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would have required the use of two taller towers for accomplishing the same results.

The tower was designed for the tabulated loads shown on figure 211. Stress diagrams were drawn for each of the loads separately and combined for the various conditions to obtain the maximum stress in all members. This tower is unique in that the wire loads as applied to the tower imposes torsional loads at all three crossarm levels.

The design requirements for these members are consistent with the requirements of the Bureau's Design Standards No. 10, Transmission Structures. The leg angles are high-strength structural steel angles in accordance with ASTM A 440 and the web system and crossarms are standard strength A-36 material.

This tower was also provided with an encaged ladder and inspection and maintenance platforms as described under subsection (b) above.

(d) Model Aids Design. -A three-dimensional scale model of Glen Canyon features was built by the Bureau's engineering laboratories. The model projects the spatial relationships of major elements of the unit-powerplant, switchyard, bridge, and transformer circuit structures.

The model was used to check the planned solution to the difficult space problem of positioning the catenaries of conductors from the powerplant to the rim towers. A fine-link chain was suspended between the model rim towers and powerplant takeoff brackets to simulate the catenaries of the conductors and check all critical electrical clearances, tower heights, phase configurations, and rock trimming along the edges of canyon rims. Templates representing the maximum sideswing of conductors under transverse windloading were also used to check critical electrical clearances from the conductor sideswing positions to the canyon walls. For these checks to be valid, it was necessary that the model be of greater than normal accuracy with respect to topography and positioning of critical structures. Close checks between the model and calculations demonstrated that this effort worthwhile.

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110. STEEL SWITCHYARD STRUCTURES. The 345-kilovolt switchyard is the first Bureau switchyard which encompasses this high voltage. Therefore, all of the steel structures were newly designed for this first usage at Glen Canyon.

The several structure outlines were determined by the increased requirements for electrical clearances and

heavy electrical equipment loads. These outlines are consistent with the existing structure outlines for previously designed 230- and 138-kilovolt switchyards.

The switchyard structures are of hot-dip galvanized structural steel, field assembled with high-strength bolted connections. The major structures were designed to withstand the loads imposed by conductors and overhead ground wires, wind and dead loads, and the loads imposed by the supported electrical equipment. The minor structures were designed for wind and dead loads and the weight of the supported equipment.

The takeoff structures and the transformer structures were designed for the tabulated loads shown on the drawings and also for the National Electrical Safety Code medium loading conditions of 1/4-inch radial ice at 57 pounds per cubic foot at 15° F. and a wind pressure of 8 pounds per square foot. The structures were analyzed as multiple-bay single-story portal frames in the transverse direction and as cantilevers in the longitudinal direction.

The maximum stresses in the individual space frame-type towers were obtained by combining unit stress diagrams for the various conditions of loadings including vertical loads, dead loads, and horizontal torsional shears produced by torsional moments of unbalanced longitudinal wires.

Wire tensions for conductors, ground wires, and tension buses were determined for the most severe condition of wind and temperatures as shown on figures 206, 209, 212, and 213. The wires of the approach spans of transmission lines and transformer circuits which anchor to the switchyard structures were slacked off to approximately one-half to two-thirds of the maximum tensions used throughout the lines in order to effect economies in the switchyard structures. This was permissible because the switchyard approach spans were not critical with respect to electrical clearances to the lower level of strain buses.

Stringing instructions for conductors and ground wires were calculated to insure that the design loads of the structures will not be exceeded (figs. 214 and 215). Tensions for conductors and ground wires within the switchyards were established by the following criteria:

(1) Strength of wires, insulators, and hardware.

(2) Limitation of tension at normal temperatures to avoid vibration in the wires.

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Figure 211.-Transformer circuits steel structures-Assemblies of tower No. C4-T1.

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1-11-63 ADDED CONNECTION BOLT REFERENCE FOR
D. Alb LADDER AND PLATFORM,AND BEND LINE
"6-22-62 REVISED PLATFORMS. ADDED TOWER DESIGN LOADS
D-om AND CONNECTION BOLT REFERENCE DRAWING

UNITED STATES

DEPARTMENT OF THE INTERIOR
BUREAU OF RECLAMATION

COLORADO RIVER STORAGE PROJECT

MIDOLE RIVER DIV-GLEN CANYON UNIT ARIZONA-UTAN

GLEN CANYON POWER PLANT
TRANSFORMER CIRCUITS-STEEL STRUCTURES
TRANSFORMER CIRCUIT NO. C4
TOWER NO. C4-TI

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ASSEMBLIES

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Figure 212.-Transformer circuits steel structures-Assemblies of towers C1-T2, C2-T2, C3-T2, and C4-T2.

ACT CHIEF STRUCT AND ARCH. BRANG 557-D-2602

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Figure 213.-Switchyard 230-kilovolt steel takeoff structure-General plan and elevations.

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Conductors:

NOTES

Transformer circuits No.1, No. 2 and No. 3,
2167M.GM, ACSR (KIWI).

Transformer circuit No. 4, 954 M.C.M, ACSR (Cardinal).
Ground wires:& dia 7 strand, high strength, galvanized
steel cable, spanto C4-72. dia, 7 strand, all
other spans where ground wires are shown
Tabulated values for sag of conductors include
insulator deflection.

All phases in any one span to be strung to the same sag
Spring assembly, item No 23, 4900 lb. capacity, approximate
deflection = te per 1000 lbs.

All conductors in the power plant approach spans for Circuit
No.1 between CI-PP & CI-TI, Circuit No 2 between C2-PP
& C2-TI, and Circuit No 3 between C3-PP & C3-TI
are to be strung prior to stringing the conductors and
ground wires in the intermediate spans between towers
ti-Ti & CI-TZ, C2-TI & C2-T2, and C3-TI & C3-72
All conductors and ground wires in the canyon crossing span
for Circuit No. 4 between towers C4-TI & C4-T2 are to be
strung prior to stringing the conductors and ground wires in
the switchyard geproach spans between C4-T2 & C4-$y, and
C4-72&. All other spans may be strung at any
elected sequence.

Transf Circuit No. 4

C4-TI

Points of attachment.

SAG MEASUREMENT

Figure 214.-Transformer circuits stringing requirements.

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