Lightweight Power System Ready to Fly

The U.S. Air Force and Army needed a lightweight electrical power system that could be transported by air to serve provisional bases. And they wanted switchgear for their new deployable power generation and distribution system that could be stacked two-high to save space aboard transport aircraft and in storage.

They also specified a special steel skid for permanently mounting the gear. The skid would be integral with the enclosure, serving as both a pad and lifting support. The gear would need to pass the MIL Spec E-810 20-hr. shaker-table vibration test, verifying that stacked units could withstand 10,000 miles of travel aboard military aircraft. It would also need to pass tests verifying that switchgear performance is not affected after the gear has been subjected to low pressure at an altitude of 40,000 ft.

The engineering contractor for the new system chose an underground distribution switchgear for primary switching and secondary distribution that would be easy to operate and require minimal training of ever-changing military personnel. Moreover, the SF6-insulated unit that they specified would be small and light weight—ideally suited for airlifting.

Multiple units of a manually operated 15.5-kV model were furnished to switch and protect loads fed by 920-kW generators. All of the units have a 600-amp continuous current rating and 16-kA short-circuit and fault-interrupting capabilities. Each unit includes two load-interrupter switch ways and four fault-interrupter ways. Optional voltage indicators are also included.

The switchgear enclosure was completely redesigned and outfitted with the requisite integral steel skid. The skid and enclosure frame utilize heavy-duty steel I-beams and channels. Four alignment pins at the top corners of the enclosure facilitate stacking of the units. Stacked units are lifted by eyebolts on the skid frame.

Channels at the bottom allow forklift handling; reinforced tabs at the lower corners of the skid allow the gear to be dragged along the ground. Turnbuckles, attached to eyebolts on front and rear sides of the skid, hold stacked units together during transport. Plates, attached to the floor of the enclosure, protect the switchgear during transport and storage and can be removed for cable entry while the gear is in use.

The switchgear passed the rigorous shaker table tests imposed by the specifications. And the special design retained all the unique features of the standard-production model. To date, several of these units have been sent to bases overseas. Others are scheduled for shipment in the near future.