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Technical requirements for medium-voltage transformers for use with SINVERT central inverters

Application manual 04/2012

Technical requirements for medium-voltage transformers for use with SINVERT central inverters

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SINVERT Technical requirements for medium-voltage transformers for use with SINVERT central inverters Application manual

04/2012 A5E03827321-02

Technical requirements for medium-voltage transformers

1

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Siemens AG Industry Sector Postfach 48 48 90026 NRNBERG GERMANY

A5E03827321-02 04/2012 Technical data subject to change

Copyright Siemens AG 2012. All rights reserved

Technical requirements for medium-voltage transformers for use with SINVERT central inverters Application manual, 04/2012, A5E03827321-02 5

Table of contents 1 Technical requirements for medium-voltage transformers ......................................................................... 7

1.1 Rated voltages and low-voltage infeed..........................................................................................7 1.1.1 Rated voltages ...............................................................................................................................7 1.1.2 Low-voltage and high-voltage winding...........................................................................................7 1.1.3 Interconnection of the components................................................................................................8 1.2 Voltage peaks and filtering.............................................................................................................9 1.2.1 Transformer design........................................................................................................................9 1.2.2 Design of surge arresters (AC-side) ..............................................................................................9 1.3 Short-circuit voltages .....................................................................................................................9 1.4 Types of construction...................................................................................................................10 1.5 Special requirements for oil-immersed transformers...................................................................10

Table of contents

Technical requirements for medium-voltage transformers for use with SINVERT central inverters 6 Application manual, 04/2012, A5E03827321-02

Technical requirements for medium-voltage transformers for use with SINVERT central inverters Application manual, 04/2012, A5E03827321-02 7

Technical requirements for medium-voltage transformers 11.1 Rated voltages and low-voltage infeed

1.1.1 Rated voltages The rated voltage is dimensioned to the respective low voltage dependent on the inverter type: Inverter Rated voltage SINVERT TL 500/1000/1500/2000 328 V SINVERT PVS 500/1000/1500/2000 288 V SINVERT PVS 585/1170/1755/2340 340 V SINVERT PVS 600/1200/1800/2400 370 V SINVERT PVS 630/1260/1890/2520 370 V

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Figure 1-1 Configuration example of a medium-voltage transformer 1200 kVA

(370 V / 370 V / 21 kV)

Technical requirements for medium-voltage transformers 1.1 Rated voltages and low-voltage infeed

Technical requirements for medium-voltage transformers for use with SINVERT central inverters 8 Application manual, 04/2012, A5E03827321-02

A separate isolated low-voltage and high-voltage winding is required for each inverter subunit.

If several low-voltage windings are available (four-winding transformer design), the transformer must be suitable for use with asymmetrical load of the low-voltage and high-voltage windings.

The high voltage is selected between 8 kV and 66 kV dependent on country-specific, grid-operator-specific, and project-specific requirements.

Note The country-specific grid frequency, standards and regulations, as well as the stipulations of the local grid operator must be complied with.

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Figure 1-2 Basic principle of interconnecting components in the inverter station

in a configuration with SINVERT PVS 2000 or SINVERT PVS 2400 inverters

Technical requirements for medium-voltage transformers 1.2 Voltage peaks and filtering

Technical requirements for medium-voltage transformers for use with SINVERT central inverters Application manual, 04/2012, A5E03827321-02 9

1.2 Voltage peaks and filtering

1.2.1 Transformer design The technical design of the transformer must be suitable for operation with pulsed

inverters. The voltage peaks can reach 1500 V to ground (pulses). The rms value of the voltages

to ground must not exceed 800 V. The low-voltage winding must be designed for gradients dU/dt up to max. 500 V/ s to

ground. For dry-type transformers, a shield winding (dU/dt filter) between the low-voltage winding

and the high-voltage winding can be dispensed with by means of appropriately implemented design measures.

Overvoltage protection in accordance with VDE 0101, Section 5.2.2.7 (spark gaps to VDE 0532-14) is required for all transformers.

1.2.2 Design of surge arresters (AC-side) The surge arresters must be suitable for pulsed operation. The surge arrester must be effectively designed for voltages of 1500 V and 800 V AC.

One surge arrester must be installed per phase. It must be ensured that no grounding or artificial neutral point is caused by this

installation.

1.3 Short-circuit voltages The short-circuit voltage Uk must be selected at 6%. In doing so, 5.4% to 6.6% must be

maintained. With four-winding transformers, the short-circuit voltage between the low-voltage

windings must be 10%. If the high-voltage winding is not connected, the measurement is carried out by short-

circuiting one low-voltage winding, and voltage infeed at the second up to the rated current.

For thermal dimensioning, the respective site conditions and isolation classes must be taken into account.

Technical requirements for medium-voltage transformers 1.4 Types of construction

Technical requirements for medium-voltage transformers for use with SINVERT central inverters 10 Application manual, 04/2012, A5E03827321-02

1.4 Types of construction The permissible types of construction are Dy5Dy5 and Dy11Dy11. The neutral point must not be brought out on the low-voltage side. At least 5 voltage levels must be brought out on the high-voltage side:

-5.0%, -2.5%, rated voltage, +2.5% and +5%

Note In the case of thin-film modules, a range of up to -15% may be required, depending on the manufacturer.

Since it is an infeed transformer, the rated voltage must be 5% higher than the rated grid voltage (rated grid voltage 20 kV, rated transformer voltage 21 kV).

When using the transformer in conjunction with the Siemens 8DJH switchgear, the rated voltage of the transformer must not exceed 24 kV.

1.5 Special requirements for oil-immersed transformers If oil-immersed transformers are used, oil sumps must be provided and acceptance-tested by an appointed person depending on the location of use (water regulations). In water reserves, special permits must be obtained for transporting and using oil sumps. With oil-immersed transformers, a suitable dU/dt filter shield winding must be provided between the low-voltage and high-voltage winding. This must be grounded on the tank.

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Subject to change without prior noticeOrder No.: A5E03827321-02 Siemens AG 2012

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Technical requirements formedium-voltage transformers for use withSINVERT central inverters, 04/2012OverviewLegal informationTable of contents1 Technical requirements for medium-voltage transformers1.1 Rated voltages and low-voltage infeed1.1.1 Rated voltages1.1.2 Low-voltage and high-voltage winding1.1.3 Interconnection of the components

1.2 Voltage peaks and filtering1.2.1 Transformer design1.2.2 Design of surge arresters (AC-side)

1.3 Short-circuit voltages1.4 Types of construction1.5 Special requirements for oil-immersed transformers

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