152. Intake Facilities and Penstock. Water from Lewiston Reservoir is supplied to the powerplant turbine from the river outlet works. The intake structure, outlet conduit, high-pressure gates, flowmeter, and stilling basin, all in the river outlet works, were previously discussed in section 147.

(a) Butterfly Valve. --A 36-inch, rubber-seated, hydraulic cylinder-operated butterfly valve is provided at the inlet to the turbine. The valve is provided with a four-way solenoid control valve, two manually operated shutoff valves, a hydraulically operated locking device, a manually operated hydraulic pump and a manually operated four-way control valve, together with connecting piping. All the above listed items are located on the front of the butterfly valve. The net weight of the valve is 2,257 pounds.

(b) Turbine Draft Tube. --The turbine draft tube consists of a straight conical welded plate section leading to a concrete pit opening to the powerplant tailrace, as shown on figure 122. A mandoor is provided near the top of the draft tube in an access passage to permit access to the underside of the runner. Stoplog guides are provided at the discharge end of the concrete pit to permit unwatering the draft tube.

153. Hydraulic Turbine and Governor. (a) Turbine. --The turbine is a vertical-shaft Francis type, rated at 525 horsepower when operating at 600 revolutions per minute under an effective head of 60 feet. Best efficiency is expected at an output of 450 to 500 horsepower when operating under an effective head of 60 feet. Warranted best efficiency of the turbine is 87 percent.

The effective head on the turbine will vary between 40 and 70 feet. The controlling water surface elevations in Lewiston Reservoir are as follows:

The turbine is expected to operate normally with a constant discharge of 75 second-feet, allowing power output to vary with the head, provided the output does not exceed the generator rating (fig. 123). Figure 117 indicates the general arrangement of the turbine and generator in the powerplant.

The turbine-operating characteristics and design information are shown on figure 123. The turbine spiral case is designed for an internal pressure of 35 pounds per square inch which is the maximum operating pressure plus water hammer. The turbine is designed and constructed so that all removable parts can be removed from above through the circular opening beneath the generator. The gate ring is split in half since it is too large to pass through the opening in one piece. The turbine runner can be lowered three-eighths inch to permit disengaging the flange coupling male and female parts and can be raised a sufficient amount to permit inspection and dismantling of the generator thrust bearings. When the shaft flange is disconnected, the runner will rest on a ledge and will support the turbine shaft.

The turbine runner is of 18-8 stainless steel cast in one piece. There are no wearing or seal rings provided. The turbine shaft and governor gate shaft are made of forged steel. The turbine shaft is provided with a split, stainless steel sleeve where it passes through the packing box.

The turbine guide bearing is a babbitt-lined, cast-iron shell made in two sections to permit dismantling. An oil reservoir is provided below the bearing, which is also split in halves and is clamped to and supported on the turbine shaft. The reservoir revolves with the shaft. The bearing is self-lubricated by means of the centrifugal force imparted to the oil, causing the oil to rise through an internal pipe to the top of the bearing from where it flows by gravity back to the reservoir between the bearing surface and shaft. A sight gage is provided on the bearing to indicate oil level when the turbine is running.

The turbine is provided with 12 cast-steel wicket gates which are operated by means of an outside gate ring, links, and connecting rods from the governor gate shaft. The link connecting each gate to the gate ring is designed to break in the event one or more gates become blocked, so as not to damage the gates or other more important parts. Each gate stem is provided with three bronze-bushed, greaselubricated guide bearings and a packing box. Grease fittings are provided at all points of the gate-operating mechanism requiring lubrication.

A cam-operated vacuum breaker or air valve is provided to admit air to the turbine runner when necessary to improve turbine operation. The vacuum breaker is operated by an adjustable cam attached to the gate-operating ring.

(b) Governor. --The governor for controlling the turbine is of the oil-pressure, gate-shaft type with electrically driven speed-sensitive elements. The normal operating oil pressure will vary between approximately 180 and 200 pounds per square inch and the governor capacity is such that the turbine gates can be operated a full stroke in 3 seconds.

The major governor components are a type HR governor unit and an oil pumping unit, both located on the generator floor.

Figure 122.--Lewiston Powerplant turbine and auxiliaries--Turbine erection procedure and details.

154. Generator. The generator is of the vertical-shaft, hydraulic-driven, alternating-current, synchronous type, rated as follows:

The generator is designed for clockwise rotation when viewing the unit from above. A thrust bearing and an upper guide bearing are provided above the rotor, and a lower guide bearing is provided below the rotor. All bearings are of the oil-immersed, self-cooled type. The thrust bearing and upper guide bearing are located in a common oil reservoir, and the lower guide bearing is located in a separate oil reservoir. The thrust bearing is a vertical self-equalizing "Kingsbury" type, and is designed to support the entire weight of the rotating parts of the generator, exciter, and turbine, including the unbalanced hydraulic thrust of the runner, at any speed up to the full runaway speed of the turbine (1,170 r. p. m.). The thrust bearing is supported by a radial arm bracket resting on the generator stator. This bracket also supports the exciter which is directly coupled to the generator. The above load on the upper bearing bracket is transmitted successively through the bracket to the generator stator frame and thence to generator soleplates and the foundation. The lower guide bearing is supported by a bracket attached directly to the stator frame. The thrust bearing and upper guide bearing are insulated electrically from ground to prevent shaft current from passing through the bearings. Terminals for testing the insulation are provided in the generator terminal cabinet.

