on the rotor spider serve as blowers for the generator. The cooling system with one heat exchanger out of service should maintain a satisfactory air temperature when the generator is operated at rated output. The water requirement for the heat exchangers is 2,200 gallons per minute. A small rotor fan with radial blades is installed under the main exciter for circulating cooling air through the exciter. The housings are practically airtight to insure effective operation of the automatic carbon dioxide fire-extinguishing system. The units are provided with pressure relief doors on the side of the housings for relief of excessive carbon dioxide pressure. Each generator is equipped with two independent ring headers supported near the stator winding and above the rotor, one for the initial discharge and one for delayed discharge from the high-pressure carbon dioxide gas supply. The initial discharge header has eight nozzles located at even intervals around the periphery of the housing, and the delayed discharge header has six nozzles located at even intervals around the periphery of the housing. A thermo-switch is located in the hot air passage ahead of each cooler. The thermo-switches are of the single-pole, fixed-temperature, self-resetting tubular-shell type rated at 0.5 ampere and designed to close a 125-volt, direct-current, ungrounded circuit when the surrounding air reaches a temperature of 185° F., thereby effecting the release of the carbon dioxide. Release of carbon dioxide may also be initiated by a break-glass station located on the a-line wall of the generator floor. Four electrical strip heaters, each rated 4,500 watts, 3-phase, 480 volts, are used to prevent condensation within the windings when the temperature approaches the ambient air temperature. The heaters are symmetrically spaced below the stator winding, and the heater contactor is controlled by a differential temperature control device which operates the heaters to maintain the temperature inside the generator at a minimum of 10° F, above the outside temperature. A braking system consisting of air-operated brakes mounted on each of the lower bearing bracket arms is provided for each generator. The brake shoes are applied to the brake ring on the lower side of the rotor and are designed with sufficient capacity to bring the rotating parts to a stop from one-half normal operating speed within 7-1/2 minutes after the brakes are applied. The brakes are also designed for use as hydraulic jacks to lift the generator and turbine rotating parts to permit removal or adjustment of the thrust bearings. A 440-volt, 3-phase, 60-cycle electric-motor-operated high-pressure oil pump is used to operate the jacks. (c) Excitation System.-A direct-connected, direct-current, vertical-shaft, shunt-wound type exciter, mounted on top of each generator, was selected to provide generator excitation. The main exciter is connected directly to the generator field through a shunt with no main field rheostat. The field current of the alternating-current generator is controlled by varying the field excitation of the main exciter. Voltage regulators acting in conjunction with the rotating magnetic amplifier automatically control the exciter field current. Following any load rejection up to 115 percent of rated output on the generator, the voltage regulating equipment is designed to restore generator terminal voltage to within 5 percent of the voltage being held before load rejection. The regulators will maintain average generator voltage within plus or minus 0.5 percent when operating under steady load conditions for any load or excitation within operating range of the generator. Under steady speed conditions for any overspeed up to 150 percent of normal, the voltage regulators will maintain generator voltage within 5 percent of the value the voltage regulators were holding before overspeed. For an overspeed between 150 and 175 percent of normal, the voltage regulators will maintain generator voltage within 10 percent of the value the voltage regulators were holding before overspeed. A permanent magnet generator and housing are mounted on each exciter bracket and shaft. The following data were calculated by the manufacturer as applicable to the exciters: (1) The exciter rating at 150 revolutions per minute is 655 kilowatts, 500 volts, and 1,310 amperes. (2) The field current of the exciter at rated output as per (1) above is 79.6 amperes. (3) The exciter response ratio is 2.0. (4) The maximum voltage when delivering rated current is 750 volts. (5) The maximum temperature rise at rated output for: Armature winding (by thermometer) is 40° C. (6) The weight of: A complete exciter is 38,100 pounds Rotating parts is 12,700 pounds (7) The direct-current requirements of excitation control system is 125 volts and 0.98 ampere. (8) Additional data: The number of poles is 12. The current density in the brushes at rated load is 78.6 amperes per square inch. The maximum reduction in commutator depth, measured on the radius, permissible for turning down is 0.5 inch. (9) The voltage regulator voltage time response is 0.03 second. (10) The excitation system voltage response ratio is 1.7. (11) The continuous capacity in amperes of rotating and magnetic amplifiers and associated equipment supplying excitation current to the main exciter is 80 amperes. 85. GENERATOR ASSOCIATED EQUIPMENT. (a) Generator Surge Protective Equipment.-The surge protective equipment for each generator is mounted in a separate assembly. Surge protection from external high-voltage surges is provided by grounding each main lead of the generator through a lightning arrester and capacitors connected in parallel. The lightning arresters are 15-kilovolt, station-type arresters which are used to limit the amplitude of lightning impulse waves. The capacitors are single-pole, station type, having an electrostatic capacity of 0.25 microfarad and are connected two in parallel to each phase to increase the capacity to the necessary 0.5 microfarad per phase. The capacitors reduce the steepness of the wave front of a surge so as to decrease the turn-to-turn and coil-to-coil voltage stresses in the generator windings. (b) Generator Neutral Grounding Equipment. -The stator winding of each generator is wye-connected and the neutral is connected with a cable to one terminal of the high side of a distribution transformer. The distribution transformer is rated 167-kv.