Effect of external DC field on current transformers with amorphous and nanocrystalline cores

Abstract

Nanocrystalline and amorphous stress-annealed and field annealed tapes are used for cores of DC-tolerant current transformers. We analyze the influence of external DC field of arbitrary direction on the performance of these transformers. For the realistic core shapes the demagnetization is high, which leads to effective external field suppression. However, DC tolerant transformers are tolerant to the DC component of the current and not to the external field -they can be saturated by 30 mT field from permanent magnet. This means that for the practical applications in domestic energy meters some external shielding is required.