The transient electromagnetic response of a magnetic or superparamagnetic ground

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 854-860 ◽  
Author(s):  
T. Lee
Keyword(s):  
Transient Response ◽  
Direct Current ◽  
Free Space ◽  
Electromagnetic Response ◽  
Time Constants ◽  
True Value ◽  
Transient Electromagnetic ◽  
Current Value ◽  
The Wire ◽  
Weakly Magnetic

The effect of superparamagnetic minerals on the transient response of a uniform ground can be modeled by allowing the permeability of the ground μ to vary with frequency ω as [Formula: see text] Here [Formula: see text] and [Formula: see text] are the upper and lower time constants for the superparamagnetic minerals and [Formula: see text] is the direct current value of the susceptibility. For single‐loop data it is found that the voltage will decay as 1/t, provided that [Formula: see text] and [Formula: see text] Here, a is the radius of the wire loop and b is the radius of the wire, t represents time and [Formula: see text] is the permeability of free space. Even if a separate transmitter and receiver are used, the transient will still be anomalous. For this case the 1/t term in the equations is less important, and more prevalent now is the [Formula: see text] term. These results show that a uniform ground behaves in a similar way to a ground which only has a thin superparamagnetic layer. A difference is that whereas the amplitude of the 1/t term could be drastically reduced by using a separate receiver, this is not the case for a uniform ground. A magnetic ground for late times will decay as [Formula: see text]. However, if the conductivity of the ground is estimated from apparent conductivities it will be found that the value of the conductivity will be incorrect by a factor that is related to the susceptibility [Formula: see text] of the ground. For a weakly magnetic ground the estimated conductivity [Formula: see text] is related to the true value of the conductivity [Formula: see text].

scholarly journals Diagnosis for Conductor Breaks of Grounding Grids Based on the Wire Loop Method of the Transient Electromagnetic Method

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Shengbao Yu ◽  
Guanliang Dong ◽  
Nannan Liu ◽  
Xiyang Liu ◽  
Chang Xu ◽  
...  
Keyword(s):  
Topological Structure ◽  
Electromagnetic Response ◽  
Height Difference ◽  
Measuring Point ◽  
Wire Loop ◽  
Loop Method ◽  
Transient Electromagnetic ◽  
Grounding Grid ◽  
Grounding Grids ◽  
The Wire

The wire loop method of the transient electromagnetic (TEM) method is used to nondestructively detect conductor breaks of grounding grid. For this purpose, grounding grids serve as an underground wire loop, and the measuring points are arranged on the ground. At each measuring point, a receiving loop is employed to detect the electromagnetic response generated by transmitting the current of the transmitting loop. Conductor breaks can be diagnosed by analyzing the slices of the electromagnetic response. We study the effect of loop size and height difference through the simulation of an intact 2×2 grounding grid, confirming that it is easier to obtain the topological structure using a small transmitting loop and a small height difference. Furthermore, simulations of an intact 4×4 grounding grid and grids with different locations of conductor breaks are also conducted with a small transmitting loop. It is easy to distinguish the topological structure of the grounding grid and the locations of conductor breaks. Finally, the detection method is applied experimentally. The experimental results confirm that the proposed method is an effective technique for conductor break diagnosis.

Transient electromagnetic response of a polarizable ground

Geophysics ◽  
1981 ◽  
Vol 46 (7) ◽  
pp. 1037-1041 ◽  
Author(s):  
T. Lee
Keyword(s):  
Time Constant ◽  
Transient Response ◽  
Induced Polarization ◽  
Electromagnetic Response ◽  
Relaxation Model ◽  
Reverse Polarity ◽  
Transient Electromagnetic ◽  
Show Evidence ◽  
Positive Time

When a uniform ground has a conductivity which may be described by a Cole‐Cole relaxation model with a positive time constant, then the transient response of such a ground will show evidence of induced polarization (IP) effects. The IP effects cause the transient initially to decay quite rapidly and to reverse polarity. After this reversal the transient decays much more slowly, the decay at this stage being about the same rate as a nonpolarizable ground.

