April 29, 2002
System II Switchgear . . . Shining “Star” of a Radio Telescope Electrical System.
The Green Bank Telescope, located at the National Radio Astronomy Observatory in Green Bank, West Virginia, operates continuously, 24 hours a day, every day, to serve scientists from all over the world.
The telescope is used to study distant stars, galaxies, and other celestial objects . . . even molecules in between the stars. Its huge dish collects the weak radio signals emitted from these objects, concentrating for a time on a single, tiny point on the object, then moving on to another. The radio signals are reflected to the focal point of the dish, then to a feed horn that channels the signals to the receiver for amplification. The data is subsequently assembled to form a composite picture of the object.
Despite its enormous size (485 feet high) and weight (16 million pounds), the telescope is designed to be aimed with an accuracy of one arc-second . . . about the width of a human hair viewed from a distance of 45 yards. To achieve such great precision, the 2,004 metal panels comprising the surface of the dish are delicately positioned from the underside by 2,209 motor-driven pistons.
Without reliable electric power to run the telescope and associated equipment, many important research projects would come to a standstill. The management of the observatory was thus naturally concerned about problems they were experiencing with the breaker gear serving the facilities. Anxious to avoid outages, they began searching for the most reliable switchgear available. They chose S&C System II Modular Metal-Enclosed Switchgear. The observatory specified 13.8-kV System II Switchgear for their 4.16-kV distribution system. Such gear would provide additional BIL capability, which the facility engineer deemed desirable at the 2700-foot altitude of the installation. Metering was specified for the gear as well, along with communication equipment to transmit the data, via fiber-optic cable, to the main office a mile away.
To meet these special requirements, S&C provided the six-bay lineup shown in the photo and single-line diagram.
An incoming bay (Bay 6 at far right) and four feeder bays (1 - 4) are each equipped with a three-pole S&C Mini-Rupter Switch, a set of S&C SM-40 Power Fuses, and three single-phase current transformers.
A metering bay (Bay 5) includes low-voltage circuit breakers, power monitors for the incoming line and feeders, and an Ethernet communication module. A control power transformer in this bay serves the metering, communication equipment, interior lights, and heaters. The voltage transformer in Bay 6 provides sensing for the power monitors.
The System II Switchgear provides reliable, economical switching and protection for the facilities. An additional five-bay lineup is scheduled to be installed in spring 2002.