Protecting from Disruptive Arc Flashes

High Hazard levels on outdated equipment introduced unnecessary operational and personnel safety issues.

Challenges

With Arc Flash Hazard levels well over 100 cal/cm2 on all the 4160V Switchgear Auxiliary Systems, our client was at risk of catastrophic equipment damage and life-threatening electrical hazards.

Working with the original electro-mechanical relays or tightening intervals would undermine system reliability and would be limited by technology.

A study was needed to plan a relay upgrade on every cubicle to provide multi-level protection.

Solutions

Enginuity Global applied new Schweitzer protective relay technology for a permanent, modern solution that reduced the Arc Flash Hazard level below 8 cal/cm2.

Plus — as a bi-product of the networking — these relays could also be connected to the plant SCADA/DCS system for power monitoring, alarming, event viewing, and engineering modifications.

Implemented a “Fast Bus” system, which operates like Zone-selective Interlocking by using inter-relay communication to determine fault locations and trip within 8 cycles for a fault on the switchgear bus.

Achieved by networking together the SEL-751, SEL-787, and SEL-710 relays over copper ethernet. We used the IEC61850 protocol to manage a sensitive overcurrent pickup through the main relay and the feeder relays.

If both relays pick up, the bus trip is blocked and the feeder relay can operate under normal overcurrent protection. If only the main relay picks up, the main trips immediately.