An analytical representation for first and subsequent stroke currents is proposed, simple application examples are given. The waveforms able to reproduce the characteristic concave profile at front of currents, including or not a second peak that usually observed in data available from direct measurements on actual lightning. They also reproduce, with good accuracy, median parameters describing lightning measured short instrumented towers. proposed have advantage using sum Heidler functions...

Jordan's formula to calculate the surge impedance of vertical conductors is revised and extended take into account systems with multiple conductors. Experimental data hybrid electromagnetic model are applied in order validate derived expressions. Additionally, successfully used representation an actual tower as a multiconductor system. The obtained results indicate usefulness expressions if engineering analysis direct strikes over elevated strike objects required

This paper investigates the influence of considering actual insulation volt-time curves both in calculation lightning-induced voltages and estimation number flashovers an overhead wire may experience per year due to nearby lightning strokes. The flashover mechanism is modeled according with integration method, which used as a reference for comparisons simplified 1.5 CFO criterion traditionally performance distribution lines. Sensitivity analysis show dependence on shape front time assumed...

The impact of the frequency dependence soil resistivity and permittivity on lightning overvoltages induced overhead lines over lossy ground is investigated. Visacro-Alipio expressions were implemented hybrid electromagnetic model to take this effect into account. Systematic simulations performed considering representative current waveforms first subsequent strokes different stroke locations near simulated line. In general, results indicated that responsible for a reduction overvoltage. This...

Lightning overvoltages due to direct strikes over a 138-kV transmission line and voltages induced on single-conductor overhead by nearby were simulated using realistic representation for the first-stroke current waveform that includes pronounced initial concavity followed sharp rise at half peak double peaks, in addition median time parameters taken from traditional database of instrumented towers. The results compared those yielded single-peaked given two Heidler functions, which is...

An unconventional technique to improve the lightning performance of transmission lines, consisting addition grounded wires properly positioned below phase conductors, is assessed. Overvoltages developed across insulator strings existing 230-kV lines in response direct strikes towers were simulated using an electromagnetic model. Minimum reductions these voltages ranges 19%-32% and 26%-44% achieved for 20- 80-Ω tower-footing grounding resistances due one two underbuilt wires, respectively....

Lightning overvoltages across insulator strings of existing 138- and 69-kV transmission lines were simulated using the hybrid electromagnetic model. It was found that, though reduction tower-footing grounding resistance is very effective to decrease lightning caused by first strokes, this saturated around 750-600 kV for typical currents subsequent strokes. The performance these estimated strokes be relevant cause backflashovers in lines.

The relevance of subsequent strokes on the lightning performance 138-kV lines is assessed. An electromagnetic model was used to simulate overvoltages experienced across insulator strings due direct strikes towers an existing line in order determine critical peak current required flashover using integration method. From distributions, estimates outage rate backflashover were developed considering contribution first and strokes. It found that, depending value tower-footing grounding...

This paper proposes closed-form expressions for the calculation of ground-return impedance and admittance underground cables. The proposed are shown to reproduce integral equations Xue with great accuracy a wide range ground resistivities frequencies. An error analysis, comparison available in literature, time-domain simulations demonstrate performance equations, which avoid improper integrals present an accurate typical cable arrangements.

Different physical models that describe the time variation of channel resistance are investigated in a lightning return stroke model. Such consider one three following hypotheses: (1) decays exponentially with time; (2) radial expansion core, which is assumed to be described by strong‐shock approximation, or (3) varies according different arc (defined Toepler, Barannik and Kushner et al.). Analyses illustrate effect time‐varying on currents corresponding electromagnetic fields. It shown...

A new lightning return‐stroke model based on a distributed circuit approach is formulated. The DNUTL (Dynamic Non‐Uniform Transmission Line) allows the computation of time and height dependence channel parameters contemplates corona sheath core losses representation. capacitance inductance are calculated by applying an original simple recursive equations. Electromagnetic fields generated at several distances from base presented for given set parameters. obtained results indicate that...

Events of a class, consisting the subsequent strokes multiple-stroke flashes presenting largest peak current, have features that make their effects very severe in terms insulation stress, notably combination relatively intense current and short front time. According to instrumented-tower measurements, median 27.2 kA is around 55% higher than whole set time 0.7 μs. The frequency such events significant since 80% lightning are flashes.

Cable models for high-frequency studies require the calculation of per-unit-length parameters in a wide frequency range. Analytical methods, such as ones implemented traditional electromagnetic transient simulators, are frequently used this purpose. However, they accurate only cable systems which cables sufficiently apart from each other, and specific geometries presence other wired metallic structures is neglected. This hampers their application to calculate assembled trays or pipes,...

The influence of a periodically grounded neutral conductor on voltages induced by first and subsequent negative strokes in single-phase overhead lines for different ground resistivity values is investigated means computational simulations using the hybrid electromagnetic model. Configurations medium- low-voltage networks were assumed. Currents with median parameters obtained from measurements Mount San Salvatore Morro do Cachimbo stations adopted. While simulation stroke considered current...

In this paper, two time-domain procedures are proposed for the calculation of lightning-induced voltages using lossy transmission line models available in electromagnetic transient simulators. both procedures, influence incident field is represented form current sources that connected externally at ends illuminated line. One formulated directly phase-domain and compatible with universal model (ULM). The second procedure modal domain by Marti. Both validated taking as reference a first order...