Quantcast Motor-Generator Sets Used With Generator-Field Control - mo1180228

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9.6.14 Driving-Machine Brake
9.6.14.1 Inspection Made with Power On. Close the mainline switch and proceed. Run the car
and observe the operation of the brake. The brake should not chatter. It may apply on or before
the completion of the slowdown and leveling operation. Check to see that the brake is
automatically applied on normal stops. The clearance between the brake shoe and the brake
drum when the car is running should not be greater than necessary to permit free running.
Examine the brake pins to determine whether they are properly lubricated and not frozen, and
that the cotter pins are in place and open. Note any harsh and abrupt brake action. Motors of
motor-operated brakes should be examined as described previously. In addition to the above, on
mechanical brake installations, note that the operation of the brake actuating device releases the
brake only when power is applied in the machine. Many control systems, by design, stop the
elevator electrically when it reaches the floor, then allow the brake to set. This is done to prevent
a bump on stopping, which is caused when the brake sets. Brake operation should be checked,
where applicable, to see that this feature is working properly.
9.6.14.2 Inspection Made with Power Off. Open the mainline switch and proceed. Examine the
brake and-drum to determine that the brake linings are free of oil and whether there is any
scoring of the drum. The design of the actuating linkage of some brakes is such that a single unit
or link is used both to govern the spring pressure applying the brake shoes when the brake
applies and the amount of clearance between the brake shoes and the brake drum when the brake
is released. With this type of design, it is possible to improperly adjust the releasing feature so
that it will prevent the brake application. The adjustment of this type of brake should be
examined to determine that the adjustment is such that the brake shoes are not prevented from
properly applying and that there is sufficient margin in the adjustment for the brake lining wear.
Be sure to check the oil level of oil immersed coil type brakes. Also, the brake coil leads,
connections, and windings should be examined to check insulation conditions and physical
connections. In addition many brakes have electrical contacts that are used in various control
functions. These should be checked to assure proper contact operation, insulation on wire and
contacts, and condition of connections.
9.6.15 Motor-Generator Sets Used With Generator-Field Control
Motor-Generator sets and exciters that are part of the hoist control system should operate
smoothly without excessive noise or vibration and should be inspected as previously described
for driving machine motor.  Motor-Generator sets and rectifying units used to convert AC to
DC for the operation of one or more dumbwaiters, but which are not one of the units of
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