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performed several times. Remember that the fan motor is also equipped with bearings to
which the above instructions apply.
Measurements on the motor
Measurement of field current, field voltage, field current with display parameters in the
SINAMICS DCM: r50035
Field voltage by means of an external voltmeter and comparison with the calculated voltage,
see above.
Measurement of the armature voltage, armature current through display parameters in the
SINAMICS DCM:
Current: r50019, voltage: r50038
It may be necessary to check by measurement with an additional measuring instrument.
Field resistance: with ohmmeter, desired result: rated field voltage / rated field current
according to the motor rating plate, measured value is approx. 25% lower than calculated for
a cold winding.
Armature resistance, several milliohms to ohms depending on motor size, milliohmmeter
required.
Precautions when operating the SINAMICS DCM on an old motor
By old motor, we mean a motor that is at least 20 years old that was not originally designed
for operation on the converter, e.g. retrofit replacement of motor power supply through a
Ward-Leonard generator set by a converter.
Because the old motor was usually designed to have a power margin, no special precautions
are usually required with regard to additional losses due to converter operation. However, the
current commutation with greater current ripple due to converter operation must be taken into
account. The current ripple of the direct current (rms value of the current ripple) is calculated.
This should not be greater than 10 % of the rated current of the motor in the worst case.
Siemens technical advisers will support you in calculating the smoothing reactor required in
the DC circuit to comply with the above current ripple data. Please state the nominal line
voltage and the rating plate data of the motor.
It is helpful to specify the armature resistance and the armature inductance of the motor. If
this data is no longer available, we will estimate it and allow a margin in the reactor rating.
If the motor was already being operated with a converter and a smoothing reactor is in use,
this must be retained when the 6RA80 is retrofitted.
Lower rates of current change are permissible on old motors than on modern DC motors.
High rates of current change on the old motor can result in the occurrence of overcurrent
peaks in the armature current (due to commutation problems). Therefore activate the current
setpoint integrator in the SINAMICS DCM: Set p50157 = 1, p50158 = approx. 0.04 s.
If an iron-cored smoothing reactor is used, set p50153 = 2.
