Siemens SINAMICS G130 Engineering Manual page 171

Information about motor remagnetization:
With a number of applications, for example, crane hoisting gear, elevators, cableways or cable liners, the drive is shut
down repeatedly at relatively short intervals by the issue of an inverter pulse disable command and the motor is reliably
halted by the sole action of mechanical holding brakes. To restart the drive, the mechanical holding brake is released
and the inverter pulse disable command is canceled. So that the motor can then produce the required torque as quickly
as possible, it is often remagnetized very rapidly. For this purpose, the shortest possible magnetizing time is selected
and the full overload capability of the inverter is utilized during remagnetization of the motor.
Every time the motor is remagnetized in this way, very high temperature swings occur as a result of the combination
of low output frequency and high current load and can have an extremely negative impact on the lifetime of the
IGBTs in the inverter in the applications described above. This is especially true when the application requires the
motor to be remagnetized rapidly at periodic intervals ranging from a few seconds to several minutes and, as regards
the configuring process, this scenario must be treated like a periodic load duty cycle with extremely high load
fluctuations.
In order to avoid a substantial reduction to the inverter IGBT lifetime with applications of this kind, a remagnetizing
period should be programmed that is long enough to ensure that the remagnetizing current does not exceed around
70 % of the inverter rated current. In applications for which an inverter pulse disable during standstill is not essential
for the process or for safety reasons, the inverter should continue to switch during the standstill period so that
remagnetization of the motor after restart becomes completely unnecessary.
Calculation example 1
A variable-speed drive must occasionally (around 3 times a day) perform a heavy duty start on a 690 V supply
system. The diagram below shows the motor current characteristic I(t) over time. The maximum ambient temperature
in the converter room is specified as 45 °C and the installation altitude is 400 m.
Motor current I(t) over time during starting
1. Select the converter
A SINAMICS G150 in degree of protection IP20 is selected as the drive converter. Its rated data are V = 690 V and
I = 575 A. It has, according to the Catalog D11, a base load current I
rated
I of 1.5 I = 771 A. We shall now use a calculation to check whether the selected converter operating on the
ShortTime * H
factory-set pulse frequency is capable of occasionally performing the required heavy duty start under the specified
conditions:
2. Determine the current derating factor k
With the following derating factors
·
k = 0.933 (ambient temperature 45 °C, installation altitude < 2000 m, degree of protection IP20),
Temp
·
k = 1.0 (factory-set pulse frequency)
Pulse
·
k = 1.0 (no parallel connection of S120 Motor Modules)
Parallel
·
k = 1.0 (not a periodic load duty cycle, but only an occasionally required overload)
IGBT
the current derating factor k
= ×
k k k
D Temp Pulse
3. Determine the permissible short-time current:
With a base load current I
H
= ×
.
I 1 5
ShortTime
This value corresponds to the motor current of 720 A required at the beginning of the heavy duty start and is
therefore just within the permissible limit.
Fundamental Principles and System Description
:
D
is
D
× × =
k k 0 . 933
Parallel IGBT
= 514 A and a derating factor k
× = × ×
. .
k I 1 5 0 933 514
D H
of 514 A and therefore a short-time current
H
× × × =
1 . 0 1 . 0 1 . 0 0 . 933
.
= 0.933, the permissible short-time current is
D
=
A 720 A
.
SINAMICS Engineering Manual – November 2015
Engineering Information
171/528
Ó Siemens AG