Dave W. P. Thomas

The Transmission Line Modeling Method to Represent the Soil Ionization Phenomenon in Grounding Systems

This paper presents an extended methodology based on the transmission line modeling method (TLM) aiming at a soil ionization representation for the simulation of grounding systems. This natural phenomenon can be represented by considering the variation of the conductive components present in the TLM circuit. The proposed analytical formulation is introduced with a focus on the computational implementation of the TLM method in one dimension. The method is not subject to divergent solutions, being numerically stable and the methodology can be incorporated into a general algorithm irrespective of the soil properties or characteristics of the grounding electrode and lightning surge.

Integration of Behavioral Models in the Full-Field TLM Method

The accurate simulation of digital circuits requires the inclusion of field phenomena. Issues such as signal integrity, crosstalk, and external EMI are of paramount importance in the design stage, due to the decreasing feature size and increasing clock frequency of modern digital systems. This paper addresses issues with the incorporation of field phenomena in the simulation of digital systems, by embedding behavioral descriptions of digital ICs into a full wave field model. The paper successfully simulates digital circuits incorporating the external electromagnetic interference (EMI) environment of operation; further research is required to incorporate the internal EMI effects in the IC silicon. The transmission-line modeling method is used for the field model, while the input/output buffer information specification models the digital IC behavior.

An Improved Soil Ionization Representation to Numerical Simulation of Impulsive Grounding Systems

This paper presents a hybrid method based on the transmission line modeling method (TLM) aiming to represent the soil ionization effect for grounding systems simulation. This natural phenomenon can be better represented by taking into account the variation of the conductive components present in the TLM circuit and considering the residual resistivity remaining in the soil. The proposed analytical formulation is developed with a focus on the computational implementation of the method. The model is validated by comparing synthetized test results with measured data and other numerical models (residual resistivity, TLM, and analytical model). High precision together with an easy to implement formulation indicates that the methodology presents potential for real-life applications.

Arc fault generation and detection in DC systems

Arc fault are a common fault in electrical systems and can go undetected by traditional protection schemes and cause significant damage. To investigate the characteristics of arc faults in DC systems and their detection methods, an arc generation unit is described and arc characterization during initiation is investigated in this paper. Different conditions of arc current, air gap length and load inductance are considered to examine the effect on arc initiation. Arc fault detection algorithms based on spectrum analysis, Wavelet packet decomposition and current variation are then presented and discussed. Experimental results demonstrate that the presented methods can recognize the initiation of an arc.

Fault identification for “More Electric” Aircraft distribution systems

The proposals for the “More Electric Aircraft” place a significant, increased demand on the electrical power distribution system. To increase safety and reduce aircraft maintenance times on the ground, there is a greater need to quickly identify and locate electrical faults within the electrical distribution system. The work presented in this paper forms an initial study into the use of power system harmonic impedance measurement for identifying and locating faults within power cables. The method is passive — i.e. it does not require the injection of any test signals — and can potentially be embedded into a centralised equipment controller to provide intelligent, real time diagnostics. The method monitors the harmonic line-line self-impedance at strategic points in the distribution system; this is obtained by measuring load voltage and current. Faults can be identified and located within a few fundamental cycles, and therefore provides a “backup protection” system which does not require bus current measurement. It also can provide details of the fault location and could therefore be a significant aid to aircraft maintenance. The paper derives the theoretical basis of the scheme and provides simulation results for a proposed aircraft power system to demonstrate the validity of this approach to detect and locate faults within the system.

Novel Formulation to Determine the Potential on the Soil Surface Generated by a Lightning Surge

This paper presents the development of an analytical formulation for estimating the potential on the soil surface, caused by electric current calculated on a grounding conductor. The formulation has a great significance in its use in conjunction with 1-D numerical methods, which are not able to determine such potentials directly. The proposed study focuses on lightning surges considering the frequency dependence of the soil properties. First, the subject is introduced emphasizing important aspects related to the analysis and representation of grounding systems against lightning. Afterward, the proposed analytical formulation is introduced with a focus on the computational implementation of the transmission line modeling method in 1-D. Simulations were carried out considering a typical horizontal electrode used as grounding in the power electric system. The formulation was validated by comparing the results with the solution based on the electromagnetic model (CDEGS Software), which is considered the most stringent for the solution of full Maxwell equations due to their minimum approaches. The results demonstrate that the generalized formulation presents good accuracy, contributing to an improved representation of grounding systems based on numerical techniques in 1-D.

Effective length study of grounding electrod reached by lightning based on Transmission Line modelling Method

This paper presents a study about the effective length of a horizontal grounding electrode used to dissipate electrical current to the earth proceeding from a lightning surge. The work discusses the influence of the soil parameters in the scattering process considering fasts and slow wave shapes. Initially an introduction about the problem is made, with a brief description about the effective length concepts. An algorithm based on the Transmission Line Modeling Method in one dimension (TLM-1D), taking into account the soil ionization phenomenon, was developed in order to evaluate the transitory behavior of the grounding. The simulation results show that a significant part of the electrode is not effectively used for scattering the surge current to the soil and that the effective length of the conductor is dependent mainly on the soil resistivity and the wave shape.

Application of digital filtering techniques in three-dimensional multi-scale problems

The paper describes a technique based on a digital filter boundary to describe the electromagnetic properties of a fine embedded object. The digital filter parameters are first extracted from a fine mesh simulation around the fine object and then inserted into a coarse mesh for large scale simulation. The technique is illustrated by an example of a conducting post in a TLM model of an interconnect. The example demonstrates significant computational savings.

On-line fault diagnostic for AC zonal marine distribution systems

This paper presents a new protection scheme for AC zonal distribution system proposed for future marine power systems based on active impedance estimation. This technique actively imposes small transient disturbances onto the system at a point of measurement to excite the system in real time and estimate the system impedance over a broad frequency range at that point. The identified impedance can be used for fault discrimination. The performance of this proposed technique is investigated by experiment. The scheme exploits the increased use of power electronic devices to provide a useful complement to traditional protection strategies and can also provide the necessary back up protection during extreme protection failure, without the need for communication channels.

Measurements and modelling in the frequency range 2-150 kHz

• Changing use of power supplies and new technologies • Increased distortion in the frequency range 2-150kHz • Both conducted and induced interference paths • Time/frequency characteristics make measurement and modelling challenging • Methods of measurement discussed • Methods for modelling described • More research required