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Home / Technical Articles / Using full potential of IEC 61850 with these 2 functions for digital substation automation

Introduction to IEC 61850

Since IEC 61850 was published as an international standard for communication in substations, the standard has found broad acceptance on the markets. In the first substations to use it, the primary aim was successful implementation of existing concepts and solutions using the new technology.

Using full potential of IEC 61850 with these 2 functions for digital substation automation
Using full potential of IEC 61850 with these 2 functions for digital substation automation

This positive experience from the initial projects secured the trust of the substation operators. However, these substations did not yet make use of the potential of IEC 61850.

With the rapidly growing number of implemented substations, confidence grew in the equipment and the first applications arose that made specific use of the new technology.

The most frequent control application was the decentralization of switchgear interlocking using GOOSE messages.

The new communication standard contains much more comprehensive definitions than other protocols and is primarily intended to improve interoperability between devices from different manufacturers, provide long-term investment protection and implement efficient exchange of object-oriented data models between engineering systems.

In addition, IEC 61850 offers the possibility of replacing parallel wiring with Ethernet and of implementing fast information exchange between devices. This article chiefly deals with this aspect and contrasts these concepts with the conventional approach.

Two practically proven examples demonstrate how modern solutions for digital substation automation incorporating new functions from IEC 61850 increase the benefit for users.

The application examples are:

  1. Distributed synchro-check
    1. Conventional concept
    2. Concept using peer-to-peer communication
    3. Benefit of the solution
  2. Mash station automatic switching
    1. Mesh station automatic switching
    2. The solution
  3. Summary

1. Distributed synchro-check

The synchro-check function checks before closure of a circuit-breaker whether the electrical parameters of the two subnetworks are within the defined limits.

This check is necessary to limit transient phenomena on connection. For this purpose, the voltage of the feeder to be switched is compared with the busbar voltage for magnitude and phase angle, and frequency values.

For safety and cost reasons, a voltage transformer is rarely mounted directly on a busbar in modern systems. To determine the voltage on the busbar, a reference bay is selected by application software. The bay control unit (BCU) in this reference feeder switches the voltage to a ring line via a relay.

This ring line distributes the voltage to all bays and the BCU in the feeder to be switched picks off the voltage from the ring line. Now, all necessary information is available and the BCU autonomously checks whether the synchro-check conditions are fulfilled.

If the voltage amplitude, angle, and frequency differences are within the defined limit values, release is performed by the synchro-check function and the circuit-breaker closes.

Configuration for the distributed synchro-check
Figure 1 – Configuration for the distributed synchro-check

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1.1 Conventional concept

Implementation of the distributed synchrocheck function with digital control technology has been state of the art for many years.

In most substations with this functionality, the logic for determining the reference bay is implemented centrally in the station control unit.

This means the control at station level issues a command to close the circuit-breaker of a bay A. This command is received in the station control unit and the reference bay is selected in centralized logic that takes account of the relevant position indications and information items. Then the station control unit sends a command to the selected BCU in the reference bay to close the ring line relay.

The BCU of bay A can then run the synchrocheck.

Command sequence in the conventional concept
Figure 2 – Command sequence in the conventional concept

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1.2 Concept using peer-to-peer communication

Since the introduction of IEC 61850, a new communication service has been available for efficient distribution of information between devices of the bay level.

The application described here shows how the GOOSE (generic object-oriented substation event) mechanism can be used to advantage.

This represents a decisive change as compared with the conventional, centralized concept. Having received the command from the control point with switching authority, the BCU distributes the information “Reference bay search” to all other BCUs in a GOOSE telegram. The same logic to determine the reference bay runs in parallel in all BCUs.

As in the conventional concept, the logic considers the position indications and additional information items in determining whether each feeder can be used as the reference bay. The non-bay-specific data that is required for selection is also exchanged among the BCUs in GOOSE messages.

In typical substations, several bays are usually suitable for use as reference bays. A single reference bay is selected by taking into account a previously defined sequence in the local logic. The BCU that is located in a reference bay due to the topology information and is at the head of the sequence sends the “Reference bay found” message to all other BCUs in a GOOSE telegram and connects the voltage via the ring line relay.

The ensuing test of the synchro-check conditions in the BCU of bay A and release of the control command is performed in the same way as in the conventional concept.

Sequence when peer-to-peer communication is used
Figure 3 – Sequence when peer-to-peer communication is used

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1.3 Benefit of the solution

Migrating the logic function from the BCU to the bay level improves the availability of the solution. Depending on the level of system availability required, redundant implementation of the station control unit can be dispensed with.

If one BCU fails, the BCU with the next highest priority is used as the reference bay. The synchro-check function is available for switching via the remote interface, the station control, and also for switching from the local control. This ensures reliable and synchronous switching in all operating cases.

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2. Mesh station automatic switching

A mesh station is a type of primary substation configuration that is economical in its use of circuit-breakers.

Although there are many variants, the typical configurations are single switch and four switch meshes, the names inferring the number of circuit-breakers used to accomplish the layout.

A mesh corner is where busbars connect circuit-breakers, transformers and feeders – a four switch mesh has four mesh corners, whereas a single switch mesh has 2 corners. Feeders or transformers connect to mesh corners via motorized disconnectors to provide individual isolation and it is possible to have more than one transformer connected to the mesh corner.

A mesh corner would typically have a feeder and up to two transformers connected – this means with four circuit-breakers, a station could be built with 4 feeder and 8 transformer circuits.

If a circuit-breaker requires maintenance, it may be taken out of the mesh without any loss of supply.

Mesh station
Figure 4 – Mesh station

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2.1 Mesh station automatic switching

Following a trip event for the mesh to ‘selfheal’, an automatic switching and delayed automatic reclose (DAR) system is required.

For example, for a feeder fault, all circuit-breakers connected to the feeder’s mesh corner must trip, including any transformer low-voltage circuit-breakers and remote substation circuit-breakers through intertrip signalling.

How does it work? The mesh station circuit-breakers have priorities and dead timers, so after the fault a mesh circuit-breaker will attempt closure which, if successful, will result in all other circuit-breakers closing in a controlled sequence.

If the first circuit-breaker to automatically close trips then the feeder is deemed to have a persistent fault and the mesh DAR system opens the feeder disconnector at both ends of the circuit – after the feeder has been removed from the mesh corners, the mesh circuit-breakers commence automatic reclosure.

For transformer faults, once circuit-breakers have tripped, the transformer is automatically isolated by opening its disconnector before the mesh circuit-breakers reclose in their sequence.

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2.2 The solution

A solution with one BCU per mesh corner was developed. This gave the benefits of reduction of installation costs and using a future proof industry standard rather than a bespoke solution.

The automatic switching and delayed automatic reclosure functions were developed using a graphical logic tool which was used to diagnose the bay control units. A test system shows a single line diagram of the substation from which switchgear positions can be manually changed, analog values controlled and protection events signaled.

The visualization interfaces to PROFIBUS input/output devices which are in turn connected to the bay control units being tested. The test system responds to events, i.e. simulates disconnector opening/closing and allows test sequences to be easily created and replayed for repeatable testing.

Using this test system, the specific functioning of the delayed automatic reclose (DAR) function can easily be verified in the BCUs and there is no further obstacle to successful commissioning of the substation.

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The examples discussed show that IEC 61850 offers a wide range of application possibilities exceeding by far current applications.

A thorough analysis will reveal the advantages of IEC applications. However, it is for the operator of the substation and its supplier to decide on the degree to which alterations of existing concepts and systems should be made.

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Reference // Efficient Energy Automation with the IEC 61850 Standard Application Examples by Siemens

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


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