Global nonlinear inversion of transient EM data from conducting surroundings using a free‐space plate model

Geophysics ◽  
2000 ◽  
Vol 65 (3) ◽  
pp. 783-790 ◽  
Author(s):  
Shashi P. Sharma ◽  
Pertti Kaikkonen
Keyword(s):  
Free Space ◽  
Synthetic Data ◽  
Electromagnetic Response ◽  
Model Parameters ◽  
Nonlinear Inversion ◽  
Conductive Plate ◽  
Transient Electromagnetic ◽  
Conducting Body ◽  
Geological Conditions ◽  
Very Fast Simulated Annealing

A platelike conducting body in free space is used as a model to invert transient electromagnetic data using the very fast simulated annealing procedure as a global optimization tool. When the host rock conductivity is non‐zero, acceptable fits between the observed and computed responses are difficult to obtain. In general, the conducting body is assigned a lower conductance, larger dimensions (strike length and depth extent) and a smaller depth than the true values. We approximate the response of a conducting host to yield reliable estimates of model parameters as well as a good fit between the observed and computed responses. Our procedure is based on the assumption that the observed electromagnetic response is the sum of the response due to the conductive target and the response due to conducting surroundings (host and overburden). It is also assumed that the host response is laterally invariant, implying a layered earth and fixed source‐receiver geometry. The validity of the superposition assumption is tested against the full solution for a conductive plate in a finite conducting host. The efficacy of our approach is demonstrated using noise‐free and noisy synthetic data and two field examples measured in different geological conditions.

The effect of a conductive half‐space on the transient electromagnetic response of a three‐dimensional body

Geophysics ◽  
1985 ◽  
Vol 50 (7) ◽  
pp. 1144-1162 ◽  
Author(s):  
William A. SanFilipo ◽  
Perry A. Eaton ◽  
Gerald W. Hohmann
Keyword(s):  
Half Space ◽  
Free Space ◽  
Eddy Currents ◽  
Three Dimensional ◽  
Vertical Component ◽  
The Body ◽  
Electromagnetic Response ◽  
Loop Current ◽  
Transient Electromagnetic ◽  
Space Response

The transient electromagnetic (TEM) response of a three‐dimensional (3-D) prism in a conductive half‐space is not always approximated well by three‐dimensional free‐space or two‐dimensional (2-D) conductive host models. The 3-D conductive host model is characterized by a complex interaction between inductive and current channeling effects. We numerically computed 3-D TEM responses using a time‐domain integral‐equation solution. Models consist of a vertical or horizontal prismatic conductor in conductive half‐space, energized by a rapid linear turn‐off of current in a rectangular loop. Current channeling, characterized by currents that flow through the body, is produced by charges which accumulate on the surface of the 3-D body and results in response profiles that can be much different in amplitude and shape than the corresponding response for the same body in free space, even after subtracting the half‐space response. Responses characterized by inductive (vortex) currents circulating within the body are similar to the response of the body in free space after subtracting the half‐space contribution. The difference between responses dominated by either channeled or vortex currents is subtle for vertical bodies but dramatic for horizontal bodies. Changing the conductivity of the host effects the relative importance of current channeling, the velocity and rate of decay of the primary (half‐space) electric field, and the build‐up of eddy currents in the body. As host conductivity increases, current channeling enhances the amplitude of the response of a vertical body and broadens the anomaly along the profile. For a horizontal body the shape of the anomaly is distorted from the free‐space anomaly by current channeling and is highly sensitive to the resistivity of the host. In the latter case, a 2-D response is similar to the 3-D response only if current channeling effects dominate over inductive effects. For models that are not greatly elongated, TEM responses are more sensitive to the conductivity of the body than galvanic (dc) responses, which saturate at a moderate resistivity contrast. Multicomponent data are preferable to vertical component data because in some cases the presence and location of the target are more easily resolved in the horizontal response and because the horizontal half‐space response decays more quickly than does the corresponding vertical response.

