Motors-D81.1-complete-English-06-2020

© Siemens 2020
Synchronous reluctance motors for SINAMICS converters – VSD4000 line
Orientation
4
■ Technical specifications
Separately driven fan
For the technical specifications of the separately driven fans,
see page 1/77 "Technical specifications of separately driven
fans".
Bearings
For converter operation, as a result of the basic principle employed,
electrical bearing stress is created through the bearing
lubricant film due to a voltage that is capacitively coupled in.
The physical cause of this is the common-mode voltage at the
converter output that is inherent in the control method for a converter:
The sum of the three phase voltages is – in contrast to pure line
operation – not equal to zero at every point in time.
In order to apply currents to the motor which are sinusoidal as far
as possible (resulting in smoother running, lower oscillation
torques, and lower stray losses), a high pulse frequency is required
for the converter's output voltage. The related (very
steep) switching edges of the converter output voltage (and
also, therefore, of the common-mode voltage) cause correspondingly
high capacitive currents and voltages on the machine's
internal capacitances.
In the worst-case scenario, the capacitive voltage induced via
the bearing can lead to random arcing through the bearing lubricating
film, thus causing premature bearing aging or damage.
This physical effect, which occurs in isolated cases, has mostly
been observed in connection with larger motors.
EMC-compliant installation of the drive system is a basic prerequisite
for preventing premature bearing damage via bearing
currents.
The most important measures for reducing bearing currents are:
• Insulated motor bearing at the NDE.
Recommended from frame size 225 and higher:
• Use cables with a symmetrical cable cross-section:
L1
L3 L2
PE
Concentric
Cu or Al shield
L1
PE
• Preference given to a line supply with isolated neutral point (IT
system).
• Using grounding cables with low impedance over a wide
frequency range (DC up to approximately 70 MHz): for
example, braided copper ribbon cables, HF finely stranded
wires.
• Separate HF equipotential-bonding cable between motor
housing and driven machine.
• Separate HF equipotential-bonding cable between motor
housing and converter PE busbar.
• 360° HF contacting of the cable shield on the motor housing
and the converter PE busbar. This can be achieved using
EMC screwed glands on the motor side and EMC shield clips
on the converter side, for example.
PE
L3 L2
PE
L1
L3 L2
Steel reinforcement
G_D011_EN_00065
4/8 Siemens D 81.1 · 06/2020