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close this bookElectrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages)
View the documentIntroduction
Open this folder and view contents1. General information about electrical machines
Open this folder and view contents2. Basic principles
Open this folder and view contents3. Execution of rotating electrical machines
Open this folder and view contents4. Synchronous machines
Open this folder and view contents5. Asynchronous motors
Open this folder and view contents6. Direct current machines
Open this folder and view contents7. Single-phase alternating current motors
close this folder8. Transformer
Open this folder and view contents8.1. Transformer principle
Open this folder and view contents8.2. Operational behaviour of a transformer
close this folder8.3. Three-phase transformer
View the document8.3.1. Three-phase transformation with single-phase transformers
View the document8.3.2. Three-phase transformers
View the document8.3.3. Vector groups
View the document8.3.4. Application of three-phase transformers in power supply
View the document8.3.5. Parallel operation of transformers
View the document8.3.6. Technical data of customary transformers

8.3.1. Three-phase transformation with single-phase transformers

For economical reasons the transmission of electric power these days is not undertaken by single-phase systems but by three-phase systems. Thereby, three-phase alternating voltage has to be transformed into another, like frequency and number of phases. The transformation is possible by means of three identical single-phase transformers.

The resultant voltages must not only possess the same value but shall also evidence a mutual phase displacement of 120 degrees.

Consequently, the mains connection of the single-phase transformers must ensure a delta or star circuit despite the spatially separate installation of electric primary and secondary winding connections.

Figure 136 - Transformation through three single-phase transformers

In view of their size, big transformers of this kind come as so-called three-phase (transformer) bank. They are generally added by a fourth single-phase transformer. This latter unit constitutes the reserve and can be switched on if another transformer fails.

Material and space requirements are usually too great for medium and small power units for this kind of transformation. The constructional fusion into a unit leads to substantial material economies.

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