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 5 minutes after the brakes are applied. The brakes are also designed for used as hydraulic jacks to lift the generator and turbine rotating parts to permit removal or adjustment of the thrust bearing. A hand-operated high-pressure oil pump is used to operate the jacks.

(c) Excitation System. --A direct-connected, direct-current, vertical-shaft, shuntwound-type exciter, mounted on top of each generator and equipped with a rotating magnetic amplifier unit for excitation of the exciter, 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. A voltage regulator acting in conjunction with the magnetic amplifier automatically controls the exciter field current.

Following any load rejection up to 115 percent of rated output on the generator, the voltage regulating equipment will restore generator terminal voltage to within 5 percent above or below the voltage being held before load rejection. The regulator 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. The regulator was specified to respond within 15 cycles, on a 60-cycle basis, after the generator voltage varies more than 5 percent from normal. Under steady speed 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 which the voltage regulator was 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 main

exciter:

(1) The rating is 250 volts, 200 kilowatts, and 800 amperes at 240 revolutions per minute.

(2) The field current is 19.65 amperes at full-load output for exciter at rated voltage.

for:

(3) The response ratio, as defined in the ASA Standards, is 1.0.

(4) The ceiling voltage at rated current is 325 volts.

(5) The maximum temperature rise, measured by the thermometer method,

The armature winding is 40° C.;

The field windings is 40° C.;

The commutator is 55° C.;

The core and mechanical parts is 40° C.; and

Bare copper is 50° C.

(6) The weight of:

A complete exciter is 13, 400 pounds; and

Rotating parts is 5, 000 pounds.

(7) The direct-current requirement of the excitation control system is 20 amperes maximum continuous current from the regulator.

(8) Additional data:

The number of poles is six;

The brush current density at rated load is 50.8 amperes per square inch; and The maximum permissible wearing depth of the commutator is 1/2 inch on the radius.

(9) The continuous ampere capacity of the regulator power stage is 20 amperes direct current.

99. Generator Associated Equipment. (a) Generator Surge-Protective Equipment. --The surge-protective equipment for each generator is mounted in the switchgear assembly adjacent to the generator. Surge protection from external high-voltage surges is provided by grounding each main lead of the generator through a lightning arrester and capacitor connected in parallel. The lightning arrester is a 12-kilovolt, station-type arrester which is used to limit the amplitude of lightning impulse waves. The capacitor is a single-pole, station type, having an electrostatic capacity of 0.25 microfarad. The capacitor reduces the steepness of the wave front of a surge so as to decrease the turnto-turn and coil-to-coil voitage 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 50 kilovolt-amperes, 12, 000 to 120/240 volts, single-phase, 60 cycles. The other terminal of the high side is connected to the station grounding system. The secondary terminals of the distribution transformer are connected to a 32-kilowatt, 133-volt, 241-ampere continuous rating, 0.55-ohm grid resistor, having 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.

(c) Generator-Voltage Switchgear. --One indoor, metal-clad -type switchgear assembly for each generator is located immediately upstream from each generator. The switchgear assembly for generator units 1 and 2 contains a 3, 000-ampere, 13, 800-volt, 3-pole, electrically operated, air-type generator voltage circuit breaker cubicle and a 1,200ampere, 13, 800-volt, 3-pole, electrically operated air-type station-service circuit breaker cubicle. The switchgear assembly for generator unit 3 contains a 3, 000-ampere, 13,800-volt, electrically operated air-type generator-voltage circuit breaker cubicle and an auxiliary compartment cubicle.

The circuit breakers are three-pole, single-throw, drawout type, electrically operated for both close and trip with provisions for emergency manual trip operation. The circuit breakers are trip-free in all positions and can be manually closed for test or maintenance. Mechanical interlocks are provided to prevent the removable elements from being removed from or placed in operating position while the circuit breaker is closed, and to prevent the circuit breaker from being closed unless the primary disconnecting devices are in full contact or separated by a safe distance.

The generator circuit breaker cubicle is provided with an extension to the main bus for connection to the generator through nonsegregated phase bus. Connection is made to the power transformer low-voltage bushings through a nonsegregated phase bus from the top of the station-service circuit breaker cubicle for power transformers associated with generator units 1 and 2, and from the top of the auxiliary compartment for the power transformer associated with generator unit 3. Connection is made to the station-service transformer bushings through a 5-inch conduit by three 15, 000-volt-insulated singleconductor power cables from the bottom of the station-service breaker cubicles associated with generator units 1 and 2.

The switchgear has been provided with three current transformers on the generator side of the breakers and three on the transformer side of the breakers. The transformers have a ratio of 3000/5 and are used for generator and transformer differential relaying. Generator units 1 and 2 are also provided with three wye-connected current transformers for transformer differential relaying and three wye-connected current transformers for overcurrent relaying on the station-service transformer side of the station-service breaker. The differential relays are located on the main control board. The above switchgear was furnished under invitation No. DS-5603.

