The IEC 60870-5-103 protocol is defined for a single-function protection device with limited set of functionalities. Problem that arises in a multiple functionality IED are mainly related to the larger amount of Class 1 events typically generated during a fault. Modern multifunctional IEDs may create up to 20-40 times more events during a fault compared to single function devices that were the basis for the IEC 60870-5-103 standard. IEC 60870-5-103 has some limitations:
- The protocol is defined to be used on serial interfaces (max. allowed baud rate 19200 bauds).
- The protocol can only transfer one change event per Class 1 poll.
- Unbalanced communication: the master must poll all IEDs in the network cyclically which means that the master cannot remain polling out events from a certain IED for a very long time, since this degrades the overall response time from the whole substation.
The IED includes some possibilities to fasten up and optimize the IEC 60870-5-103 communication. However, it is necessary to verify that these features are accepted by the network and the IEC 60870-5-103 master used.
- Remove unnecessary Class 1 objects. Even if the IED can provide a lot of valuable information, it is not feasible to send everything on slower serial links.
- Remove falling edge events for selected Class 1 objects.
- Serial communication speed can be increased up to 115.2 kbauds. However, observe that all IED’s on a multidrop link must support the same communication speed.
- GI data optimization which means that not all data is sent as GI data in a GI cycle.