crane.

Each transformer is protected from the entrance of oxygen or moisture by a cushion of inert gas maintained above the oil. The gas pressure is controlled by a nitrogen gas cylinder, pressure regulator, gages, and valves. This equipment is in a control cabinet mounted on the side of each transformer.

Each transformer was purchased equipped with the following accessories:

(1) Dial-type liquid thermometer.

(2) Hottest spot temperature indicator.

(3) Liquid-level indicator.

(4) Mechanical pressure relief device.

(5) Winding thermal relay.

(6) Fault pressure relay.

(b) 4.16-Kilovolt to 115-Kilovolt Transformer Bank. --This transformer bank consists of three single-phase, 60-cycle, oil-immersed, self-cooled, forced-aircooled power transformers. Each transformer is rated at 3,333/4,444 kv.-a., 4,160 delta volts to 115,000 grounded wye volts. A spare transformer was provided for use when it would be necessary for one transformer to be out of service. The transformer bank rating of 3,333/4,444 kv.-a. was considered adequate and economically desirable based on expected operating conditions.

The low-voltage winding of each transformer is provided with full capacity taps 2.5 and 5.0 percent above and below rated voltage. These taps are required because of probable voltage fluctuation on the 115-kilovolt line. An externally operated tap changer to be operated only when the transformer is de-energized was provided on each transformer. The transformers are equipped with external radiators with supplemental forced-air cooling equipment. Each transformer is designed to carry its normal continuous self-cooled kilovolt-ampere rating with a temperature rise by resistance not to exceed 55° C. and a hot-spot temperature not to exceed 65o C. Each transformer will carry continuously its forced aircooled rating of 133-1/3 percent of normal self-cooled rating with a temperature rise by resistance not exceeding 55° C. and a hot-spot temperature not exceeding 70° C.

Each transformer, when filled with 17, 200 pounds of oil, has an approximate total weight of 40, 800 pounds.

Each transformer was furnished with one single-pole, station-type, outdoor, lightning arrester suitable for a 115,000-volt 3-phase grounded wye circuit. These four transformers were furnished by the Westinghouse Electric Corp. under specifications No. 2189.

(c) 4.16-Kilovolt to 34.5-Kilovolt Transformer. --This transformer, for the Shoshone and Pilot Butte system, is a 3-phase, 60-cycle, oil-immersed, selfcooled, forced air-cooled power transformer. The transformer is rated at 8,333/10,417 kv.-a., 4,160 delta volts to 34,500 wye volts, and will carry any expected load on the 34.5-kilovolt branch. Provision was made for the installation of a second 3-phase, 8, 333/10,417-kv.-a., 4.16/34.5-kilovolt transformer to be connected to generator unit 1 switchgear bus should the need arise at a future date. The two 8,333-kv.-a. transformers would then be connected for parallel operation.

The high-voltage windings are provided with full capacity taps 2.5 and 5 percent above and below rated voltage. Provision of these taps involved no extra charge. The transformer has an externally operated tap changer to be operated only when the transformer is de-energized.

The transformer is equipped with external radiators with supplemental forcedair cooling equipment. It was designed to carry its normal continuous self-cooled kilovolt-ampere rating with a temperature rise by resistance not to exceed 55o C., and a hot-spot temperature not to exceed 65° C. The transformer will carry

continuously its forced-air cooled rating of 125 percent of normal self-cooled rating with a temperature rise by resistance not exceeding 50° C. and a hot-spot temperature not exceeding 65° C.

The transformer, when filled with 14,800 pounds of oil, has an approximate total weight of 51,200 pounds.

The transformer was furnished with three single-pole, station-type outdoor lightning arresters suitable for a 34,500-volt 3-phase grounded-neutral circuit. The transformer was furnished by the Westinghouse Electric Corp. under specifications No. 2189.

81. Communication. -(a) Manual Telephone Switchboard. --A manual telephone switchboard and associated facilities were leased from the Mountain States Telephone and Telegraph Co. to serve the powerplant and Government camp areas. It was determined that this leased service would be the most economical to provide telephone communication in the local area as well as to the Bell system through the telephone company's Thermopolis exchange. A carrier telephone channel also permits the Boysen operators to talk to Shoshone Powerplant and Thermopolis and Casper substations. Emergency telephone communication is also possible over the Boysen-Alcova carrier relaying channel and over the supervisory control system to Thermopolis and Lovell substations. Boysen Powerplant has a fixed radio station for communication to the operation and maintenance mobile radio system which has fixed stations at Shoshone Powerplant and Billings.

(b) Coupling Capacitor Potential Devices. --Three coupling capacitor potential devices are installed on each of the 115,000-volt lines to provide potential for line relaying, etc. The coupling capacitor portion of one of these devices is also used for phase-to-ground coupling of carrier relaying, telephone, and telemetering channels.

(c) Carrier-Current Equipment. --Carrier-current equipment was provided at Boysen Powerplant to permit telephone communication to the rest of the power system, for carrier relaying the 115-kilovolt lines to Thermopolis substation and Alcova Powerplant, and for supervisory control and telemetering. The carrier telephone channel uses single-frequency automatic-duplex equipment and has sets at Shoshone and Boysen Powerplants and Thermopolis and Casper substations. The carrier relaying channel to Thermopolis is used for supervisory control and selective telemetering the Thermopolis and Lovell substations from Boysen Powerplant. The signals are relayed between Thermopolis and Lovell over another carrier relaying channel. The megawatts interchange between the Bureau's Region 6 and Region 7, as metered at Alcova Powerplant, is telemetered continuously to Boysen Powerplant on a frequency shift carrier channel. All of the carrier channels are trapped to minimize losses into the station bus and all channels are coupled phase-to-ground.

82. Illumination. - (a) General. -- The number of lighting fixtures and the wattage of Tamps used to obtain the desired levels of illumination for various tasks were established by the lumen method and/or the point-by-point method of calculation. In areas where high-level illumination was desired, fluorescent lighting fixtures are installed. The incandescent lighting fixtures have prismatic glass reflectors. The glass reflector illuminates the ceiling and provides good distribution of direct light.

(b) Fluorescent Lighting. --The offices, records room, and other areas where the higher levels of illumination are required have direct-indirect louvered lighting units with metal side panels. The complete unit directs 40 percent of the light upward and 60 percent downward. The control room was designed for three rows of two-lamp louvered troffer-type fixtures (see figs. 39 and 40), to provide an average intensity of 40 foot-candles "in service. It was necessary to change the original design in the field due to interference with the ventilating system. In revising the layout, four fixtures were removed from the center row, and two units installed separately at 90° to the original units. The direct-current emergency lighting units were inserted between the three fixtures in front of the board, and at each end of the units turned 90 to the center row. The original design called