In energized substation testing practice, the safest state is Test/Blocked.
Interaction with the test bit
Processing also depends on the received quality field:
• In On or Blocked: data with test bit = TRUE is not processed;
• In Test or Test/Blocked: test data is accepted;
• In Off: nothing is processed.
Hierarchy matters
IEC 61850 defines a hierarchy between Logical Device and Logical Node. If a higher level is in Test, the lower levels are restricted to compatible modes (Test, Test/Blocked, or Off).
Essential best practices
• Block outputs during testing;
• Ensure that only IEDs in simulation process test frames;
• Prepare the substation network for the additional traffic coming from the test devices, i.e., traffic with simulation frames (double bandwidth).
When properly applied, the simulation feature allows testing the complete logic without interrupting service, one of the great advantages of digital substations.
