Integrating an Open-Source IEC 61850 MMS Client with Commercial Protection Relays: Architecture, Engineering Workflow and Secondary-Injection Validation in a 150 kV Line-Bay Testbed

Open-source IEC 61850 software is widely used in smart-grid research, but it has mostly been validated against software-emulated servers. This paper integrates OpenPLC61850, an open-source programmable logic controller (PLC) featuring an integrated Manufacturing Message Specification (MMS) client, with the Siemens SIPROTEC 5 distance (7SX85) and backup overcurrent (7SJ82) relays of a 150 kV transmission-line bay. The client runs in a virtual machine on the station bus and is engineered through a reproducible two-stage workflow that combines offline tagging of Substation Configuration Language (SCL) files with online data-set and report engineering. Seven interoperability gaps were identified and resolved, among them a firmware-specific suffix in report names, data-set granularity, double-point decoding, device-side switching authority and setting-group control through the Setting Group Control Block, which SCL-based tools do not expose. The client was extended with select-before-operate breaker control and remote setting-group switching. Protocol traces and secondary injection with an OMICRON CMC 356 test set showed that, for both relays, an identical fault trips the relay in one setting group and not in the other, with the appropriate group selected by the PLC, while the operation times agree with the manufacturer’s specifications. The results establish a reproducible path for using open-source clients with commercial protection devices.