Transformer Types - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information
On the basis of the formulas specified on the previous page and assuming that η
for the motor efficiency, the required rated apparent power S
a) When a standard distribution transformer is used
S > 1.40 P
T * W
S > 1.30 P
T * W
/cos φ
S > 1.20 P
T W AI
*
b) When a converter transformer is used:
S > 1.15 P
T * W
/cos φ
S > 1.1 P
T * W AI
The following output ratings are standardized for unit transformers:
100 160 250 315
The no-load ratio must be specified on the transformer order. The no-load voltage on the low-voltage side is generally
5 % higher than the voltage under full load. If, for example, a transformer for 10 kV in the primary circuit and 690 V in
the secondary circuit is required, then it must be ordered for a no-load ratio of 10 kV / 725 V.
The purpose of taps is to allow adjustment of the ratio to the actual line voltage. With a standard transformer, the
high-voltage winding has tap points equaling ± 2.5 %. These HV-taps can be adjusted by means of reconnectable
jumpers when the transformer is de-energized. Additional taps are available at extra cost on request.
Circuits and vector groups
The high-voltage and low-voltage windings of three-phase transformers can be star- or delta-connected. These
connection types are identified by the letters specified below (capital letters: high-voltage side, small letters: low-
voltage side):
• Y, y for star-connected windings
• D, d for delta-connected windings
In the vector group code for each transformer, these letters are followed by a digit. This states (in units of 30 degrees)
the phase angle ϕ by which the voltages on the high-voltage side lead those on the low-voltage side. For example:
ϕ = n
30°
*
The vector groups of standard distribution transformers are normally Dy5 or Yy0 on which the neutrals are not
brought out.

Transformer types

Oil-immersed transformers or dry-type transformers (GEAFOL) are suitable to feed drive converters.
The oil-immersed transformer is generally cheaper to buy. However, in most cases, the transformer needs to be
installed outdoors. This transformer type can be installed indoors only if it can be directly accessed from outside.
Precautions must be taken to protect against fire and groundwater pollution. Although the transformer should ideally
be sited at the central power distribution point, this is often not possible.
The procurement costs for a GEAFOL transformer are higher. Due to its design, i.e. without fluid or combustible
insulating agents, it can be installed indoors and thus at the central power distribution point. It is often the most cost-
effective transformer type in installations with a relatively high energy density owing to its low losses and the fact that
no groundwater protection measures need be taken.
Transformers must be selected with a view to achieving the optimum cost effective solution for the entire plant, i.e. to
reduce investment and operating costs to a minimum. The following factors need to be considered:
•
Procurement costs of transformers
•
Required measures at installation site
•
Operating costs incurred by losses, particularly in the distribution system
SINAMICS Engineering Manual – May 2008
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© Siemens AG
For G130 converters without LHF, G150 without LHF and for
units with S120 Basic Infeeds and S120 Smart Infeeds
For G130 or G150 converters with Line Harmonics Filters LHF
For S150 converters and units with S120 Active Infeeds
For G130 converters with/without LHF, G150 with/without LHF and for
converters with S120 Basic Infeeds and S120 Smart Infeeds
For S150 converters and units with S120 Active Infeeds
400 500 630 800
where n = 1, 2, 3, ..., 11.
Motor
for the unit transformer is calculated as follows:
T
1000 1250 1600
≈ 0.95 is the typical mean value
2000 2500 [kVA]