-a., 12,000 to 120/240-volt, single-phase, 60-cycle. The other high-voltage terminal of the transformer is connected to the station grounding system. The secondary terminals of the distribution transformer are connected to a 0.12-ohm grid resistor, having a 30-second rating of 1,320 amperes, and a ground protective relay. The distribution transformer and resistor neutral grounding was used because of the lower cost in comparison with reactor grounding and because it eliminates most of the disadvantages of an ungrounded system. The sizes of the transformer and resistor were based on the charging current in case of a line-to-ground fault, which depends on the capacitance to ground of the interconnected generator voltage equipment. The neutral grounding equipment was furnished by General Electric Co., under invitation No. (D) 90,657-B. Each circuit breaker is normally pneumatically operated, but provision has been made for an emergency manual trip operation. The circuit breakers are trip-free in all positions and can be manually closed for test or maintenance. Visual indication of the circuit-breaker contact position from the front of the cubicle has been provided. Each air circuit breaker has been provided with interlocks to prevent opening or closing of the disconnecting switch unless the circuit breaker is open, to prevent access to the interior of the housing or cubicle unless the disconnecting switch is open, and to prevent closing of the disconnecting switch when the interior of the housing or cubicle is open. The switchgear is provided with extensions of the main bus for connection to the generators through isolated phase bus at the bottom, and for connection to the power transformer low-side delta network through isolated phase bus at the top of the cubicle. The switchgear has been provided with three current transformers on the generator side of the breakers and six on the transformer side of the breakers. The line side transformers have an ampere ratio of 7,000/5 and are used for generator differential relaying. The generator side transformers have an ampere ratio of 7,000/5 and are used for transformer differential relaying. The differential relays are located on the main control board. The switchgear assemblies were furnished by General Electric Co. under invitation No. DS-5828. (d) Main Buses.-The generator-voltage bus structures are completely metal enclosed, providing phase-isolated arrangement of the conductors and all associated circuit equipment. Phase isolation is obtained by placing each conductor in an individual metal enclosure and separating each phase enclosure so that an insulating air space exists between them. This assures maximum protection against phase-to-phase faults. The enclosures are suitable for installation either indoors or outdoors as is required by this particular installation. No special arrangements are necessary for indoor-outdoor transitions except that isolating barriers are used where the bus structures pass through the transformer deck. The conductors are aluminum and are jointed to the conductors of the adjacent section by flexible connectors designed to compensate for movement caused by temperature changes or uneven settling of the supporting structure. Flexible connectors are also used for bus connections to the generators, switchgear, and transformers. The conductors are designed to carry their full rated current without exceeding a temperature rise of 50° C. above an external ambient temperature of 40° C. One insulator, designed to withstand short circuit stresses, is mounted at each supporting ring to support the conductor inside the enclosure. Each bus structure is connected to a ground bus so that there can be no circulating ground currents through the bus structure. The ground bus is then connected to the station ground system. Each bus structure is complete with a grounding switch for protection of personnel during maintenance procedures. The grounding switch is a 3-pole, single-throw, gang-operated switch with a momentary current-carrying capacity of 120,000 amperes. Each switch can be opened or closed with an operating mechanism by one man. The grounding switch is equipped with six single-pole, control circuit, auxiliary switches which can be readily changed to circuit opening or circuit closing as required, and so constructed that false indication cannot be given if the mechanism fails to make a complete stroke of the grounding blade. Each switch is located adjacent to the even-numbered switchgear cubicles. Each bus structure is equipped with an air compressor to maintain the internal portion of each bus at a positive pressure of 1 inch of water with respect to atmospheric pressure. This feature was included to aid in keeping dust and water vapor from entering the bus enclosure. Check valves are installed in the piping supplying each separate section of each bus structure to prevent migration of air from one section of bus to another. The air compressor for each bus structure is located beneath the grounding switch adjacent to the even-numbered generator switchgear cubicles. (9) Oil sampling device. (10) Upper and lower filter press connections. (11) Wheels, lifting lugs, and jacking pad for lifting and moving the transformer horizontally. (12) Two grounding pads on each transformer tank with a terminal connector for one 500,000-circular mil stranded copper cable on each grounding pad. (13) Diagrammatic nameplate. (14) Oil drain and water valves. (15) Oil flow indicator, with alarm contacts, for each pump assembly. (16) Differential pressure switches which are activated by water pressure differential across each cooler. (17) Differential pressure switches which are activated by the difference in heat exchanger oil and water pressure. (18) Pressure-vacuum gage, for indication of gas pressure in the transformer tank, with alarm contacts. (19) High-pressure gage, for indication of gas cylinder pressure, with alarm contacts. 87. SHUNT REACTORS. The shunt reactor installation was of temporary duration at Glen Canyon Powerplant. The shunt reactor installation was located on the transformer deck of the powerplant and was divided into two groups, with one group located on each side of the 230-kilovolt power transformer installation for units 7 and 8. The reactors were removed from the powerplant after the fifth generating unit was placed in service, and were then placed in service at the Pinnacle Peak Substation. The purpose of their installation at Glen Canyon Powerplant was to provide the reactive kilovolt-amperes required for line voltage correction until adequate reactive capability was available from the generating units. Each group of reactors was rated at 48,000 kv.-a. and was comprised of two banks of three reactors each. All banks were connected in delta. Suitable bus bar connections were provided to permit removal from service of any one 24,000-kv.-a. bank. A temporary |