Download The Wahleach Hydroelectric Development

The Wahleach Hydroelectric Development
There are a number of relatively high-head hydroelectric plants in British
Columbia and the Pacific coast states. In December 1952, the Wahleach Plant was
placed in service by the British Columbia Electric Company, Ltd. To serve it, water
is diverted through a 2-mile tunnel from Wahleach Lake to a penstock partly
underground and partly on the surface of the steeply sloping Four Brothers'
Mountain to a powerhouse on the left bank of the Fraser River approximately 78
miles from the river mouth. The single generating unit representing the full
development operates under supervisory control from the company's central
office in Vancouver, a distance of 72 miles. A transmission line, the first of its
kind on the North American continent, is associated with this development, but
designed for later extension to the company's Bridge River Plant, approximately
110 miles to the north. This line is designed for 345-kv operation with two
parallel conductors per phase. It is presentl y operating at 230-kv with only
one of the two conductors, but full insulation has been provided for the high er
voltage and hardware is in place to permit the second conductor to be added
with a minimum of change when it ts desired' to operate
at 345 kv.
Commencement of Construction.—After preliminary studies had indicated the
practicability of the project, detailed field studies were commenced in May 1949. A
Vancouver firm of consulting engineers was employed on this work and in
later phases of the projec t. The field studies for the location of the damsite and
reservoir were completed by the end of 1949; investigation of the various sites for
the components of the development was resumed in 1950 as soon as weather
conditions permitted. The powerhouse was located a 1 / 2 mile fro m the site for
the initial plan, and the tunnel line established from the intake to the
powerhouse.
Powerhouse and Tailrace.— The substructure of the powerhouse is of
reinforced concrete on rock foundations. The lowest portion of the structure is
at elevation 41 feet, the center line of the turbine at 70 feet, and the
generator supports at 90 feet.
The superstructure is structural steel with precast aerocrete roof and asbestos
cement siding. The frame supports two 130-ton travelling electric overhead cranes.
These cranes were transferred from another plant and one was returned after
erection of the unit was completed. On the upstream side of the building is a
steel and concrete wing housing the control equipment and low-voltage switchgear. The main b uild ing is 8 7 feet lo ng b y 6 1 feet wid e and the wing is 7 0
feet long by 18 feet wide.
Turbine.— The turbine is of the 6-nozzle vertical-shaft impulse type, rated to
deliver 82,000 horsepower at an effective head of 1,880 feet and at 360 rpm.
Efficiencies of 88 per cent at full load and 90 per cent at 3 / 4 load have been
guaranteed, but tests have not yet been made to determine actual values. The six
nozzles are supplied from a spiral casing made up of five steel castings, the first
having an inlet diameter of five feet 10 inches. Diameter of each nozzle is
8 5 / 3 2 inches. Jet deflectors are provided to reduce the amount of water striking
the buckets if load is reduced rapidly. The runner, bolted to the bottom of
the 25-inch diameter shaft, has 22 buckets each 23 inches wide. Outside diameter
of the runner is 125 3/4 inches and pitch diameter 1051/2, inches.
The turbine is controlled by a governor which transmits the proper movement to the
needle valves by a conventional servomotor mechanism through a rock-shaft
linkage. The governor is actuated by a hydraulic unit mounted on the top of the
generator shaft. Although this type of unit is now commonly used with steam
turbines, it is comparatively new in its application in hydroelectric plants.
Generator and Transformer.— The generator is rated 75,000 kva, 0.8 lagging
power factor, 13,800 volts, 3 phases, 60 cycles, 360 rpm, 60-degree-centigrade rise,
and has class B insulation. It is of conventional design, weight of both turbine
and generator being supported by one thrust bearing near the upper end of the
shaft. The main exciter, pilot exciter, and governor control unit mounted above the
thrust bearing are direct-connected to the generator shaft. Due to the rela tively
high speed and the small number of poles for a water wheel driven generator
of this capacity, the stator has an outside diameter of only 20 feet 8 inches.
To assist in maintaining rigidity, the stator is encased in a concrete enclosure
23 feet square and 16 feet high between two floors of the building. The overall
height from the bottom of the turbine to the top of the generator is slightly
more than 49 feet.
The stator windings are wye-connected, with the neutral completely insulated from
ground. Ground detection is provided by a 25-kva 13,800/220-volt transformer,
having its primary connected between the neutral and ground, and with a suitable
alarm device on its secondary. The stator winding is in two parallel circuits per
phase, with six line and six neutral leads brought out of the machi ne,
permitting the use of double primary current transformers with primaries in
opposition for split-phase protection. Additional current transformers on line and
neutral leads are utilized for differential protection. Indication and record of
temperatures within the windings are obtained from 10-ohm resistors imbedded
between coils in the stator slots.
The rotor is made up of a fluted forged-steel shaft, supporting a laminated
steel rim to which the field poles are in turn attached. A noncontinuous
amortisseur winding is provided in the pole faces. The flutes being integral
with the shaft contribute materially to its rigidity, making it possible to maintain
the critical frequency well above the overspeed of the turbine. Maximum
overspeed is 667 rpm. A segmental braking surface on the underside of the
spider provides for bringing the machine to rest. The brake mechanisms can
also be used as jacks to lift the rotor off the thrust bearing for maintenance or
adjustment.
The main exciter is rated 240 kw, 250 volt s, and the pilot exciter 7 kw, 250
volts. The main transformer is rated 75,000 kva, 3 phases, 60 cycles, 13.8-kv
delta to 230-kv wye, with the high-voltage neutral solidly grounded. The highvoltage winding has full capacity taps at 250, 240, and 220 kv, with one of
reduced capacity at 210 kv. Two forced-oil water-cooled heat exchangers external
to the transformer provide the necessary cooling, each cooler having sufficient
capacity to keep the transformer in operation at 75-per-cent load. The transformer,
complete with oil, weighs 157 tons.
