|Electrical Machines - Basic vocational knowledge (Institut für Berufliche Entwicklung, 144 p.)|
|8.3. Three-phase transformer|
Basic information on parallel operation
The extension of existing electrotechnical installations makes it necessary to parallel connect further transformers to the existing ones.
Excessive transmission ratings may also necessitate multiple operation of several transformers.
Parallel operation signifies the upper and undervoltage inter-switching of several transformers.
Conditions for parallel operation
In order to prevent the transformers being preloaded or subject to unequal load distribution amongst themselves because of compensating currents, the following conditions must prevail:
- the vector group must have the same index figure
- same transformation ratio
- same short circuit voltages U. They shall not deviate by more than 10 per cent from one another
- rated power ratios should not be greater than 3 : 1.