A cryogenic sensing element for measurement current transformers

Abstract

The design of a cryogenic sensing element for superconducting DC current transformers working up to 100 kA at 4.2 K is proposed. Limitations of µ-metal magnetic characteristics at cryogenic conditions are overcome by a soft Ni 81-Mo 5-Fe magnetic alloy (referred to as cryogenic permalloy). An optimized geometrical design allows cores saturation due to mechanical constraints to be avoided. The effectiveness of the design is demonstrated through electromagnetic simulations exploiting measurement results from the characterization of cryogenic permalloy samples. Moreover, a preliminary lab-scale cryogenic DCCT prototype for a nominal current of 20 kA is implemented and characterized. A typical precision of the transducer below ±0.05% is achieved along with nonlinearity better than ±0.05%.

MgB2cylindrical superconducting shielding for cryogenic measurement applications: a case study on DC current transformers

“…For the last category, the superconductor can work according to the field level either in the Meissner or in the mixed state [8]. In high-field environment, superconducting shield plays a crucial role to improve sensor performance [10].…”

Design, Assembly, and Commissioning of a Cryogenic DC Current Transformer Designed for Measuring Currents of up to 80 kA

“…In particular, the design proposed in [15] is recalled, and assembly and commissioning of the new current transducer are described.…”

“…The MACC+ power amplifier can generate maximum 1 A, that means a coil of 80 000 turns would be required for 80 kA. Hence, the implementation and performance of such a device would be critical [15]- [22]. Consequently, a new power stage is required.…”

“…In Fig. 4, the hysteresis loop measured at 4.2 K, for a maximum excitation field of 27 Am −1 (the measurement set-up is described in [15]), of the three CryoDCCT's cores is shown (out of a batch of six cores): Differences are within 8%. The only remarkable difference of these results, compared to the μ-metal characteristics at room temperature, is a smaller residual field of 30%.…”

“…In a previous paper [15], the authors reported on the design of a new cryogenic sensing element for a DCCT capable to overcome the aforementioned limitation. The proposed sensor is based on: An optimized geometrical design of the sensing element, exploitation of a magnetic alloy suitable for cryogenic applications (referred to as cryogenic permalloy), and mitigation of cores saturation through a combination of ferromagnetic and superconducting shield [16].…”