Maria Helena Murta Vale

The Response of Grounding Electrodes to Lightning Currents: The Effect of Frequency-Dependent Soil Resistivity and Permittivity

A methodology is proposed and applied to determine the variation of soil resistivity and permittivity in the typical range of lightning current frequency components. The response of horizontal electrodes buried in high- and low-resistivity soils subjected to currents with lightning waveform patterns was measured and also simulated, taking this variation into account. The waves of the simulated and measured grounding potential rise are nearly the same but are quite different from the simulated waves considering the conventional assumption of constant values for soil resistivity and permittivity.

Methodology for evaluation of grid-tie connection of distributed energy resources - Case study with photovoltaic and energy storage

The availability of reliable energy sources for all people, especially electricity, indicates an imbalance in the living conditions of a society. Therefore, new systems must be implemented to couple energy storage and renewable energy generation for the grid reliability improvement and increase access to electricity. This paper proposes a methodology to establish a general index focused on the insertion of distributed photovoltaic generation and energy storage using batteries. This methodology was applied in the IEEE 14-bus electric power system with load variation from different energy providers for the period of one year. The simulation results allow of the best performance evaluation to add distributed photovoltaic generation and/or energy storage in a real electric power system in different buses. The proposed methodology will allow planners to at the same time visualize different aspects by means of a single index that includes technical, economic and environmental aspects.

Power system reactive compensation: evaluation of expansion plans taking into account electromagnetic transient restrictions

In this paper, the authors present developments regarding Power System Capacitive Shunt Reactive Compensation and Voltage Control, with respect to Expansion Activities, in an Electromagnetic Transient context. The definition of the amount and location of shunt reactive compensation to be installed in power systems considers several aspects, as reactive power optimization, short circuit calculations, voltage stability and harmonic analyses, among others. Different alternatives must be evaluated, regarding their impact (positive and negative) to system behavior, in order to select the most adequate compensation. Expansion decision process usually does not include studies about the transient impact of reactive shunt compensation caused by switching operation. Traditionally, this is done only after expansion definition, when the detailed project is elaborated, mainly to prepare equipment specifications. In this paper, it is proposed an innovative procedure to include a technical evaluation of different shunt compensation based on a preview of the overvoltage and overcurrent values caused by the corresponding capacitors bank switching. The new methodology is designed to (i) indicate the critical system buses that must be carefully investigated, considering transient behavior, and (ii) promote the adequate shunt compensation adjust. The proposed procedure is detailed and results of its application in real systems are presented.

Unusual features of negative leaders’ development in natural lightning, according to simultaneous records of current, electric field, luminosity, and high‐speed video

The development of downward and upward leaders that formed two negative cloud-to-ground return strokes in natural lightning, spaced only about 200 µs apart and terminating on ground only a few hundred meters away, was monitored at Morro do Cachimbo Station, Brazil. The simultaneous records of current, close electric field, relative luminosity, and corresponding high-speed video frames (sampling rate of 20,000 frames per second) reveal that the initiation of the first return stroke interfered in the development of the second negative leader, leading it to an apparent continuous development before the attachment, without stepping, and at a regular two-dimensional speed. Based on the experimental data, the formation processes of the two return strokes are discussed, and plausible interpretations for their development are provided.

Assessing events of upward lightning measured at Morro do Cachimbo Station

Some data of currents of lightning events measured in Morro do Cachimbo Station during the period 2008-2012 are presented, comprising 9 downward negative first strokes (4 of them pertaining to multiple-stroke flashes), 8 unconnected upward leaders developed in response to downward negative leaders approaching the ground and 5 negative upward lightning. The current waves of all negative upward lightning are presented along with an example of representative waves for first stroke and unconnected upward leader currents. Parameters of such currents are summarized.

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

Original simultaneous records of currents, close electric field and high-speed videos of natural negative CG lightning striking the tower of Morro do Cachimbo Station are used to reveal typical features of upward positive leaders before the attachment, including their initiation and mode of propagation. According to the results, upward positive leaders initiate some hundreds of microseconds prior to the return stroke, while a continuous uprising current of about 4 A and superimposed pulses of a few tens amperes flow along the tower. Upon leader initiation, the electric field measured 50 m away from the tower at ground level is about 60 kV/m. The corresponding average field roughly estimated 0.5 m above the tower top is higher than 0.55 MV/m. As in laboratory experiments, the common propagation mode of upward positive leaders is developing continuously, without steps, from their initiation. Unlike downward negative leaders, upward positive leaders typically do not branch off, though they can bifurcate under the effect of a downward negative leaders secondary branch approaching their lateral surface. The upward positive leaders estimated average two-dimensional propagation speed, in the range of 0.06 × 106 to 0.16 × 106 m/s, has the same order of magnitude as that of downward negative leaders. Apparently, the speed tends to increase just before attachment.

A useful tool using lightning location system data for computing voltage sag analysis into expansion planning activities

This work presents fundamental aspects of a computational tool the authors developed for application in voltage sag analysis in the expansion planning activities. This tool introduces the use of lightning-location-system data to perform analyses of voltage-sag severity along the power system and to identify critical spots responsible for the system vulnerabilities. A case study is presented.

Parallel processing applied on the electric grounding systems design

Electrical engineering is a source of problems that can take advantage of the parallel processing on computing. It happens once the kind of numeric solution is often done by the evaluation of linear equations put in matrix style. Concrete encased grounding systems are a powerful answer to the grounding design problem. It uses the metal embedded in the concrete structure of the building as grounding electrodes. Nevertheless, the great demand of computer processing, necessary to calculate such a grounding system, makes it difficult to use sequential program implementation. This paper presents the basis of the engineering problem and a parallel tool, called PENCAPS, that implements the numeric solution developed to solve concrete encased electrode grounding systems.

PENCAPS: a parallel application for electrode encased grounding systems project

The design of concrete encased electrode grounding systems by conventional computation procedures is a time-consuming task. It happens once the electromagnetic representation of the physical system requires the calculation of large full matrices. Recently, the possibility of paralleling the procedures involved in such calculations led the authors to implement a C language parallel application, based on MPI (Message Passing Interface). This article presents the engineering problem associated to this development and the fundamental aspects regarding this application, including the evaluation of its efficiency for solution of large grounding systems.