A Better Solution for Overhead Lateral Circuit Protection.

Conventional lateral circuit protection has required some concessions. Over 90% of temporary faults on overhead distribution circuits occur on laterals. Over the years, utilities have dealt with lateral protection in a couple of ways.

Some utilities employ a “fuse blowing” philosophy: The substation feeder breaker is properly coordinated with the lateral fuse, so that the fuse will clear any downstream fault within its rating . . . not the breaker.

The problem: Service to customers on the lateral is permanently interrupted — even for a temporary fault. And the utility must deal with the high cost of service calls to replace lateral fuses.

Other utilities employ a “fuse saving” philosophy: The first trip of the substation feeder breaker is intentionally miscoordinated so that the breaker operates faster than the lateral fuse to clear a fault downstream of the lateral fuse. The second trip of the breaker is slower so that if the fault is still present, the lateral fuse will operate to clear it.

The problem: All customers on the feeder experience a momentary interruption for all faults.

S&C’s new TripSaver™ Dropout Recloser eliminates these problems. It’s ideally suited for protection of laterals that experience frequent momentary faults. This self powered, electronically controlled, single-phase vacuum fault interrupter is available for installation in new or existing cutout mountings. A two-insulator, branch feeder style mounting is also available.

TripSaver eliminates the permanent outage that results when the lateral fuse operates in response to a momentary fault. Utilities using “fuse blowing” will see an improvement in SAIFI without sacrificing MAIFI.

And TripSaver eliminates the momentary interruption on the feeder in instances where the breaker is tripped to save the lateral fuse during a momentary fault. Utilities using “fuse saving” will see an improvement in MAIFI without sacrificing SAIFI.

TripSaver features an open-close-open-dropout operating sequence with a 5-second reclosing time interval. The interrupter resets five seconds after dropout, ready for the next sequence. The first opening operation features very fast — 1.5- to 2-cycle — clearing time, as shown below. The second opening operation features a time-current characteristic equivalent to either a 50K or 100K fuse. See the sample TCC curves in Figure 1 below.

This operating sequence provides excellent coordination with the substation feeder breaker and downstream transformer fuses.

Figure 1. TCC for second operation, equivalent to a 50K fuse TCC for first operation.

To learn more, contact your local S&C Sales Office.

View additional information on the TripSaver Dropout Recloser.