49
If only the short-circuit power S’
k1
on the high-voltage side of the line transformer is known,
S’
k2
can be calculated as follows:
S’
k2
= S
T
/ (u
k
+ S
T
/ S’
k1
); S
T
: Transformer apparent power, u
k
: Short-circuit power
transformer in p.u. e.g. 0.06 for 6% uk.
Effects of the commutation notchs on loads in the same power system:
If several 6RA80 are operated in the same network, they do not usually affect each other, so
long as the voltage dip is not higher than that defined by the threshold of the phase-failure
monitoring in parameter p50353 (factory setting 40% means 60% dip permissible).
However, it cannot be ruled out that these steep-edged voltage dips might damage other
loads. Examples of this are switched-mode power supplies for supplying power to
automation units, computers and their monitors, but also loads such as fluorescent lamps
with electronic starters and power-factor correction capacitors for low-voltage motors.
That is one of the reasons why higher performance current converters are usually supplied
via a separate converter transformer, fed from the high-voltage side of the power system. If
problems arise with consumers on the same network with line-commuted current converters,
the lower-cost solution is usually to provide a separate transformer for the weak network
loads rather than implement additional measures on the high-power current converter.
Note:
Overcurrent or thyristor damage can occur if a 6RA80 is operated in a power system
without sufficient commutating reactance in its infeed.
The commutating reactance is the sum of all reactances in the incoming circuit of the
SINAMICS DCM: Line reactance plus transformer reactance plus reactance of the
commutating reactor.
RFI suppression filter:
RFI suppression filters reduce conducted radio frequency interference from the power
system (RF interference).
The filters listed in Catalog D23.1 / Operating Instructions are used to maintain radio
interference level A1. If these requirements are specified by the plant operator, RFI
suppression filters must be installed. As RF interference is lower on DC drives than on AC
drives with frequency converters, filters are only implemented on the former if the customer
makes a special request.
Note:
The filters specified in the catalog are intended for grounded power systems.
Alternative special filters for use in IT systems are available on request.
The filters must be installed on the line side in front of the commutation reactor (mandatory if
using filters). If the filter and commutation reactor are installed in the wrong sequence, this
will cause a fuse to blow in the current converter infeed.
Interference suppression filters do reduce RF interference but not the level of the harmonics
on the line side.
Smoothing reactor in the DC circuit:
See "DC Motor" – "Old motor"
Reactive-power compensation, series-resonant circuits for harmonics:
These supplementary components with capacities parallel to the power system must be
implemented with an inductor to prevent unacceptable resonance levels in the line infeed.
See "Cosine Phi" for reactive power levels.
If capacitors are used at the SINAMICS DCM input, e.g. for power factor compensation,
commutation reactors of at least 2% uk must be implemented in front of the SINAMICS DCM
input to prevent overcurrents occurring in the SINAMICS DCM.
A calculation of the line-side harmonics can be performed by Siemens advisory services on
request. In complex converter installations, the harmonics must be measured on the infeed
network.
Note:
High line-side harmonics can cause damage to other consumers on the same network,
for example, to power factor correction capacitors of low-voltage motors.
Line-side overvoltage protection 7VV3002:
If the SINAMICS DCM is connected directly to the winding of a converter transformer without
there being an open isolating point in front of the SINAMICS DCM (e.g. open main contactor)
when the transformer is disconnected in the primary circuit, an overvoltage protection module
