Geo Brick Drive User Manual
Motor Setup
208
Field Weakening
Field weakening consists of decreasing the stator current component (lowering the magnetization current
Ixx77) in order to allow AC induction motors to achieve speeds superior to the specified base speed
(name plate). The lower the magnetization current, the higher is the speed that can be achieved.
Mag Current
Ixx77
Voltage/
Speed
(RPM)
Base
Speed
Nominal Field
Weakening
Nominal, at full motor voltage (230V)
208 VAC bus, Higher Ixx77
208 VAC bus, Optimized Ixx77
208 VAC bus, Lower Ixx77
Max Speed(s)
Before Field
weakening
Field weakening can be set up experimentally with the goal of finding the “lowest” minimum value of
Ixx77 which allows the motor to run at the user’s desired top speed, without exceeding the maximum
motor specified speed (i.e. bearings, overheating limitations).
The magnetization current Ixx77 can then be adjusted on the fly depending on the commanded speed, rpm
range scheduling in a background PLC for example, to provide good torque for positioning (e.g. rigid
tapping) at lower speeds, and allow high speed operation (e.g. for cutting) at the same time. In most cases,
the slip gain Ixx78 need not be changed.
Summary of Contents for Geo Brick
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