XHXC105 Transformer Demagnetizer| Residual Magnetism Remover After DC resistance measurement, turns ratio tests or other DC tests, residual magnetism remains in the transformer core because of the inherent hysteresis of ferromagnetic materials. If the transformer is re-energized with residual flux in the core, half-cycle saturation produces a large inrush current rich in harmonics — increasing reactive consumption, risking protective relay misoperation, and even causing