Maximum Step Voltage Research Articles

Design Of A Main Substation Grounding System Based On Variations In Area and Number Of Electrodes

The function of the grounding system is to limit the voltage between equipment and the ground and neutralize the voltage that arises at the ground surface due to fault currents flowing in the ground. An unsafe grounding system can disrupt system reliability and human safety in the substation area. This research aims to simulate the design of a substation grounding system with the influence of variations in location and number of electrodes installed in grids and rods in swampy soil conditions with different soil resistivity values. The impact of these parameters is on the resistance value, touch voltage, and step voltage at a weight of 70 kg by using the CYMGRD application as a medium to see the effectiveness and optimization of whether the substation grounding system with variations in the outside area and variations in the number of electrode rods meets the requirements without exceeding safe limits on systems or humans. This grounding system design is designed for two cases, namely case 1: the maximum touch voltage and maximum step voltage values exceed the permitted touch voltage and maximum step voltage, so conditions like this are included in the criteria for being unsafe and can endanger personnel in the field. Case 2: the touch voltage and step voltage values are smaller than the permitted touch voltage and step voltage values, so this design is included in safe conditions and meets the criteria for a good and safe grounding system.

Effects of Soil Profile on the Transient Performance of Substation Grounding System

<table width="593" border="1" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top" width="387"><p>Lightning transient characteristic of the grounding grid is fundamental for optimum performance of lightning protection of a substation. In order to design an appropriate grounding system for such substation, it is important to study its transient characteristics because the high impulse current is significantly different compared to power frequency current. In this paper, substation grounding grid model was developed using CDEGS software to analyze the grid transient performance in terms of ground potential rise (GPR), touch voltage and step voltage when the grounding system is struck by a lightning impulse current. Several parameters, such as lightning current amplitude, feed point and the number of sub-grids, were altered to study their relationship with the transient performance. The maximum transient GPR, touch voltage, and step voltage increase as the lightning current amplitude increase. The maximum transient GPR and step voltage are the highest at the corner of the grounding grid while the maximum touch voltage is the highest at the centre of the grounding grid. In addition, the maximum transient GPR and step voltage decrease when the number of sub-grid increases. In contrast, the touch voltage slightly increases as the number of sub-grid increases. The maximum transient GPR, and step voltage are the highest at the 2-layer and the lowest at the uniform soil or single-layer soil.</p></td></tr></tbody></table>

Reducing the Effect of Lightning on Step and Touch Voltages in a Grounding Grid Using a Nature-Inspired Genetic Algorithm With ATP-EMTP

This paper discusses the step and touch voltages, based on body resistance, in a grounding grid after a lightning strike at a 434-/21-kV substation. To ensure grounding grid safety, the maximum step and touch voltage should not exceed the safety criteria defined by the IEEE Std. 80. In this paper, ATP-EMTP and a genetic algorithm are used to analyze and optimize the step and touch voltages in a power grid. The voltages are calculated under normal conditions of a lightning strike at a power system. Thevenin’s theorem is applied to calculate the step and touch voltages. The genetic algorithm is applied in ATP-EMTP to obtain the minimum level of step and touch voltages in the grounding grid after lightning strikes the power system. The step and touch voltages at different positions of the grounding grid are explained in this paper using the ATP-EMTP and the genetic algorithm. The computer simulation shows that the proposed scheme is highly feasible and technically attractive.

A New Maximum Step Voltage Calculation Method of On-Load Tap-Changer for Symmetrical Two-Core Phase-Shifting Transformer

In order to select a reliable and economical type of transformer on-load tap-changer (OLTC), it is necessary to accurately determine the maximum step voltage in the process of engineering design. Because both configuration and operating conditions of a phase-shifting transformer (PST) are more complicated than those of conventional transformers, it is far harder to accurately calculate the maximum step voltage. The existing calculation methods have the shortcomings of inadequate accuracy or weak applicability. To solve these problems, based on the equivalent circuit of a PST, this paper at first derives the quantitative relations between operating conditions and the step voltage. Subsequently, the effect of different load conditions, including the load current and the phase angle difference between the load voltage and current, on the step voltage is fully investigated. This investigation reveals a law about the changes in step voltage under different load conditions. Next, a new calculation formula for the maximum step voltage is proposed, and its accuracy is verified with two practical examples. Finally, an error analysis is carried out to demonstrate the generality of this approach. The calculation method offers appealing accuracy and is very suitable for the economical and reliable selection of OLTC for symmetrical two-core PSTs in the process of engineering design.

