Investigation of skin effect on coaxial cables Coaxial cables describe a type of cables that has an inner conductor surrounded by an insulator, which is surrounded by another layer of conductor and insulator combination. The advantage of coax cables is the electromagnetic field only exists in the space between the inner and outer conductor and therefor can be installed next to metal objects without any loss of power. An example application for coax cables is as a transmission line for radio frequencyand cable television signals. This research topic investigates the behavior of the current density inside the cable core at DC and AC with different frequencies (50 Hz, 5 khz). DC AC 50 Hz AC 5 khz The figures above show the current density inside the coax cable. Due to its homogeneous distribution, the skin effect is visible, which describes the tendency of a current to be distributed near the surface of a conductor, is non-existent for direct current. The skin effect becomes visible at AC-50-Hz with the current density being higher at the outer surface of the coax cable. The higher the AC frequency, the more prominent the skin effect becomes as shown in the third figure. Comparison DC to AC-50-Hz Comparison DC to AC-5-kHz The diagrams above show a geometrical comparison of the current density between DC to AC50-Hz and DC to AC-5-kHz. It is shown that the skin effect has a rather small impact on the current density at AC-50-Hz but becomes a considerable factor at AC-5-kHz. Regardless of the chart run, the area beneath the graphs which represents the current, remains constant.
Simulation of a 110 kv high voltage cable sleeve High voltage cable sleeves are made of silicone rubber and used to insulate high voltage cable joints and control the occurring electrical field. This research topic investigates the behavior of the electrical potential and field strength with a FEM (Finite-Element-Method) simulation software. In the simulation the material properties of plastics for high voltage applications, relative dielectric constants and specific electrical conductivities were used. Electrical potential Electrical field strength Electrical field strength enlargement The simulations show a homogeneous distribution of the electrical potential and field strength. Furthermore, an enlargement of a section of the high voltage sleeve has been produced in order to show a more precise distribution of the electrical field strength and how the shape of the high voltage sleeve influences it. Overhead Power Line Overhead power lines are used in electric power transmission and distribution to transmit electrical energy in long distances. Overhead power lines come in different structures
depending on the transmission distance and voltage level and use aluminium-conductor steelreinforced (ASCR) cables as conductor. This research topic investigates the skin- and proximity-effects in a current carrying conductor using a FEM (Finite-Element-Method) simulation software for an overhead power line with different bundle arrangements and different frequencies. 4 bundle 50 Hz 4 bundle 5 khz 6 bundle 50 Hz 6 bundle 5 khz 8 bundle 50 Hz 8 bundle 5 khz The figures above show the magnetic field distribution for three different bundle arrangements at different frequencies. It can be shown that the skin- and proximity-effect is more prominent at higher frequency.
Current density 4 bundle Current density 6 bundle Current density 8 bundle The diagrams above show the current density for the different bundles with a comparison between AC-50-Hz and AC-5-kHz. The carried out simulations show that the current density is considerably higher at higher frequency. The diagrams also visualize that the current density is multiple times higher on the outer part of the conductor compared to the inner part. Graphite Spark Gap Spark gap is an old high voltage measuring device and can be used as a high voltage switch. It consists of an arrangement of two conducting electrodes separated by a gap filled with gas. When the voltage difference between the electrodes exceeds the breakdown voltage of the gas filled gap, a spark forms which ionizes the gas and drastically reduces its electrical resistance. This allows a current to flow through the electrodes until the path of the ionized gas is broken or the current is reduced below a minimum value. This research topic investigates the simulation of a high voltage graphite spark gap for lightning impulses and surge current applications.
Graphite Spark Gap The spark gap, as seen in the figure above, has a geometrical Rogowski profile. This profile guarantees a homogeneous electrical field between the electrodes of the spark gap in consideration of the gap distance and diameter of the electrodes. Electrical potential Electrical field strength Electrical field strength enlargement The figures above show the simulated graphite spark gap regarding their electrical potential and field strength. It is visible that the upper electrode of the spark gap has high electrical potential while the bottom electrode has low electrical potential. Furthermore the simulation visualizes the homogeneous electrical field strength in-between the electrodes.
An enlargement of the upper electrode shows peaks of the electrical field strength at positions where two different materials meet.