Transient electromagnetic response of a thin conducting plate embedded in conducting host rock

Geophysics ◽  
1985 ◽  
Vol 50 (8) ◽  
pp. 1342-1349 ◽  
Author(s):  
S. S. Rai
Keyword(s):  
Time Constant ◽  
Transient Response ◽  
Onset Time ◽  
Electromagnetic Response ◽  
Late Time ◽  
Host Medium ◽  
Transient Electromagnetic ◽  
Conducting Plate ◽  
Free Air ◽  
Em Method

The transient response of a thin, rectangular conducting plate in a conductive host medium is presented for a horizontal‐loop electromagnetic (EM) system considering both a step and pulse EM method (PEM) excitation. For a shallow plate‐like conductor, the current‐gathering effect is preceded by a blanking effect. However, for deeper plates, current gathering was not observed. The effect of increasing plate depth, the ratio of the time constant of the plate to that of the host, and the plate time constant on the temporal characteristics of blanking and current gathering are investigated. The onset time for current gathering is independent of the plate time constant and is essentially a property of the host medium. At later observations (⩾5 ms) the decay of the plate in the host resembles the decay of the plate in free air. An interpretation scheme is proposed to determine plate parameters for Crone PEM measurements using the responses in two relatively late time channels.

Quasistatic transient electromagnetic response of a permeable nonuniformly conducting cylinder

1976 ◽  
Vol 54 (21) ◽  
pp. 2134-2139
Author(s):  
S. K. Verma ◽  
M. S. Joshi
Keyword(s):  
Distribution Pattern ◽  
Transient Response ◽  
Magnetic Permeability ◽  
Large Time ◽  
Initial Response ◽  
Pulse Response ◽  
Electromagnetic Response ◽  
Conductivity Distribution ◽  
Conducting Cylinder ◽  
Transient Electromagnetic

The step-pulse response of a permeable and a radially nonuniformly conducting cylinder is obtained. Effects of the conductivity distribution pattern and the magnetic permeability on the transient response are examined in detail. It is found that: (i) the initial response (for t → 0) remains unaffected by both the inhomogeneity and the permeability of the cylinder; (ii) the large time response is governed only by the permeability; and (iii) the conductivity inhomogeneity is reflected only during intermediate times. Finally, the implications of the results for predicting the parameters of the cylinder are discussed.

Approximate calculations of the transient electromagnetic response from buried conductors in a conductive half‐space

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 918-924 ◽  
Author(s):  
J. D. McNeill ◽  
R. N. Edwards ◽  
G. M. Levy
Keyword(s):  
Half Space ◽  
Free Space ◽  
Target Location ◽  
Electromagnetic Coupling ◽  
Practical Interest ◽  
Electromagnetic Response ◽  
Galvanic Current ◽  
Transient Electromagnetic ◽  
Space Modeling ◽  
Space Response

The transient electromagnetic (TEM) response from a conductive plate buried in a conductive half‐space and energized by a large‐loop transmitter is investigated in a heuristic manner. The vortex and galvanic components are each calculated directly in the time domain using an approximate procedure which ignores the electromagnetic coupling present in the complete solution. In modeling the vortex and galvanic current flows, the plate is replaced with a single‐turn wire loop of appropriate parameters and a distribution of current dipoles, respectively. The results of calculations of the transient magnetic field at the surface of the earth are presented for a few selected cases of practical interest. The relative importance of the vortex and galvanic components varies with the half‐space resistivity. The vortex component dominates if the half‐space is resistive, in which case free‐space algorithms suffice for numerical modeling. Furthermore the measured responses give much useful information about the target, and large depths of exploration should be achieved. As the half‐space resistivity decreases, a significant half‐space response is observed, caused by currents induced in the half‐space itself. This response can be very large. Spatial variations in it caused by relatively small changes in resistivity, i.e., geologic noise, obscure the response from deep targets making them difficult to detect. The effect of the half‐space is also to delay, distort, and reduce the vortex component in comparison with the free‐space response. The behavior of the galvanic component is determined by the haft‐space current flow. The presence of this component explains the large enhancement of overall target response seen at early times over relatively resistive ground and the departure from an exponential decay seen over more conductive ground, again with respect to responses predicted by free‐space modeling. In more conductive ground the galvanic component completely dominates the vortex component, resulting in the loss of useful diagnostic information. Although target location and depth can still be determined, target shape and orientation are poorly defined. Because of galvanic current saturation good conductors are difficult to distinguish from poor ones.

