Redundancy Protocols for IEC 61850: PRP, HSR, and DLR
Introduction
IEC 61850 is a global standard for communication in electrical substations and power automation systems. To ensure high availability and fault tolerance, redundancy protocols such as Parallel Redundancy Protocol (PRP), High-availability Seamless Redundancy (HSR), and Device Level Ring (DLR) are employed. These protocols minimize network downtime and ensure seamless data transmission in case of failures.
1. Parallel Redundancy Protocol (PRP)
Overview
PRP is a redundancy protocol defined in IEC 62439-3 that provides seamless redundancy by duplicating network traffic over two independent Ethernet networks (LAN A and LAN B). This ensures zero recovery time in case of a network failure.
Key Features
- Operates at Layer 2 (Data Link Layer).
- Uses two independent and parallel networks for redundancy.
- Packets are sent simultaneously over both networks.
- The receiver accepts the first-arriving packet and discards the duplicate.
- Provides zero recovery time (0 ms) upon link failure.
- No requirement for reconfiguration or path recalculation after a failure.
Use Cases
- Substation automation under IEC 61850.
- High-reliability industrial control systems.
- Mission-critical power grid protection and monitoring.
Advantages
- Instant failover without packet loss.
- No need for specialized switches, as redundancy is handled at the end devices.
Disadvantages
- Requires two completely independent network infrastructures.
- Increased network load due to duplicated traffic.
2. High-availability Seamless Redundancy (HSR)
Overview
HSR is another redundancy protocol defined in IEC 62439-3, designed for ring topology networks. Unlike PRP, which uses two separate networks, HSR enables redundancy within a single ring network by forwarding packets in both directions.
Key Features
- Operates at Layer 2 (Data Link Layer).
- Uses a ring topology where each node forwards frames in both directions.
- Every frame is sent in duplicate, traveling in opposite directions.
- The destination node receives the first copy and discards the duplicate.
- Zero recovery time (0 ms) upon link failure.
- Eliminates the need for additional network switches.
Use Cases
- Substation automation systems (IEC 61850-9-2 sampled values and GOOSE messages).
- Industrial automation requiring real-time communication.
- High-reliability smart grid infrastructure.
Advantages
- Does not require additional infrastructure beyond ring topology.
- Zero failover time ensures uninterrupted communication.
- More cost-effective than PRP as it uses a single network.
Disadvantages
- Not suitable for large, complex networks with multiple paths.
- Requires HSR-compatible devices.
- Can lead to increased network congestion due to duplicate packets.
3. Device Level Ring (DLR)
Overview
DLR is a redundancy protocol developed for EtherNet/IP networks, commonly used in industrial automation. It provides high-speed failover in ring networks by utilizing ring supervisors to detect and reroute traffic when a link failure occurs.
Key Features
- Works on Layer 2 (Data Link Layer) for rapid network recovery.
- Designed primarily for industrial Ethernet applications.
- Uses a Ring Supervisor node to monitor network health and reroute traffic if a failure occurs.
- Provides recovery times of less than 3 ms.
Use Cases
- Industrial automation and factory automation networks.
- Manufacturing systems using EtherNet/IP.
- Robotics and motion control systems.
Advantages
- Fast failover mechanism (<3 ms recovery time).
- Cost-effective for small and medium-sized industrial networks.
- Compatible with standard Ethernet switches.
Disadvantages
- Not designed for large-scale power substation automation like PRP and HSR.
- Requires a Ring Supervisor node for efficient operation.
Comparison Table of Redundancy Protocols
| Feature | PRP | HSR | DLR |
|---|---|---|---|
| Network Layer | Layer 2 | Layer 2 | Layer 2 |
| Topology | Two independent LANs | Ring | Ring |
| Recovery Time | 0 ms | 0 ms | <3 ms |
| Packet Duplication | Yes | Yes | No |
| Infrastructure Requirement | Two separate networks | Ring network | Standard Ethernet hardware with a Ring Supervisor |
| Application | Power substations, critical automation | Power automation, smart grids | Industrial Ethernet, automation |
| Complexity | High | Medium | Low |
Conclusion
PRP, HSR, and DLR are crucial redundancy protocols ensuring high availability and reliability in industrial and power automation networks.
- PRP is ideal for mission-critical applications requiring absolute network reliability with no failover time.
- HSR is a cost-effective alternative for redundancy in ring networks with zero failover time.
- DLR is best suited for EtherNet/IP-based industrial networks requiring fast but not seamless recovery.
The choice of protocol depends on the application’s fault tolerance requirements, topology, and infrastructure constraints. By implementing the right redundancy protocol, industries can ensure continuous operation, minimize downtime, and enhance system resilience.
