Improved Protection and Control Testing utilizing IEC 61850

Authors: Benton Vandiver III, and Bharadwaj Vasudevan, ABB, USA

Digital Substations

Traditional substations have always relied on copper cables for connecting primary equipment like circuit breakers and conventional current and voltage transformers with protection relays and control devices. But digital communication technologies and standards are driving the evolution of something new – digital substations
The defining feature of a digital substation is the implementation of a digital process bus. The IEC 61850 process bus enables the substitution of point-to-point copper connections between Intelligent Electronic Devices (IED), other devices (e.g. instruments transformers, gas monitoring, etc.) and switchgear by means of a safe, standardized optical communication bus. Thanks to the process bus, real-time measurement signals, and status information can be broadcast throughout a substation without complex wiring schemes.
In the late nineties, the world’s first digital substation was commissioned in Australia for Powerlink, a transmission service provider in Queensland. Even though the concept has evolved since then, the basic principles remain the same; substituting heavy and bulky current and voltage sensors with small and integrated sensors and substitute signaling copper wires with fiber optic communication buses. From 2008 onwards, the IEC 61850-9-2 process bus was introduced between non-conventional instrument transformers and protection and control equipment.

Digital substations enable electric power utilities to increase productivity, reduce footprint, increase functionality, improve the reliability of assets and, crucially, improve safety for service personnel. Digital substations exploit the benefits of digital protection, control, and communication technologies, mirroring the trend towards digitalization seen in many other industries. This trend towards digitalization also applies to other areas of the substation.
Within medium voltage switchgear panels, the horizontal exchange of IEC 61850-8-1 Generic Object Oriented Substation Event (GOOSE) and sampled analog values reduces wiring and accelerates the testing and commissioning. Digitalized technology can now continuously monitor mission-critical functions of high and medium voltage switchgear as well as substation transformers, while performing real-time simulation and diagnostics, ensuring that the pro-active management of the assets’ lifecycle is realized. The increasing amount of data in the substation calls for better solutions to turn this data into actionable information, including that the data is secure, accessible, and properly archived. The latest substation data management and asset health management tools provide a power utility a convenient way to take advantage of the latest advances in this area.
The Digital substation concept has also paved the way for innovative switchgear solutions such as the Disconnecting Circuit Breakers with integrated Fiber Optic Current Sensors (DCB with FOCS). (Figure 1).

 Digital Substation Design
The high-level engineering workflow required to design a digital substation is defined as a part of the IEC 61850 standard in the substation automation system process. A very basic engineering workflow is shown in Figure 2.

The design process starts with the system specification. Using the appropriate system specification tool (SST), the engineer begins to create the electrical design for the substation. On top of this, the engineer also defines the requirements for the desired network topology, including all the data exchange and function association (allocation of logical nodes (LNs)) using the same tool. The idea behind this tool is to provide a standard-based document which contains all the information for starting the detailed engineering. The output of such a tool is called a System Specification Description (SSD) file which is used as the input file to start the system configuration.
To complete the system design, we also need individual device descriptions. These files are called the IED configuration description (ICD) files. A vendor-neutral System Configuration Tool (SCT) can be used to import all the SSD and ICD files and build a detailed design. Some of the basic information included in this process are data mapping for Bay level (GOOSE) communication, client-server (MMS) communication, and process level [Sample Values(SV)] communication, etc., that are as per the specifications. The output of this activity is what the standard calls a System Configuration Description (SCD) file. This is the most important file for our topic of discussion in this paper.

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