Dangerous Voltages Research Articles

접지전류의 주파수에 따른 대지표면전위 상승 및 위험전압의 분석

The most important object of grounding systems is to protect human being from electric shock. Touch and step voltages are measured to evaluate the performances of grounding systems. Dangerous voltages have been largely studied by the power frequency fault currents, on the other hand, the ground current containing the high frequency components and surge currents haven

ELECTROSTATIC ANALYSIS OF TRANSMISSION LINES TO SIMULATE CORONA DISCHARGE AT HIGH VOLTAGE

This paper presents the results of Boundary Element Method (BEM) numerical procedures of voltages distribution between transmission lines in order to investigate the theoretical corona discharges. The algorithm of the voltage distributions are coded in Mathematica studying size of the system under controlling Neumann and Dirichlet boundary conditions. Conducting experimental work at a high voltage (HV) is potentially very dangerous. Therefore, simulation is a vital research approach, and computer modeling ofiers signiflcant advantages to estimate optimal calculation over established system to prevent dangerous voltage and not to exceed the corona voltage. In this paper, the BEM results are verifled with Finite Element Methods (FEM) which is coded in Mathematica too.

Shock Hazard in the Presence of Protective Residual-Current Devices

The application of residual-current principle, as carried out by zero-sequence current protective devices, is one of the most efficient ways to reduce the hazard of electric shock in case of a failure of the equipment's basic insulation to ground. Highly sensitive and regularly tested residual-current-operated circuit breakers without integral overcurrent protection (RCCBs) devices are rightfully recognized worldwide by standards and codes as an effective means to protect persons against direct and indirect contact with energized parts by disconnecting the supply in a timely fashion. These devices are also referred to as ground-fault circuit interrupters. The protective action of the RCCBs, however, can be nullified not only due to internal malfunctions of the device but also due to particular ground-fault conditions. In these dangerous situations for persons, for example, accidental direct contact with two parts at different potentials, the residual current flowing through the RCCB is below its residual operating value, and therefore, it cannot trip. This hazardous circumstance exposes persons to dangerous touch voltages despite the presence of an efficient protective device, which cannot be blamed for not intervening. This paper seeks to clarify these particular fault conditions occurring even in the presence of healthy RCCBs.

축소모델을 이용한 접지전극 주변의 위험전압 평가

본 논문에서는 접지에 관련된 문제를 실제 현장데이터로부터 해결할 수 있는 유용한 방법을 제안하기 위하여 실규모와 축소모델 접지전극 주변에서 측정된 접촉전압, 보폭전압과 표면전위분포에 대한 실험결과를 기술하였다. 사례연구로서 가로등, 교통신호등과 제어기와 같은 도로시설물의 설치에 사용되는 콘크리트 기초좌대 주변의 대지표면전위분포와 위험전압을 측정하고 검토하였다. 균질의 토양을 모의하기 위하여 직경이 1,160[mm]인 반구형 용기를 사용하였다. 그 결과, 축소모델을 이용하여 측정한 결과는 실규모 설비에서 얻은 결과와 잘 일치하였으며, 축소모델 실험은 산악, 지하, 수중 등과 같이 접근할 수 없는 장소에 설치된 접지전극 주변의 위험전압을 평가하는 유용한 수단으로 이용될 수 있음이 확인되었다.

Predicting Voltage Droops Using Recurring Program and Microarchitectural Event Activity

Shrinking feature size and diminishing supply voltage are making circuits more sensitive to supply voltage fluctuations within a microprocessor. If left unattended, voltage fluctuations can lead to timing violations or even transistor lifetime issues. A mechanism that dynamically learns to predict dangerous voltage fluctuations based on program and microarchitectural events can help steer the processor clear of danger.

