SIEMENS
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Siemens MD 50.8 · 2017
Configuring guide
Configuring a motor for inverter operation
2
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Permissible voltage stress
More stress is placed on the insulation of the motor winding with
inverter operation than with line operation. The voltage stress
also depends on the type of inverter used. The inverter subjects
the motor winding to stress specially as voltage pulses are
quickly switched.
The maximum voltage is influenced by the rise time of the
pulses, the cable length and the type of cable used between
motor and inverter.
Output filters at the inverter can reduce the maximum motor
voltage to uncritical values. When using output filters, the control
type, pulse frequency, output frequency, and limit torque that
can be realized need to be observed, among other factors.
With inverters without output filters, impermissible voltage peaks
can occur even with a relatively short motor cable. Regenerative
operation, in particular, can stress the motor insulation. This
stress occurs predominantly during vertical motion and is
dependent on the line voltage, inverter type, cable length, and
cable type.
For further details, see
chapter "Motor options", page 6/8
.
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Bearing currents
Additional bearing currents can flow when motors are operated
from inverters. They are mainly caused by the steep voltage
rises which occur during switching. Without output filters,
significant voltage variations can occur at the winding terminals.
This phenomenon mainly occurs for larger machines.
EMC-compliant installation of the drive system is a basic
prerequisite for preventing premature bearing damage as a
result of bearing currents.
The most important measures for reducing bearing currents are:
•
Insulated motor bearing at the non-drive end (NDE).
•
Using cables with a symmetrical cable cross-section:
•
Preference given to a line supply with insulated neutral point
(IT system).
•
Using grounding cables with low impedance over a wide
frequency range (DC up to approximately 70 MHz):
e.g. braided copper straps, HF finely stranded conductors.
•
Separate HF equipotential-bonding cable between motor
housing and driven machine
•
Separate HF equipotential-bonding cable between motor
housing and inverter PE busbar
•
360° HF contact of the cable shield at the motor housing and
the inverter PE busbar. This can be achieved using EMC
screwed glands on the motor end and EMC shield clips at the
inverter, for example.
•
Using motor reactors at the inverter, common-mode filter at the
inverter output.
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Mechanical stress, grease service life
High speeds that exceed the rated speed and the resulting
increased vibration alter the mechanical smooth running
operation and the bearings are subject to increased mechanical
stress. This reduces the grease service life and the bearing
service life.
More detailed information on request.
L1
L2
L3
L1
L2
L3
L1
L2
L3
PE
PE
PE
PE
Concentric copper or
aluminum shield
Steel armor
G_D087_EN_00074
© Siemens AG 2017