General Notes - WEG CFW-11 Applications Manual

Introduction to the Crane
Being:
P = Braking resistor power (kW);
R
P = Motor rated power (kW);
M
%ED = Braking duty cycle.
NOTE!
Refer to the CFW-11 user's guide, table 3.3, to verify the ohmic value of the braking resistor to be
used according to the frequency inverter model.

1.5.3 General Notes

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The braking resistor selection can be optimized if the customer provides the power calculated for the load
hoisting or for its horizontal motion. E.g., supposing that the power calculated for the hoisting of an overhead
crane is 62 kW, the used motor would be a 75 kW (commercial value). In this case, the braking resistor can be
obtained from the calculated power, in other words, 0.7 x 62 = 43.4 kW. The same procedure can be adopted
for the horizontal motion;
■
The installation condition, vibration, protection degree and painting, must be observed for the braking resistor
specification;
■
For the replacement of slip ring motors by standard motors, use a minimum factor of 1.2. The inverter
selection criteria remain the same, adopting the current of the new motor. Another criterion that can be adopted
is to use a motor whose frame is the same of the slip ring motor, provided that the ratio between the power of
the new motor and the old one is close to 1.2. The slip ring motors used in cranes usually have bigger frame
sizes than the same power range standard motors. The main advantage of adopting this criterion is the easy
mechanical adaptation of the new motor.
Crane Horizontal Motion | 13