A new model for a safety analysis in a system of earthing systems interconnected through bare‐buried conductors

PurposeThe purpose of this paper is to present a mathematical model for studying the effects of the interconnection through bare‐buried conductors (BBC) of the secondary substations' earthing system of an urban area.Design/methodology/approachThe developed methodology is based on three main points: the solution of the transmission lines' equations for the formulation of a lumped parameters model of a BBC considering the conductive effect; the division of the distribution network into simpler sub‐systems; and the calculation of all the voltages and currents of the medium voltage (MV) network and of the earthing systems using a multiport approach.FindingsThe methodology has been applied to various situations giving precious information on the behaviour of the earthing systems interconnected by means of BBC in presence of conductive effect. The results of the simulation allow to quantify the reduction of the dangerous voltages appearing during an earth fault, in presence of interconnection between the secondary substations' earthing systems, realized by means of BBC.Research limitations/implicationsSome factors can influence the precision of the methodology. Indeed, for a correct simulation of the system it is necessary to know several electrical and geometrical parameters, among all the resistivity of the soil that, often, is known with a large degree of uncertainty.Practical implicationsUtilities are quite interested in this topic. The study of interconnected earthing systems in MV networks with the purpose of identifying safe extended areas named global earthing systems (GES) has important management and economic consequences.Originality/valueThe paper presents an original lumped parameters model of the BBC, able to simulate these elements with a high accuracy, also in presence of the conductive effect, and that can be easily included in the more general model of a distribution line, in order to perform the analytical study of the GES in MV networks. The model proposed allows one to overcome the limits of the application to the MV networks of similar models present in the literature for the study of the same topic in the high‐voltage networks.

접지설비 절차에 따른 개선된 접지실비 모델

The ANSI/IEEE Std. 80-2000 method has been commonly used to design grounding system for the South Korea domestic market. However, the appropriateness of this method to the ground design environment has not yet been examined. This paper presents a new design grounding system method that complements the ANSI/IEEE Std. 80-2000 method, when the new method is a lied to thickness, dangerous voltage, and grid spaced computations for grounding conductors. Furthermore, this paper examines reliability and economic efficiency issues by comparing of the ANSI/IEEE Std. 80-2000 Annex B`s case study with the original method.

Finite difference time domain simulation of earth electrodes soil ionisation under lightning surge condition

The non linear effects of soil ionisation on the behaviour of earth electrodes are investigated by a finite difference time domain numerical scheme. A time variable soil resistivity is used in order to simulate the soil breakdown; step by step the resistivity value is controlled by the local instantaneous value of the electric field compared with the electrical strength, fixed for the soil. No a priori hypothesis about the geometrical shape of the ionised zone around the electrodes has to be enforced. Simulation results related to complex earth electrodes of limited extension are reported. The model has been validated by comparing the computed results with data available in technical literature. A discussion about dangerous earth voltages is reported, by underlining the role of soil ionisation. Electrodes of larger extension can be straightforwardly simulated by means of larger computational resources.

위험전압 검토에 따른 개선된 접지설비 모델

국내 접지설계시 가장 널리 사용되는 것은 IEEE Std. 80 위험전압 계산식이나 국내 접지설계 환경의 적정성 여부는 검토되지 않고 있다. 따라서, 본 논문에서는 IeEE Std. 80 접촉전압 계산식의 적용한계를 검토하고 그 문제점을 극복하기 위해 IEEE Std. 80 접촉전압값과 컴퓨터 모의실험값을 비교하여 접촉전압 계산식의 보정계수 KSUBa/SUB를 유도하였다. 또한, 유도된 모델 중 Logistic 모델 형식의 보정계수를 적용할 경우 최대 오차율이 10[%]미만인 것을 검증함으로써 고가의 프로그램을 사용하지 않고도 안전하고 경제적인 접지설계를 할 수 있는 방법을 제시하였다.

Protection Against Electric Shock Using Residual Current Devices in Circuits with Electronic Equipment

One of the means of protection in the case of fault in low voltage systems is automatic disconnection of supply. Automatic discon-nection of supply is required where a risk of harmful pathophysiological effects on humans can arise, resulting from dangerous touch voltage. In order to fulfil this requirement, residual current devices (RCDs) are used as protective devices. In circuits with electronic equipment various frequencies and distorted earth fault current can occur. The analysis indicates that earth fault current frequency other than the rated value often causes improper operation of RCDs. In some cases the protective device cannot trip at all and thus protection against electric shock is not effective. In circuits with electronic equipment transient and steady state leakage current can occur so it causes the RCDs unwanted tripping. This paper presents special problems of selection and operation of RCDs in circuits with electronic equipment, based on the laboratory and field investigations. Ill. 11, bibl. 6 (in English; summaries in English, Russian and Lithuanian).

