This section contains some explanations of IEC 61850 related terms. If you disagree with certain statements please send an e-mail with suggestions to improve the explanations. You can also suggest other IEC 61850 related terms or concepts that should be explained here.
A data set in IEC 61850 is a list of variables that can be observed and transmitted together in a more efficient manner. Data sets can be defined by CID/SCL files or can be created by MMS clients via the MMS protocol. At the MMS layer data sets are mapped to MMS named variable lists. Data sets are tied to Logical Nodes but their member variables can be located at different logical nodes and even different logical devices (or MMS domains). Data sets are used to define list of variables that can be transferred via MMS read and write services, reporting (mapped to MMS information reports), GOOSE, or sampled values (SV) services.
GOOSE (Generic Object Oriented Substation Event) is a protocol specified in IEC 61850-7-2 and IEC 61850-8-1 for communications in SAS (Substation Automation Systems). GOOSE (as well as the Sampled Value Service specified in IEC 61850-9-2) is an application protocol on top of Ethernet and is usually used in switched Ethernet networks for fast event exchange between substation equipment. As it sits directly on top of Ethernet it is only applicable in local networks and is not routable by IP routers. GOOSE is of very simple complexity and can be used by much simpler devices than the more complex MMS services. GOOSE can be either configured statically and documented by an CID/SCL file or configured dynamically by manipulation of the MMS mapped Goose Control Block via MMS read and write services. The purpose of GOOSE is the transmission of data defined by a data set. Events can be distributed station wide by using multicast ethernet addresses.
Intelligent Electronic Device (IED)
In the context of Substation Automation Systems (SAS) the term Intelligent Electronic Device is used to denote a monitoring or control device in a substation that is equipped with a modern micro-controller and a communication interface. In the context of IEC 61850 IED just means a device that implements one of the IEC 61850 communication protocols. Typcial examples of IEDs are multi-function protection devices.
Reports are unsolicited data messages sent by the server. The sending of reports is triggered by preconfigured events. Triggers can e.g. be if the value or quality of a variable in the monitored data set changes. The sending of reports is configured and controlled by Report Control Blocks (RCB). Each RCB can be allocated by a single MMS client. Each RCB is also related to a specific data set that is monitored by this RCB. RCBs are usually configured in the SCL file that describes the server IED. IEC 61850 distinguishes between buffered and unbuffered reporting. In unbuffered reporting events will not be logged and reported if the associated client for the unbuffered report control block is not connected. In the case of buffered reporting the events will be logged for a specific amount of time and sent later when the client is connected again.
Sampled Values services also uses a special protocol on top of ethernet for fast distribution of sampled values inside of the substation. Sampled values as well as GOOSE works according to the publisher/subscriber model. There can either be a single subscriber (in case of unicast sampled values) or multiple subscribers. In the latter case multicast addresses are used and the subscribers (clients) need to be configured to listen to the specified multicast address. The subscriber address is part of the SVCB (Sampled Values Control Block).
Substation configuration language (SCL)
The substation configuration language is an XML based file format to describe IEDs and their relations. It is intended to be used to describe a whole substation and all of its communication properties. SCL can be used to configure IEC 61850 compliant IEDs. The data model (the organization of the data of a device) is most often defined in an SCL file. This SCL file can then be transformed by a tool into a description that can be used by a IEC 61850 client or server device. There are different types of SCL files. The most commonly used types are:
- ICD (IED Capability Description) – describes the capabilities of an IED in terms of available services, data models, and configuration options. It can be seen as the electronic data sheet of a device.
- SCD (Substation Configuration Description) – contains the IED configurations of the whole substation or parts of it. It usually contains the configured IEDs, communication setup, and relations between the IED. The SCD file usually contains multiple IED sections.
- CID (Configured IED Description) – contains the complete configuration for a single IED. This file is usually be downloaded to the IED as part of the final device configuration.