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The goal of arc-flash protection is to minimize the damaging effects of released energy. Such protection requires rapid and reliable communication among protection system components. Arcing faults in switchgear are rare events but their consequences can be severe. Characterized as electrical explosions, the radiation, heat, pressure waves, and flying particles associated with an arc flash can injure or kill personnel. These impacts can also destroy systems components, ruin switchgear, and trigger process outages that result in unanticipated expense.
In traditional, relay-based protection, arcing time consists of arc detection time, the protection relay’s operation time, the operation time of the device that extinguishes the arc, and the communication delay between components. The relay time is dominant delay in this traditional overcurrent protection. Either a circuit breaker (CB), fuse, or a short circuit device extinguishes the arc.
In more modern systems, protection is based on the simultaneous detection of overcurrent and light and provides an extremely fast response. In this scenario, the dominant component of the arcing time is the circuit breaker operation time (which is only tens of milliseconds) and relay time (which is even more miniscule).
When detecting an arcing fault via simultaneous light and overcurrent detection, the arc protection system sends a trip command to both the very fast short-circuit device and the appropriate circuit breaker. The short-circuit device then creates an intentional short circuit and extinguishes the arc within a few milliseconds by eliminating the voltage. Meanwhile, the circuit-breaker begins to operate and breaks the current after some tens of milliseconds.
Communication between various protection system components and communication to an upper-level control system are essential elements of more advanced arc-flash protection approaches. Within the realm of the IEC 61850 standard, Generic Object Oriented Substation Events (GOOSE) messaging protocol is what provides that rapid communication.
Studies have shown that GOOSE-based communication is as fast as direct serial communication. Because communication is Ethernet-based, all topologies supported by Ethernet are also supported by the new arc-flash protection system. This includes line, star, tree, and mixed or hybrid topologies. Looped connections are not supported by standard Ethernet, but new I/O units are equipped with special hardware that can accommodate ring networks.
An IEC 61850/GOOSE-based arc-flash protection system shares the same four basic components as the traditional proprietary systems: sensors, I/O units, central units, and cables. However, within the IEC 61850/GOOSE based context, the central unit is an optional component. The system architecture is distributed instead of centralized, and the system can operate perfectly without the central unit. This makes the system more robust. The central unit can, however, still serve as a centralized information collection and communication device that can be used as a gateway for relaying information to SCADA systems, for example.
Over the last 10 years, older arc-flash protection systems have proven to be robust, fast and reliable. However, the very fact that older systems are proprietary introduces a number of limitations. This is why the new IEC 61850- and GOOSE-based system was developed. This new system has been validated through testing. The Ethernet backbone provides open access to different network protocols while offering new freedom when designing networks. GOOSE communication over Ethernet is now proven to be fast enough to be applied to arc protection systems.
To learn more, visit our entire suite of arc flash control solutions.