The generator is of the open type, and is air cooled. The cooling air enters the generator from the turbine room below. Fan blades on the generator rotor circulate the cooling air through the generator, and discharge it into the generator room through openings in the stator. The exciter provides its own cooling air circulation by means of fan blades on its rotor.

(a) Characteristics.--The following data were calculated by the manufacturer. generators show some variations from these values.

Factory tests on the

(1) Continuous synchronous condenser capacity when operating at rated voltage:

Zero power factor overexcited--241 kilovolt amperes

Zero power factor underexcited--328 kilovolt amperes

(2) Starting current at full voltage:

(Locked rotor) as a motor, in amperes--less than 3,150 amperes

(3) Field current and nominal collector-ring voltage required at rated kilowatt output, rated voltage, and rated power factor--38. 6 amperes, 102 volts.

(4) Field current at no-load--21. 4 amperes.

(5) Induced field current at full voltage:

(When starting as a motor) O percent speed.....32 amperes

50 percent speed. ...32 amperes

95 percent speed.....25 amperes

(6) Starting torque (across-the-line starting as a motor) in percentage of full-load torque-60 percent.

(7) Pull-in-torque in percentage of full-load torque--100 percent.

(8) Time required to accelerate from 0 to synchronous speed as a motor--6 seconds.

(9) Allowable stall time at rated voltage--15 seconds.

(10) Field resistance at 75° C. --2.65 ohms.

(11) Rating of strip heaters--732 watts, 3 phase, and 208 volts.

(12) Flywheel effect (WR2) of rotating parts--6,500 pounds at 1 foot radius.

(13) Quantity of oil required to fill each generator bearing--30 gallons for entire generator.
(14) Weight in pounds of:

Complete generator, including exciter--21,500 approximately
Rotating parts--4, 400 approximately

Heaviest part (wound stator)--7,900

Shipping weight (heaviest part)--18,950 (assuming generator assembled complete minus base parts)

(15) Rating of exciter in kilowatts, volts, and amperes at rated speed:

(b) Generator and Turbine Lubrication.-

7-1/2 kilowatts
125 volts

60 amperes
600 r. p.m.

(1) The generator upper guide bearing and thrust bearing are located in a single oil reservoir. The lower guide bearing is located in a separate reservoir. Each reservoir operates as a completely self-contained unit. No supplementary cooling is provided for the bearings. Each reservoir is equipped with oil filling and drain connections and an oil level sight gage to indicate level of oil in the reservoir.

(2) The turbine guide bearing is oil lubricated and is provided with an oil reservoir, containing approximately 1-1/2 gallons of oil, immediately below the bearing and rotates with the shaft. The oil is circulated through the bearing by means of centrifugal force, which causes the oil to rise to the top of the bearing through an internal pipe from which point it flows by gravity through the bearing back to the reservoir. An overflow from the top of the bearing to the reservoir prevents the oil chamber at the top of the bearing from overflowing.

(c) Brakes and Jacks. --The generator is not equipped with brakes or jacks.

(d) Generator Accessories and Protective Devices. --The generator is equipped with the following accessories, all of which are located at the generator:

(1) Space heaters.--Three space heaters were furnished with the generator to prevent the formation of condensation during prolonged shutdown periods. Operation of the heaters is entirely manual by means of a circuit breaker on the station-service distribution power board.

(2) Overspeed switch OS. --The switch is an adjustable, self-resetting device. It has an adjustment range of contact settings between 125 and 165 percent of rated generator speed. The contacts have been factory set to operate at 125 percent of rated speed.

(3) Bearing temperature relays BG. --Each guide and thrust bearing is equipped with a manual-resettype thermal protective relay.

(4) Bearing insulation testing terminals.--These terminals are located in the generator terminal cabinet.

(5) Gages. --The following indication gages are provided:

Thrust bearing metal temperature
Upper guide bearing metal temperature
Lower guide bearing metal temperature

Oil level gages for each bearing oil reservoir

(e) Generator Grounding Surge-Protective Equipment.--The stator winding of the generator is wye connected. The neutral of the winding is grounded through a 500-volt-ampere, 600- to 12-volt, molded-type potential transformer. A 32-ohm, 150-watt continuous resistor is connected to the secondary of the transformer. A ground-trip relay is connected in parallel with the resistor, and acts to trip the generator air circuit breaker and shut down the unit in event of excessive generator ground current.

Surge-protective equipment consists of lightning arresters and capacitors wye connected and grounded, located in the generator and station-service control equipment.

(f) Generator Excitation Control and Voltage Regulator.--The main exciter output is connected to the generator field through a field contactor. The field contactor also provides for proper switching of the generator field discharge resistor.

The generator field excitation is changed by means of the manually operated exciter field rheostat. In addition, a direct-acting, rheostatic-type automatic voltage regulator operates to regulate the generator output voltage during emergency operation. No provisions are made for automatic voltage regulation during normal operation, and the voltage regulator is completely disconnected during this mode of operation.

(g) Limits and Precautions for the Generator. --In accordance with ASA Standards, the generator is designed to operate at rated kilovolt-amperes, frequency, and power factor, at any voltage not more than 5 percent above or below the rated voltage, but not necessarily in accordance with the standards of performance established for operation at normal voltage rating. The manufacturer's warranties will not apply if this voltage is exceeded.