Pole Ground Research Articles

Analysis on Intensity Matching Coefficient of Power Distribution Circuit Based on System Reliability Theory

The design intensities of four parts, i.e. ground conductor, hardware fittings, pole tower and foundation are greatly different, so it is difficult to evaluate the reliability of the whole power distribution circuit exactly. In this thesis, the intensity distribution functions of ground conductor, hardware fittings, pole tower and foundation have been calculated respectively, and then based on the system reliability theory, the reasonable failure sequence of power distribution circuit conforming to economic optimization principle is recommended. Under the assumed failure sequence, the calculation about intensity matching coefficient at the target confidence level is implemented, and finally, the intensity matching coefficients of ground conductor, hardwire fittings, pole tower and foundation of power distribution circuit are given.

Earth Current and GPR Distributions Due to Lightning and Effect of a Distribution Line

This article investigates the transient characteristics of earth currents and grounding potential rises (GPRs) produced by lightning strikes directly to the earth and to a vertical conductor with a grounding electrode. Influences of the earth depth and the distance from the lightning channel are discussed based on a field test and finite-difference time-domain (FDTD) computed results. The validity of the FDTD is confirmed in comparison with the field test results. Based on the FDTD results, a large portion of the lightning current is observed to flow along the earth surface during a transient period. The current density is roughly proportional to 1/ r 2 ( r : distance from the lightning base) for the lightning to the earth surface, and 1/ Lr for the lightning to a vertical conductor with a grounding electrode of length L . The GPR shows similar characteristics. Electromagnetic field radiated from the lightning to the earth contributes to the peak of the earth-surface current, and it becomes dominant when r is larger than 10 m. The pole grounding of a distribution line nearby the lightning absorbs a portion of the lightning current and, thus, the current density becomes larger toward the distribution pole.

Distribution characteristics of circular grounding ground potential in HVDC transmission system

This paper presents a model of double-ring type grounding pole unequal depth embedding for high-voltage direct current (HVDC) transmission system; and introduces calculation formula of DC ground potential distribution when double-ring type grounding pole is unequal buried. Furthermore the ground potential distribution and stride voltage level around the grounding pole and influence of grounding depth and soil parameters on the current field are discussed in this paper. The electric field zoning model of the ring current source is established by using the power system grounding pole analysis software CDEGS to verify the feasibility of this method. As the model is able to make the grounding current overflow density and potential distribution as uniform as possible, there is no serious local current concentration.

The influence of boot longitudinal flexural stiffness on external mechanical work and running economy during skate roller-skiing: A case study

This case study examines the impact of boot longitudinal flexural stiffness on the total external mechanical work of a skier’s centre of mass per distance travelled in the forward direction ([Formula: see text] EX (J/m)) and on running economy during skate roller-skiing under submaximal steady-state conditions. Moreover, it analyses time derivatives of total W EX, of W EX performed by the roller-skis and poles, respectively, and of the directly useful mechanical work (the sum of the work to overcome centre of mass’ gravity and rolling resistance) within a typical roller-skiing cycle. Multiple roller-skiing trials (G3 technique) were performed by one subject on an inclined treadmill with boots of soft, intermediate, and stiff flexural stiffness. The orientation and magnitude of the roller-ski and pole ground reaction forces, body kinematics, VO2, and lactic acid concentration were monitored. The stiff boots had 13.4% ( p < 0.01) lower [Formula: see text] EX compared to the intermediate boots, and 20.7% ( p < 0.001) lower [Formula: see text] EX compared to the soft boots. Regarding running economy, the soft boots had 2.2% ( p < 0.05) higher VO2 compared to the intermediate boots, but the same VO2 compared to the stiff boots. In conclusion, the soft boots had significantly higher [Formula: see text] EX and running economy, while stiff boots had significantly lower [Formula: see text] EX and intermediate boots significantly lower running economy. Moreover, [Formula: see text] EX appears to be a better indicator of the boot flexural stiffness impact on energy efficiency than running economy.

