Operation At Motors With Electrically Isolated And With Common Winding Systems - Siemens SINAMICS G130 Engineering Manual

5.9.3

Operation at motors with electrically isolated and with common winding systems

The motor can have either electrically isolated winding systems or a common winding system. The kind of winding
system combined with the number of inverters in the G150 parallel connection determine the decoupling measures
which need to be implemented at the outputs of the parallel-connected inverters or Motor Modules of the G150.
The two possible variants, i.e.
·
motor with electrically isolated winding systems,
·
motor with a common winding system,
are discussed in more detail below.
Operation of G150 parallel converters with motors that have electrically isolated winding systems
Motors within the output power range of the G150 parallel converters generally have multiple parallel windings. If
these parallel windings are not interconnected inside the motor, but connected separately to its terminal box(es), then
the motor winding systems are separately accessible. Many drives can be configured in such a way that each motor
winding system can be supplied by exactly one of the parallel-connected inverters or Motor Modules of the G150.
There are however configurations in which this type of arrangement is not possible. Both variants are permissible and
are described below.
1. The number of separate winding systems exactly matches the number of G150 inverters
In this case, it is merely necessary to ensure that the motor-side currents are balanced by:
·
Use of symmetrical power cabling between the inverters and the motor (cables of identical type with the
same cross-section and length).
Due to the complete electrical isolation of the winding systems, this arrangement offers the advantage that no
decoupling measures need to be implemented at the converter output in order to limit any potential circulating
currents between the parallel-connected inverters (no minimum cable lengths and no motor reactors or filters) and
thus the best possible quality of current balance is achieved.
The motor-side inverters can utilize both space vector modulation and pulse-edge modulation. Pulse-edge
modulation makes it possible to achieve a maximum output voltage which is almost equal to the value of the input
voltage (97 %). (For further details, please refer to chapter "Fundamental Principles and System Description",
sections "Maximum attainable output voltage with space vector modulation SVM" and "Maximum attainable output
voltage with pulse-edge modulation PEM".)
Despite the current-balancing measures described above, it is not possible to obtain an absolutely symmetrical
current distribution which means that the currents of the rectifier sections or inverter sections in a SINAMICS G150
parallel converter are 7.5 % lower than the currents of the individual rectifiers or inverters. Allowance is already made
for this reduction factor in the current values specified in catalog D 11 and in the table shown a few pages above in
this manual.
Parameter p7003 must be set to "1" during commissioning (multiple electrically isolated winding systems).
2. The number of separate winding systems does not exactly match the number of G150 inverters
The number of separate winding systems that can be implemented in the motor depends on the number of motor
poles. While the values in brackets are theoretically possible, they are generally not feasible in practice owing to lack
of space.
Number of motor
poles
2
4
6
8
Possible number of separate winding systems as a function of the number of poles
As a result, it is not always possible to assign a separate winding system of the motor to each of the parallel-
connected G150 inverters or Motor Modules. However, it is possible to assign electrically isolated winding systems to
more than one inverter or Motor Module – as illustrated in the example below of a motor with three winding systems
and a G150 converter with two inverters or Motor Modules.
Possible number of separate winding systems
2
2, 4
2, 3, (6)
2, 4, (8)
Engineering Information
SINAMICS Engineering Manual – November 2015
SINAMICS G150
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Ó Siemens AG