IEC 61850 Testing: A Practical Guide for Protection Engineers

IEC 61850 has transformed substation design. The shift from copper wiring to Ethernet-based communication brings significant benefits in reduced cabling, improved interoperability, and enhanced monitoring. But it also changes how we test protection systems. This guide explains what protection engineers need to know to test relays in an IEC 61850 environment.

The Three Key Components

GOOSE (Generic Object-Oriented Substation Event)

GOOSE messages replace conventional hard-wired binary signals between IEDs. A trip signal, an interlock, a breaker status indication — all can be transmitted as GOOSE messages over the station bus. GOOSE is multicast, publisher-subscriber, and extremely fast (typically < 4 ms).

For testing, this means your test set must be able to:

• Subscribe to GOOSE: Monitor the relay’s GOOSE outputs to detect trip commands, start signals, and alarms — replacing the binary input monitoring used in conventional testing.
• Publish GOOSE: Simulate GOOSE messages from other IEDs — for example, publishing a breaker status GOOSE to test the relay’s reclosing logic, or a blocking signal to test a busbar protection scheme.

Sampled Values (SV)

Sampled Values (IEC 61850-9-2LE) digitize CT and VT outputs at the merging unit and stream them as Ethernet packets — typically 4,000 samples per second for 50 Hz systems. The relay receives SV streams instead of analog secondary signals.

Testing a relay that subscribes to SV requires a test set that can publish SV streams. The VT-RP300, for example, generates calibrated test waveforms, encodes them as SV packets, and streams them to the relay under test. The relay responds as if it were receiving real measurements from a merging unit.

MMS (Manufacturing Message Specification)

MMS provides client-server communication for SCADA and engineering access. While not directly involved in protection tripping, MMS is used to read event records, disturbance recordings, and settings during testing. Your test software should be able to read MMS data to automatically extract the relay’s event report after each test shot.

Three Testing Scenarios

Conventional Testing (No Process Bus)

The relay has analog CT/VT inputs and uses GOOSE for inter-device communication only. Test approach: inject analog currents and voltages normally; subscribe to GOOSE outputs to detect relay response.

Hybrid Testing

The relay uses analog inputs for protection but GOOSE for all binary I/O. Test approach: inject analog signals; subscribe to outgoing GOOSE and publish incoming GOOSE to simulate the full scheme.

Full Digital Testing (SV Subscriber)

The relay has no analog inputs — protection functions use SV streams only. Test approach: stream SV packets with the test waveforms; monitor GOOSE and MMS for the relay response.

Practical Tips for IEC 61850 Testing

1. Get the SCL files first: Request the Substation Configuration Description (SCD) file from the system integrator. It contains the GOOSE and SV configuration for every IED in the substation. Import it into your test software to automatically configure communication parameters.
2. Test one IED at a time: Just like in conventional testing, isolate the IED under test. For digital schemes, this means ensuring your published GOOSE and SV messages don’t interfere with other IEDs on the network. Use VLAN segmentation if necessary.
3. Verify the communication before testing protection: Confirm that your test set can subscribe to the relay’s GOOSE outputs and that the relay subscribes to your SV stream. A communication failure during a test is frustrating and wastes time.
4. Document GOOSE subscriptions: In a digital scheme, knowing which IEDs subscribe to which GOOSE messages is essential for understanding protection dependencies. Build a subscription matrix as part of your test documentation.

This article was prepared by the VA-TEK engineering team. Learn more about our VT-RP300 with IEC 61850 support.