The IP.com Journal (v10n5A)
Juergen Carstens - Contact
firstname.lastname@example.org; phone +49-89-636-82995
SIEMENS AG 2010
English (United States)
3 pages / 139.1 KB
Air Core Current Transformer with Multiple Coils and Compensation of Discontinuous Areas
Idea: Yingzong Min, CN-Shanghai; Weigang Chen Ph.D., CN-Shanghai; Feng Du Ph.D., CN-
Shanghai; Hong Jiang Ph.D., CN-Shanghai; Zeliang Xu Ph.D., CN-Shanghai; Yue Zhuo Ph.D., CN-Shanghai
Sensors for the indirect measurement of current in a conductor have become a major component in industrial applications. The most common used variant is a round shaped air core coil placed around a conductor. In general, air core coils have some disadvantages regarding their anti-jamming performance as well as their sensitivity to position variations of the measured primary conductor. Closed shape air core coils solve these problems to a certain degree. But they are not suitable for high accuracy measurements because in practical applications it is difficult to control the winding process due to its closed structure. Especially small sized coils suffer from this effect.
To overcome the above mentioned problems, air core transformers with multiple separate coils are known. However, in a simple solution where the coils are disposed in a polygonal contour, the magnetic circuit in the area between two ends of coils is not continuous. As a result, the current measurement accuracy can be easily disturbed by external interferences. The discontinuous area can be compensated, for example, by a larger number of turns of wire at the ends of the coil. Thus, the inductance in the ends of coil is bigger than that in the center of the coil. The disadvantage of this solution is that the winding process is complex.
Another possibility to solve the disadvantages of the closed shape air core coils is to use PCB (Printed Circuit Board) air core transformer. The traces in the PCB act as the windings. By this way, high measurement accuracy can be achieved due to the high manufacture accuracy of PCB. However, the output of PCB air core transformer is too weak to satisfy the output requirements. The reasons for the weak output are the manufacturing limitations of winding turns and the dimension requirements for a small size of the whole current transformer.
In order to achieve high measurement accuracy while having a convenient winding process at the same time, it is proposed to use air core transformers with multiple separate coils and compensate the discontinuous area between two ends of coils by one of the novel measures, which are described subsequently.
1) Placing coils on different faces of one PCB
The air core transformer consists of several coils forming a closed polygon to surround the primary conductor for current measurement. The coils are mounted on different faces of one PCB and are classified into two types. The type A coils are mounted on the first face of a PCB. The type B coils are placed on the opposite side of the same PCB. Both coil types have a square or rectangle form and are placed symmetrically. The relative position of type A and type B coils is optimized to ove...