Andrzej Sowa

Surge current distribution in building during a direct lightning stroke

A direct lightning strike to a building may cause damage or interference in the operation of electronic equipment inside the structure and may even be dangerous to the people in the more critical case. In order to decide on an efficient lightning protection system, it is important to determine the lightning current distribution in the building. Knowledge of the current distribution is obtained from model measurements and from theoretical calculations. The strike points are assumed in different places on the buildings roof. The results concerning the lightning current distribution in high and low buildings are presented and discussed.<<ETX>>

Lightning overvoltages in wires within the buildings

Electromagnetic fields generated by lightning currents may cause damage or interference in the operation of electronic and electric systems. Particularly hazardous to equipment operating within a building is a direct lightning strike to the building or its vicinity. For this reason, a theoretical determination of currents and voltages induced by lightning electromagnetic pulses in simple arrangements of unshielded cables is presented. These calculations are carried out with the help of a mathematical function which exactly describes the shape of the lightning current. The values of induced voltages are evaluated during simulation tests under natural conditions.<<ETX>>

Lightning transients in control lines at the large urban area HV substation

In the HV substation, damage to or malfunction of the electrical and electronic equipment is very often caused by switching operations in primary circuits, earthing faults and lightning strokes. Electronic devices are very sensitive for any transient state. A direct lightning stroke into an open air high-voltage substation is considered. In this case, lightning current flows through conductive-earthed structures above ground and in earthing grids. This current induces voltage and current in low-voltage cables, which can cause severe problems in control, measurement and secondary circuits. The paper presents a computer analysis of lightning transients induced in low voltage wiring in the case of lightning strikes in the area of the substation.

Step and Touch Voltage Distributions at GSM Base Station during Direct Lightning Stroke

One of the tasks of earthing system is to ensure safety for people during various fault conditions. The objective of this paper is to provide knowledge about the actual step and touch voltage distributions in and around a freestanding base station for mobile communications during direct lightning strike into the communication tower. The final purpose is to limit the danger for people that can be present in the vicinity. Scalar potential at the earth surface as well as step and touch voltage distributions were calculated based on field theory approach.

A new composite absorbing material which is highly effective at the lower frequencies of the VHF range, and its applications

The authors present here a new composite absorbing material, which is highly effective at the lower frequencies of the VHF range. Due to the effectiveness of these materials it is possible to produce flat very thin double-layer absorbers made of ferrite and the new composite material. Such an arrangement shows the unique properties at the lower end of the VHF range - its reflectivity is markedly reduced in comparison to the reflectivity of just ferrite.

Hybrid absorber using new absorbing composites

In this paper, the authors analyse the usefulness of a new composite absorbing material which can be used to make two-layer hybrid absorbers incorporating a ferrite base layer, using the method of homogenization and the transmission line approach. The results acquired show the possibility of obtaining a reflectivity in the range -20 dB and better in the frequency-range from around 30 MHz up to several GHz, using a thickness of absorber significantly less than that which is used with current types of absorbers given in this document.

Lightning transients in the control and supervision systems on the HV substation

Electronic devices incorrect operations caused by lightning transients has been observed on the HV substation. This concerns specially the digital devices used in high voltage measuring and controlling techniques. This paper presents a calculation results lightning transients in the control and supervision devices signal inputs during direct lightning strike to the HV substation.

Electric power supply sourced from within fiber optic cable

In the paper, authors present an example of a simple and cost effective system of electric power supply by means of optical fiber. In many cases of physical measurements, it is very important to avoid excessive distortion to measured quantity. One of this is measurement of electromagnetic field of radio frequency. This is of concern in both, far- and near field examination. RF field measurement can be performed by direct measurement of the field at a point of interest or by measurement of the field scattered by a dedicated probe. One of the most important properties of this method is its low influence to the field under test. The full advantage of the system can be taken when the probe can be powered and controlled be means of optical fiber.

Decreasing lightning shock hazard at the HV substation by the modification of the grounding system

One of the tasks of the grounding system is to ensure safety for people during various fault conditions. Fatal lightning shock hazards depend on the surface potential that occurs when a lightning current is injected into the grounding system or induced in it. The main objective of the paper is to improve the grounding system of the typical HV substation. The quality of this modification is measured by the drop of the step voltage distribution and by the cost of it.

An effective solution to the problem of the ferrite tile gap effect

Due to the high permeability of ferrite, the presence of air gaps between adjacent tiles diminishes the performance of both the absorber and the anechoic chamber dramatically. The effectiveness of using gap fillers based on ferrite powder (e.g. ferrite rubber) is constrained due to the poor properties of ferrite powder. The problem can be solved effectively only with the use of higher permeability magnetic materials. A family of new magnetic materials has been developed by the authors. Among them is a material which can be plastic and can serve well as a gap filler. The permeability of the material is far higher than that of any mixture containing ferrite powder, even at high concentrations. In this paper, we show the effectiveness of high permeability material for filling these gaps. Due to the high permeability of the new filler the reflectivity of a resultant layer made of tiles with gaps is practically identical to that of a solid sheet of ferrite.