Overview
IEC TR 61850-90-20:2025 is a Technical Report from IEC TC57 that documents practical use cases of redundancy in power utility automation systems. The report focuses on duplication of function and devices and on redundancy of information flow at the message level. It describes common redundancy schemes (standby, active‑active, modular, 1:N, partial) and illustrates them with state diagrams and collaboration figures for real-world scenarios. Functional safety is explicitly out of scope, and the report is not a design handbook - design guidance is left to textbooks and engineering practice.
Key technical topics and requirements
- Redundancy schemes: definitions and examples of cold, warm and hot standby, 1:N, active‑active (hot‑hot), load‑balanced active‑active, and dual/triple modular redundancy.
- Device redundancy: use of physically separate devices providing the same function so failover minimizes downtime and avoids data loss.
- Message‑level redundancy: handling duplicated information flows to and from redundant devices, including implications for receivers and state management.
- Communication services referenced: use of IEC 61850 services for redundant communication - notably MMS (IEC 61850‑8‑1) for supervision and configuration, GOOSE and SV (IEC 61850‑9‑2) for time‑critical, unacknowledged messaging.
- Use cases: specific sequences and interaction diagrams for startup, state changes, redundant reporting, and service‑on‑demand scenarios involving redundant clients and servers.
- Operational considerations: techniques for switching application entities off to prevent conflicting outputs, and supervision approaches for unacknowledged services where sender awareness is limited.
- Scope limitations: not a guideline for redundancy system design; some figures omit electrical wiring or redundant coils where irrelevant to the use case.
Practical applications
- Provides a catalogue of redundancy use cases that can be used to:
- Inform requirements and test scenarios for substation automation projects.
- Define expected behavior for redundant clients and servers in IEC 61850 implementations.
- Support interoperability testing, commissioning plans and vendor acceptance criteria.
- Particularly relevant to substation engineers, system integrators, utility automation architects, test engineers, and equipment vendors who implement or validate redundancy behaviors and message handling.
Related standards and references
- IEC 61850 series (communication for power utility automation)
- IEC TR 61850‑90‑2 (background on IEC 61850 between substations and control centres)
This Technical Report is intended as a practical reference for implementing and testing message‑level redundancy in IEC 61850‑based automation systems, supporting higher system availability and resilient communication architectures.