Dangerous Voltages due to Direct Lightning Strike into the Communication Tower

This paper presents a novel technique for computing dangerous voltages due to direct lightning strike into the communication tower and associated earthing system, which is based on the use of the well-known ATP-EMTP software package. The earthing grid and the communication tower structure are approximated by the circular cross section conductors. In numerical model, conductors are subdivided into segments (1D finite elements) and Clark's model with distributed constant parameters is then applied. Because of the limitations of ATP-EMTP software package, the leakage resistance of buried segments is modelled as additional lumped parameter. Analytical expressions for distributed and lumped segment parameters are derived using the average potential method. Mutual electromagnetic coupling between segments is neglected due to the limitations imposed by the ATP-EMTP software package, which is based on transmission line approach. Separate computer program is developed for obtaining the earth surface transient potential distribution, from which step and touch voltages are then computed.

Overvoltage protection concept for DC railway systems

Protection concepts for DC railway systems are introduced, considering the different insulation of the rails and the earthing concepts. The requirements and ratings for gapless MO-surge arresters (or short: arresters) are based on the relevant EN standards and national guidelines. A newly developed hybrid voltage limiter, which combines overvoltage protection and the protection against dangerous touch voltages, is introduced.

Influence of cobalt oxide addition on electrical properties of ZnO-Pr6O11-based varistor ceramics

Influence of cobalt oxide addition on electrical properties of ZnO-Pr6O11-based varistor ceramics

Artifact-Suppressing Amplifier for EMG Registration during Repetitive Peripheral Magnetic Stimulation (RPMS)

To induce a most physiological proprioceptive inflow to the CNS, the intensity and the repetition frequency of the RPMS are adapted by a closed loop control to induce coordinated movements. For the closed loop control and the quantification of the therapeutic outcome it is necessary to measure the (remaining) voluntary muscle activity, while the RPMS is applied. This is essential, since the patient is advised to assist the induced movements as far as possible. Therefore an RPMS artefact-suppressing EMG amplifier has to be developed to measure the activity of the stimulated muscle during the stimulation. Hereby the stimulation coil is located directly above the two EMG electrodes. Such amplifiers are well-known and established for functional electrostimulation, while artefact-suppressing amplifiers for RPMS are fairly unknown. Because of RPMS impulses, a high (compared to the EMG) voltage is induced into the EMG electrodes. This voltage changes the charge of the skin capacity and therefore the DC offset of the EMG. The induced voltage also elicits an impulse response of the filters in the EMG amplifier. Hence an artefact suppression is necessary, otherwise the amplifier is permanently in saturation since the RPMS impulses are repeated with 20Hz. The trigger signal for the stimulation device is also used for the artefact suppression. The artefact suppression itself runs on three levels: Voltages higher than 1.4 V at the EMG electrodes are filtered by antiparallel diodes independent of the stimulation impulse. If the suppression is triggered, the input to the difference amplifier is shorted by two bipolar transistors and the input to the DC offset compensation is grounded. With this suppression unit its is possible to reduce the gap in the measured EMG down to 3 ms. In addition to the artefact suppression, the following requirements (excerpt) are fulfilled in the developed EMG amplifier: selectable amplification gain, bandwidth of 3Hz to 15 kHz, an anti-aliasing filter with a selectable edge frequency, a 50Hz band-stop filter and an active shielding (no external pre-amplifier module). Due to a difference amplifier and the artefact suppression the input resistance is at least 500 MOhm and the patient is protected form dangerous high voltages by an isolation barrier (3 kVrms). Also a conventional speaker module is integrated into the designed amplifier.

