Substations are moving to IEC 61850 process buses. Must the new test set speak “digital”?

Classical relay testing injects analog quantities: 100 V voltage and 5 A (or 1 A) current waveforms into the relay terminals, where the relay's own input transformers digitize them. In an IEC 61850 process-bus substation,  the digitization happens much earlier - in the merging unit next to the instrument transformers - and the relay receives measurements as optical Ethernet frames instead of copper currents and voltages.

Sampled Values (SMV 9-2LE) - current and voltage samples delivered as optical Ethernet frames; the test set must generate sampled values that behave exactly like the merging unit's output.

GOOSE messaging - trips, blocks and interlocking travel over the station bus as GOOSE telegrams; the tester must send and receive GOOSE to verify the relay's logic and its interface with the bay controller.

Analog capability remains essential - most installed relays are still conventional. A future-proof test set therefore offers both worlds: analog 100 V/5 A outputs for the installed base and optical SMV/GOOSE interfaces for digital bays - the same set migrates with the substation.

Configuration & tooling - digital testing relies on SCL engineering files (SCD/CID); the software should import the substation configuration directly to bind channels and publish GOOSE correctly.

Buy a set that outputs analog 100 V / 5 A for today's relays and optical GOOSE/SMV for tomorrow's process-bus bays - one instrument that migrates with your substation.