The size of the Class 1 event buffer in the IED is 500 events. The IEC 60870-5-103 standard does not define any method of indicating Class 1 event buffer overflows. Instead, the standard suggests that the master performs a general interrogation integrity scan every 15 minutes (or more), to detect indications that have not been updated spontaneously.
The IED contains a special overflow Class 1 ASDU 1 indication. The default setting of this overflow indication is FUN = 10, INF = 255. The FUN/INF definition can be changed if required. This object creates an ON event when the overflow occurs. It is also possible to take the overflow operation completely out of use and operate without any overflow indication as the IEC 60870-5-103 standard defines. The IEC 60870-5-103 instances can also be configured differently.
- Class1OvInd n: takes the overflow object into use. Settings: No indication, Both edges, Rising edge.
- Class1OvFType n: defines the Function Type (FUN) for the overflow indication.
- Class1OvInfNo n: defines the Information Number (INF) for the overflow indication.
- Class1OvBackOff n: defines how many events have to be emptied from the Class 1 event buffer until new ones are collected. Default setting is “500” (meaning the whole event buffer must be emptied).
The overflow operation preserves the oldest events in the buffer. The overflow Class 1 event is given the time stamp of the indication that first created the overflow situation. In other words, the indication event is lost and replaced with the Class 1 overflow event.