Safety Assessment of AC Grounding Systems Based on Voltage-Dependent Body Resistance

This paper presents the safety assessment of a grounding system at an indoor-type 161/23.9-kV substation based on voltage-dependent body resistance. For a grounding system to be safe, the maximum actual touch and step voltages should not exceed postulated safety criteria. Thus, the safety assessment of a grounding system is referred to a procedure by which the actual maximum touch and step voltages are computed and compared to the maximum allowable (safe) touch and step voltages. The safety criteria in terms of allowable body current have been defined by two widely accepted standards, i.e., the IEEE Std. 80 and the IEC 60479-1. Then, the allowable body current is translated into the allowable touch and step voltages. However, the two standards differ in their definitions of body resistance. The IEC 6047-1 provides data for the body resistance as a function of body voltage and data for the body resistance as a function of path, while the IEEE Std. 80 uses a constant value of 1000 $\Omega$ for the body resistance. Thus, a comparison of allowable touch and step voltages computed by these two standards is included in this study.

Achievement of the best design for unequally spaced grounding grids

The configuration of grounding grids which are used to earth electrical substations could be equally or unequally spaced. Unequally spaced grids were introduced to improve the requirements of the grids such as grounding grid resistance (Rg), ground potential rise (GPR), maximum touch voltage (Et) and maximum step voltage (Es) values.Also, unequal spacing can reduce the cost of the grids and enhance the level of safety for people and equipments. In this paper two different approaches were used to determine the best possible configuration of grounding grid. These approaches based on sequential multiplicative and sequential power techniques.

Signal Detection for Optical AC and DC Voltage Sensors Based on Pockels Effect

A new signal detection technology is presented to improve the stability and robustness of the optical voltage sensors (OVSs) based on Pockels effect for the measurement of ac and dc voltages. The closed-loop error of the OVS is a weak and nonlinear signal vulnerable to unavoidable noise. Simultaneously, the nonlinearity and noise in physical components of OVSs are the major causes of performance deterioration of system in practical high-voltage applications. We design a signal detection hardware that can precisely extract nonlinear closed-loop error and be applicable for the measurement of ac and dc voltages. Based on the signal detection hardware, we analyze the dynamic model of closed-loop OVSs considering the effects of nonlinearity, noise, and time-delay. The control scheme of OVS is proved to obtain exponential stability with a desired attenuation level of noise. The experimental results show that the OVS has a wide bandwidth up to 24.5 kHz, the maximum step voltage 19.5 kV, the accuracy of ac and dc voltage within 0.2% and 0.5%, respectively. The experimental results validate the effectiveness and usefulness of our proposed detection method.

Optimal Methodology for the Grounding Systems Design in Transmission Line Using Mixed-integer Linear Programming

A novel optimization methodology is proposed for the design of transmission line grounding systems, taking into account technical and economical considerations. The grounding systems design of transmission lines is stated as a mixed-integer linear programming problem, in terms of the construction characteristics, and the particular requirements of the tower grounding schemes at the supports of each different line sections in order to minimize the investment costs subject to the maximum allowed line outage rate due to the lightning activity, excavation volume limits for lowering environmental impact, allowed maximum step voltage, and the limitation of the ground potential rise value. The methodology is tested on a real case consisting of a 230-kV transmission line, 85.4-km long, with 180 towers. Results are presented and compared to the design obtained through conventional tower design approaches with important reductions in the investment costs, encouraging the use and further development of the methodology.

Microwave response of long intrinsic Josephson junctions fabricated on Bi-2212 single crystals

The microwave response properties of Bi2Sr2CaCu2O8+x long intrinsic Josephson junctions have been experimentally and theoretically investigated. We fabricated a mesa structure consisting of 14 junctions, 50 μm long and 4 μm wide, and observed the microwave-induced steps in the I-V characteristics under irradiation with microwaves in the range 5–8 GHz. The step voltages were proportional to the square root of the microwave power, implying that the steps were produced by the motion of fluxons created by the microwaves. The Josephson frequency corresponding to the maximum step voltage was estimated to be 570 GHz. The step voltage decreased with increasing temperature, which can be explained by the decrease of the Swihart velocity. We performed a numerical simulation using coupled sine-Gordon equations and obtained a power dependence of the step voltage similar to the experimental result, and demonstrated standing waves of electric fields with in-phase plasma oscillation in all the junctions. These facts suggest that the steps observed in the experiment were produced by plasma resonance excited by the external microwaves.

Calculation of ground resistance and step voltage for buried ground rod with insulation lead

Procedures for installing ground rods can be categorized into the driven ground rod methods and the buried ground rod methods. The leads of ground rods are also classified into two types—bare conductor leads and insulation leads. The analytical results herein elucidate a method for determining ground resistance, earth surface voltage, position and magnitude of the maximum step voltage for the buried ground rod with the insulation lead. The ground resistance, earth surface voltage and step voltage in the driven ground method exceed those of the buried ground rod with the insulation lead. Ground resistance, earth surface voltage and step voltage decrease as the depth of the buried ground rod increases. The position of the maximum step voltage varies with the buried depth of a ground rod with the insulation lead. The distance of the maximum step voltage from the ground rod increases with the depth of the buried ground rod. Results of this study provide a valuable reference for ground designs that protect humans and electrical equipment.

