WEG MVW3000 A0040 V023, User Manual

Page: 22 / 125

3-2 | MVW3000
3
Product Characteristics
The transformer configuration is made in star – extended delta, with phase-shifting angles j ° between the
secondary windings of one same phase. The main primary windings (star connection) and the auxiliary input
windings (also star) do not present phase shifting between each other.
The transformer is designed according to the number of cells used on the inverter. 3x3xn windings (number of
motor phases x number of cell input phases x number of cells per phase) form n isolated secondary windings that
process 1/(3n) of the converter rated power, totalizing one secondary winding per cell.
Motor Voltage [kV] 2.3 3.3 4.16 5.5 6-69 7.2 8
Secondary Windings 3x2=6 3x3=9 3x4=12 3x5=15 3x6=18 3x7=21 3x8=24
The transformer secondary windings have phase-shifting designed according to the number of cells and the
specified harmonic level, and it may be engineered upon the customer’s request The phase-shifting help cancel
the harmonic components coming from the non-controlled semiconductors devices. As each cell has a 6-pulse
diode rectifier at the input, and the secondary windings have a phase-shifting between each other, the transformer
primary winding perceives multiples of six pulses in its windings.
The bigger the number of pulses, the smaller the phase-shifting angle between the secondary windings, and
the smaller the Harmonic distortion rate observed by the transformer primary winding. Smaller phase-shifting
angles imply more complex manufacture and parameter control of the transformer. Thus, a good complexity-
performance ratio is sought.
For the 18-cell MVW3000, the 36-pulse transformer Figure 3.2 on page 3-3 is used, which offers good
cost effectiveness with great performance regarding harmonic component cancellation and reduced cost, in
comparison to transformers with more pulses.
Table 3.1 on page 3-2 contains the possible input transformer configurations for different numbers of cells
installed on the MVW3000 panel.
Table 3.1: Possible number of pulses to obtain in relation to the number of cells
Cells per Phase Total Cells Number of Pulses
2 6 36, 18
(1)
, 12, 6
3 9 54, 18
(1)
, 6
4 12 72, 36, 24
(1)
, 18, 12, 6
5 15 90, 30
(1)
, 18, 6
6 18 108, 54, 36
(1)
, 18, 12, 6
7 21 126, 126, 42
(1)
, 18, 6
8 24 144, 72, 48, 36
(1)
, 24, 18, 12, 6
(1) Standard option .
Figure 3.2 on page 3-3 indicates the connection points for the power cell inputs, in this case, the phases R, S
and T. The windings with 690 V
rms
of rated voltage process 1/18 of the converter rated power, in the case of the
18-cell MVW3000.