high mechanical strength. The starting windings shall be designed to
permit any pole or group of poles to be removed.
2.1.9
Exciter
Each synchronous motor shall be provided with a direct connected exciter
without brushes, commutators, or additional bearings. The exciter shall be
capable of supplying continuously, and without overheating, the excitation
for the motor to which it is connected when the latter is operating at
rated power factor, voltage, frequency, and horsepower. The
field-protective function and the field switching and application function
shall be accomplished by semiconductor elements mounted on suitable heat
sinks supported on the motor rotor and ventilated by rotation of the rotor.
The exciter shall be either built into or so arranged that it is
ventilated from the main motor enclosure. The enclosure of the exciter
shall be of drip-proof construction comparable to that of the motor. The
control system shall apply excitation to the motor field at the speed and
phase angle required to obtain maximum pull-in torque. Exciter windings
shall be insulated as specified in paragraph GENERAL REQUIREMENTS. The
field coils shall be adequately insulated between turns and from the pole
pieces and shall be thoroughly braced to withstand the stresses which could
be imposed under maximum pump speed.
2.1.10
Shaft
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NOTE: Hollow shaft pumps shall be used whenever
possible, since they are more readily adjusted.
Pumps requiring large motors (above 1,000 hp) are
limited by the available motors. The exact motor
capabilities and sources of supply shall be
investigated when using hollow shafts with motors
above 1,000 hp. Solid shafts shall be used only
when the available motor designs require their use.
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The motor shaft shall be made of high grade steel, finished all over, and
of ample size to drive the pump under maximum load conditions. [The shaft
shall be of the solid type and shall be connected to the pump shaft with a
rigid adjustable coupling.] [The shaft shall be of the hollow type and
shall be connected to the pump shaft above the thrust bearing in a manner
that will permit the pump impeller to be adjusted vertically]. The
Contractor shall coordinate the connection with the pump shaft and shall
furnish a motor shaft with all provisions, fittings, and devices required
to conform to the shafting arrangement specified in Section 15131A VERTICAL
PUMPS, AXIAL-FLOW AND MIXED-FLOW IMPELLER-TYPE, paragraph SHAFTS. See
paragraph GENERAL REQUIREMENTS for treatment against corrosion.
2.1.11
Bearings
2.1.11.1
Thrust Bearings
Thrust bearings shall be spring type located above the rotor. A design in
which each pivot shoe rests upon a support of metal which may take a
permanent deformation in order to equalize the load on the bearing shoes,
or in which individual shoe pivots are supported on spring plates or spring
disks, is not considered to be of the self-equalizing type and will not be
acceptable. The stationary shoes shall be babbitt-lined. The thrust
bearing shall have ample capacity to support the maximum pump hydraulic
SECTION 16222A
Page 19
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