BS EN 61788-8:2010 pdf download
BS EN 61788-8:2010 pdf download.Super conductivity Part 8: AC loss measurements一 Total AC loss measurement of round superconducting wires exposed to a transverse alternating magnetic field at liquid helium temperature by a pickup coil method.
3.9
magnetization method for AC loss
method to determine the AC loss of materials from the area of the loop of the magnetization curve
NOTE When pickup coils are used to measure the change in flux, which is then integrated to get [he magnetization of stationary coiled specimens, the method Is called the pickup coil method.
[IEC 60050.81 5:2000. 815-08-15, modIfied)
3.10
pickup coil method
method to determine the AC loss of material5 by evaluating electromagnetic power flow into the materials by pickup coils
NOTE The pickup coil arrangement consists essentially of a primary winding (a superconducting magnet supplied with C tam, varying current) and a pair of secondary windangs (pickup coals), one of whIch (th, main pickup coil) contaaia the specimen to be measured and Hi. other (the compensation coil) plays Iwo roles: 1) ii compensates the sqnel from the main pickup coil when empty; 2)11 supplIes lii, fiofd sweep information.
Here the coaxial and concentric arrangement of the pickup coils as shown in Figure iii used as the standard one for the AC Ipss measurement In order to obtain sufficient vol urn, of th. wire specimen to be measured and at the same time to expose it to a transverse magnetic rield. it must be wound into a ooi[ The specimen so prepared is also referred to as the coiled specimen
background loss
apparent loss obtained by the pickup coil method in the case where no specimen is located Inside the pickup coils
NOTE The background loss gives the experimental error in me system of th. AC loss measurement by the pickup coil method- It results from phase shift of electrical signal In the compensation process, an additional magnetic moment Induced an many components of experimental hardware, and eslernal noise. The background loss can be reduced by adjusting the expenmentat setup and cornp.nsat.d by subtracting it from measured AC toss as siown in 7.4.2.
3.12
effective cross-sectional area of the coiled specimen
total specimen volume divided by the larger of the specimen coil height or the pickup coil height
3.13
bending strain
strain in percent arising from pure bending defined as b = 100 r I R, where r is a half of
the specimen thickness and R is the bending radius
[IEC 60050-815:2000, 815-08-031
NOTE In the pickup coil method, the coiled specimen by react and wind technique is prepared with an attention to the permissiv, level of bending strain
3.14
n-value (of a superconductor)
exponent obtained in a specific range of electric field strength or resistivity when the voltage current 0(I) curve is approximated by the equation (Jo(’
(IEC 60050.81 5:2000. 815-03.101
4 Principle
The test consists of applying an alternating transverse magnetic held to a specimen and detecting the magnetic moment of shielding currents induced in the specimen by means of pickup coils for the purpose of estimating the AC losses defined In 3.1.
5 Apparatus
5.1 Testing apparatus
The testing apparatus shall be constructed such that the pickup coils and a coiled specimen are arranged In a uniform alternating magnetic field applied by a superconducting magnet.
The coils of the testing apparatus are arranged as described below. Typically, the main pickup and compensation coils are coaxially positioned on the outside and inside of the coiled specimen, respectively
The applied alternating magnetic field shall have a high uniformity as shown in 71.5.
The testing apparatus has a sub-system that calculates the magnetization and the AC loss of the specimen by integrating the signal of the pickup coils. A typical electrical circuit for the AC loss measurement Is given in Figure 2.
5.2 Pickup coils
Pickup coils shall be made of very fine insulated wire. such as insulated copper wire with a diameter of 0,1 mm, to avoid eddy currents at low temperatures.
The pickup coil formers shall be made of non-metallic and non-magnetic material such as glass fiber reinforced plastic, phenol resin. etc.
The main pickup coil shall be arranged coaxially and adjusted concentrically outside the compensation coil. The standard arrangement is shown schematically in Figure 1. where the height of the compensation coil is the same as that of the main pickup coil. The number of turns in the compensation coil shall be usually adjusted to be a little larger than the balance level in which the total interlinkage flux of the applied magnetic field into the compensation coil is equal to that into the main pickup coil.
The pickup coil system shall be constructed so that the coiled specimen can be taken in and Out easily from the system.
The pickup coil method has geometrical errors In relation with the arrangement of the coiled specimen and the pickup coils. The geometrical error Is mentioned briefly in Annex C. To achieve a low uncertainly due to geometrical effects of less than 1 %, the following arrangement for the coiled specimen and the two pickup coils shall be the standard one a height 0130 mm for the coiled specimen, a height of 10 mm for the pickup coils, a coil radius 0118mm for the specimen, and a 2 mm difference between the radii of the specimen and each pickup coil. In the case where the arrangement of the specimen and pickup coils are a little different from the above standard one, the geometrical error in the arrangement shall be estimated, as shown In Annex C. If the geometrical error cannot be estimated quantitatively, the calibration indicated in Annex D may need to be performed.
