Each motion of a crane is required to be controlled by a separate
controller. Each controller is required to be electrically and mechanically
interlocked between directions; mechanical interlocks are not required for solid
state controllers. Bridge and trolley motor stepped control systems on bridge
cranes, rotate motor stepped control systems on portal and floating cranes, and
travel motor stepped control systems on portal cranes are required to be provided
with a drift point between OFF and the first speed control point in each
direction. All electrical components are required to be located so they are
easily accessible for inspection and maintenance.
On all cranes with cabs, an operator controlled warning horn capable of
producing a maximum audio signal of not less than 100 db at 10 feet is required.
On outdoor cranes, a thermostatically controlled anti-condensation heater
is required to be installed in each control panel enclosure. It is required to be
selected to provide 7 watts per cubic foot. All heaters are required to be fed
from a separate panel dedicated to equipment heater and battery charger circuits.
AC Control Equipment. All AC control circuits are required to be fed
from a single phase, air cooled, double wound transformer with a grounded metal
screen between the primary and secondary windings of the transformer. "Single
phasing" protection is required to be provided in all AC controllers for hoist
drives. Plugging protection is required to be provided for bridge and trolley
drives with AC squirrel cage motors.
For bridge and trolley drives with AC squirrel cage motors, an electrical
torque reduction unit, utilizing solid state components, is available to operate
with each motor's electromagnetic controller to limit torque when the motor is
starting or changing speed. The unit is specifically designed and marketed as a
standard commercial product for use on cranes. Maximum torque is adjustable. The
length of time the unit limits torque, subsequent to motor starting or changing
speed, is adjustable. If used, the unit is required to be sized so as to provide
sufficient starting torque to initiate motion of the motor from standstill with
rated load under the hook.
sinusoidal pulsewidth modulation type in accordance with NEMA ICS 7. Each
controller is required to include a full wave rectifier and a three-phase
inverter. Each adjustable frequency controller is required to be selected so that
its continuous current rating is not less than 200 percent of full load motor
current; their peak inverse voltage ratings are required to be greater than 200
percent of the working peak inverse voltage. A flux vector controller is required
to enable the motor to develop full torque continuously at zero speed. Each
controller is required to include as a minimum: electronic instantaneous
overcurrent protection, undervoltage protection, DC bus overvoltage protection,
ability to withstand output line-to-line shorts without component failure, and
continuous auto restart for source related faults only. Transients and harmonics
protection are required to be provided; provision of standing wave protection is
required for specific installations. Acceleration time and deceleration time are
required to be independently adjustable from 2 to 20 seconds. The motors are
required to run smoothly, without torque pulsations at the lowest speed, and are
required to be energized at a frequency not exceeding 60 Hz at the highest speed.
Motor overload protection is required to