Alimak Scando 650 DOL, Technical Description

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Arrangement of power supply
Direct On Line (DOL) starting of electric motors results in a very
high starting current. The current must overcome the resistance
in the cables which results in a voltage drop. This voltage drop
occurs not only in the trailing cables, but also in the power
supply cable installed between the jobsite distribution board and
the electric panel ”B” at the base. The total voltage drop is the
sum of the voltage drop in all the cables. The consequence of
the voltage drop is a substantial reduction in the output torque
of the motor.
In order to avoid starting problems it is of the utmost importance
that the main power supply is adequately sized with respect to
the starting current and the voltage drop. The following data
should be noted:
– During starting conditions, in the upward direction with rated
load, the voltage drop must not exceed 15% of the rated
voltage when measured at the motor terminals. In the Base
panel, the voltage drop of the incoming power supply
terminals must not exceed 3% of the rated voltage during the
starting conditions.
– Once the rated speed is established during upward travel with
rated load, the voltage drop must not exceed 5% of the rated
voltage when measured at the motor terminals. In the Base
panel, the incoming power supply voltage should, in practice,
not drop at all, i.e. not exceed 1 – 2 % drop.
– Except for the above mentioned supply voltage levels
during start and running conditions, the quality of the
main power supply to the lift/hoist must be in accordance
with the requirements of EN 50160:1999.
Client’s power supply
Supply cables to hoists with DOL or Y/D starting
The 3-phase power supply cable from the jobsite distribution
board to the ”B” panel at the base can be calculated from the
formulas below. The formulas are applicable for the most common
types of hoists having 1 or 2 motor drive machinery with DOL-
starting at 400V, 50Hz and 460V, 60Hz.
Note: If an earth leakage circuit breaker, ELCB, (ground fault
circuit breaker) is to be used, the trip-out value should be
chosen for equipment protection i.e. 500mA.
Use of 30mA ELCB is not recommended as it continuously
trips due to the motor starting current.
ALIMAK 34734 - 1/01
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