Maximum step voltages of combined grid-multiple rods ground electrodes

Expressions are suggested for assessing the maximum step-voltages and associated parameters of combined grid-multiple rods ground electrodes buried in uniform soil. The expressions proposed are successfully verified by comparison to exact computer calculations performed for a wide set of square and rectangular ground grids reinforced by ground rods distributed around the grid perimeter and within the grid.

Ground terminations of lightning protective systems

In a lightning protective system, the ground terminations must be designed to keep within fixed values the step voltage both inside and outside the protected structure and the maximum total voltage. Design criteria shall take into account that the behavior of ground systems is affected by their length, by soil resistivity, by amplitude and wave shapes of lightning currents. In this paper, investigations carried out on ground terminations when subjected to impulse currents are presented and typical phenomena which characterize their behavior are summarized. Theoretical analysis of the transient phenomenon and new experimental results on each electrode are presented. On the basis of maximum step voltage and of the statistical variation of lightning currents, the design of ground terminations is analyzed and curves for their practical sizing are given. Provisions to avoid discharges into the soil between ground conductors and buried cables or pipes are given, together with computation methods to evaluate overvoltage amplitudes between live conductors and ground in shielded cables.

Improved 1 V and 10 V Josephson voltage standard arrays

1 V and 10 V Josephson voltage standard arrays are fabricated on the basis of an improved design, using a modified technology. The Nb/Al/sub 2/O/sub 3//Nb trilayer is deposited directly on the Si wafer. The edges of the base electrodes are insulated by an anodization process. The maximum step voltage increases linearly with the external microwave voltage. Switching between different voltage levels is possible by simple switching of the dc voltage bias. A laboratory-made, oversized circular waveguide reduces the attenuation of the experimental set-up.

Nonuniformity correction factors for maximum mesh- and step-voltages of ground grids and combined ground electrodes

Correction factors for calculating maximum mesh and step voltages associated with grid and combined grid-multiple rod ground electrodes are defined and calculated for a wide set of ground electrodes and various two-layer soil structures. The results obtained are presented as graphs appropriate for a straightforward practical application. Empirical expressions for correction factors matching well with the calculated data are also proposed providing an insight in the most effective ground electrode parameters which might be important in the design process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Parametric analysis of foundation grounding systems surrounded by two-layer soil

Results of extensive research, conducted using a program designed to calculate the grounding resistance and touch and step voltages for foundation grounding systems surrounded by two-layer soil, are presented and discussed. It is shown that soil and concrete properties, as well as the grid burial depth, significantly influence the maximum touch and step voltages. A number of charts related to the most frequent cases of soil-concrete structures are given for a practical assessment of the touch voltages of such grounding systems. >

A new formula for calculation of the maximum step voltage in a substation grounding grid

This paper introduces an analytical formula for calculation of the maximum step voltage at a substation grounding grid, based on a new theoretical analysis method. The accuracy of this formula is checked by the results obtained from both the computer program calculation and the model test. Evaluations of the formulae commonly used to calculate step voltage in various countries are also given.

Static and dynamic properties of short, narrow, variable-thickness microbridges

The electrical properties, including the Josephson-effect response to microwave radiation, have been studied for extremely small, high-resistance microbridges of Pb-In alloy and unalloyed In, with dimensions ranging from 300A to 2000A. The I c R product of In and Pb-In microbridges decreases smoothly as the bridge cross section is reduced, approaching the Ginzburg-Landau limit of 0.64 mV/K for the smallest bridges. The voltage range of microwave response and the temperature range of hysteresis-free operation both increase (improve) as the bridge is made narrower, in agreement with Joule heating theory. For example, an 8 ohm Pb 0.9 In 0.1 bridge with all dimensions ≤500 A has a maximum step voltage of V_{\max} = 1.5 mV and a nonhysteretic temperature range of \DeltaT_{no hyst} = 1.2 K. Bridges of unalloyed In can show still better response due to a longer coherence length, and nonhysteretic operation over the full temperature range below T c is possible.

Evaluation or Resistivity Tests for Design of Station Grounds in Nonunirorm Soil

The actual soil formation at a prospective station site usually can be approximated by an assumed 2-layer stratification. The method of establishing characteristic parameters of such a formation by 4-electrode tests is reviewed. As the main result of this study, curves are presented to determine, from these parameters, the apparent resistivity values to he used in computing the resistance of a grounding grid in a 2-layer soil. During the design of such a grid, the maximum touch and step voltages that might occur during a ground fault have to be evaluated in addition to the station ground resistance.