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DC magnetization
DC magnetization can be applied to the motor to
• heat the motor to remove or prevent condensation, or
• to lock the rotor at, or near, zero speed.
Pre-heating
A motor pre-heating function is available to prevent condensation in a stopped
motor, or to remove condensation from the motor before start. Pre-heating involves
feeding a DC current into the motor to heat up the windings.
Pre-heating is deactivated at start, or when one of the other DC magnetization
functions is activated. With the drive stopped, pre-heating is disabled by the safe
torque off function, a drive fault state, or the process PID sleep function.
Pre-heating can only start after one minute has elapsed from stopping the drive.
A digital source to control pre-heating is selected by parameter 21.14. The heating
current is set by 21.16.
Pre-magnetization
Pre-magnetization refers to DC magnetization of the motor before start. Depending
on the selected start mode (21.1 or 21.19), premagnetization can be applied to
guarantee the highest possible breakaway torque, up to 200% of the nominal
torque of the motor. By adjusting the pre-magnetization time (21.2), it is possible
to synchronize the motor start and, for example, the release of a mechanical brake.
DC hold
The function makes it possible to lock the rotor at (near) zero speed in the middle
of normal operation. DC hold is activated by parameter 21.8. When both the
reference and motor speed drop below a certain level (parameter 21.9), the drive
will stop generating sinusoidal current and start to inject DC into the motor. The
current is set by parameter 21.10. When the reference exceeds parameter 21.9,
normal drive operation continues.
Program features 93
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