SIEMENS
5/8
Siemens D 15.1 · 2017
Engineering Information
Output voltage and current
5
■
Function
(continued)
Once the input voltage falls below 65 %, the drive reduces out-
put power to a slightly negative value and maintains synchro-
nism with the motor for longer than five cycles. Once the input
voltage has recovered, the drive first magnetizes the motor and
then starts to generate torque. There is no delay in drive restart.
If the input voltage has not recovered after five cycles, the drive
maintains synchronism with the motor as long as the power cells
can operate without input power or as long as there is motor
voltage (to synchronize to). The drive trips as the input medium
voltage is lost if one of the power cells fails or the motor voltage
drops significantly.
With all cells operational
The maximum output voltage of the drive in terms of the number
of ranks (rows of cells) and the secondary-side cell voltage is
given as:
Where:
N
=
the number of rows of cells in the drive
(or total number of cells = 3*N)
V
cell rating
=
630, 690 or 750 V (depending on the design)
V
input
=
actual input voltage
V
input rated
=
rated input voltage
Tap_setting =
1.00 (for 0 % tap), 0.95 (for +5 % tap) or
1.05 (for -5 % tap)
The above formula is valid for all air-cooled drives.
Output voltage capability of the drive must be calculated based
on worst-case line voltage (minimum value).
With overmodulation (for 750 V cells only)
When the control operates with overmodulation to boost the
voltage, then the maximum output voltage increases by 5 %.
Note:
It is recommended not to use overmodulation. However, in
exceptional cases, overmodulation can be utilized but only after
consulting the factory or your local Siemens sales representa-
tive.
Example of calculating the output voltage capability
Consider a drive with 18 cells, each rated for 690 V. The maxi-
mum output voltage that can be delivered for the +5 % tap with
rated line voltage is (with N = 6 and
V
cell
= 690 V):
V
out
= 1.78 · 6 · 690 V · 0.95 · 1.0 = 7000 V
where 1.0 is the ratio of actual to rated line voltage.
V
out
= 1.78 × N ×
V
cell_rating
× Tap_setting ×
V
input
V
input_rated
© Siemens AG 2017