Protection network redundancy protocols

Historically, protection and control (P&C) schemes relied on hardwired communication: direct, point-to-point connections between Intelligent Electronic Devices (IEDs). The problem with that approach is it’s difficult to correct, modify, and update P&C logic.

Schneider Electric redundancy protocols whitepaper

Thankfully, Ethernet has emerged as the preferred means of communication. The IEC 61850 standard’s GOOSE (Generic Object-Oriented Substation Events) messaging has done away with such hardwiring and greatly simplified engineering changes.

GOOSE replaces traditional, hardwired IED coordination with station bus communications. When an event is detected, the IEDs use a multicast transmission to notify devices configured to receive those data. Performance requirements are stringent: For example, in order to trip a breaker without delay, no more than 3ms is allowed to elapse between when the event occurs and when the message is received.

Now, onto Ethernet redundancy. The point of redundancy is to make sure the network can survive a single failure by providing alternate data paths when a link fault occurs. There are two basic redundancy techniques that ensure data communication:

  • Active redundancy, where both links are active at the same time
  • Passive redundancy, where one link is active and the other is in standby mode

Because it takes longer to reconfigure the network in the event of a failure, passive redundancy is not suitable for high-availability environments like substations, metal refineries, chemical plants, and other electro-intensive applications.

IEC 61850 specifies two active redundancy protocols, Parallel Redundancy Protocol (PRP) and High Availability Seamless Redundancy Protocol (HSR). PRP and HSR both duplicate all transmitted data and enable zero switchover time if links or switches fail. Today’s IEDs embed these protocols in order to create higher-availability Ethernet networks that allow interoperability, zero ms reconfiguration time (with no loss of data), and full compatibility with IEC 61850 requirements.

Stay tuned for my next posts, where I’ll get into the details of both HSR and PRP. Or read my latest white paper for information about Optimizing Protection and Control Schemes Based on GOOSE Messages.

Schneider Electric CIRED 2015

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