Testing Automation and Control

Authors: Thomas Schossig and Andreas Klien, OMICRON electronics GmbH, Austria

IEC 61850 was published as an international standard in the early 2000s and is the established norm for substation automation projects (SAS). Edition 2 and the upcoming amendment 2.1 increases the acceptance worldwide. Since protection is available, there is a recognized need for testing. Protection devices are tested regularly and demonstrate functionality as well as parameter set. There are no such traditions for SAS and SCADA. This article shows why this topic becomes important.

Definitions in the standard

Data Model and Mode Test: According to IEC 61850-7-4 every IED contains a data model with logical nodes (LN). The LNs are organized in logical devices (LD). The node contains information such as startup of protection or the position of circuit breakers. Additionally, every LN contains an attribute Mode (Mod).

There are 5 of them defined: ON; Blocked; Test; Test/blocked; OFF

Taking into account the settings of an entire LD there is a resulting Behavior (Beh). Annex A2 contains a table showing the complex dependencies.

Simulation Indication: With edition 2 for GOOSE and Sampled Values a new information was introduced allowing to distinguish between real and simulated messages. This “S-indication” (simulated) is valid for the entire physical device (LN LPHD, Physical Device), its functionality can be compared with conventional test switches.

Interlocking CILO: All classes of LNs starting with C indicate “control”. So “CILO” indicates interlocking and releases a control device once the conditions are fulfilled. There is one instance of this LN per switched device. All relevant position indications must be subscribed. Realizing the interlocking is a "local issue" only.

Supervising with LGOS: IEC 61850 7-4 defines the class LGOS as LN. The first letter (L) indicates the system character of the node. This node was introduced with edition 2 and allows supervision of GOOSE subscriptions.

Life Cycle of SAS

The standard does not describe the testing of SAS but the lifecycle of a project (part 4). Commonly used terms such as FAT - Factory Acceptance Testing and SAT - Site Acceptance Testing appear. Considering the entire cycle Figure 1 we can describe the project - from specification to working with equipment. The project starts on a desk specifying and using this for tenders. Part 6 of IEC 61850 describes the engineering of the SAS. Additionally, the non - IEC-61850 parameters such as protection settings must be defined with vendor specific tools. The phase is finalized with FAT and the commissioning follows. This ends with SAT. But even after SAT maintenance might follow and security updates become more and more important.

Testing the SAS

Interlockings: Realizing interlocking in IEC 61850 was one of the first applications of IEC 61850 GOOSE. The multicast mechanism makes it easy to transmit position indications of for instance disconnector to other feeder’s bay controllers or centralized interlocking IEDs.

Different approaches realizing interlocking have been discussed between utilities. There are advantages and disadvantages for the centralized as well as for the decentralized approach.

Realizing these approaches, the topic of testing became important. Working groups with utilities in Germany have been discussing testing approaches and sequences and brought the topic into the international standardization. Figure 3 shows the components involved.

The testing scenario could be realized as in Figure 2.

One out of n:  Another typical example is the one-out-of-n check. This avoids commands in case of other commands running.

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