Alireza Khakpour

Spectroscopic Investigation of a Cu—Cr Vacuum Arc

Experiments on high-current arcs carried out in an ultrahigh vacuum chamber are presented in this paper. For contact separation the lower electrode is moved by a mechanical-pneumatic device simulating the conditions of a vacuum circuit breaker. The arc behavior of the Cu-Cr test electrodes after the electrode separation without application of external magnetic field is observed by a high-speed video camera. Besides the usual electrical measurements, the emission in the gap along the electrode axis is investigated by spatially resolved optical emission spectroscopy. Differences are found in the intensity distribution of atomic and ionic lines along the gap.

An Improved Arc Model Based on the Arc Diameter

This paper introduces an improved electrical arc model based on the arc diameter variation. In the conventional arc models, the arc diameter is considered as an implicit parameter in arc model constants. In case of decreasing arc diameter along with the arc extinction, the arc voltage decreases as well. The arc diameter can be implemented as a function of current into the arc model. The results illustrate that by applying the arc diameter as a function of arc current in the arc model, the simulated arc voltage is much closer to the measured values. In particular, the arc voltage behavior at the zero crossing can be controlled more precisely. However, based on the model considered for the arc diameter, additional parameters of the arc model should be estimated using measured data. The results confirm that even applying a simple arc diameter model can improve the arc voltage simulation.

Electrical Arc Model Based on Physical Parameters and Power Calculation

This paper presents an electrical arc model based on physical parameters of the arc including temperature, enthalpy, pressure, and also arc geometry. In this model, different mass flows and power losses are considered. The different powers including radiative and turbulent power as well as power gain and loss carried by axial and radial mass flows are calculated and simulated as a function of physical parameters. Moreover, the different arc diameter expressions and their influence on power losses are examined by arc experiments with high-speed imaging and arc dynamic behavior analysis. This model can provide the dynamic behavior of the arc easier in contrast to more complex physical models. The comparison with conventional arc models, such as Schwamaker, Habedank, Kema, and Schwarz, illustrates that the new arc model can better reproduce electrical measurements.

Facts based fault current limiter utilization in HV grid

Futures load and generation model of Tehran power network depicts fast increase in demand and development of power network. By 2015, Two new generating stations are expected to be installed which result in the increase of short-circuit capacity of a few substations in excess of the interrupting rating of exiting circuit breakers. This paper intends to analyze the consequences of employing thyristor protected series capacitor (TPSC) based short-circuit current limiter (SCCL) in Tehran power grid. Short-circuit, transient stability and transient recovery voltage studies were carried out by using DIgSILENT and EMTP softwares. The results demonstrate that SCCL installation can reduce fault current level in four substations of Tehran power network and improve transient stability margins. On the other hand, rate of rise of recovery voltage across some circuit breakers will exceed the value specified in standard which can be coped with by adding extra capacitor.

Video Spectroscopy of Vacuum Arcs During Transition Between Different High-Current Anode Modes

This paper presents spectroscopic results of high-current anode phenomena in a vacuum arc discharge between CuCr electrodes. AC (alternative current) 50-Hz and 10-ms pulsed dc (direct current) are applied as interrupting current. Time and space resolved optical emission spectroscopy (video spectroscopy) is used to examine the temporal and spatial distribution of different atomic and ionic copper lines. During the transition from low-current mode to different high-current modes, including footpoint, anode spot, and intense arc mode, the intensity of Cu I, Cu II, and Cu III line radiation is examined near the anode, the cathode, and in the interelectrode gap. The results show that during the formation of anode spot and intense mode the intensity and the distribution of all lines change noticeably in the different spectral regions. In fact, higher ionization states represent the arc dynamics behavior during transition to high-current anode modes. Significant differences have been found, for example, in the spatial structure of Cu II and Cu III lines in the anode spot mode. The results for Cu I lines indicate an active role of atoms together with the ions in different charge states in high-current anode modes. The impact of threshold current and transferred charge of the formation of high-current anode modes in case of ac and pulsed dc is also investigated regarding the intensity of copper lines near the anode.

Impact of Different Vacuum Interrupter Properties on High-Current Anode Phenomena

This paper presents the impact of current waveform and frequency on the formation of high-current anode phenomena in a vacuum interrupter experiment. Different waveforms including the alternative current pulses of 50, 180, and 260 Hz and direct current pulses of 5 and 10 ms are compared. The impact of different opening times and contact speeds on the high-current anode mode formation is investigated. The results show that both instantaneous current and total transferred charge are important in the formation of high-current anode modes. Therefore, the arcing time has a strong influence. Two types of anode spot modes with different electrical and optical characteristics are also observed. The transitions between different high-current modes are examined systematically, resulting in existence areas dependent on threshold current and gap length. The latter are determined for different contact materials including Cu, CuCr7525, and CuCr50 and different contact diameters.

