 | Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.) |
 |  | 4. Electrical Machines |
| | 4.3. Transformers |
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4.3.2. Three-phase Transformers
Three-phase transformers in parallel connection
Transformer station with two
transformers connected in parallel
Usual groups of connection for transformers
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Designation |
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Indicator Diagram |
Circuit Diagram | | ||
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Identification number |
Group of connection |
High Voltage |
Lower Voltage |
High Voltage |
Lower Voltage |
Transformation |
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Three-phase power transformers | ||||||
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Dd 0 |
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0 |
Yy 0 |
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Dz 0 |
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Dy 5 |
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5 |
Yd 5 |
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Yz 5 |
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Dd 6 |
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6 |
Yy 6 |
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Dz 6 |
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Dy 11 |
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11 |
Yd 11 |
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Yz 11 |
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Single-phase power transformers | ||||||
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Explanations for the table
The table shows the commonly used circuits according to the relevant Standard of the International Electrotechnical Commission (I E C). When multiplying the identification number by 30°, the phase shift of the high voltage side with respect to the lower voltage side is obtained.
Dd 6 means:
D = high voltage side delta connection
d = lower voltage side delta connection
The lower voltage is shifted with respect to the high voltage by 6 x 30° = 180°.
Due to these different circuits, different operational behaviour is attained.
The ratio of transformation is calculated as follows:
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