Communication Latency Calculation in Complex IEC 61850 Based Substation

IEC 61850 has become the de-facto standard to follow for communication in a substation. The use of IEC 61850 based Client-Server communication service and Publish-Subscribe communication-service, which include Generic Object Oriented Substation Events (GOOSE) and Sampled Values (SV) have aided in the deployment of a more communication-intensive architecture in substation when compared to a non-IEC 61850 based substation. Performance of Protection and Control Systems (PACS) is now additionally influenced by the communication system in a substation. The fault-clearance time in an IEC 61850 based substation now includes the operating time of the protection Intelligent Electronic Device (IED) relay and the communication delay between protection IED and a Switchgear Control Unit (SCU). This paper proposes a method to calculate communication latency in a complex IEC 61850 based substation. It is vital to determine communication latency for understanding the overall performance of PACS. Latency calculation is also essential to optimize PACS design to achieve the requirements of various applications. The communication latency calculation method proposed in this paper uses the Substation Configuration Description (SCD) file to accurately determine the communication path and data flow between a publisher and subscriber. The method also calculates the coincident messages or traffic in the communication path between publisher and subscriber, which aids in determining the latency accurately.