Design, Assembly, and Commissioning of a Cryogenic DC Current Transformer Designed for Measuring Currents of up to 80 kA
CERN1
TL;DR: In this paper, the CryoDCCT has been used for measuring the secondary current of a 80 kA superconducting transformer feeding a sample of NbSn 3 cable at the Facility for Research on Superconducting Cables (FRESCA) at CERN.
Abstract: A new cryogenic dc current transformer (Cryo-DCCT) has recently been designed and assembled at CERN. The device, whose design is based on that of a high-accuracy 600 A market solution suitable for room temperature applications, is optimized for measuring currents of up to 80 kA and for operation at 4.2 K. The CryoDCCT has been conceived with the objective of preserving the metrological performance of the original commercial device in the new extended range of operation. For reducing the effect of interfering magnetic fields arising from test conditions, it incorporates ferromagnetic and MgB 2 superconducting shields. In this paper, the design of the CryoDCCT and the results of the commissioning of the device at CERN are reported. The effectiveness of the current transducer is analysed and discussed. This new device will be used for measuring the secondary current of a 80 kA superconducting transformer feeding a sample of NbSn 3 cable at the Facility for Research on Superconducting Cables (FRESCA) at CERN.
Citations
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TL;DR: A four-spectral line interpolation fast Fourier transform algorithm based on trapezoidal convolution window is proposed to improve the extraction accuracy of the dc and harmonic components from the measured signal.
Abstract: With the global trend to develop digital substation automation systems, measurement devices are required to be reliable, of small size and light weight and of acceptable accuracy in a wide frequency band. This article presents a combined high voltage direct current measurement method which comprises the above-mentioned features that makes it suitable for smart grids protection and control applications. The proposed measurement method utilizes Hall sensor array for dc current measurement. DC voltage is measured using a voltage divider circuit while the harmonic currents are measured using a square Rogowski coil made of four straight bars along with a high precision digital integration algorithm. A four-spectral line interpolation fast Fourier transform algorithm based on trapezoidal convolution window is proposed to improve the extraction accuracy of the dc and harmonic components from the measured signal. Experimental results show that the error variation of the proposed method is less than 0.098% for voltage measurement while it is less than 0.104% for current measurement. The harmonic measurement ratio error is less than 0.2% and the angle error is less than 8'.
47 citations
TL;DR: A quasi-digital dc current sensor with rated current of ±600 A while overload current of about ±750 A is proposed in this paper, based on the open-loop self-oscillating fluxgate technology, but its originality is using a microcontroller unit to detect the duty cycle of the exciting voltage of the fluxgate.
Abstract: A quasi-digital dc current sensor with rated current of ±600 A while overload current of about ±750 A is proposed in this paper. The new sensor is based on the open-loop self-oscillating fluxgate technology, but its originality is using a microcontroller unit to detect the duty cycle of the exciting voltage of the fluxgate. Compared with the published similar method, the whole signal chain of the new sensor is quasi-digital and without low-pass filter and analog-to-digital converter required when connected to digital systems. A precisely theoretical equation with respect to the linear dependence between the duty cycle and the current to be measured is established. Based on the equation, factors affecting the sensor sensitivity, accuracy, and resolution are determined, which constitutes the theoretical basis on the optimization design of the new sensor. The sensor linearity is improved using the least-squares polynomial fitting method. Some key specifications including the linearity, repeatability, and power supply effect of the sensor are characterized. The measurement results show that the linearity of the new sensor with the theoretical equation is better than 1.7% in the full scale of ±600 A, and can be improved to 0.3% when the fifth-order polynomial fitting method is used.
24 citations
Cites background from "Design, Assembly, and Commissioning..."
...Typical examples include the traditional power grids [1], [2], electrowinning industries [3], and nuclear research [4], [5], as well as the emerging renewable energy (e....
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TL;DR: In this article , a 1-D thermo-hydraulic study of 10 kA rated MgB2 current feeders system with 20 K helium for SST-1 tokamak as a case study is presented.
Abstract: Current feeders system (CFS) is one of the most critical part of a large-scale superconducting (SC) magnets based machines like a tokamak or accelerator. One end of the SC feeder is connected to magnets and another end is connected to the power supply via optimised current leads (CL) for energizing the magnets. So far, low temperature superconductor (LTS) is the popular choice for such applications. For high temperature superconductor (HTS) applications, cuprate oxide based coated conductors or magnesium diboride (MgB2) wires are the options. MgB2 despite of its superconducting transition temperature of 39 K,is now gaining wide attention for SC feeders system due to its lower raw material cost and ease of availability than 2G HTS tapes. To assess its suitability, we report 1-D thermo-hydraulic study of 10 kA rated MgB2 current feeders system cooled with 20 K helium for SST-1 tokamak as a case study. For varying mass flow rate, temperature margin along the feeder are calculated considering helium at 20 K, 4 bar (a) with cooling inlet from magnet side. Such a feeder yields a temperature margin of 6 K–16 K across its entire length depending up on mass flow rate of helium. There is also a possibility of cooling the binary current lead (HTS + MgB2) from cold helium coming out from the feeder. From our study, MgB2 current feeder system provides benefits of higher temperature margin, lower mass flow requirement and cryogenic savings by use of 20 K helium as coolant compared to LTS based feeders. In future, it could provide a safe, reliable and cryogenic operational cost saving solution for SC current feeders for Tokamak applications.
