motors. Control shall provide continuous-speed adjustment from
minimum speed (2 percent at no hook load) to full speed. Control
shall provide automatic-regenerative braking for speed reduction
and slow down before brake setting. Control shall provide a
minimum 50-to-1 speed range.
f.
Bridge and trolley main central systems shall employ ac
adjustable-frequency, speed-regulated, control of ac squirrel cage
motors. Control shall provide continuous-speed adjustment from
minimum speed (2.5 percent at no-hook load) to full-speed.
Control shall provide automatic regenerative or dynamic braking
for speed reduction and slow down before brake setting. Control
shall provide a minimum 40-to-1 speed range with constant torque
acceleration, for base and subbase speeds.
2.4.6.4
Drift Point
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NOTE: Provide bridge and trolley directions
normally oriented to main compass headings.
Select method of festoon suspension. For multiple
girder cranes select underneath footwalk and for
single girder cranes select auxiliary girder. If a
hoist thermal sensor is specified, include
requirement for yellow pilot light. If a
micro-drive is specified, include the sentence, "A
2-position [_____]."
Pendant handles are required only if pendant is in
an explosion area. Monorail cranes do not require
an independent track for pendants.
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Trolley and bridge main control systems shall have a drift point between
OFF and first speed control point in each direction or shall have a
separate pushbutton.
2.4.6.5
Micro-Drive Motor and Clutch Control
Micro-drive system shall be designed such that when micro-drive is selected
at control station, all main motors shall be disconnected, and all
micro-drive clutches shall be energized. Operation of micro-drive motors
shall be from crane control station. Micro-motor control systems shall
provide single-speed in each direction by means of an
electrically-operated, full-magnetic, [reduced] [full] voltage type
starter. Power shall not be applied to any micro-motor unless all clutches
are fully engaged. If a clutch disengages during operation of
micro-motors, the mainline contactors shall open and all brakes shall set.
Application of power to any main motor shall be prevented with any clutch
engaged. A transfer switch shall be provided at crane control station to
allow transfer from either mode of operation to the other only when all
brakes have been set for not less than 5 seconds. A single CLUTCH-ENGAGED
green pilot light shall be provided [at the pendant station] [in the cab]
when all clutches are energized; individual CLUTCH ENGAGED pilot lights
shall be provided on drive control panels.
SECTION 14630A
Page 38
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