Hardware Requirements, Configuration Of The Power Sections - Siemens SIMOVERT Master Drives 6SE70 Betriebsanleitung

09.02
3.8.2

Hardware requirements, configuration of the power sections

The sub-currents of the 3-phase AC supplies are decoupled on the line side (line side with respect to the unit
terminals) through inductances (due to the secondary leakage inductance of the 12-pulse transformer,
commutating reactors).
Note: A 12-pulse transformer alone is not always sufficient for decoupling because the two secondary windings
of the transformer are magnetically coupled. When the "12-pulse master" and the "12-pulse slave" are directly
supplied from a "high-power" 12-pulse transformer (i.e. without the intermediate connection of commutating
reactors), the DC link currents (in non-pulsating operation) each comprise 30 degree current blocks because at
intervals of 30 degrees, a commutating process takes place from secondary winding 1 to secondary winding 2
or vice-versa. Only if you use a 12-pulse transformer with sufficiently large secondary leakage inductances (or
low magnetic coupling between secondary winding 1 and secondary winding 2) or if you use a " double-tier
transformer", in which no magnetic coupling exists between the two secondary voltage systems, is it possible to
dispense with additional commuting reactors.
The following points must be complied with:
• Supply of the power sections of the 12-pulse master and the 12-pulse slave from galvanically isolated
3-phase AC systems
• Decoupled infeeds - i.e. commuting reactors after the 12-pulse transformer or 12-pulse transformer with
sufficiently large secondary leakage inductances (or low magnetic coupling between secondary winding 1
and secondary winding 2) or use of a "double-tier transformer".
• Identical inductances in the 12-pulse master and 12-pulse slave power section branches.
• Identical voltage levels at the 12-pulse master and 12-pulse slave, otherwise with a control angle of 0
degrees, this will cause unequal current division (with a control angle of 0 degrees, closed-loop control is not
possible - the unit with the higher voltage level carries more current).
• With Ud reduction, current asymmetry (as a result of a control angle of 0 degrees and differing voltage
levels) can be prevented or considerably reduced.
• An output reactor must not be used in the DC link.
Recommended power section configurations:
Note: It is of no consequence whether the "12-pulse master" or "12-pulse slave" is supplied by the delta winding
of the 12-pulse transformer. It is only important that a phase offset of 30 degrees is present between the two
galvanically isolated supplies. In contrast to the following configuration examples, the "12-pulse master" and
"12-pulse slave" can also be exchanged with respect to their connection to the "12-pulse transformer".
a) Power section incoming feeder for two power supply units
Refer to the notes in Chapter 3.1 for details of the decoupling (commutating) reactors between the 12-pole
transformer outputs and the incoming supply rectifier bridge.
"12-pulse transformer"
Mains
Figure 3.15 Power section incoming feeder for two power supply units
Siemens AG 6SE7087-6AK85-0AA0
Common Rectifier Operating instructions
Reactor
12-pulse master
Reactor
12-pulse slave
DC link
X117
X117
ENGLISH
Connection
3-23