The abstract model for the transmission of sampled values is used for the digital output of voltage and current transformers. IEC 61850-9-1 seems to fulfill all the requirements to connect one measuring point (voltage and current of a three-phase system) to protection, control and metering. Why should we use IEC 61850-9-2 or a bus topology combining IEC 61850-9-2 with IEC 61850-8-1?

IEC 61850-9-1 is an approach that remains simple both with regard to the network topology as well as with regard to the configuration capabilities of the devices. This will facilitate the introduction of the new technology. On the other side, there are some good reasons that may require the use of a more flexible approach like IEC 61850-9-2 or a bus topology combining IEC 61850-8-1 and IEC 61850-9-2 ("process bus").

• Information content: using the same network topology as with IEC 61850-9-1 (point-to-point connections) additional data sets may be predefined and encoded according the specification in IEC 61850-9-2. An example of a requirement for additional datasets is the higher resolution and higher sampling rate used for power quality metering.
  
• Configuration capabilities: still using the same network topology as with IEC 61850-9-1, but implementing the complete mapping according to IEC 61850-9-2. This allows for online verification and configuration of the communication behavior.
  
• Network topology: replace the point-to-point connection by a switched Ethernet network. Data sets as defined both in IEC 61850-9-1 and in IEC 61850-9-2 may be supported. A network topology may reduce the complexity of the wiring.
  
• Device diagnostic: implementing a complete object model and additional services according to IEC 61850-8-1 leads to additional capabilities like device diagnostic and monitoring, download of SW upgrades and configuration files.
  

The items above may be used for a stepwise migration from IEC 61850-9-1 to IEC 61850-9-2 or a process bus. A process bus approach will be the result of implementing all steps. Such an approach will definitely reduce the complexity of the wiring between switchgear, current and voltage transformers and protection, control and metering devices.

The following figure shows the possible mappings that may be used in combination over the same wire.

Keywords:
communication network topology, mappings, part 8, part 9, sampled values

provided by Christoph Brunner
ABB Switzerland Ltd
Convenor of TC57 / WG12