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SOFT STARTERS
In the surface mines, asynchronous motors with
collector rings drive the high power conveyor belts. An example for the
usual solution is that 6 motors of 630kW each drive a belt of a length
of 3km. The VHJ Ltd. has developed dry resistance starting and load distributing
equipment for the start and load distribution of the motors, which drive
especially such long conveyor belts. The soft start can take place in
91 grades and the load distribution in 18 grades. The dry resistance stages
connected to the collector ring are short circuited by thyristors operating
in a full wave control mode. This solution decreases substantially the
number of the resistance stages and it does not increase the reactive
power taken by the motor.
The heat-pipe cooling – fitted to the circumstances
of the mine - ensures the transmission of the loss power without moving
components in natural ventilation mode.
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