Special Insulation For Line Supply Voltages > 500 V In Converter-Fed Operation; Bearing Currents - Siemens SINAMICS G130 Engineering Manual

Special insulation for line supply voltages > 500 V in converter-fed operation
The standard insulation of the 1LA and 1LG motors is designed such that unrestricted operation on a SINAMICS
converter is possible only on line supply voltages up to 500 V +10 %. Motors operating on higher line supply voltages
require stronger insulation. Alternatively, filters such as the dv/dt filter or sine-wave filter must be provided at the
converter output.
Asynchronous motors of types 1LA8 / 1PQ8 and 1LG6 are also available with special insulation for converter-fed
operation on line supply voltages from > 500 V to 690 V, which means that no filters need to be provided at the
converter output. These motors are identified by an "M" in the 10th position of the order number, e.g. 1LA8315-
2PM80.
Synchronous motors of type 1FW4 are designed specifically for converter operation and therefore feature special
insulation as standard.
The diagram and the table below show the permissible voltage limits for motors with standard insulation and for those
with special insulation for converter-fed operation on voltages ranging from > 500 V to 690 V.
Permissible limit values V
PP
A: Standard insulation
B: Special insulation
Winding insulation
A = standard insulation
B = special insulation
Permissible voltage limits for Siemens low-voltage motors with round-wire windings up to 690 V
In comparison to standard insulation, the ratio between insulation material and copper within a single slot is less
favorable with the special insulation, causing a slight reduction in the rated output of motors with special insulation.

Bearing currents

The fast-switching IGBTs in the inverter cause steep voltage edges which generate bearing currents in the motor.
Under unfavorable conditions, these currents can reach relatively high values, cause damage to the bearing and
therefore reduce its lifetime.
To prevent damage caused by bearing currents, it is advisable to provide an insulated bearing at the non-drive end
(NDE) of motors operating on a converter supply. The insulated NDE bearing is standard on all 1LA8 motors that are
designated as suitable for converter operation (9th position of order no. = "P", e.g. 1LA8315-2PM80). Insulated NDE
bearings are available for 1LG4/1LG6 motors of frame size 225 and above as option L27. The use of this option is
highly recommended at converter operation.
In systems with speed encoders, it must be ensured that the encoder is not installed in such a way that it bridges the
bearing insulation, i.e. the encoder mounting must be insulated or an encoder with insulated bearings must be used.
For further information, please refer to the section "Bearing currents caused by steep voltage edges on the motor" of
the chapter "Fundamental Principles and System Description".
for Siemens insulation systems:
Line supply voltage
V
Line
≤ 500 V
> 500 V to 690 V
Phase-to-phase Phase-to-earth
V V
PP permissible PE permissible
1500 V 1100 V
2250 V 1500 V
SINAMICS Engineering Manual - May 2008
Motors
Engineering Information
DC link voltage
V
DCLink permissible
750 V +10 %
1125 V +10 %
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