(d) Main Buses. --The generator-voltage bus structures are completely metal enclosed and of the nonsegregated phase type. The outdoor portion of the bus is weatherproof. A seal is provided where the bus duct passes through the wall to isolate the outdoor portion from the indoor portion. Provisions are made for expansion and contraction of the bus conductors caused by temperature changes. Flexible connectors are 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 the ambient temperature outside the enclosure. Each phase of the three-phase bus is completely encased in molded insulation. The insulated bus is supported in the housing with insulating supports. A clamp-type grounding lug is provided on the bus housing near the generator end and near the power transformer terminals. The grounding lugs are connected to the station ground system.

100. Main Power Transformers. The main power transformers (fig. 132) are located on the transformer deck and consist of three 3-phase transformers. Each transformer is an outdoor, FOW type (oil-immersed, forced-oil cooled with forced-water cooler) with the following ratings:

Each transformer is connected delta on the low-voltage side and solidly grounded wye on the high-voltage side. The transformers are equipped with constant-pressure oilpreservation equipment and a cooling system consisting of heat exchangers equipped with motor-driven oil pumps.

Transformer accessories include the following:

(1) Dial-type liquid thermometers with alarm contacts.

(2) Oil-level gage with low-level alarm contacts.

Figure 132. --View of transformer deck of Flaming Gorge Dam and
Powerplant. Powerplant is on the left and the dam is to the right.
Shown are the three unit transformers with lightning arresters and
interrupter switches. Tracks are for positioning and moving the
transformers to the interior of the powerplant for servicing.
P591-421-5202A, March 30, 1964.

(3) Winding temperature relays with ambient temperature compensation and three electrically separate sequence contacts.

(5) Fault pressure relay.

(6) Pressure relief device.

(7) Oil inlet valve.

(8) Oil outlet valve.

(9) Oil sampling device.

(10) Devices for lifting essential parts and for moving the transformer horizontally.

(11) Upper and lower filter press connections.

(12) Two grounding pads on each transformer tank and two terminal connectors for 500, 000-circular-mil stranded copper cable.

(13) Diagrammatic nameplate.

(14) Oil and water drain valves.

(15) Solenoid valves in cooling water inlet to each heat exchanger.

(16) Undervoltage relay for alarm on low voltage on the oil pump motor supply.

(17) Differential pressure switches for remote annunciation for water-pressure differential across each heat exchanger. 1/

(18) Differential pressure switches which activate on differential in heat exchanger oil and water pressure.1/

(19) Time delay relay which operates an annunciator on heat exchanger oil and water pressure differential.

(20) Oil flow indicator for each oil pump assembly.

(21) Pressure vacuum bleeder.

(22) Connection between tanks with shutoff valve.

(23) Weathertight breather.

(24) Sump chamber and drain valve in reservoir tank.

1/The functions of these items will be changed at a later date to those of a waterpressure switch and waterflow indicator.

Forced-oil, water-cooled-type transformers were selected to insure that they would fit in the limited transformer deck area between the face of the dam and the powerplant. Another factor for selecting FOW cooling was because of possible ventilating difficulties in the semienclosed transformer area.

The transformers are equipped with single-flanged cast steel wheels to permit moving of the transformer on rails.

The power transformers were manufactured under invitation No. DS-5571.

E. Miscellaneous Mechanical and Electrical Equipment

1. Mechanical

101. Bulkhead Gates. Six bulkhead gates are provided to seal the turbine draft tubes from the tailwater in the event that it is necessary to unwater the turbine units for inspection and maintenance of either equipment or structure.

(a) General Description. --The six bulkhead gates and related equipment (figs. 133, 134, and 135,) were furnished under invitations No. 90, 021-A and 90, 025-A. A gate having nominal dimensions of 12.25 feet wide by 8.10 feet high was selected for each of the draft tube openings. The gates and lifting frame operate in steel guides embedded vertically in the concrete structure. The gates are raised and lowered by means of a 5-ton electric hoist which operates on a monorail over the gate slots. An automatically engaging lifting frame is used for raising and lowering the gates.

The gates are normally stored in the upper portion of the gate slots. The gates are supported by latches so located that the lifting lug on the gate is just below the deck slot covers and is therefore easily accessible from the deck. The latches consist of hinged bars which will automatically engage the gate guide lugs during the raising cycle, and may be laid back out of the path of the gate guide lugs to allow the gate to lower.

Inasmuch as the gates must be raised and lowered only under balanced head conditions, a filling valve is incorporated in the gate lifting stem of each gate for the purpose of creating the balanced head prior to raising the gates. In the event that high-pressure penstock water is unintentionally admitted to the turbine and draft tube while the gates are in place, a gate will blow off of its seat shearing the bolts which fasten the lower guide lugs to each side of the gate. The top guide lugs are rigidly fixed to the gate, enabling the gate to swing out in the event that the lower guide lugs shear. The estimated weight of the six gates is 37, 200 pounds.