High-Availability Industrial Network Design with HSR and PRP for Electrical Substations

The Reliability Challenge in Electrical Substation Networks

Electrical substations are the nervous nodes of any power system. In practice, they control the flow of electricity powering entire cities, industries, and hospitals. Any single second of communication interruption between protection devices can cause widespread blackouts or catastrophic damage to expensive transformers. Historically, engineers used dedicated serial cables or traditional Ethernet networks that suffered from delays and single points of failure. If a cable broke or a switch burned out, the control room went temporarily blind, which is unacceptable in the modern power sector.

To solve this critical problem, the industry adopted the international standard IEC 61850, which digitized the substation using Ethernet. However, common commercial protocols like RSTP (Spanning Tree Protocol, a mechanism that blocks redundant ports to prevent network loops) take precious seconds to recalculate alternative routes after a failure. In power systems, seconds are an eternity. Engineering needed a zero-recovery-time mechanism where the loss of a physical path creates no perceptible delay in data packets. This is the scenario where seamless redundancy protocols known as PRP and HSR come into play.

Understanding How the PRP Protocol Works in Duplicated Networks

The PRP (Parallel Redundancy Protocol) solves the network failure problem by duplicating the physical infrastructure. In practice, imagine you need to send an urgent letter and, to ensure it arrives, you write two identical copies and dispatch them through two completely different and independent delivery companies. If one company loses the package or the delivery truck breaks down, the second letter arrives intact and at the exact same moment. This is precisely what PRP does with Ethernet data packets inside the substation.

The originating device, called a DANP (Dual Attached Node for PRP), takes the original network packet, adds a small timestamp and a sequence identifier, and sends it simultaneously across two separate, complete local area networks known as LAN A and LAN B. On the other side, the receiving device listens to both networks. The first packet that arrives is accepted immediately for processing, while the second duplicate packet (arriving shortly thereafter through the other network) is transparently discarded. In practice, if LAN A suffers a fiber optic cut or a switch failure, LAN B delivers the data without any delay, guaranteeing zero interruption time.

Exploring the Ring Architecture of the HSR Protocol

While PRP duplicates the entire physical infrastructure, requiring two switches and two cables for every point, HSR (High-availability Seamless Redundancy) takes a different approach based on a ring topology. In practice, think of a circular racing track where runners lap in opposite directions. If there is a hole in one section of the track, the runner going in the other direction can still complete the journey and deliver the message to the final destination without service interruption.

In HSR, each device connected to the network has two Ethernet ports and acts as a forwarding node, forming a closed physical ring. When an IED (Intelligent Electronic Device, a field computer specialized in protecting and monitoring electrical equipment) needs to transmit a message, it injects the data frame into both ports simultaneously. The frame travels around the ring in both clockwise and counter-clockwise directions. The destination device receives the first copy and uses it, while the second copy continues circulating until it is removed by the originating node to prevent infinite network traffic. If a cable breaks or a device fails, neighboring nodes detect the ring opening in microseconds and reflect the packets back, keeping communication intact.

Design Criteria and Choosing Between HSR and PRP

Deciding between implementing PRP or HSR in an electrical substation involves analyzing costs, cabling complexity, and project scope. In practice, PRP offers greater flexibility and easier maintenance in large installations because it relies on two independent, parallel Ethernet networks. You can use commercial switches as long as they support the performance and packet forwarding requirements demanded by substation standards, although final nodes must be PRP-compatible to duplicate messages.

On the other hand, HSR eliminates the need to buy twice as many switches and duplicate all fiber optic cable infrastructure across entire buildings, since the devices themselves form the logical and physical ring. However, HSR requires absolutely all equipment connected to the ring to have native HSR ports or the use of conversion devices called RedBoxes (Redundancy Boxes that allow traditional Ethernet equipment to connect to HSR or PRP networks). In the table below, we compare the main operational trade-offs between the two technologies to guide engineering decisions. To complement this implementation in production environments, see our related technical analyses on Fault Isolation and Recovery in High-Availability Ring Network Topologies and Signal Conditioning Circuit Design for High-Precision Industrial Transducers.

Final Considerations for Field Implementation

The successful deployment of high-availability networks with HSR and PRP requires rigorous planning, bench testing, and strict type approval from IED and switch manufacturers. In practice, the engineering team must map the traffic flow of GOOSE messages (Generic Object Oriented Substation Events, ultra-fast messages used for circuit breaker tripping) and Sampled Values, ensuring that bandwidth and QoS (Quality of Service, a mechanism that prioritizes critical packets on the network) are perfectly configured throughout the architecture.

Ultimately, investing in HSR and PRP infrastructures is not just a technical caprice, but an imperative necessity to meet modern reliability standards in the power sector. With the accelerated transition toward smart grids and fully digitized substations, the robustness of the communication layer becomes the foundation supporting the stability of society's entire energy infrastructure.