Simpler Data Center Bus Protection with GOOSE
Achieve the same level of protection more easily and without common limitations with a new method for protecting data-center buses from outages.
There are a virtually unlimited number of scenarios that can result in a data center power bus outage. Internal bus faults can quickly cause severe damage due to the high resulting currents. Traditional bus protection schemes include high- and low-impedance bus differential, and switchgear arc flash detection. These bus differential schemes are widely used for substation and switchgear buses including single bus, transfer bus, and breaker-and-a-half bus arrangements. Arc-flash detection is used only in enclosed switchgear. Each of these protection schemes provides a level of protection but is hampered by limitations.
Traditional protection schemes
In the low-impedance approach, the CT currents flow into a junction point where they are monitored by an overcurrent relay. Due to possible CT saturation during an external fault, the relay must be desensitized in order to operate correctly. A time-delay element may also be required to suppress tripping. Compared to other conventional schemes, this method is typically less sensitive and may be slower to respond to a fault.
The high-impedance approach adds a high-impedance relay. As with the low-impedance scheme, voltage across the high-impedance component will normally be close to zero. During internal bus faults, high current in the high-impedance component creates a large voltage that will be detected by the relay, resulting in a trip. This approach offers both higher sensitivity and speed compared to the low-impedance method.
Arc-flash detection relies on relays and either individual optical sensors or sensor ropes to detect the light of an arc flash. This scheme provides a high-speed response but may not be sufficiently sensitive to low-impedance bus faults.
An additional drawback to both impedance- and arc-flash-based schemes is that they can’t easily accommodate system expansions or increases in system fault current.
GOOSE-enabled bus protection
An improved approach eliminates the dedicated bus protection relay, relying instead on each breaker’s relay, such as the feeder protection relay or breaker failure relay. A “master” relay performs the bus-protection role, with another relay assigned as a backup to the master. All relays involved in bus protection communicate via IEC61850 GOOSE (Generic Object Oriented Substation Event) protocols.
IEC61850-compliant relays are usually equipped with multiple Ethernet ports with Parallel Redundancy Protocol (PRP). This enables double-star or self-healing ring network topologies that effectively achieve 100% communication availability. Of the two, the double-star creates less network disturbance during future expansions, offers faster trouble shooting, has minimum communication latency, and is easier to maintain.
Reducing the cross wiring of related relays means huge savings in engineering, installation labor/time, and materials associated with traditional copper wiring.
New versus existing schemes
The GOOSE-enabled scheme has been proven to reliably protect the bus against internal and external faults, and accomplishes this at a lower cost than traditional methods. For new installations, costs are reduced by avoiding the expense of additional, protective relays. Lifecycle costs are reduced through reduced copper-wire installation and maintenance. Long-term, the new scheme provides a much simpler path to future expansions or modifications.
This new scheme can be thought of as a no-cost, parallel bus-protection layer in addition to existing high- or low-impedance differential relays. It is appropriate where the following conditions exist:
- Circuit breakers lacking a dedicated CT for a differential relay
- Existing switchgear lacking space for a stand-alone differential relay
- Where wiring a new/additional standalone differential relay would be difficult
- Supplemental switchgear protection is needed
The core logic of the scheme is simple yet effective for protecting data-center substation and switchgear buses with one or multiple contributing sources. In data centers, where modifications and expansions are common, the logic can be easily and affordably modified to adapt to changes in the power system, or when adding/subtracting contributing circuit breakers.
For additional information on this topic, including technical details, request a copy of the white paper “Bus Bar Protection: A New and Reliable Approach”.