Ernst-Dieter Wilkening

Effect of contact material on the extinction of vacuum arcs under line frequency and high frequency conditions

In two different test arrangements, the influence of different contact materials (Cu/Cr and Cu/Cr with additives of Zn, Sb, and Li/sub 2/O) on reignition or extinction of vacuum arcs is studied. The following line frequency conditions are achieved in a synthetic Weil-Dobke circuit transient recovery voltage: 36 kV, currents: 800-4800 A, 50 Hz. High-frequency (HF) currents are generated by means of an L-C circuit, with amplitudes of several hundred amperes and frequencies in the range of several hundred kilohertz. The reignition voltage at the HF current zeros and its statistical distribution are evaluated. Cu/Cr 75/25 shows the highest values, in agreement with the tendency at 50 Hz. Like at line frequency, the additives reduce the reignition voltage, and hence increase the reignition tendency. Cu/Cr with higher Cr content has a smaller breaking capacity.<<ETX>>

Modeling the Arc Splitting Process in Low-Voltage Arc Chutes

Investigations on the arc splitting process in low- voltage arc chutes have shown that a threshold voltage has to be exceeded before new arc roots form. When an arc spot has been formed, the electrode fall is nearly constant and rather independent of the current. In simulations a thin layer of elements with a nonlinear current density-voltage characteristic surrounding the splitter plate represents the formation of new arc roots. To model this behavior a characteristic with a voltage hump at low current densities and a constant final voltage at higher current densities has been presented in former publications. In this paper, the influence of the magnitude of the voltage hump is studied. A lower voltage hump yields a smaller arc loop around the front edge of the splitter plate and an earlier subdivision of the arc. A too high voltage hump makes arc splitting impossible. A comparing simulation without any arc root model, but only with the properties of the metallic plates, shows that a realistic simulation of the arc splitting process needs special treatment of the arc roots. The results are compared and verified on the basis of experimental results. Hence, the arc splitting process is analyzed concerning arc voltage and current through the plate as well as location of the arc roots.

The influence of circuit parameters and contact materials on the reignition of high-frequency vacuum arcs

The extinction or reignition of high-frequency transients plays an important role in the generation of voltage surges. Investigations with currents of several hundred amperes peak and current frequencies from 100 kHz up to 1 MHz were made to examine the reignition behavior of short vacuum gaps using different contact materials. The experiments were carried out in an UHV (ultrahigh vacuum) test chamber connected to an LC test circuit with voltages in the 10-kV range. The statistical distribution of the reignition voltage after current zero of HF vacuum arcs yields two probable reignition mechanisms, the cold gap behavior and the plasma-influenced reignition. The reignition tendency increases with rising di/dt and rising current frequency. The reignition voltages of the examined contact materials increase in the sequence: OFHC Cu, Cr, Cu/Cr 75/25.<<ETX>>

Optical Investigations of High-Current Vacuum Arc Behavior on Spiral-Shaped and Cup-Shaped RMF-Contacts

Vacuum circuit breakers are mostly equipped with radial magnetic field (RMF) contacts forcing the electric arc on a circular motion by a self-induced magnetic field. Using a high-speed-camera with a recording rate above 25,000 frames per second the appearance of vacuum arcs was investigated from two 90 degrees displaced views regarding three different contact designs with CuCr 75/25 as contact material. Spiral shaped contacts and cup-shaped contacts with diameter of 68 mm and 65 mm, respectively, and spiral shaped contacts with diameter of 90 mm were investigated with 45 Hz short-circuit currents of amplitudes up to 85 kA. From the high-speed films arc motion, shape and velocity as well as current density were determined in consideration of arc voltage and current strength. Results were compared to former publications.

Hybrid DC Circuit Breaker Feasibility Study

Recently, a growing number of dc systems exist based on the development of electrical energy consumption. For low-voltage dc grids, switching devices are needed that have to meet technically sophisticated requirements. These devices have to handle fault currents of several hundred amperes and system voltages up to 1000 V. A typical dc circuit breaker has to provide low on-state losses, light weight, and small volume. On the way toward fulfilling these requirements, hybrid circuit breakers can represent the optimal solution. A hybrid dc circuit breaker combines the advantages of mechanical contacts and semiconductors. In this paper, such a device has been designed and constructed using a commercial switch and electronic components in the laboratory. The breaking performance of this experimental prototype has been investigated, and thus the interruption of the nominal and failure currents in the case of different time constants can be identified. The investigated hybrid switching device has been optimized in order to maximize the switching capacity and the protection of the semiconductors.

Breaking performance investigation of hybrid DC circuit breakers: An experimental approach

Recently, a growing number of DC systems exist, based on the development of electrical energy consumption. For low voltage DC grids, switching devices are needed which have to meet technically sophisticated requirements. These devices have to handle fault currents of several hundred amperes and system voltages up to thousand volts. A typical DC circuit breaker has to provide low on state losses, light weight and small volume. On the way toward fulfilling these requirements, hybrid circuit breaker can represent the optimal solution. Hybrid DC circuit breaker combines the advantages of mechanical contacts and semiconductors. In the current work such device has been designed and constructed using a commercial switch and electronic components in the laboratory. The breaking performance of this experimental prototype has been investigated, thus the interruption of nominal and failure currents in case of different time constants can be identified. The investigated hybrid switching device has been optimized in order to maximize the switching capacity and the protection of the semiconductors.

Experimental research ondirect current switchgear

Fundamental changes in energy supply have lately led to an increasing use of DC technology for example in electric vehicles. The electrical requirements of switchgear and protective devices for low-voltage direct current grids are technically sophisticated. System voltages up to 600 volts and nominal currents of several 100 amperes are the normal load conditions in modern automotive direct current grids. Powerful lithium-ion accumulators, used as energy sources, are able to generate fault currents of several kilo amperes in case of electrical failures. Furthermore there are special demands from the automotive industry considering volume, weight and on-state power losses. To ensure full personal protection it is necessary to control the system parameters properly in every operating condition. Applied switchgear and protective gear have to be able to conduct, make and break every possible rated current or fault current. Therefore these systems have been investigated, which lead to the testing of samples of commercial switchgear in order to derive their suitability in electric car grids. Investigations include the current carrying and break capacity of commercially available contactors as well as the influence of the electromechanical actuator.