The master should initiate a GI always after the IED has reported a Class 1 event buffer overflow. The IED starts then to send GI data through the Class 1 event buffer. As the standard defines, new events always have higher send priority than GI data in the IED’s Class 1 buffer. The standard also defines that all data that are subject to GI is sent by the IED.
Optimization of GI data is a non-standard feature. As default the Optimize GI n parameter is set to "Standard behaviour", meaning that the GI cycle operates as defined by the standard. GI optimization strives to send less data to the master through the Class 1 report. The GI optimization in the IED is based on two facts:
- It is enough to send a certain Class 1 data once to the master after a GI initiation. This could be either the GI data report or a spontaneously updated data report. In either case the master has the true position of the Class 1 data in its database.
- The IED also remembers which specific Class 1 data objects changes that has overflown. After the GI initiation only these marked Class 1 data objects are reported through the GI cycle.
| Parameter value | Description |
|---|---|
| Standard behaviour | No optimization. |
| Skip spontaneous | Enables the IED to not send GI data for those objects that already have been spontaneously updated by the IED (that is, sent as Class 1 events) after the initiation of a GI. |
| Only overflown | Enables the IED to send only the Class 1 data that it knows have overflown in the Class 1 buffer. The first GI cycle initiated after a master Reset CU or Reset FCB does not use this feature, that is, the IED keeps track of that it actually has reported a value at least once to the master since the last reset. |
| Combined | Combines the two optimization features explained above. |