(19) The sustained, root-mean-square, single-phase, short-circuit current is 4, 100 amperes.

(20) The sustained, root-mean-square, phase-to-neutral, short-circuit current is 6, 580 amperes.

is 40.

Excitation corresponding to full load

(21) The maximum value of no-load, balanced, telephone-interference factor

(22) The maximum value of no-load, residual, telephone-interference factor is 25.

(23) The calculated regulation, in percent of rated voltage, is 17.4 at 1.0 power factor and 25.7 at 0.95 power factor.

(24) The field current and nominal collector-ring voltage required for rated kilowatt output at rated voltage and power factor are 710 amperes and 220 volts, respectively.

(25) The approximate maximum operating temperature at rated load for:

Armature winding (by embedded detector) is 95o C.
Field winding (by resistance) is 95o C.

Collector rings (by thermometer) is 90o C.

Cores and mechanical parts (by thermometer) is 80° C.

(26) The maximum line-charging capacity of one generator, neglecting heating, without the generator becoming completely self-excited, when operating at normal rated voltage and frequency, and the excitation reduced to zero when connected to a transmission circuit or circuits open-circuited at the receiving end is approximately 33, 000 kv. -a.

(27) The moment of inertia of the rotating parts (WR2) of one generator and exciter, in pounds at a radius of 1 foot, is 12, 600,000.

(28) The amount that the rotor must be raised to dismantle the bearings is 5/8 inch.

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

The thrust bearing and upper guide bearing is 790 gallons.
The lower guide bearing is 132 gallons.

(30) The approximate quantity of water, for one generator, at 25° C. required to cool:

The surface coolers is 580 gallons per minute.
The thrust bearing is 26 gallons per minute.
The lower guide bearing is 9 gallons per minute.

(31) The pressure loss through each cooler is 5 pounds per square inch.

(32) The net volume of air within the housing and ducts of one generator, for which carbon dioxide for fire protection must be provided, is 7, 750 cubic feet.

(33) The weight of:

One complete generator, including exciter, is 482, 000 pounds.
Each exciter is 14, 500 pounds.

Rotating parts, including exciter, is 242, 000 pounds.

Rotating parts of exciter is 4, 500 pounds.

Heaviest individual part as disassembled for shipment is

51, 000 pounds.

The total weight of the heaviest part that must be lifted by
crane during assembly or disassembly is 245, 000 pounds.

(34) The recommended viscosity of lubrication oil, in seconds Saybolt, at 104° F. or 100° F. is 300.

(35) The number and rating of electric heaters for preventing condensation in stator windings during shutdown is four heaters at 2 kilowatts each.

(b) Construction Details.--The generators were manufactured and installed by the United Power Control Corp. (formerly Pacific Oerlikon Co.) under specifications No. DC-3904. Each generator is of the vertical-shaft type with a combination thrust and upper guide bearing above the rotor and a lower guide bearing below the rotor. The entire weight of the rotating parts of each generator and turbine is supported by the thrust bearing; this weight, in turn, is supported by the upper-bearing bracket which also supports the main and auxiliary (pilot) exciters, and the permanent magnet generator. The entire load is transmitted through the upper-bearing bracket to the stator frame, then to the soleplates and into the concrete foundation. The lower bracket supports the lower guide bearing and air brakes.

The generator thrust bearing is a self-equalizing Kingsbury type provided with a high-pressure lubricating system to force oil between the bearing surfaces of all shoes prior to starting and to maintain the forced oil film until sufficient speed has been attained to maintain a full-thickness dynamic film. This lubricating system is also used to insure adequate oil film at reduced speed during shutdown. The thrust and upper guide bearings have a common oil reservoir which is water cooled. The upper guide bearing consists of

a one-piece circular babbitted surface bearing against the machined outer vertical surface of the thrust block. The lower guide bearing consists of two half shoes which are bolted together to form a circular babbitted surface bearing against the machined outer vertical surface of a journal provided on the generator shaft. The lower guide bearing has a watercooled oil reservoir.

Two equally spaced resistance temperature detectors (R. T. D. 's) were provided in the bearing metal of each thrust bearing and one in the bearing metal of each upper and lower guide bearing for remote temperature indication. Two thermostat relays were provided in the bearing metal of each thrust bearing and one in the bearing metal of each upper and lower guide bearing to operate an alarm upon development of excessive bearing temperatures.

The stator frame rests upon six soleplates. The soleplates (having integral shear keys) were placed in blockouts in the concrete foundation, fastened to the foundation by means of eight 1-1/2-inch foundation bolts, and the blockouts filled with cement grout. The stator frame is fastened to each soleplate by means of five 1-1/2-inch bolts and four dowel pins. The frame soleplates support a maximum vertical load of 121, 000 pounds per sole plate on the generator foundation and a maximum tangential load of 185, 185 pounds per sole plate, based on short-circuit conditions, on the generator foundation. Four equally spaced lower bracket soleplates were designed for a vertical load in excess of that represented by the total weight of the rotating parts (turbine runner, generator rotor, exciter armatures, and permanent-magnet generator) and for a tangential load in excess of that required for braking.

