necessary to provide safe and convenient operation. The compressors in the 100-p.s.i. service air system are equipped for either automatic or manual control. The compressor for restoring the high-pressure air cushion in the governor pressure tank is equipped for manual control only.

(m) Tailwater Depressing System. -A tailwater depressing system is provided to reduce power consumption when a unit is motoring. This system unwaters the turbine runner by releasing stored compressed air into the draft tube through holes in the head cover, runner, and shaft. The system is designed to depress the water to about 3 feet below the runner and keep it near that level while a unit is motoring. The supply of stored compressed air at a pressure of 85 to 105 pounds per square inch is adequate for unwatering two units simultaneously in about 30 seconds. Unwatering one unit can be accomplished somewhat faster. System pressure can be restored in approximately 5 minutes after depressing one unit and approximately 10 minutes after depressing two units, after which the 100-c.f.m. compressor should be able to maintain the depressed level.

All necessary operations for the depressing system are automatic, under control of a master switch. A tandem float switch in the draft tube controls admission of air. Piping to the floats is specially arranged to minimize misoperation caused by slugs of air and water.

(n) Sewage Pumping Units.-The sewage pumping units are provided to transfer the domestic waste drainage from the powerplant to a sewage treatment unit outside the plant. Package units consisting of steel receiving tanks, centrifugal pumps, float switches, and the necessary controls for pump operation, were selected for this purpose. Each unit contains two pumps, each pump sized to meet the expected demand, thus permitting one pump to be removed from service for maintenance. Three units are provided-one with a capacity of 250 gallons per minute, one with a capacity of 150 gallons per minute, and one with a capacity of 75 gallons per minute.

(0) Water Level Gages.-Indicating and recording water level gages for the forebay and afterbay are located in the main control room. The afterbay stilling well, with float-operated level indicator and transmitter, is located in the machine shop bay of the powerplant. The forebay stilling well, with float-operated level indicator and transmitter, is located in the dam.

(32) The moment of inertia of the rotating parts of one generator and exciter, in pound-feet squared at a radius of 1 foot is 72,100,000.

(33) The amount that the rotor must be raised to dismantle the bearings is 0.25 inch.

(34) The quantity of oil, for one generator, required to fill:

The thrust bearing is 2,100 gallons. The upper guide bearing is 160 gallons. The lower guide bearing is 200 gallons

(35) The approximate quantity of water, for one generator operating at 115 percent rated kv.-a., at 25° C. required to cool:

The surface coolers is 2,200 gallons per minute.
The thrust bearing is 130 gallons per minute.
The upper guide bearing is 6 gallons per minute.
The lower guide bearing is 6 gallons per minute.

(36) The net volume of air within the housing and ducts of one generator, for which carbon dioxide for fire protection must be provided, is 21,000 cubic feet.

(37) The weight of:

One complete complete generator, generator, including direct-connected exciter, is 1,550,400 pounds. Rotating parts, including direct-connected exciter, is 740,000 pounds.

Heaviest individual part as disassembled for shipment is 146,000 pounds. Heaviest part that must be lifted by crane during assembly or disassembly is 704,000 pounds.

(b) Construction Details.-The eight generators were manufactured under invitation No. DS-5522 by General Electric Co. Each generator is a vertical-shaft synchronous machine with a thrust bearing and a guide bearing above the rotor and a guide bearing below the rotor. The thrust bearing supports the entire weight of the rotating parts of the generator, exciter, and turbine. The upper bearing bracket supports the thrust bearing and its load as well as the stationary parts of the exciter and transmits this entire load to the stator frame. The stator frame is supported on a concrete foundation by 12 foundation caps. Each of the six caps under the upper bearing bracket arms will support a vertical load of 360,000 pounds and the six alternate

caps between the bracket arms will each support a vertical load of 40,000 pounds. Each cap will support a maximum tangential force of 220,000 pounds based on single-phase, short-circuit conditions.

The lower guide bearings and the combination airbrakes and lifting jacks are supported by the lower bearing bracket. The lower bearing bracket is supported by six soleplates, each of which will support a vertical load of 164,000 pounds during jacking, and a tangential force due to braking of 2,800 pounds.

The thrust bearing was made by the General Electric Co., and consists of 10 babbitted stationary segments and a cast iron runner. The cast iron runner is secured to the rotor shaft by means of the thrust collar, and the stationary shoes are mounted on a flexible support of precompressed springs. The thrust bearings and guide bearings are insulated to prevent circulating currents from passing through the bearing surfaces. Test terminals are provided for use in connection with testing of the bearing insulation. The upper guide bearing, the thrust bearing, and the lower guide bearing are each located in separate oil reservoirs. Heat from the bearings is removed by water-cooled cooling coils provided in each oil reservoir. The bearings are self-lubricated except during starting or stopping operations when high-pressure oil is forced between the bearing surfaces of the thrust bearing to help maintain an oil film.

The stator winding is wye connected. The armature windings are provided with ASA class B insulation. The armature windings were designed to withstand the maximum 3-phase, short-circuit current of the generator. Twelve resistance temperature detectors were provided in the stator windings for temperature detection and indication.

The field poles also are provided with ASA class B insulation. The field poles were provided with amortisseur windings of the low-resistance type to improve stability under fault conditions and to reduce voltage distortion under conditions of single-phase fault.

Devices for the following purposes are furnished with each generator:

For indication on the generator instrument panel:

(1) Thrust bearing oil temperature.

(2) Upper-guide bearing oil temperature.

(3) Lower-guide bearing oil temperature.

(4) Cooling air temperature, each cooler.

(5) Thrust bearing cooling water supply pressure.

(6) Upper-guide bearing cooling water supply pressure.

(7) Lower-guide bearing cooling water supply pressure.

(8) Air cooler water supply header pressure. (9) Thrust bearing high-pressure oil system pressure.

(10) Two air cooler water-supply header pressure switches (separately adjustable).

(11) Two bearing cooling water-supply pressure switches (separately adjustable).

For indication at the apparatus:

(1) Cooling water supply temperature located in the air cooler water supply header.

(2) Bearing cooling water supply temperature located in water supply line.

(3) Cooling water return temperature located in the water outlet from each surface cooler.

(4) Thrust bearing water return temperature located in thrust bearing water outlet.

(5) Upper-guide bearing water return temperature located in upper-guide bearing water outlet.

(6) Lower-guide bearing water return temperature located in lower-guide bearing water outlet.

(7) Oil level sight gage at each reservoir.

The following devices are furnished with the generator for remote operation of alarm for excessive temperature or loss of pressure, control of bearing cooling water, and starting control interlock:

(1) One thrust bearing oil level float switch for low- and high-level alarm and starting interlock.