Fast video registration of transition processes from diffuse mode to anode spot mode in high-current arc with copper-chromium electrodes

Transition process from a diffuse to anode spot mode in high-current vacuum arc discharge with Cu-Cr electrodes has been studied experimentally. Images of the arc were recorded with a frequency of about 25000 frames per second synchronously with the acquisition of current and voltage waveforms. Experiments clarify that after the current reaches a certain threshold value (4 to 5 kA for bulk-type, 2-cm electrodes), the arc discharge passes from diffuse mode to the mode with anode spot and voltage increased by ~20 V. In this mode, bright anode jet appears; cathode micro spots are reduced in number and grouped in front of the anode jet with the formation the cathode macro spot. In such a threshold regime, the discharge can change to the anode-spot mode and back to diffuse mode many times, with transition time in the microsecond range. With increasing current amplitude, anode spot mode becomes more stable, cathode and anode macro-jets are coming closer together forming a quasi-continuous radially-constricted discharge channel. The constriction of discharge is accompanied by increasing power density on both electrodes. In the case of TMF type electrodes, the constricted plasma channel moves azimuthally along the electrode lobe.

Impact of AC and pulsed DC interrupting currents on the formation of high-current anode modes in vacuum

The impact of waveform and frequency of the interrupting current on high-current anode phenomena has been studied experimentally. For arc ignition two different excitation modes have been applied - AC with varying frequency (50 Hz, 100 Hz, 180 Hz, 260 Hz) and pulsed DC with varying pulse width (5 ms, 10 ms). The results show that both instantaneous current and total transferred charge are important in the formation of high-current anode modes. However, these parameters depend on frequency, current slope (di/dt), and arcing time. The experiments have been conducted using different contact materials, namely Cu and Cu75Cr25.

Spatial distribution of charged particle emission in a copper-chromium high-current vacuum arc

Summary form only given. Vacuum circuit breakers are widely used in high-power systems, because they are compact, reliable and provide excellent switching capabilities even at high currents up to tens of kA. The main tendency of vacuum circuit breaker development is nowadays to extend their ability to operate even at higher voltages and higher currents. Despite numerous studies of the vacuum arc properties there is still a lack of spectroscopic investigations of high-current vacuum arcs for advanced switching applications. Nevertheless fundamental investigations are required for a deeper understanding of the plasma properties and the physical processes taking place during current interruption.This contribution presents results obtained by optical emission spectroscopy applied to a high-current vacuum arc model experiment. The experimental setup allows to reproduce the arc behavior observed in real circuit breakers at 50 Hz sinusoidal currents with peak values of 2.3 kA. Copper Chromium (Cu-Cr) electrodes with 20 mm diameter are used, which are separated at a controlled velocity of 1.1 m/s to ignite the discharge. Overview spectra as well as highresolution spectra are shown (spectral resolution down to 30 pm). The optical emission spectroscopy is accompanied by high-speed video imaging to observe the arc behavior in general. By imaging of axial and radial sections of the arc onto the entrance slit of a spectrograph, spatial distributions of neutral and charged particle emission can be determined. In case of electrodes made of Cu-Cr alloys it is possible to detect emissions from Cu I, Cu II, Cu III as well as Cr I, Cr II and Cr III. Due to the multitude of partly overlapping spectral lines line identification is an important issue before conclusions can be drawn. Along the arc axis different zones can be discriminated where different ionization stages achieve maximum emission. To give an example, neutral atoms radiate strongly in the vicinity of the electrodes, which is an expected behavior due to the eroded electrode material and the correspondingly high particle density. The results can reveal new information about charge distribution in the gap and describe elementary processes which are taking place in switching plasmas during current interruption giving options to increase the interruption behavior in future.

Study of high-current arcs and its interaction with side walls and layers

Summary form only given. The interaction of arcs with materials e.g. of the electrodes or of side walls are key issues of the functionality in many arc applications. An electrode configuration with a stable and reproducible arc operation as well as with optical access is preferable for the experimental analysis and fundamental study of such interactions. A setup with copper electrodes under ambient atmosphere in distances of several centimeters is used in this study. Arcs with currents of several kA are operated for few milliseconds between the electrodes which are placed inside ceramic nozzles to fix the arc attachment area. The electrode erosion promotes a stable arc operation. Electrical measurements and optical emission spectroscopy of copper lines are used to characterize the arc properties. Radiation transport and a simple arc power balance are utilized to estimate the arc temperature and the energy transport to the arc surrounding or to side walls. The interaction of the arc with materials is studied by mounting plates parallel and in distances of several millimetres to the arc axis. Beside pure materials, ceramic plates coated with oxide or hydroxide powder layers of approximately 1 mm thickness with simple binding agents are considered. The erosion of the materials and layers is qualitatively studied by high speed imaging of the fume formation. The thermal impact of the arc is analysed by pyrometric measurements at the back and the front side of the test plates. First results demonstrate the appropriability of powder layers to protect side walls from thermal load and destruction.