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Páginas: 17 (4150 palabras) Publicado: 11 de junio de 2012
Controlled Induction Motor Drives Supplied by
Frequency Converters on Belt Conveyors –
Modeling and Commissioning
Borislav Jeftenić1, Leposava Ristić2, Milan Bebić3, Saša Štatkić4
Faculty of Electrical Engineering University of Belgrade;
Bulevar Kralja Aleksandra 73, 11000 Belgrade, Serbia
Tel: (+381 11) 3218 364, fax: (+381 11) 324 86 81
Abstract - During the past two decades, drive and control
system of belt conveyors on open pit lignite mines have seen
significant advances. The main demand for new construction of
belt conveyors was the increase of reliability, unit capacity,
minimization of personal, reduction of maintenance cost,
increase of safety, reduction ofconsumed energy, etc. The paper
presents detailed mathematical model of the belt conveyor
suitable for analyses of both static and transient operating
regimes. The model includes electrical drive system of the
conveyor, and the mechanical part, with the special attention
given to the elastic nature of the belt. Simulation results of the
developed model for the drive with frequency converter arepresented. Experimental results from the field measurements
confirm the validity of the model.



One of the demands for the modern conveyor is the
operation with variable speed. Speed control of conveyors is
justified, since most of the time conveyors operate with less
then maximum capacity. In such a case, by the reduction of
belt conveyor speed, the available loadcross-section is
exploited to the greatest possible degree. The main
advantages of the belt conveyors with variable speed drives
are [1]:
• Optimal loading of the belt based on variable speed (in
the range from 50 to 100%) as a function of the current
material inflow. Reference speed of the conveyor is
calculated based on the measured cross-section of material
inflow (load cross-section).
•Reduced wear of gears and belt due to the controlled start
and stop of the conveyor.
• Elimination of belt slippage on drums during the start and
in operation.
• Adequate load distribution among drive drums.
• Equal loading of motors on the same drive drum.
Beside direct positive effects, there are other indirect
advantages seen through the maintenance process:
• Easier maintenance.
•Longer operation life of gears and bearings.
• Significantly improved protection of the equipment.
Given their high robustness and low price, cage induction
motors are very suitable for application on open pit mines.
This is the reason for wide acceptance of variable speed
drives with cage induction motors which are naturally fed

from the frequency converters on belt conveyors.
Control systemsused in frequency converters enable their
use in the system of automatic speed control of the belt
conveyor. Moreover, they offer features which are expected
from novel control systems, such as comfort, accurate and
reliable setting of the ramp time for achievement of the full
speed, drive overload level, method of breaking (regenerative,
dynamic breaking), etc.
Rated speed is required forachievement of full capacity of
the conveyor, but less-than-rated capacity can be achieved
with reduced speed. On the other hand, the required power is
a function of speed and loading of the belt. Fig. 1 shows the
family of curves for required drive power as a function of
capacity for different conveyor speeds [2]. The figure also
shows lines connecting points with the same belt loading. Itis
obvious that the same capacity, less than maximum, can be
conveyed with different speeds, therefore requiring different
power. For example, capacity of 60% can be conveyed with
70% power at rated speed, but also with 55% power if the
speed equal to 60% of the full speed is selected. With this in
mind, and considering the operation of the belt with reduced
capacity, it is clear that...
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