Method Of Calculating The Required Apparent Power S Of A Unit Transformer - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information
Total power factor λ for line-commutated SINAMICS converters and Infeeds
SINAMICS G130, G150, S120 Basic Infeed and S120 Smart Infeed
Relative short-circuit power RSC
> 50 (strong line supply)
15 ... 50 (medium line supply)
< 15 (weak line supply)
Total power factor λ for line-commutated SINAMICS converters with LHF compact
SINAMICS G150 with option L01
Relative short-circuit power RSC
No significant dependency on RSC
Total power factor λ for self-commutated SINAMICS converters and Infeeds
SINAMICS S120 Active Infeed and S150 with factory setting of cosφ
Relative short-circuit power RSC
> 50 (strong line supply)
15 ... 50 (medium line supply)
< 15 (weak line supply)
Typical values of the total power factor λ for SINAMICS converters and Infeeds
Note:
For the SINAMICS drives with unit transformers of the correct rating described in this engineering manual, the
relative short-circuit power RSC at the PCC of the converter as a result of the normal transformer impedance is
typically between RSC = 25 (transformer with v
1.3.1.2

Method of calculating the required apparent power S of a unit transformer

The required apparent power S of the unit transformer can be practically calculated with relative ease using the
formula below:
Key to formula:
·
P
·
η
Motor
·
η
Converter
·
λ
·
k
For output power of > approx. 50 kW, i.e. the lowest converter rating for which unit transformers are used, the
following values are accurate approximations:
·
η = 0.93 ... 0.97
Motor
·
η ≈ 0.98
Converter
·
η ≈ 0.96
Converter
·
λ ≈ 0.93
·
λ = 1 or λ = cos φ
·
k = 1.20
·
k = 1.15
·
k = 1.10
·
k = 1.00
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= 4 %) and RSC = 15 (transformer with v
k
³
S k
*
l
Shaft power of the motor or output power of the matched converter
Motor efficiency
Converter efficiency
Line-side total power factor
Factor which allows for the effects of transformer stray losses as a result of line-
side harmonic currents
η ≈ 0.93 for motor output of 50 kW rising to η ≈ 0.97 for motor output of 1MW
For G130, G150 converters and converters with S120 Basic Infeeds or
S120 Smart Infeeds
For S150 converters and converters with S120 Active Infeeds
For G130, G150 converters and S120 Basic Infeeds and S120 Smart Infeeds
For S150 converters and units with Active Infeed:
AI
λ = 1, if cos φ = 1 is parameterized with an Active Infeed (factory setting),
AI
λ = cos φ , if cos φ
AI
For systems with a standard distribution transformer and G130 without LHF,
G150 without LHF, S120 Basic Infeeds and S120 Smart Infeeds
For systems with a standard distribution transformer and
G130 or G150 with Line Harmonics Filters (LHF and LHF compact)
For systems with a standard distribution transformer and
S150 and S120 Active Infeeds
When a converter transformer is used irrespective of the converter type
100 % load
≈ 0.87
≈ 0.90
≈ 0.93
100 % load
≈ 0.985
to "1"
1
100 % load
≈ 1.00
≈ 1.00
≈ 1.00
P
h h
* Converter * Motor
≠ 1 is parameterized with an Active Infeed
AI
= 6.5 %).
k