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Description
3.5 Options
3.5.50
Demagnetization device for output transformer for starting converters
(option L30)
The demagnetization of the output transformer is required when starting from standstill. To
demagnetize, the demagnetization equipment generates a medium voltage from the auxiliary
voltage (e.g. 3 AC 400 V) and feeds this into the system. The demagnetization equipment
applies a defined AC voltage to the output transformer, and this AC voltage is then slowly
controlled to zero. In this way, the operating point of the output transformer is brought back into
the range suitable for making measurements, so that the measured signals required for tracking
are transferred without being falsified. This ensures correct position tracking during operation
with an output transformer. The excitation current is applied to the standing machine, and the
induced voltage is measured (tracked) at the machine terminals. The exact position of the rotor
is determined by the position of the three terminal voltages.
During this demagnetization procedure, the demagnetizing medium voltage is fed back into the
system via the step-up transformer.
If a step-up transformer is positioned between the converter output and the motor, this
measuring-circuit voltage is reduced in the ratio of the transformation ratio. The step-up
transformer can become distorted in its magnetic characteristic curve or saturated due to prior
activation. As a result, the measuring signal required for tracking may be distorted or may not
be transmitted. Incorrect tracking is possible.
In order to cancel the physical effect of the magnetization error, a demagnetization device is
used. The demagnetization equipment applies a defined AC voltage to the transformer, and this
AC voltage is then slowly controlled to zero. This brings the operating point of the step-up
transformer back into the neutral zone, thus enabling undistorted transmission of the
measuring signals required for tracking.
Warning and alarm messages to the transformer are evaluated via the additional TM15 module.
These are solely binary signals. Up to eight signals are output per step-up transformer or step-
down transformer.
The figure shows the principal outlay of the demagnetization device. The circuit consists of a low-
voltage converter with an output filter and a low-power step-up transformer. The
demagnetization device has no other interfaces, except the 3AC 400 V infeed, for example.
54
3rd Party LCI Control Upgrade
Operating Instructions, 02/2022, A5E31872818
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