ABB ACS880-304LC Series, Руководство по оборудованию, Страница: 59 / 178

Selecting the supply transformer
The supply modules do not have input chokes. Thus, the supply transformer (or
generator) must be dimensioned according to the apparent power of the supply unit
(
S
n
) and the supply transformer impedance Z
k
(trafo). The supply nominal impedance
Z
k
must be at least 5% calculated with nominal apparent power of the supply modules.
In a 6-pulse system, the transformer's nominal short-circuit impedance must be
according to the following equation. The same impedance requirement also applies
to a generator when used as the supply.
× Z (trafo) > 5%
S
S (trafo)
n
n
k
Definitions
S
n
ACS880-304LC +A019 nominal apparent power
S
n
(trafo) Transformer or generator nominal apparent power
Z
k
(trafo) Transformer or generator nominal short-circuit impedance
Example:
Diode supply unit: ACS880-304LC-1540A-7+A019 → S
n
= 1840 kVA
Transformer nominal power is, for example, 2500 kVA
(trafo) > 2500 kVA
1840 kVA × 5%
k
Z
→
Z
k
(trafo) ≥ 6.8%
The same rule also applies to 12-pulse transformers when the nominal values are
calculated based on the total power of the 12-pulse transformer. If the nominal values
are calculated per 6-pulse windings (power per winding is half of the power of the
12-pulse transformer), then half of the reactance (≥ 2.5%) is sufficient.
If the necessary transformer impedance
Z
k
cannot be fulfilled, it is also possible to
install a separate 3-phase AC choke in addition to transformer (or generator) impedance
to reach the necessary minimum impedance of 5%. Separate chokes are not available
from ABB.
Note: Since the supply modules do not have input chokes, the THD currents and
voltages have to be taken into account when dimensioning the system. If necessary,
it is also possible to install a separate 3-phase AC choke to reach lower THD levels.
Electrical installation 59
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