The stator winding is wye connected. The armature coils are completely insulated with class B insulation. The armature windings were designed to withstand the maximum 3-phase, short-circuit current of the generator. The line-to-ground short-circuit current is limited by neutral grounding equipment to approximately the capacitive charging current obtained on such a fault. Twelve resistance temperature detectors were provided in the stator windings for temperature detection and indication.

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. The amortisseur windings were designed to produce a ratio of quadrature-axis subtransient reactance to direct-axis subtransient reactance of not more than 1.35.

The generator shaft consists of a steel forging with an integral flanged half coupling which is connected to a flanged half coupling on the upper end of the turbine shaft. The shaft, 25 inches in diameter, was designed to operate at the runaway speed of 328

revolutions per minute without harmful vibration or distortion. The shaft has a 4-inchdiameter hole bored axially throughout its entire length, to permit visual inspection of the interior for possible flaws.

Each generator is equipped with air-operated brakes which may be controlled from the governor actuator cabinet. The brakes have sufficient capacity to bring the rotating parts of the generator and turbine to a stop from one-half normal operating speed within 7-1/2 minutes after the brakes are applied without the aid of field excitation on the generator. However, for automatic shutdown the brakes are automatically applied when the unit has decelerated to 49 revolutions per minute. A detachable brake ring is provided on the lower side of the rotor. The brakes were also designed for use as hydraulic jacks to lift the generator and turbine rotating parts a sufficient distance to provide for removal or adjustment of the thrust bearing. The jacks are operated by a handoperated, high-pressure oil pump.

Each generator was furnished with a practically airtight housing which forms an enclosed cooling system. Eight water-cooled surface coolers are spaced symmetrically around the periphery of the generator stator wrapper plate. Blades attached to the rotor serve as a blower to circulate the air. The surface coolers were designed to remove the heat losses under rated load conditions with water at 20° C. flowing at 580 gallons per minute. Each air cooler is provided with one thermostat relay which operates an alarm upon development of excessive temperatures.

The enclosed cooling system also provides for utilizing up to 25 percent of the generator heat losses for heating the generator room. Hinged doors permit the entrance of cool air into the generator from the pit below and the discharge of heated air from the generator housing into the generator room. The hot-air door is normally manually controlled; however, release of carbon dioxide in the automatic fire extinguishing system automatically closes the door. Opening or closing of the hot-air door causes opening or closing of the cold-air doors. The generator housings are practically airtight to insure effective operation of the carbon dioxide fire extinguishing system. A pressure relief door was provided in the side of the upper portion of each generator housing for the relief of excessive pressure.

Each generator was furnished with four 460-volt, 2-kilowatt space heaters placed on the lower bearing bracket below the stator windings. An adjustable thermostat was furnished for controlling the operation of the heaters. The purpose of the heaters is to prevent condensation in the generator windings during periods when the generator is shut down.

Each generator has a metal protective equipment housing for enclosing surge protective equipment and potential transformers. This housing is joined to and matches the generator housing in material, finish, height, and general appearance.

Three bushing-type current transformers having ratios of 2, 000/5/5 amperes are connected in wye in the generator neutral leads (one transformer per phase) for differential relaying protection. Three bushing-type current transformers having ratios of 2,000/5/5 amperes are located in the main generator leads. One secondary of each main lead transformer is used for generator differential relaying protection and one for metering. One current transformer having a ratio of 2, 000/5 amperes is located in each of phases A and B of the generator main leads of units 2 and 4 and in phases B and C of units 1 and 3 for operation of the voltage regulating equipment.

Two potential transformers connected in open delta, rated 400 volt-amperes, 12,000/120 volts are used for metering and synchronizing. In addition, two potential transformers connected in open delta, rated 12, 000/130 volts were furnished for operation of the voltage regulating equipment. These potential transformers are located in the generator protective equipment housing.

(c) Excitation System.-- Each generator field is excited by a direct-connected, vertical-shaft, shunt-wound, 205-kilowatt, 250-volt, main exciter mounted on top of the generator. There are no rheostats or other adjustable devices in the generator field circuit; therefore, the generator field current can be adjusted only by varying the induced voltage in the exciter. Since the generator and exciter are direct connected and normally rotate at fixed speed, the field flux in the exciter is the only factor that can be changed

readily. Thus the alternating current of each generator is controlled by varying the field current of the main exciter field. The main exciter was designed to have a speed of response, as defined in the Definitions of Electrical Terms (ASA-C43) of the American Standards Association, of not less than 0.5. The excitation for the separately excited automatically controlled shunt field is supplied by a pilot exciter mounted on top of the main exciter. The pilot exciter output is connected to the main exciter field through a regulating rheostat and a circuit breaker. For manual voltage regulation the generator field excitation is manually changed by means of the rheostat in the shunt field circuit, and for automatic regulation it is changed by an Oerlikon Engineering Co. type KO voltage regulator which automatically controls the position of the rheostat.

