A new design of the tubular shunt is presented which offers a reduction of the response time up to 10 times without changing the volume of the resistive material and preserving a regularly shaped response. A new formula is derived which gives the necessary data for calculating the improved shunt. Another possible design option is also presented which gives a shunt with zero response time but then the response curve indicates a larger overshoot. A simple mechanical design is presented, particularly suitable for heavy current shunts in the microohm range. Two such shunts were built for precise recording of steep front, short-circuit currents with a large asymmetry. They were designed according to the new formula and experimentally examined with a step impulse current. The measured response time of these shunts are in agreement with the calculated data.

Micro-ohm shunts for precise recording of short-circuit currents

By exploiting the fast Fourier transform, the integral-transform approach is shown to have important advantages in obtaining solutions to electromagnetic transient-field problems. The method is applied to a range of transientscreening problems in the design of a superconducting a.c. generator, and several important characteristics of screens in this type of machine are brought out.

Penetration of transient magnetic fields through conducting cylindrical structures with particular reference to superconducting a.c. machines

The density distribution and the equivalent depth of penetration of pulsed currents produced by a plane wave incident normally upon a plane conductor are investigated. In particular the cases i(t)=I0p(t), [I0/(t)12]p(t), I0e−αtp(t), where p(t)=U(t)[minus]U(t[minus]T0), are considered.

Diffusion of Pulsed Currents in Conductors

Practical calculations of transient resistance effects in conductors are reported. Included are the current density distributions in cylindrical and semi-infinite solid conductors for an applied surface step electric field E, and the density in a flat wide conductor. Two analogies are used to yield useful results: thermal diffusion in a cylinder and voltage transients on a semi-infinite transmission line. Results are applied to the calculation of time constants of a transmission line and force build-up in a solenoid.

Transient Resistance of Conductors

Estimation of the temperature rise in cylindrical conductors subjected to heavy 10/350 μs lightning current impulses

Electric current density penetrates or ``soaks'' into an electric conductor starting from the surface during current transients in a manner physically and mathematically analogous to thermal diffusion in transient heat flow. This useful concept is used to explain physically and evaluate numerically transient resistance and inductance of conductors subjected to rectangular current wave impulses.

K. W. Miller

Papers

Diffusion of Electric Current Into Rods, Tubes, and Flat Surfaces