The harmonic and transient electromagnetic response of a thin dipping dike

Geophysics ◽  
1983 ◽  
Vol 48 (7) ◽  
pp. 934-952 ◽  
Author(s):  
P. Weidelt
Keyword(s):  
Formal Solution ◽  
Harmonic Excitation ◽  
Electromagnetic Response ◽  
Approximate Determination ◽  
Finite Conductivity ◽  
Circular Loop ◽  
Decay Modes ◽  
Transient Electromagnetic ◽  
Free Decay

An exact solution is given for the electromagnetic induction in a dipping dike of finite conductivity, represented as a thin half‐sheet in a nonconducting surrounding. The problem is formulated for arbitrary dipole or circular loop [Formula: see text] configurations. The formal solution obtained by the Wiener‐Hopf technique is cast into a rapidly convergent triple integral suitable for an effective numerical treatment. A good agreement is found between numerical results and analog measurements available for harmonic excitation. The transient response is obtained as a superposition of the half‐sheet free‐decay modes and is illustrated by some numerical examples for coincident loops, including a diagram for the approximate determination of conductance and depth of a vertical dike.

Mounting wires as a source of ignition in electrical cabinets

2021 ◽  
pp. 27-35
Author(s):  
Геннадий Васильевич Боков ◽  
Антон Александрович Назаров ◽  
Денис Геннадьевич Боков
Keyword(s):  
Electrical Equipment ◽  
Ignition Source ◽  
Insulation Material ◽  
Single Wire ◽  
Current Value ◽  
The Wire ◽  
Characteristic Features ◽  
In Fire ◽  
Wire Insulation

Приведены результаты исследований монтажных проводов электрических шкафов на воспламеняемость под воздействием тока. Выделены три зоны сверхтока, имеющие отличительные особенности появления источника зажигания. Показано влияние изоляции провода на частоту появления воспламенения в местах присоединения его к элементу электрооборудования. Представлены данные о воспламеняемости поливинилхлоридной изоляции в диапазоне пожароопасных значений сверхтока. Предложено характеризовать электрический провод как потенциальный источник зажигания площадью, образованной зависимостью времени воспламенения изоляции в интервале возможных сверхтоков. Wires are widely used for internal installation of electrical cabinets. Number of fire cases caused by wires takes one of the first places in fire statistics. Application of wires in the cabinets has its own fire-prone aspects peculiarities as concerns initiation of electrical nature ignition source. It appears both at single wire laying and at laying in cords where wires touch each other also in connection points of electrical apparatuses and devices located in the cabinet. The article considers issues of ignition source appearance in wires taking into account specifics of their installation in electrical cabinets. Ignition source appearance in a single wire and in wires contacting each other has a difference. There are given experimental data on inflammation frequency of wire insulation material at single wire laying and also at higher resistance in electrical elements connection points. Zones that differ in characteristic features of wire as an ignition source are given in the range of possible overcurrents. Zone A is characterized by insulation ignition with low probability due to low current density that is not enough to heat the wire up to the critical temperature Т, at which thermal decomposition products of wire insulating polymeric cover ignite. Zone B is designated in the range of overcurrent ratio from 2,5 to 18 compared with the long term permissible current value, in which insulation inflammation is observed due to fast conductor heating taking into account the influence of connection points with devices and apparatuses where increased transient resistance is present. It is experimentally confirmed that with the increase in transient resistance at the point of conductor connection with electrical equipment elements, the inflammation frequency of wire insulation increases. At the same time, the overcurrent range where ignition source appears reduces. It is proposed to use the area limited by the dependence of the time before insulation inflammation from the minimum to the maximum current value at which ignition occurs as a characteristic of the wire as an ignition source.

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