectures by grouping on IEDs as well as different organisational structures by means of logical devices lead to different names, even if an IED and its tool supports free naming for the non standardized parts. And the free naming is not mandatory according to IEC 61850, and naturally introduces additional engineering and testing effort - especially at LN instance level.

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Relion advanced protection & control.
BeijingSifang June 2016