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Home / Technical Articles / A must-have checklist for IEC 61850 communications in digital substations

IEC 61850-Based Communications

This article aims to inform the reader of important considerations when designing an IEC 61850 based substation communication system. There is a brief background introduction to substation communications, to give the reader context for the implementation of IEC 61850 based communications systems.

A must-have checklist for IEC 61850 communications in digital substations
A must-have checklist for IEC 61850 communications in digital substations - Bay protection control cabinet on a pre-IEC61850 marine substation (main MV SWBD). All binary and analog signals are sent between IEDs via hard wired interface.

Then a discussion of how digital IEC 61850 based systems compare to traditional hardwired substation communications.

Finally, we explore important factors for the engineer to consider when designing an IEC 61850 based substation, so that they will hopefully avoid some of the common and perhaps hidden pitfalls of implementing such a system.

Table of Contents:

  1. Substation Communications Background
  2. Advantages and limitations of IEC 61850 Communications
    1. Hard Wired
    2. Digital Communications – IEC 61850
  3. Design Consideration for IEC 61850 Communications Systems:
    1. Robust Performance
  4. IEC 61850 Network Topology:
    1. PRP (Parallel Redundancy Protocol)
    2. Other Redundancy Protocols
    3. Orphaned IEDs
  5. Network Switch Selection and Configuration:
    1. Redundancy Protocol
    2. Bandwidth Limitation
    3. VLAN (Virtual LAN)
    4. Alarm Output
  6. Protection Software Configuration On Substation IEDs
    1. Combining IEC 61850 With Hardwired Signals
    2. IED Response to Communications Failure
    3. Transient Events and GOOSE Data Transfer
  7. Template Engineering
  8. Designing For Testing and Commissioning
  9. Choice of Software
  10. Testing a Partial System
  11. Conclusion
  12. BONUS 🔗 Download IEC 61850 Communications Guides and Studies (PDF)

1. Substation Communications Background

Power systems have been increasing in internal complexity and system level interconnectivity since the adoption of electricity as a means of industrial power transfer at the turn of the 20th century. The modern substation or main power distribution systems may have thousands, or tens of thousands of different analog and binary signals sent between equipment inside the switchgear, or to external interfacing systems.

The increase in interconnectivity generally results in increased safety, reliability, supervision, and controllability of modern power systems.

In the recent past, many of these signals would be sent directly from point to point by individual wired connections. This would be horizontally, between bay level protection equipment and control devices, as well as vertically to upstream PMS and SCADA systems, as well as downstream to lower level protection devices or end consumer equipment.

As power system control and protection equipment has evolved from purely electromechanical systems, to electronic control, and eventually digital logic based systems, there is now the possibility to perform the majority of substation communication in a digital manner. The current industry standard for communications between protection devices is IEC 61850.

This standard defines communication protocols for intelligent electronic devices (or IEDs) at electrical substations, and was first published in 2003.

Figure 1 – A completely electromechanical protection relay, ABB HRU instantaneous overcurrent relay with harmonic restraint. All internal signal processing and protection triggering is performed by passive circuit components and mechanical devices.

Figure 1 – A completely electromechanical protection relay, ABB HRU instantaneous overcurrent relay with harmonic restraint

There is often a lot of industry talk about “digital substations”, referring to a high level of automation including the use of IEC 61850 compatible devices. While there are undoubtedly many advantages to “digitization” of substations, like any new development, IEC 61850 enabled communications should be viewed as another tool in the design engineer’s arsenal.

Its advantages and limitations must be understood, so that it can be used, often in conjunction with other design options, to achieve the optimal solution for the design challenge at hand.

Figure 2 – A collection of discreet electronic protection relays installed on an 11 kV cruise vessel substation. These devices use active electronics and/or digital processing units to perform signal processing and protection triggering. This allows for greater accuracy and precision as well as setting options, when compared to purely electrotechnical systems.

A collection of discreet electronic protection relays installed on an 11 kV cruise vessel substation
Figure 2 – A collection of discreet electronic protection relays installed on an 11 kV cruise vessel substation

Unfortunately, this means there is no single answer as to the ‘right’ way to implement an IEC 61850 based system. The design engineer must understand the context in which the system will operate, such as specific process considerations and the necessary balance between reliability, cost, and performance.

This digital numerical device performs various protection and control tasks with the heart of the device being a FPGA chip. Such a chip allows for highly parallel digital signal processing, such that multiple protection functions can be active simultaneously on the one device.

Within the device is a communications card allowing connection and communications with an IEC 61850 network.

Figure 3 – A thoroughly modern IED protection relay, the ABB REG630

A thoroughly modern IED protection relay, the ABB REG630
Figure 3 – A thoroughly modern IED protection relay, the ABB REG630

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2. Advantages and Limitation of IEC 61850 Communications

In order to understand the relative advantages of digital substation communications we need to first define, and then compare the alternative methods of device signaling. Here we take a very brief overview of hard wired signaling and IEC 61850 based communications to contrast the strengths and vulnerabilities of each method.


2.1 Hard Wired

Hard wired signals are the most basic and fundamentally cross compatible type of signaling interconnection. A signal pathway will generally consist of a dedicated input on the receiver device, and one or multiple outputs on the sender equipment. The sending outputs can be arranged in parallel or series, as the signaling purpose requires.

These can be both analog and discrete logic level signals. i.e. open/close type signals.

Advantages:

  1. Readily cross compatible between different equipment.
  2. Possible to perform commissioning and fault tracing without use of special tools or software.
  3. Individual signals are relatively resistant against common failure modes in the communication system.
  4. High level of cybersecurity integrity due to each signal being a physically isolated channel and not accessible from remote access.

Disadvantages:

  1. Physical space requirements, every signal requires an additional copper wire or wire pair. The amount of cables will scale linearly, or even exponentially as the size of the installation increases.
  2. Increased weight, cost, cable way utilization, and manufacturing/installation time with increase in substation I/O.
  3. Difficulty for retrofit or modifications to the substation at a later date.
  4. Small modifications require local, physical action to rewire/re-terminate, as well as maintain wiring diagram documentation.
  5. Difficult to detect signal failure for non monitored, normally open type signals.
  6. Limitations on the amount of physical I/O a device can handle due to cost and size constraints.

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Kitab Paul Shah - Author at EEP-Electrical Engineering Portal

Kitab Paul Shah

With a broad experience in the electrical industry, my main focus is on systems engineering. To ensure that an electrical installation functions correctly as a complete system, it is necessary to have an understanding of how each part behaves internally, how they should interact with each other, expected failure modes, and the philosophy of plant operation. Previously I have been heavily involved in marine and offshore projects, both from an engineering and design side, as well as on site installation, start up, and commissioning. This has concerned system philosophy development, procurement of electrical equipment, as well as protection design and coordination for MV and LV SWBDs, rotating machines, drives, generators, AVRs, UPS, and battery energy storage.My education is Electrical Engineering Honours degree from the University of Newcastle, Australia, focusing on power systems, control theory, and power electronics. As well as an apprenticeship and full licencing as an industrial LV and HV electrician for NSW, Australia. Additionally I hold authorisation to perform electrical work in Norway and Sweden.
Profile: Kitab Paul Shah

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