A question was asked about the processing time and transfer time in IEC 61850, and whether the processing time was included in the standard. My response was:
The test specification in section 7.2.1 of IEC 61850-10 breaks down the total transfer time into:
- ta: the time required for the sending device to transmit the process value,
- tb: the time required for the network to deliver the message, and
- tc: the time required for the receiving device to deliver the value to its process logic.
It then states:
The measured output (input) latency shall be less than or equal to 40 % of the total transmission time defined for the corresponding message type in IEC 61850-5 Subclause 13.7. NOTE 1 The value of 40 % on each end of the connection leaves over 20 % for network latencies.
This maximum time applies mainly to the message types 1 (Fast messages) and 4 (Raw data messages); these messages make use of the priority mechanisms of the networks components defined in IEC 61850-8-1 and IEC 61850-9-2. Messages of type 2 may be assigned to a high priority.