S&C Pad-Mounted Gear Connects Generator Farm with Utility Grid.

Background

Satisfying peak demands has become a challenge for electric utility companies. One utility in the Southeastern United States needed a 60-MW standby power source that could be up and running quickly as dictated by demand. Their only option for providing extra power on such short notice was to use diesel generators.

The largest diesel generator commonly available would only develop 2 MW, so to provide the required 60 MW, a farm of thirty generators would be needed. The generators would be spread out with switchgear placed in between. But the new installation would have to be completed with great haste, or the project would have to be abandoned.

The utility preferred S&C as its supplier of switchgear, because they already had S&C pad-mounted gear and were very satisfied with its performance. But they still had to choose between the pad-mounted gear and free-standing metal-enclosed switchgear. S&C PMH Pad-Mounted Switchgear won out. Besides being suitable for the application, it could be completed in time to meet the utility’s tight delivery schedule — all at a lower cost. The utility then turned to S&C for help with system configuration and resolution of transformer-inrush and fault-protection issues.

How did they do it?

Thirty 2 MW CAT generators selected for the farm were divided into six clusters. Each group has five of the CAT generators, a transformer and fuel tank for each generator, and three S&C pad-mounted gear units. A riser connects each cluster to double-circuit, 13-kV, 1200-ampere bus running overhead.

The generator farm is located adjacent to a large body of water, and the water table on the site is only 2 feet below grade. At this depth, any attempt to dig a trench would only cause the ground to cave in, so it was decided to place the switchgear on wooden platforms. The photo shows two S&C pad-mounted gear units, located between two of the generators (generator on the right not shown).

In each of the power-generation clusters, an S&C Model PMH-12 pad-mounted unit receives power from three of the five generators, and a Model PMH-7 receives power from the other two. S&C SML-20 Fuses in each of these two switchgear units protect the system against faults occurring between the switchgear and the generators. Power from both of these units feeds into a second piece of PMH-7 gear, equipped with 8000-ampere Instantaneous Fault Fiter® Electronic Power Fuses. This type of fuse was chosen because the utility wanted current limiting capability, and the Instantaneous Fault Fiter was the only current-limiting fuse found that could handle the inrush current of the transformers.

Results

The S&C pad-mounted gear was delivered and installed in time to meet power demands during a period of high usage.