One of the significant features IEC 61850 has introduced is the configuration language SCL. SCL originally was the abbreviation for substation configuration language.

Now that the use of IEC 61850 beyond substations has become reality, the name will be changed to system configuration language.

The XML based SCL is used to exchange information between the different engineering tools. Traditionally, a substation automation system was designed using tools from the different IED manufacturers and a tool from the HMI / Gateway supplier.

The exchange of information between these tools had to be made manually or through Excel tables. IEC 61850-6 introduces the SCL as a common language to exchange configuration information between the tools. In addition, IEC 61850 introduces the system specification tool and the system configuration tool.

The system configuration tool allows to do the system level design like the configuration of the communication network or the information exchange between devices such that a standardized output format is produced that can be used by all the device tools to configure the individual devices.

Depending on the step in the design process, IEC 61850 SCL defines different file types that have more or less of the content of a SCL file filled in. As an example, a "system configuration description" or SCD file includes the complete configuration, while an "IED capability description" or ICD file describes the data model of an IED and the communication services it supports.

While the standard has now been introduced for more than five years, it is amazing how much confusion still exists around the interpretation of the different file types as well as of the responsibilities of the different tools – even among members of the working groups.

Edition 2 of IEC 61850-6 that has recently been published adds some clarifications that hopefully will help for a better understanding and hence for better implementations. Today, while the implementations of the products supporting IEC 61850 are typically good, that can not necessarily be said about the IED tools that should be used with these products.

A principal confusion exists around the files related to a device (or IED). Originally, the standard differentiated between an ICD file and a CID file. The ICD file is intended to be a template for an IED type, which could be instantiated multiple times – e.g. per feeder – to build a system. The CID file was intended to include all the information required to configure a specific instance of an IED in the finally designed system.

The assumption was that for an IED to be used for a specific task in a system, as a first step, a template has to be generated by the vendor specific IED tool (the ICD file), and that then this template is used to create instances with a system tool.

Reality however is, that many vendor tools are not supporting such an approach. The instances of the IEDs are created by the vendor IED tool. The file that is then produced is an instance file of an IED. Very often, such a file is referred to as CID file – which is obviously wrong. A CID file needs to include more than just an instantiated data model of an IED. A CID file needs to include everything that is required for an IED to be configured; in particular that means, the CID file needs to include e.g. the data-set definition behind a GOOSE message sent from another IED that the IED to be configured shall receive. So a CID file includes more than just the information related to one IED, and further, the CID file can only be created once the system configuration is done and an SCD file exists.

To address the requirement to be able to represent an instance of an IED, the Edition 2 introduced the new "instantiated IED description" or IID file.

This is an example of some of the clarifications and new features added by the Edition 2 of IEC 61850. IEC 61850-6 has been published as the first part of the Edition 2 at the end of 2009; Part 7-4 followed recently. I will keep you updated on the progress and new features of Edition 2 with the upcoming columns.