Selection For Overvoltage Protection - Siemens SINAMICS DCM Compact User Manual

12-pulse series connection
4.2 Configuration
4.2.5

Selection for overvoltage protection

The purpose of overvoltage protection is to protect the semiconductor valves of converters
against overvoltages between the phases of a three-phase network. The overvoltage
protection limit voltage may not exceed the blocking voltage of the valves to be protected.
Figure 4-7
The transformer is connected on the line side, as shown in the above figure. If the
transformer is disconnected under load, the magnetization energy across the arc of the
primary-side switch is not completely released. In the event of blocked firing pulses, this
energy results in an overvoltage on the secondary side of the transformer and must be
limited by the overvoltage protection.
When switching to no-load operation, the overvoltage protection must only handle the
magnetizing energy of the transformer. The magnetization energy is calculated as follows:
If the transformer is disconnected in the event of a fault, the shunted energy is greater in
relation to the load, whereby a distinction must still be made between motor and generator
load.
"SICROWBAR 7VV3002 AC overvoltage protection for thyristors and diodes" units are
available as overvoltage protection for the connection between the three line phases.
Information on the calculation of energy to be shunted in various operations and technical
data for SICROWBAR 7VV3002 can be found in the SICROWBAR 7VV3002 operating
instructions.
Internet link: SICROWBAR overvoltage protection 7VV3002 operating instructions
(http://support.automation.siemens.com/WW/view/en/17635427/133300)
Dimensioning for 10,000 operating cycles is recommended.
36
Overvoltage protection
W = Transformer magnetization energy
M
S = Transformer rated power
N
I = Transformer no-load current
o
I = Transformer rated current
N
f = Line frequency in Hz
Compact User Manual, 09/2015, A5E34871844H
12-pulse applications