Validating mission-critical ethernet networks for protection, automation, and control applications

The communications standard IEC 61850-5 identifies fast messages that perform high-speed automation, protection, and interlocking to meet or exceed a transmission time of 3 milliseconds as Type 1A, Performance Class P2/P3. Modern microprocessor-based devices and Ethernet networks routinely meet this requirement when everything is working as expected. One of the most important acceptance criteria (and perhaps least understood) is the maximum transmission time when unexpected things do happen and messages are delayed. Because not all paths in an Ethernet network perform the same, this paper introduces path performance classifications that illustrate the minimum and maximum transfer times between two devices. The telecommunications performance standard IEC 60834-1 is commonly used to evaluate point-to-point high-speed automation and interlocking. It describes the overall operating time between the instant of the change of state at the command input on the source device and the instant of the change of state at the command output on the destination device. This includes propagation time and any additional delays. IEC 60834-1 further defines transmission dependability as the ability to receive each command message within the fixed actual transmission time defined by the application, in this case 3 milliseconds. IEC 61850-5 specifically states that testing and verification of the complete transfer time must be performed during site acceptance testing using the physical devices and network equipment. Methods to test and validate message transmission during normal Ethernet packet delivery as well as during path failure are introduced in this paper based on both Rapid Spanning Tree Protocol (RSTP) and Parallel Redundancy Protocol (PRP).