S&C Metal-Enclosed Switchgear — Versatility in Custom Applications.

A large Texas oil refinery needed to upgrade and expand their 12-kV distribution system. The refinery’s managers were well satisfied with the performance of their existing S&C Metal-Enclosed Switchgear. They anticipated using additional S&C gear for the project. But the new gear would need to fulfill some special features. Redundant main bus was to be connected to separate sources through up stream circuit breakers. In addition, the switchgear needed to be capable of clearing resistance-limited ground faults of up to 1000 amperes. Also, the gear had to feature arc-resistant construction.

S&C provided 13.8-kV Arc-Resistant Metal-Enclosed Switchgear having a short-circuit rating of 600 MVA. This unique gear minimizes potential injury to personnel standing nearby, should a fault occur within the gear.

The switchgear consists of nine feeder sections, each comprised of two bays. Each bay includes an S&C interrupter switch and switch operator, allowing the load to be powered from either bus — thus simplifying system maintenance. Each load is protected by S&C Fault Fiter® Electronic Power Fuses located in one of the feeder section bays. These fuses provide excellent coordination with downstream transformer primary fusing.

Each feeder section includes a specially designed relaying scheme, which detects downstream resistance-limited ground faults and sends an “open” signal to the switch operator of the switch serving the load. The relaying scheme includes a time delay. If the ground fault is cleared by a downstream fuse before the time delay expires, the relay resets, preventing opening of the switch.

See Case Study 620-1000 for a one-line diagram and complete details of this application.