Discover how merging units are transforming digital substations, improving reliability, and enabling smarter grid protection and control.
Merging units have emerged as a foundational technology in digital substations, changing the way electrical engineers approach grid measurement, protection, and control. Their role is central to the digital transformation of substations, offering both immediate and long-term benefits for power systems.
What is a merging unit, and why is it essential in digital substations?
A merging unit acts as a bridge between traditional analog signals from current transformers (CTs) and voltage transformers (VTs) and the digital world of modern substations. It digitizes these analog signals into precise sampled values, which are then transmitted over the process bus. This digital interface enables safer, more flexible, and scalable substation architectures by replacing bulky copper wiring with fiber or Ethernet connections.
How do merging units improve substation safety and efficiency?
By eliminating long copper runs, merging units reduce electrical hazards and simplify installation. This leads to faster commissioning, lower material and labor costs, and less panel complexity. Fiber or Ethernet connections also enhance immunity to electromagnetic interference, further improving operational safety and data integrity.
What role does the process bus play in this architecture?
The process bus is a high-speed digital communication channel that carries sampled values and control signals between merging units and intelligent electronic devices (IEDs). It enables real-time data sharing and supports interoperability, allowing multiple protection and control devices to subscribe to the same data stream. This approach streamlines substation layouts and makes future upgrades easier.
How do merging units ensure data accuracy and timing coherence?
Merging units rely on precise time synchronization, typically using IEEE 1588 Precision Time Protocol (PTP). This ensures that all sampled values are time-aligned across the network, which is critical for accurate protection and control functions. The use of sample counters and synchronization within a 1-second epoch guarantees consistency and reliability in grid operations.
What standards support merging unit deployment in substations?
IEC 61850, particularly the 9-2 and 61869 profiles, defines the communication protocols and data models for digital substations. These standards ensure that merging units and other IEDs from different manufacturers can work together seamlessly. Adhering to these profiles is key for interoperability and long-term system flexibility.
Where should merging units be used—new builds or retrofits?
Merging units are versatile and can be deployed in both greenfield (new) and brownfield (existing) projects. In new substations, pairing merging units with low-power instrument transformers (LPITs) creates a fully digital, compact process layer. In retrofit scenarios, standalone merging units allow the migration to a digital process bus while retaining legacy CTs and VTs. This makes them an attractive option for utilities looking to modernize without full equipment replacement.
What network design considerations are critical for merging unit success?
A deterministic, robust network is essential. Engineers should implement VLANs and Quality of Service (QoS) to manage traffic and ensure low latency for Sampled Values (SV) and GOOSE (Generic Object Oriented Substation Events) messages. Redundant time sources (grandmasters) and network redundancy protocols like PRP (Parallel Redundancy Protocol) or HSR (High-availability Seamless Redundancy) further enhance reliability.
How do merging units contribute to system observability and diagnostics?
Merging units provide quality flags, network diagnostics, and support centralized monitoring. This enhanced observability allows engineers to detect issues early, streamline testing and commissioning, and maintain high system reliability. Centralized analytics can also leverage these digital streams for deeper insights and predictive maintenance.
What are the keys to a successful merging unit strategy?
- Engineer robust time synchronization using IEEE 1588 PTP with redundancy.
- Design deterministic networks with proper VLAN and QoS settings.
- Align all IEDs to IEC 61850-9-2/61869 profiles.
- Establish a strong testing regime for SV accuracy, time alignment, GOOSE performance, and cybersecurity.
What future benefits do merging units unlock?
Merging units enable centralized protection schemes, advanced analytics, and easier substation reconfiguration through software. As substations become more software-defined, merging units serve as a flexible foundation for ongoing digital innovation and grid modernization.
Takeaway
Merging units are more than just digital interfaces—they are the backbone of scalable, future-ready substations. For any engineer planning a new digital substation or upgrading an existing yard, a well-designed merging unit strategy is essential for long-term success.
Bonus: Practical Tips for Working with Merging Units
- Always verify time synchronization status—loss of sync can compromise protection accuracy.
- Test SV and GOOSE performance under real network loads before commissioning.
- Use PRP or HSR for network redundancy to avoid single points of failure.
- Regularly review firmware updates for merging units to maintain cybersecurity.
- Tip: When migrating brownfield sites, pilot the process bus in a limited section before full deployment.