IEC 61850-90-4 TR Communication Networks and Systems for Power Utility

The IEC 61850 standard covers a wide range of issues related to the improvement of the reliability, security and efficiency of the electric power grid based on the definitions of the object models of different types of primary and secondary equipment, the communications interfaces required for the operation of the system under normal or abnormal conditions, the configuration language used at all stages of the engineering and maintenance process and many others. However, the standard does not define any specific communications architecture. This is due to the fact that the variety of substation topologies, the criticality of the substations and the performance requirements (to name just a few of the factors that have an impact on the communications architecture) does not allow the definition of a universal communications architecture that will meet the requirements of all substation applications.
In order to help the industry with the development and implementation of IEC 61850 based protection, automation and control systems, Working Group 10 of IEC TC 57 started developing technical reports focusing on specific issues that are not covered by the core standard. One of the most important technical reports is IEC 61850 90-4 TR Communication networks and systems for power utility automation – Part 90-4: Network engineering guidelines for substations.

Considering the fact that many PAC specialists are not communications experts and to ensure that there is no misunderstanding while using the report, the first sections of the document introduce terms and definitions, abbreviations and define network diagram, port, link and bridges symbols. This is followed by a brief overview of the networking aspects of IEC 61850, such as the logical functions and interfaces, the data traffic and the concept of Station Bus and Process Bus.

The following part of the technical report is very important, because it defines a list of criteria to be considered during the design of the communications network:

  • Substation topology and physical locations of IEDs
  • Protection and control application
  • Logical data flows and traffic patterns
  • Latency requirements for different types of traffic
  • Redundancy and resiliency
  • Reliability, availability, maintainability
  • Time synchronization and accuracy
  • Network management
  • Environmental issues
  • EMI immunity
  • Form factor
  • Physical media
  • Remote connectivity
  • Cyber security
  • Upgradeability and future-proof
  • Testing
  • Cost

After identifying the criteria, the report focuses on the available Ethernet technology that can be used in substation PAC systems. This includes Ethernet subset for such systems and their topology, as well as issues related to the physical, data link and network layers.
Copper and optical cabling at 100 Mbit/s and 1 Gbit/s are described, followed by unicast and multicast MAC addresses and traffic filtering in switches. This section also includes a brief overview of RSTP (Rapid Spanning Tree Protocol, ISO/IEC 10038 [ANSI/IEEE 802.1D 1998™]), PRP (Parallel Redundancy Protocol [IEC 62439-3 Clause 4]) and HSR (High-availability Seamless Redundancy [IEC 62439-3 Clause 4]).

The following section concentrates on the network topologies, starting with a discussion of general rules and reference topologies. Single bridge, star, simple ring and multiple ring topologies are described.
Being a critical components of the substation PAC system, the reliability of the communications network plays a very important role to ensure the overall reliability of the system. That is why the report also analyses the requirements for resiliency, availability, reliability and maintainability.

The following sections of the technical report cover different aspects of network configuration, such as IP address allocation of NET, BAY and device (without or with PRP).
Since the communications network is a component of the substation PAC system, performance issues are very important. This requires the estimation of MMS, GOOSE and sampled values traffic, as well as the measurement of the station and process bus performance.

This is followed by the analysis of the quality of service and latency requirements for different types of traffic. The impact of physical paths, bridges and hop counts is considered. Some specific guidelines for the engineering of IEC 61850 based networks for protection applications are included later in this section together with discussions on traffic reduction.
Time synchronization plays a very important role in IEC 61850 based digital substations with conventional or non-conventional instrument transformers. That is why a special section is dedicated to clock synchronization, covering first the requirements and sources, followed by the description of synchronization mechanisms in IEC61850 and clock synchronization protocols (including PTP Precision Time Protocol version 2 [IEC 61588/Ed.2]).

Network security, management, engineering access and testing are covered in the last four sections of the technical report.
A very important contribution of the report is the definition of the IEC 61850 bridge object model. A new logical node LCCH is introduced to represent the communication ports of bridges, which allows their modeling as IEC 61850 devices.
Several case studies are included in annexes at the end of the document.

IEC TR 61850-90-4:2013 was published in August 2013, and is available for purchase online at the IEC webstore.

IEC TR 61850-90-4:2013 is available for purchase online at https://webstore.iec.ch/publication/6025

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