Corrective

The principal components of the type KO regulator are the measuring system, a magnetic amplifier, an oil pressure servomotor, and the regulating rheostat. Voltage variations at the generator terminals are detected by the measuring system. signals from the measuring system, after amplification, are used to control the servomotor which in turn positions the regulating rheostat.

The voltage regulators were designed to maintain the average 3-phase generator voltage under steady load conditions within plus or minus 0.5 percent for any excitation within the operating range of the generator. Under steady state conditions for any overspeed up to 150 percent of normal, the voltage regulator will maintain generator voltage within plus or minus 5 percent of the value the voltage regulator was holding before overspeed. The regulator controls can be adjusted readily to vary the bus voltage from periods of light loads to periods of peak loads.

The following technical data on the characteristics of the main exciters were furnished by the manufacturer:

(1) The rating of each exciter at normal speed is 250 volts and 250 kilowatts.

(2) The field current at full-load output is approximately 22 amperes.

(3) The speed of response of the exciter, as defined in the standards of the American Standards Association, is 0.5 or better.

(4) The maximum voltage (ceiling voltage) of the exciter when delivering full-rated current is 300 volts.

(5) The maximum temperature rise of the exciter parts, measured by the thermometer method, is as follows:

103. Generator Voltage Power and Associated Equipment. - (a). Generator Neutral Grounding Equipment.--The neutral of each generator winding is grounded through a 75-kv. -a., Askarel-filled, self-cooled, single-phase, 12,000-120/240-volt distribution transformer. A 55-kilowatt, 133-volt, 415-ampere continuous, 0.32-ohm loading resistor is connected to the 240-volt secondary circuit of the transformer in parallel with a ground protective relay which detects ground faults in the generator circuit. Each resistor was designed to carry its continuous current rating with a temperature rise not exceeding 375° C. This method of generator neutral grounding was selected since, for a unit system, it limits the current occurring during a ground fault to a low value and also affords selective relaying protection.

The distribution transformers were furnished by the Gardner Electric Manufacturing Co. under schedule 2 of invitation No. DS-4395. The resistors were furnished by the General Electric Co. under schedule 3 of invitation No. DS-4395.

(b) Generator Surge Protective Equipment.--The generator surge protective equipment is enclosed in the protective equipment housing which is joined to the generator housing. The generator power leads are brought out of the generator air housing on the inside of

the protective equipment housing. Each of the three phases is connected to ground through a 12-kilovolt, single-pole, indoor, station type lightning arrester and two single-pole, 11.5-kilovolt capacitors having a capacitance of 0.25 microfarad each. The capacitors slope the front of a surge so as to decrease turn to turn and coil to coil stresses in the generator windings, whereas the arresters limit the amplitude of voltage impressed on the generator windings.

The equipment was manufactured by the Westinghouse Electric Corp. and furnished by the United Power Control Corp. under specifications No. DC-3904.

(c) Generator Voltage Switchgear.--There are two generator voltage switchgear assemblies of the indoor, metal-clad type, with one interchangeable removable circuit breaker element. These switchgear assemblies are connected between the station-service tap of generator units 2 and 3 and the station-service transformer K2C. The switchgear assemblies are located adjacent to generator units 2 and 3.

The breaker furnished, mounted in type M-36 metal-clad switchgear, is a type AM-13.8-500 magne-blast air circuit breaker of the three-pole, single-throw, indoor, vertical-lift withdrawal type rated as follows at 3, 300 feet altitude.

Each switchgear assembly was furnished with a 3-phase bus enclosed in a superstructure compartment for connecting to the station-service taps at the terminals of generator units 2 and 3. The switchgear was furnished by the General Electric Co. under schedule 1 of invitation No. DS-4395.

(d) Power Cables.-- Each generator is connected to its power transformer by insulated cable from the generator to the powerplant wall and by bare copper cable from the powerplant wall to the power transformer.

Six (two per phase) 1, 500, 000-circular-mil, standard-strand, single-conductor, varnished-cambric, lead-sheathed cables extend from the generator protective equipment housing to the powerplant wall. The selection of the 1, 500, 000-circular-mil size cable was based on a maximum copper temperature of 77o C., an ambient temperature of 40o C., and the cable in air.

Each of the 1, 500, 000-circular-mil insulated cables is terminated at both ends with single-conductor, 15-kilovolt, compound-filled potheads to protect against moisture. The porcelain insulator of all potheads is soldered to adjacent metal parts to eliminate gaskets and cemented joints. The potheads at the generator protective equipment housings were manufactured by the Anaconda Wire and Cable Co. and furnished by the United Power Control Corp. under specifications No. DC-3904. The potheads at the powerplant wall were manufactured by the G&W Specialty Co. and furnished by B. C. Watts and Co. under schedule 1 of invitation No. (D)63, 724-A.