Computational issues in the simulation of high speed ballistic impact: a review

This paper presents a review of recent developments of nonlinear constitutive material models for the applications in high speed ballistic impact of projectile into several types of targets. The objective is to comprehend some numerical approaches that have been proposed and used in the technical literatures especially regarding bullet-target interaction. Attention is given on the application of several types of computational constitutive models and simulations used to represent the projectile characteristic, ballistic penetration, failure modes in target and deformation pattern. This paper serves as a concise source to identify future direction in the area of computational mechanics of high speed collisions and provides brief literatures for those interested in conducting research into the topi

Electrostatic protection of the Solar Power Satellite and rectenna

Several features of the interactions of the solar power satellite (SPS) with its space environment were examined theoretically. The voltages produced at various surfaces due to space plasmas and the plasma leakage currents through the kapton and sapphire solar cell blankets were calculated. At geosynchronous orbit, this parasitic power loss is only 0.7%, and is easily compensated by oversizing. At low-Earth orbit, the power loss is potentially much larger (3%), and anomalous arcing is expected for the EOTV high voltage negative surfaces. Preliminary results of a three dimensional self-consistent plasma and electric field computer program are presented, confirming the validity of the predictions made from the one dimensional models. Magnetic shielding of the satellite, to reduce the power drain and to protect the solar cells from energetic electron and plasma ion bombardment is considered. It is concluded that minor modifications can allow the SPS to operate safely and efficiently in its space environment. The SPS design employed in this study is the 1978 MSFC baseline design utilizing GaAs solar cells at CR-2 and an aluminum structure

Observations of cosmic ray induced phosphenes

Phosphene observations by astronauts on flights near and far from earth atmosphere are discussed. It was concluded that phosphenes could be observed by the naked eye. Further investigation is proposed to determine realistic human tolerance levels for extended missions and to evaluate the need to provide special spacecraft shielding

Improving lightning performance on high voltage overhead shielded networks by reducing tower footing earthing resistance.

Master s Degree. University of KwaZulu-Natal, Durban, 2019.Abstract available in pdf

Measurement Techniques for Impulse Puncture Testing in Air

Impulse voltage puncture testing (IPT) in air, as per IEC-61211, is used to assess the withstand strength of class B ceramic/glass insulators primarily against very fast front voltage transients (VFFTs) in power systems. This method uses short HV impulses of front times as low as 100 ns, therefore, adequate execution and reproducible results are not ensured because no standard impulse shape exists for VFFTs, no calibration service exists for such systems below 0.84 μs and the measurement system gets affected by many factors e.g. proximity effects, interferences, clearances and stray capacitances and inductances. This study focuses on investigating the testing practices and measurement techniques, for IPT in air as per IEC-61211, to find suitable testing methodologies. Based on the results of a research survey done to know practices and capabilities of HV labs in this regard, testing was performed on a cap and pin insulator, mounted on a metal plate using ball-socket and stressed with steep front HV impulses. A 500 mm wide copper sheet was used for grounding. Measurement system comprised of a fast resistive divider, a 50 tri-axial cable, a 10:1 attenuator of 50 input resistance and a 200 MHz, 8 bit, 2.5G S/s digitizer. The dependency of results on factors like divider-insulator distances, extra cable shielding, various target test voltages, HV damping resistor and different generation circuits was studied. No puncture of insulation happened. The divider showed high overshoot in step response and low bandwidth in impulse results. Due to these reasons, along with its damage during testing, a new divider design is proposed for 500-600 kV that is modular in structure and aims to solve the problem of low bandwidth by allowing its HV arm to be placed in direct contact with insulator. A novel algorithm is also proposed to analyse the linearity of front chopped impulses. It also revealed that following exact definition of Tc in IEC-60060-1 could result in it’s wrong determination from measurement software

PERFORMANCE OF PARALLEL SURGE ARRESTERS

The operation of parallel surge arresters can improve energy absorption capability if the arresters are similar and are installed close to each other. However, it has been reported that any small difference in the individual V-I characteristics can lead to unbalance in current sharing. When the arresters are installed some distance away from each other, travelling wave effects can modify the effectiveness of parallel arresters for surge overvoltage protection and, in this case, detailed simulations are required to ascertain the level of protection. Such a situation occurs in practice with large substations or short underground cable connections. Various studies have shown that a requirement for two-arrester protection is closely dependent upon the type and length of cable used. In the case of overhead lines, the distances are much bigger and the main objective of line arresters is to reduce the flashover rates due to surge overvoltages. This is especially relevant to lines located in regions of high lightning activity, lines with compact/uprated design where the phase-to-phase and phase-to-earth air clearances are reduced. In this paper, we present a study of parallel arresters considering the separation distance and their application to overhead lines. Various scenarios of overhead line configurations were considered and the overvoltage levels were calculated for each case. Assessment of flashover performance is also conducted for a number of conditions. A number of calculation techniques were used and compared

Estimation of the lightning performance of transmission lines with focus on mitigation of flashovers

The growth of transmission networks into remote areas due to renewable generation features new challenges with regard to the lightning protection of transmission systems. Up to now, standard transmission line designs kept outages resulting from lightning strokes to reasonable limits with minor impacts on the power grid stability. However, due to emerging problematic earthing conditions at towers, topographically exposed transmission towers and varying lightning activity, such as encountered at the 400 kV Beauly-Denny transmission line in Scotland, the assessment of the lightning performance of transmission lines in operation and in planning emerges as an important aspect in system planning and operations. Therefore, a fresh approach is taken to the assessment of the lightning performance of transmission lines in planning and construction, as well as possible lightning performance improvements in more detail, based on the current UK/Scottish and Southern Energy 400 kV tower design and overhead line arrangements. The approach employs electromagnetic transient simulations where a novel mathematical description for positive, negative and negative subsequent lightning strokes, which are all scalable with stroke current, is applied. Furtermore, a novel tower foot earthing system model which combines soil ionisation and soil frequency-dependent effect is used. Novel lightning stroke distribution data for Scotland as well as novel cap-and-pin insulators with arcing horn flashover data derived from laboratory experiments are applied. For overhead lines, transmission towers, and flashover mitigation methods describing their physical behaviour in lightning stroke conditions state-of-the-art models are utilised. The investigation features a variety of tower and overhead line arrangements, soil conditions and earthing designs, as well as the evaluation of various measures to improve the performance. Results show that the lightning performance of a transmission line is less dependent on the tower earthing conditions, but more dependent on the degree of lightning activity and stroke amplitude distribution. The assessment of flashover mitigation methods shows that cost-effective and maintenance free solutions, such as underbuilt wires can effectively replace a costly improvement of the tower earthing system. However, in locations where challenging earthing conditions prevail, tower line arresters or counterpoise are the only options to maintain an effective lightning protection