Sinusoidal response of coaxial current shunts

The coaxial shunt has been used to measure heavy surge current and continuous complex current for many years. However, shunt design has in general been inconsistent and unpredictable. For the design of an accurate coaxial current shunt, bandwidth and current carrying capability are the essential criteria to be established. This paper extends the previous work of Park, and others, by showing how the sinusoidal response of an uncompensated coaxial shunt can be more accurately predicted and verified in practice. A rigorous analysis is conducted on a coaxial shunt with axial potential connections in its uncompensated form. The analysis is free from any constraints of thin tubes (up to an overall limit on physical dimensions set in the text) and contains no unjustified mathematical simplifications which would otherwise detract from the accuracy of the final results. Skin-effect performance is evaluated by the development of a shunt design equation involving shunt dimensions and material properties following from what is considered to be a unique solution of Bessels equation of zero order. This equation is solved by the use of numerical computational methods containing original subroutines. Computer predictions of coaxial shunt design are included to show the use of the method in the design of shunts having bandwidths of between 0 Hz and up to 5 MHz. Practical tests show that coaxial shunts can be produced whose performances correlate with computer-predicted design to the accuracy classification 2.5 (0.025 per unit) of BS89 (1970). Individual shunt designs maintain their performance characteristics when subjected to continuous currents of up to 500 A r.m.s. at rated frequency while shunt dissipation is kept within that laid down in BS159 (1957). The results show that coaxial shunt design can be easily applied. Shunts based on this design technique are presently used in the measurement of complex currents in power-engineering applications, particularly those to be found in- thyristor power conversion circuits.