Protective Relaying.—-The generator is provided with split-phase, differential,
overvoltage, overtemperature, overspeed, and current-balance protection. The neutral
has an overcurrent relay in the secondary of the ground ing transformer.
Operation of any of these devices opens the generator circuit breaker and field
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circuit breaker and shuts down the unit. The main and 60-kv transformers have
phase-differential and ground differential protection with overcurrent relays for
stand-by.
A gas-pressure relay fitted into the cover of the main transformer operates to
disconnect the transformer from the circuit if an arc or explosion should increase
the oil pressure rapidly. Each of the transformers in the 13.8/60-kv bank is also
equipped with this type of protection.
- For protection of the transmission line, carrier -current type relaying is
provided with a 3-zone impedance relay on each phase, and a di rectional
overcurrent relay for ground faults. Out-of-step blocking is provided to prevent
disconnection of the line under out-of-phase conditions, unless the second zone of
the relay comes into operation. Transmission-line relays are presently arranged to
trip the generator circuit breaker. Transformer protective relays are arranged to trip
the generator circuit breaker and close the motor -operated grounding blade on the
230-kv disconnecting switch to open the circuit breaker at the other end of the
line.
Automatic and Supervisory Control. — The station is designed for operation
without attendants. Supervisory control devices operated from the central control
office in Vancouver, 72 miles away, function to place the automatic starting
relays in operation, adjust voltage and load, and stop the machine.
The supervisory signals are sent from the central control office over a leased
telephone pair to the receiving substation near Vancou ver, thence by carrier
current over the 230-kv transmission line to the generating station. Continuous
kilowatt output is recorded over a separate telemetering channel in the central
control office by a telemetering unit, which also registers the kilowatt-hour output.
The unit can also be started, stopped, and controlled manually in the
powerhouse, by the simple expedient of moving a control switch from the
"Supervisory" to "Local Automatic" or "Manual" control position*.
Transmission Line.— Although presently operating at 230 kv, the transmission line
is designed and fully insulated for operation at 345 kv, using an additional
conductor per phase. Provision has been made and hardware provided for the
installation of this second-phase conductor; it will be strung prior to conversion to
345 kv, which is anticipated in the course of the next 2 or 3 years.
Apart from the extra-high voltage aspect, however, there are a number of
features of design and construction which are worthy of mention. The first
concern the use of aerial photography for acquisi tion of the right-of-way as well as
spacing and location of the line structures.
Initial reconnaissance of the route was made by helicopter, and aerial photography was
used to make final selection; then photographs of this route were obtained to a
scale of 200 feet to the inch. On these photographs were superimposed all property
lines, road boundaries, the boundaries of the proposed right-of-way and legal
descriptions of the property traversed. Final land survey for registration purposes
followed at a later date. The right-of-way acquired is 450 feet in width, to
provide for two additional similar circuits at some future date.
Concurrent with the selection of a suitable route was the design and
fabrication of the towers. The conductor selected was 795,000 circular -mil 26/7
steel-reinforced aluminum cable, using a twin bundle per phase at 18-inch centers;
phase spacing was 35 feet. The conductor was
suspended from 21 unit insulator strings, with specially
designed grading rings attached at the lower ends.
The maximum design tension in the conductor was
one-half its ultimate strength. The maximum design
loading was 1/2 inch of radial ice, plus 4 pounds per
square foot wind pressure at zero degrees Fahrenheit.
As the lightning incidence in this area is very low,
ground wires were installed for only 1/2 mile at the
line terminals.
After considerable stud y as to the type of tower
to be employed on this line, the portal type was
finally selected. Fig. 26 shows a tangent tower.
This type of tower offers a number of distinct
advantages for this application. By the use of two
masts, instead of the quadruped construction
normally used, the weight of redundant steel is considerably reduced, particularly
in the tower head. At extra-high voltages, this reduction becomes increasingly
important. Another advantage is that the two masts offer very little obstruction to
the use of agricultural equipment around the tower. This was a factor, as 59 of
the 64 miles of line pass through highly cultivated farmland. The third advantage lay
in the ease of erection for this type of tower.
The specification called for a standard mast to be designed to meet the
requirements for tangent, angle, and dead-end towers. On angle towers, the transverse
load was to be taken by internal guys, and similarly, on deadend towers the conductor
tension was to be taken by guys. Thus, the mast designed for the tangent tower could
be used for all towers, and only separate crossarms need be detailed. This effected a
considerable saving in detailing cost and simplified erection.
The maximum line span was 1,222 feet and the minimum 514 feet. The average
span was 995 feet.
Every suspension tower was to be capable of withstanding a longitudinal load due
to both conductors of one phase being broken.
In order to reduce the dynamic load on the tower masts when a conductor breaks,
it was decided that the crossarm should be designed to fail at 60 per cent of the
actual broken-wire load, that is, a safety factor of one applied to the broken -wire
load as described above. Upon failure the crossarm would swing into the line,
thus reducing both the dynamic and the static load on the tower.
A total of 340 towers were constructed on this line over a period of 8 months.
The great majority of towers were erected by completely assembling the masts on
the ground and then erecting them by means of a mobile crane. A 2-masted
tower took approximately one day to assemble on the ground and 2 hours to
erect.
Twenty-three months after commencement the line was completed; it was
energized at 230 kv on November 30, 1952.
М.А. Беляева и др. «Сборник технических текстов на англ. языке»
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