SIEMENS
SINAMICS DCM
Accessories and supplementary components
SICROWBAR AC
4/24
Siemens D 23.1 · 2014
4
■
Application
SICROWBAR AC overvoltage protection
SICROWBAR AC
is used to protect power semiconductors
(thyristors and diodes) in converters against overvoltages
between the phases of a three-phase line supply. The range of
applications is not restricted to protecting DC drive converters,
but can also be used for infeed/regenerative feedback units of
AC drive systems that are equipped with thyristors. Overvol-
tages that occur on the AC side of converters are mainly caused
by switching operations when disconnecting from the line sup-
ply at the transformer primary. This applies both to operational
switching operations (shutdown under no-load conditions) as
well as in the case of a fault (shutdown under load).
Overvoltage protection is normally used in the following con-
figuration:
■
Design
There are three device versions depending on the rated voltage:
The power section of the overvoltage protection device has a
P3C connection, 3-pulse fully controlled polygon connection.
The feeders to the polygon connection have metal-oxide
varistors that absorb overvoltage energy.
Semiconductor fuses included in the devices are accommo-
dated in a fused disconnector with integrated fuse monitoring.
The break-over diodes (BOD) and RC snubbers for the thyristors
and varistors are mounted on a printed circuit board as are also
the gate series resistors and diodes that transfer the line voltage
to the break-over diodes.
■
Mode of operation
If an overvoltage occurs, which reaches the response voltage of
the integrated firing module, then the break-over diodes trigger
and in turn trigger their associated thyristors. As a consequence,
the varistors are switched to the line supply. The varistors absorb
the overvoltage energy. An RC protective circuit protects the
thyristors against an excessively steep voltage rate of rise when
the current is interrupted.
■
Configuration
Notes on selection
The following conditions should be maintained when selecting
the overvoltage protection:
•
The limit voltage of the overvoltage protection
V
RRM55
must not
exceed the highest periodic and permissible peak blocking
voltage of the power semiconductors to be protected.
•
The rated supply voltage of the overvoltage protection must
not be exceeded.
•
Commutation overvoltages of the converter that periodically
occur must remain below the response voltage of the over-
voltage protection. The energy absorption capability of the
selected overvoltage protection should be checked. A distinc-
tion must be made between two operating cases:
- Transformer is shut down under no-load conditions
- Transformer is shut down under load
Detailed notes on configuration, standards and connection of
the overvoltage protection are provided in the operating
instructions or on the Internet at
18260008/130000
.
G_D023_EN_00073
Converter
unit
Line supply
1
4
2
W
V
U
Version
Rated voltage
Design, installation
A
Up to 580 V
Mounted in an enclosure.
For mounting in an upright position on
panels in cabinets or machine frames.
B
Up to 725 V
Mounted on a baseplate.
For installation in 600 m wide cabinets.
C
Up to 1150 V
Mounted on a baseplate.
For installation in 600 m wide cabinets.
© Siemens AG 2014