6 citations
Journal Article•
TL;DR: In this article, the fluxgate magnetometer principle of second harmonic detection is applied for designing a DC Current Transformer (DCCT) based magnetic sensor for accurate measurement of beam currents in proton accelerators.
Abstract: The fluxgate magnetometer principle of second harmonic detection is applied for designing a DC Current Transformer (DCCT) based magnetic sensor for accurate measurement of beam currents in proton accelerators .This paper presents the most suitable magnetic material which can be used as the core. It also gives the geometrical model of the magnetic sensor with exact values for its height, outer radius, inner radius and the number of turns in the sensor winding. The magnitude of the AC excitation current along with its frequency is also mentioned. The sensor voltages and the second harmonic components obtained for different values of DC beam currents have been analyzed for a variety of magnetic core materials. A highly linear sensor characteristics with sensitivity in the order of 3V/A is obtained with the usage of Vitrovac 6025 Z as the core material for the modeled sensor.
1 citations
References
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CERN1
TL;DR: In this article, a new test facility for measuring the electrical properties of the LHC superconducting cables was constructed at CERN, with the main features being: independently cooled background magnet, test currents up to 32 kA, temperature between 1.8 and 4.5 K, long measurement length of 60 cm, field perpendicular or parallel to the cable face, measurement of the current distribution between the strands.
Abstract: A new test facility (FRESCA-Facility, reception of superconducting cables) is under construction at CERN to measure the electrical properties of the LHC superconducting cables. Its main features are: independently cooled background magnet, test currents up to 32 kA, temperature between 1.8 and 4.5 K, long measurement length of 60 cm, field perpendicular or parallel to the cable face, measurement of the current distribution between the strands. The facility consists of an outer cryostat containing a superconducting NbTi dipole magnet with a bore of 56 mm and a maximum operating field of 9.5 T. The magnet current is supplied by an external 16 kA power supply and fed into the cryostat using self-cooled leads. The lower bath of the cryostat, separated by means of a so called lambda-plate from the upper bath, can be cooled down to 1.9 K using a subcooled superfluid refrigeration system. Within the outer cryostat, an inner cryostat is installed containing the sample insert. This approach makes it possible to change samples while keeping the background magnet cold, and thus decreasing the helium consumption and cool-down time of the samples. The lower bath of the inner cryostat, containing the sample holder with two superconducting cable samples, can as well be cooled down to 1.9 K. The samples can be rotated while remaining at liquid helium temperature, enabling measurements with the background field perpendicular or parallel to the broad face of the cable. Several arrays of Hall probes are installed next to the samples in order to estimate possible current imbalances between the strands of the cables.
61 citations
TL;DR: In this article, the second-harmonic type of magnetic modulator is discussed and a theoretical analysis of an idealized modulator of this type is presented, with particular reference to the influence of various controllable parameters on the signal/noise ratio and zero error.
Abstract: It is well known that certain factors, notably flicker noise and zero drift, determine the smallest signal voltage that can be satisfactorily amplified by a thermionic d.c. amplifier. Better results can often be obtained by using a suitable modulator to convert the direct current to alternating current and following this by an a.c. amplifier and rectifier. The paper discusses the advantages of the second-harmonic type of magnetic modulator for this purpose, and presents a theoretical analysis of an idealized modulator of this type, with particular reference to the influence of various controllable parameters on the signal/noise ratio and zero error. The paper also describes experimental work, which, with allowance for the idealizations in the theoretical analysis, is considered to provide a satisfactory qualitative verification of the latter. Particular emphasis is placed on the need for great care in the design of the various circuits, toeliminate additional sources of noise and zero error, and it is believed that the noise output of the apparatus described is due mainly to Barkhausen effect in the modulator cores, and is equivalent to a signal input of about 10?19 watt for a bandwidth of 1 c/s; the zero drift is, however, considerably greater than this, and is equivalent to a signal input of about 3 × 10?18 watt over a two-hour period.
35 citations
CERN1
34 citations
TL;DR: In this paper, the behavior of electronic compensated current transformers is examined with reference to a model valid for frequencies ranging from industrial to ultra-acoustic both in steady-state and in transient conditions.
30 citations
"Design, Assembly, and Commissioning..." refers background in this paper
...The working principle of the device is based on the wellknown zero flux compensation mechanism [18], for both AC and DC current components [18]–[20], to achieve the ideal current transformer ratio: N1I1 = −N2I2....
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