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Revision 8.6
SECTION 5 : COMMISSIONING
74
Step 14 (Hoist only)
Test under load conditions: Run the motion in both directions notch by notch. Specifically look out for
the operation of the brake drum. During Hoisting operation, the brake drum must not turn in reverse
(lowering direction); if this happens it may indicate one of the following:
Load is greater than the safe working load (SWL) of the Hoist motion
The supply is weak, and under load conditions it drops drastically
The Rotor resistances are not correctly designed
The motor is not performing as per manufacturers design, this may occur after several rewinds
The above mentioned problems may also be causing the motor not to accelerate to full speed under
load conditions.
During lowering operations, the following aspects must be checked:
The motor maintains the required slow speeds. When accelerated to full speed and then returned to
“neutral” position the deceleration to full stop should be achieved within reasonable time (i.e.
approximately 3 sec). At stop, the brakes should apply when the motor is at standstill or just started
turning in the opposite direction.
Failure of achieving the above may be caused by one or several of the reasons already described
above for hoisting operation.
GENERAL NOTE
It is always good practice to record in some
form all current readings during the above
tests. These readings serve as a base for
future comparisons, specifically after a motor
or a section of the rotor resistance has been
replaced for whatever reason.
Step 15
During hoisting measure the peak stator currents during acceleration to full speed under full load
conditions, ensure that these currents are well within 2.5 x motor nominal stator current. A sudden rise
in current well above this value specifically during switching of any of the rotor contactors may indicate
problems in the wiring of the rotor resistance.
This needs to be carefully checked and compared to the schematic diagrams supplied.
