Siemens SINAMICS S120 - Page 181

Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
181/528
The procedure for air-cooled converters and inverters is described below (liquid-cooled inverters on request).
The current derating factor k
Pulse-2x
to be applied practically in the case of pulse frequencies corresponding to twice
the factory setting is calculated on the basis of the relevant current derating factor k
Pulse
given for pulse frequencies
equal to twice the factory setting in the sections on specific unit types according to the formula
÷
ø
ö
ç
è
æ
-
×+×
÷
ø
ö
ç
è
æ
°
-°
×+×
÷
÷
ø
ö
ç
ç
è
æ
-
×+×=
-
-
-
-
Hz
Hzf
C
TC
V
VV
kk
OutA
Line
LineLine
PulsexPulse
50
10
05.01
40
40
2.015.01
min
max
max
2
.
Key to formula:
· k
Pulse-2x
Current derating factor to be applied practically for pulse frequencies equalling twice the factory
setting.
· k
Pulse
Current derating factor according to the tables in sections on specific unit types for pulse
frequencies equaling twice the factory setting.
· V
Line-max
Maximum line voltage:
480 V for units with line supply voltage ranges: 380 V – 480 V 3AC
510 V – 720 V DC
690 V for units with line supply voltage ranges: 500 V – 600 V 3AC
660 V – 690 V 3AC
500 V – 690 V 3AC
675 V -1035 V DC
· V
Line
Line voltage at installation site.
· T
A
Ambient temperature at installation site:
Permissible value range within the limits of the above formula: T
A
= 10 °C – 40 °C.
· f
Out-min
Minimum operational output frequency:
Permissible value range within the limits of the above formula: f
Out-min
=10 Hz – 50 Hz.
Notes:
· The calculation formula is valid only for pulses frequencies which equal twice the factory setting. For higher
pulse frequencies, the current derating factors in the sections on specific unit types must be applied
unchanged. This is because the current derating factors can be reduced as a function of influencing
parameters to only a minimal degree for these pulse frequencies and the effect is generally negligible.
· In applications where the values of the influencing parameters are so favorable as to give a current derating
factor k
Pulse-2x
> 100 %, then k
Pulse-2x
= 100 % must be set, because it is fundamentally impossible to
operate inverters continuously on currents higher than I
rated
due to the I
2
t monitoring function.
· If the system reacts to overload with a pulse frequency reduction, e.g. because the configured ambient
temperature is exceeded temporarily, the pulse frequency switchover will cause certain transient
phenomena in the current and torque similar in nature to the effects of the pulse pattern switchover between
space vector modulation SVM and pulse-edge modulation PEM. The drive must have the control capability
to withstand these transient phenomena. For this reason, overload reactions with pulse frequency reduction
are more appropriate for applications for which control quality is less critical, e.g. pump and fan drives.
Otherwise, the drive must be engineered in such a way as to guarantee that the conditions which would
allow the overload reaction to intervene in normal drive operation can never be fulfilled.
· With respect to periodic load duty cycles, it must be noted that high currents up to the maximum current I
max
combined with increased pulse frequencies trigger an overload reaction very quickly owing to the high power
losses, resulting in periodic switchover between pulse frequencies accompanied by very high temperature
swings ΔT
Chip
in the IGBTs and therefore ultimately to premature failure of the power units. When periodic
load duty cycles with high overload are configured therefore, we urgently recommend application of the
current derating factors k
Pulse
as specified in the tables in the sections on specific unit types and advise that
overload reactions with temperature-dependent reduction in the pulse frequency (p290 = 2 or 3) should not
be used. This applies in particular if the current derating factor k
IGBT
is calculated to be < 1.0 when the drive
is configured as described in section "Free load duty cycles".