Bifilar Winding Arrangement for Measuring Current Characteristics Over Long Lengths
Publication Date: 2003-Sep-24
The IP.com Prior Art Database
Steven Fleschler: INVENTOR [+3]
This paper describes and HTS tape(s) to be tested which is wound in a bifilar winding arrangement and which allows determination of the current-voltage curve or Ic over long lengths of HTS tape in a compact geometry and with low Ic suppression due to magnetic field effects. Current flow in a first tape is used to cancel the magnetic field effect of a second tape so that accurate current measurements may be obtained, even in a tightly wound spiral geometry.
BIFILAR WINDING ARRANGEMENT FOR MEASURING CURRENT CHARACTERISTICS OVER LONG LENGTHS
This paper describes an HTS tape(s) to be tested which is wound in a bifilar winding arrangement and which allows determination of the current-voltage curve or Ic over long lengths of HTS tape in a compact geometry with low Ic suppression due to magnetic field effects. Current flow in a first tape is used to cancel the magnetic field effect of a second tape so that accurate current measurements may be obtained, even in a tightly wound spiral geometry.
This invention provides a method for measuring current-voltage characteristics (I- V curves) and critical current (Ic) of high temperature superconducting (HTS) tapes.
When producing lengths of HTS wire or tapes, it is desirable to characterize the electrical transport properties of the tape. Two measures of performance are the I-V curve and the critical current (Ic). Existing methods for measuring these current characteristics of HTS tapes include tube-based and reel-to-reel-based techniques.
Using a tube-based technique, the HTS tape is wound in a loose single-layer helix on large tubes or drums. The technique is illustrated in Figure 1. The length of the drum scales linearly with piece-length. Direct end-to-end or sub-section measurements of the I-V curve and Ic are possible with this type of arrangement by applying a known current across the length of the tape and measuring the resultant voltage across the length.
The equipment used in tube-based measurements is often undesirably large, particularly as longer tape lengths are measured. As an example, commercially available "sonotubes" which have a capacity of approximately 350 m piece-length of HTS tape have a diameter of 24" and a length 58". Furthermore, the hollow section of the tube is 'unused' space so that the large spatial extent of the system is very inefficiently utilized.
In addition, the inductively wound helixes tend to 'pick up' electrical noise (EMI) from the environment (flicker from lights, 60 Hz noise from power lines, etc), thereby degrading the resolution of the I-V curve.
Electrical transport measurements may also be made using a reel-to-reel technique, as shown in Figure 2. The HTS tape is translated from reel to reel and the I-V curve and Ic of a sub-section of the entire piece-length is measured. As an example, a "continuous Ic" machine that measures the I-V curve for short lengths, e.g., one meter subsections, and compute end-to-end properties for piece-lengths, e.g., up 800 m. The end-to-end properties of the entire piece-length is mathematically computed from the data acquired on the total set of subsections. Subsection voltages for a given current can be added to produce the voltage across the entire piece-length for that current. Error is introduced when adding many voltages to produce the I-V curve for an entire piece- length due to positional uncertainty in the location of each subs...