Computer Aided Design of Transformer Station Grounding System Using CDEGS Software

This paper presents a computer-aided design of a transformer station grounding system. Fault conditions in a transformer station can produce huge damage to transformer station equipment if the grounding system is not designed properly. A well designed grounding system is a very important part of the project for transformer station design as a whole. This paper analyses a procedure for transformer grounding system design and spatial distribution of touch and step voltage on the ground surface level, using the CDEGS (Current Distribution Electromagnetic Interference Grounding and Soil Structure Analysis) software. Spatial distribution is needed for checking and finding dangerous step and touch voltages above and around the transformer station. Apparent earth resistivity data is measured and analyzed using the RESAP module of the CDEGS software. Because of the very high current flow into the grounding system during a single line to ground fault or a three phase fault in the transformer station, very high and dangerous potentials can be induced on the metallic structures including the fence, which can cause dangerous situations for people and animals near the station and for the personnel inside the station. The PLOT module of CDEGS is used to view the results of the scalar potential, step and touch voltage on the surface. Graphic displays include equipotent contour lines and potential profiles (gradients) in 3D and 2D perspective and apparent soil resistivity (Wm) versus inter electrode spacing (m). The results of alternative grid designs may be displayed simultaneously for the purpose of comparison.

Grounding Effects of HV and MV Underground Cables Associated with Urban Distribution Substations

The paper derives a model for the evaluation of the performances of composite grounding systems of urban main distribution substations and associated cable networks. The effects of the cables upon the dangerous voltages, transferred potentials, and ground fault current distribution are encompassed, including the conductive and magnetic coupling among grounding system elements as well as the nonlinearity of cables sheaths impedances. An application example is presented and some experimental data.

Decreasing the commutation failure frequency in HVDC transmission systems

In this paper we show how a fairly large proportion of those commutation failures that are due to single-phased short circuits to earth can be avoided. In a control circuit based on a digital signal processor (DSP) it is possible, with instantaneous results, to switch from a normal control strategy with equidistant firing pulses to a strategy that takes into consideration the potentially dangerous voltage changes on the supply lines, If the supply voltages are monitored continuously, it is possible to calculate the necessity of advancing the firing pulses to avoid commutation failures. In the paper such a calculation technique is described. The monitoring times may be approximately 50 /spl mu/sec apart corresponding to a distance of 0.016 radians or about 1.

A practical approach for computation of grid current

When a ground fault occurs at a substation, the part of the fault current that flows between the grounding system and the surrounding earth is known as grid current. This current determines the magnitude of the dangerous voltages within and around the station. It may vary from a few percent to almost 100% of the earth fault current. It is necessary to make an accurate estimate of grid current for an economical and safe design of ground electrode. The available analytical methods for determining the grid current require complete system data, which is voluminous and often unavailable. In this paper a simple and accurate analytical method for determining the grid current is presented. The method requires limited data. A computer program based on the proposed method has been developed and tested.

Engineering justification for tree trimming [power system maintenance

Tree-trimming programs are labor intensive and expensive. Most utilities, nevertheless, prescribe some form of tree trimming program, if for no other reason than to reduce possible outages during severe weather conditions. Other problems, however, may exist which are not normally considered as reasons for initiating a tree-trimming program. These are potentially dangerous touch and step voltages which may exist at the base of a tree that has contacted an energized circuit. To the best of the author's knowledge, there has never been an exact study to address this issue. This paper is an attempt to fill this void. It shows that hazardous conditions can indeed exist around trees that have been energized by a high voltage circuit.

EMTP models for simulation of shunt reactor switching transients

Long EHV transmission lines are generally compensated by means of shunt reactor sets. Reactor failures have directed attention to the transient overvoltages generated by reactor switching. 750 kV site measurements have shown that arrester operations or breaker restrikes could cause particularly dangerous steep reactor voltages. The paper introduces a comprehensive EMTP-type model of the reactor and the surrounding system (busbar, breaker, arrester, transformer, supply side network). The computer model has been tested by field experiments. A similar computer model has been elaborated for the study of transients, caused by de-energising reactors connected with the 18 kV tertiary winding of the 420/132 kV autotransformers. The model has been validated using a pushing into service test of a new air core shunt reactor, equipped with SF 6 circuit breakers. The computer models are easy to use for case studies, as well as in simulations to predict those variables which were not, or can not, be measured in the field tests. This paper introduces elements of the elaborated EMTP model, some steps of the model testing and verification. This paper contains the results of the computer analysis and of the field experiments.