Three-Phase Transformer Demagnetization - Raytech mini-ATOS Instruction Manual

4.3.2 Three-Phase Transformer Demagnetization

For a core-type three-phase transformer with three limbs, the demagnetization is usually performed
from the middle phase. Many times, it is enough to achieve a safe residual magnetism state to
connect the transformer to the power grid without the risk of high inrush current. However, it is not
always like this. Sometimes the demagnetization should be performed from all three phases. The
following items can be a reason to consider a three-phase demagnetization:
- When the core consists of 4 limbs or 5 limbs
- When the transformer is a shell-type
- When the aim is to achieve a very small residual magnetism to perform special tests like
SFRA
The mini-ATOS can use the advantage of the automatic multiplexer to perform demagnetization
from each phase automatically and without changing the connection setup.
90297-0.22 Instruction Manual mini-ATOS Page 18 of 92