Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
96/528
Due to the line filter which is a standard feature of SINAMICS Chassis the high-frequency interference current gets a
low-resistance return path to its source so that a high percentage of the interference current I
Leak
can flow via the filter
inside the Chassis unit. As a result, the supply system is loaded with lower interference currents I
PE
< I
Leak
and the
interference level at the point of common coupling drops to the level of category C3.
If the optional line filter is installed in the cabinet in addition to the standard line filter fitted to SINAMICS Chassis,
almost all the interference current I
Leak
is diverted before it can exit the drive system and the load on the power
supply is reduced still further (I
PE
<< I
Leak
), i.e. the interference level drops to the value defined for category C2.
High-frequency interference current at the line-side PE connection as a function of line filters
1.5.3.4 Magnitude of leakage or interference currents
The magnitude of the high-frequency leakage currents depends on a large number of drive parameters. The most
important influencing factors are:
· Level of the line voltage V
Line
or the DC link voltage V
DCLink
of the converter
,
· Voltage rate-of-rise dv/dt produced by fast-switching IGBTs in the inverter,
· Pulse frequency f
P
of the inverter,
· Converter output with or without motor reactor or motor filter,
· Impedance Z
W
or capacitance C of motor cable,
· Inductance of grounding system and all ground and shield connections.
The inductance values of the grounding system and the exact grounding conditions are normally not known so it is very
difficult in practice to precisely calculate the leakage currents that are likely to occur. It is however possible to work out
the theoretical maximum values of the leakage current I
Leak
carried by the motor cable shield if we assume that the
grounding system inductance is negligible and the line filter action is ideal. In this case, the peak value of leakage
current î
Leak
can be calculated as follows from the DC link voltage V
DCLink
and the impedance Z
W
of the motor cable:
W
DCLink
Leak
Z
V
î =
.
If we apply this formula to the converters and inverters in the SINAMICS range and assume the Infeed to be
400 V 3AC plus the maximum number of parallel motor cables n
max
and the maximum cross-sections of shielded
motor cables A
max
, then the magnitudes of the theoretical peak values î
Leak
of the leakage currents carried by the
motor cable shields are calculated to be:
· Booksize format 1.5 kW - 100 kW î
Leak
= 10 A – 30 A
· Chassis format 100 kW - 250 kW î
Leak
= 30 A – 100 A
· Chassis format 250 kW - 800 kW î
Leak
= 100 A – 300 A
1
The associated rms values I
Leak
are approximately 10 times lower when the following supplementary conditions
apply:
· Pulse frequency f
P
matches factory setting
· 300 m shielded motor cable (with n
max
and A
max
)
IPE without Line filter (category C4) IPE with Line filter (category C3) IPE with Line filter (category C2)
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