Migrating a substation from serial protocols such as IEC 60870-5-103, 101 or Modbus to IEC 61850 is planned by scenario: coexistence, with a gateway that translates the old devices; bay-by-bay replacement, as relays are changed; or a full migration in stages. What you gain is a common data model, GOOSE between bays and file-based engineering; what it costs is engineering, testing and managing a substation that will be mixed for years.
Why migrate
Many substations in service integrate their relays with serial protocols: IEC 60870-5-103 for protection, IEC 60870-5-101 toward the control center or Modbus in industrial plants. They work, but they have known limits: each manufacturer uses private parts of the protocol, interlocks between bays are hardwired, data arrives without a common model and every change requires editing address lists by hand.
IEC 61850 changes that scheme: a data model with standardized names, GOOSE to exchange signals between IEDs over the network, MMS for SCADA and engineering based on SCL files that describe the whole substation. The question is usually not whether to migrate, but how to do it without taking the substation out of service and without wasting equipment that still has service life left.
The scenarios
| Scenario | What is done | When it makes sense |
|---|---|---|
| Coexistence via gateway | Old relays keep their protocol; a gateway reads them and integrates them into the new system or SCADA | Relays with remaining service life; limited budget |
| Bay-by-bay replacement | Each bay moves to IEC 61850 when its relays are changed or its panels are reworked | Replacement plan over several years |
| Staged migration | First the station bus, gateway and SCADA; then the bays | Large substations that cannot be taken out of service |
| Full replacement | All relays, controllers and local SCADA at once | Equipment at end of life, or complete renewal |
In almost every case the substation will be mixed for a while: part on the old protocol, part on IEC 61850. The gateway is what makes that coexistence possible.
- 01SurveyInventory of devices, protocols, signals and remaining service life
- 02Target architectureNetwork, gateway, SCADA and which bays move to IEC 61850
- 03Scenario and stagesBay order, coexistence and required outages
- 04EngineeringSCD, gateway signal mapping and SCADA database
- 05TestingFAT and SAT for each stage, with the substation in service
What the survey checks
- The brand, model, firmware version and protocol of each relay and controller.
- Whether each relay accepts an IEC 61850 communication module or has to be replaced.
- The actual list of signals reaching SCADA and the control center today, compared with the documented one.
- The interlocks and inter-bay signals that are hardwired today.
- The condition of the panels, the wiring and the existing fiber network.
- The requirements of the utility or the control center receiving the signals.
What the gateway does during coexistence
The gateway reads the old relays over their protocol and their data appears in the new system. It can do this in two ways: presenting each old relay as a virtual IEC 61850 IED, or sending its signals directly to SCADA together with those of the new IEDs. In the other direction, toward the control center, the gateway also translates: IEC TS 61850-80-1 gives the guideline for passing IEC 61850 model data to IEC 60870-5-101 or 104.
What the gateway does not give is everything IEC 61850 offers. A relay read over IEC 103 does not publish GOOSE, so the interlocks and inter-bay signals involving it stay hardwired. Nor does it bring its full data model: only the signals the old protocol carries and that someone mapped. The guide on integrating the substation into the plant SCADA shows how that integration is organized.
What you gain and what it costs
You gain:
- A common data model for all new devices, with names that read the same in any brand.
- GOOSE for interlocks and inter-bay signals, with permanent link supervision.
- Engineering documented in the SCD, which makes extensions easier.
- Network speed and clearer communication diagnostics.
It costs:
- Engineering: the SCD, the gateway mapping and the SCADA database are built new or rebuilt.
- Testing: each stage requires FAT and SAT, with the substation in service.
- Training for operation and maintenance staff.
- Managing coexistence: for years there will be two ways of integrating devices.
Risks of mixed migrations
- IEC 61850 editions. New devices may be of a different edition from the existing ones, and the system configuration tool must handle both. Check it before buying, in each IED’s conformance documentation.
- Signals lost in translation. The gateway mapping may leave out qualities, time stamps or select-before-operate controls. It is reviewed signal by signal.
- Two sources of truth. If the old part is documented in lists and the new part in the SCD, neither represents the whole substation.
- Unplanned outages. Moving a bay from one scheme to the other requires disconnecting it; a badly thought-out order forces additional outages.
- Cybersecurity. The gateway and the new network open paths the serial system did not have. Segment from the design stage.
- Incomplete testing of the old part. When the gateway changes, the signals of the relays that were not touched also change path; they are tested end to end up to the control center, not only those of the new bays.
The link with relay replacement
Protocol migration usually goes hand in hand with protection modernization. The guide on replacing electromechanical relays with numerical ones covers the replacement decision; this one covers how to integrate the new with what remains. Both are planned together: the choice of new relays depends on the target communication architecture, and the bay order depends on the replacement plan.
How we help
A well-planned migration starts with the survey and the target architecture. We configure IEDs, switches and gateways remotely through our remote relay and communications configuration service, with a backup before and after every change. At Tiza Group we do the communications engineering to modernize medium, high and extra-high voltage substations and industrial plants, remotely: inventory, architecture, staged migration scenario and specification. We carry out the implementation (SCD, gateway and SCADA integration) through our control, protection and communications configuration. Tell us what you have today.
Related guides
- IEC 61850: overview
- IEC 60870-5-103
- IEC 60870-5-101
- Modbus RTU and TCP
- Replacing electromechanical relays with numerical ones
- IEC 61850 SCL files
- Media converters and serial device servers
- Mapping IEC 61850 to IEC 104 and DNP3 in the gateway
- Top-down and bottom-up IEC 61850 engineering: SSD to CID
- Configuration management of relay settings and the SCD
- Substation communications by voltage level
References
- IEC 61850-6, Configuration description language for communication in power utility automation systems related to IEDs.
- IEC TS 61850-80-1:2016, Guideline to exchanging information from a CDC-based data model using IEC 60870-5-101 or IEC 60870-5-104.
- IEC 60870-5-103, Companion standard for the informative interface of protection equipment.
- IEC 60870-5-101 and IEC 60870-5-104, telecontrol standards.
- IEC 61850-10, Conformance testing.
Frequently asked questions
Can I integrate IEC 60870-5-103 relays into an IEC 61850 system?
Yes, through a gateway or a controller that reads the relays over IEC 103 and presents them as IEC 61850 IEDs or sends them directly to SCADA. What you do not get that way is GOOSE between those relays or the full data model; for that, the relay or its communication module has to be replaced.
Should all relays be replaced at once to move to IEC 61850?
Rarely. The usual approach is to migrate by bay or in stages, taking advantage of relay end of life or extensions, with a gateway that keeps the old devices integrated in the meantime. A full replacement makes sense when most of the equipment is already at the end of its service life.
What is the risk of mixing IEC 61850 editions in the same substation?
That not all devices and tools interpret configuration files or test modes the same way. When extending a substation built on edition 1 with edition 2 devices, check which edition each IED supports and what the system configuration tool accepts before buying.