Research on the Method of Reducing Transformer DCBC Considering Converter Transformer Grouping and Receiving End Power Grid Structure

Based on the study of the influence of converter marshalling and receiving grid structure on the DC bias current (DCBC), DCBC levels of typical connection structures between converter station and its adjacent substations is analysed in this paper. Then DCBC levels of converter stations and AC substations under different connection modes of substations in AC power network are analysed. The measures to reduce DCBC of converter transformer and AC transformer considering various factors are put forward. A method to reduce DCBC of converter transformer and transformer considering converter transformer grouping and receiving end power grid structure is proposed. The measures of restraining DCBC are analysed from the aspects of operation mode selection, grounding pole location, power grid structure planning and design. Suggestions are put forward for the treatment of DCBC in the planning and design stage.

Multi-objective Optimization Configuration of Capacitor Blocking Devices based on Field-Circuit Coupled Model and Improved Differential Evolution Algorithm

The dc current of grounding pole will invade the transformer windings nearby when the HVDC system is in ground return operation, which will cause DC bias and affect the safety and stability of the system. It is an effective method to restrain dc current in transformer to install capacitor blocking devices at transformer neutral wire, but it is shown that this may increase the bias current of nearby transformers. For this reason, the installation of blocking device in a certain area can be considered as an optimization problem. An improved differential evolution algorithm is proposed to optimize the multi-objective configuration of capacitor blocking devices to suppress DC bias globally. The field-circuit coupled model is established to solve the potential. The objective function is to minimize the number of installations of the devices and the absolute sum of the total DC current of the transformer in the region, and the constraint is all DC current at the neutral point of each transformer is under the limit, then the optimal configuration model is established. Finally, the chaos mapping theory, adaptive parameters and elitism preservation strategy are introduced into the difference evolution algorithm to solve the model and obtain the optimal allocation scheme.

FDTD Analysis of Nearby Lightning Surges Flowing Into a Distribution Line via Groundings

This paper investigates lightning surges on a distribution line reported using a finite-difference time-domain (FDTD) method. FDTD simulation results show a satisfactory agreement with measured lightning currents when lightning strikes ground nearby a distribution line. The current and voltage characteristics along the line, which were not measured in the test, are calculated by the FDTD simulation. Parametric analysis shows that lightning currents and voltages are dependent on the lightning position, distance from the lightning to the nearest pole, and pole grounding resistance. A large portion of phase-wire voltage is induced by the lightning channel current, and correspondingly, a large portion of phase-wire current is produced by the induced voltage. When the lightning channel is inclined, the peak current and voltage vary by +10% to -10% depending on the inclined angle. The effect of neutral wire position in the line is also investigated, and the induced voltage at the nearest pole to the lightning can be effectively suppressed by installing two neutral wires above and under the phase wires. EMTP simulation results agree qualitatively well with the measurement and FDTD results.

Analysis of the effect of explosion grounding electrode on grounding resistance reduction

Developing cracks in the soil by means of explosions in the holes, as is called the explosion grounding electrode in this study, is a very effective way to reduce the grounding resistance in the area with high resistivity soil. In this study, the influence of the grounding grid scale and the arrangement of the grounding electrode on reducing the grounding resistance of three-dimensional grounding grid with explosion grounding electrode are studied. There is a strong shielding effect between the explosion grounding electrodes. When the distance between the explosion grounding poles is short, the effectiveness of reducing the grounding resistance by using the long explosion grounding electrode is obviously restrained. The distance between the explosion grounding electrodes should be more than half the length of the electrodes.

Study on characteristics of slow‐front overvoltage of ±1100 kV UHVDC transmission lines

The ±1100 kV Zhundong–Wannan ultra high-voltage direct current (UHVDC) transmission project is under construction in China, which has the highest operating voltage in the world. The length of the UHVDC overhead transmission line is greater than 3000 km. The electromagnetic transient process caused by grounding faults might have significantly impact on the overvoltage level of DC transmission line, which is crucial for the external insulation configuration of the overhead transmission line. This paper presents a detailed electromagnetic transient simulation model for the UHVDC transmission system using an open-loop extinction angle control principle. The simulation results demonstrate that the single pole grounding fault into a bipolar system causes the most serious damage. The maximum overvoltage is 1.628 p.u. and the 2% statistic overvoltage is 1.635 p.u., while the reference value is 1122 kV. The influence of DC filters for line overvoltage is also analysed here. Furthermore, results show that adding a no gap line arrester at the midpoint of transmission line can suppress line overvoltage, while the maximum overvoltage reduces by 0.138 p.u. The results obtained provides a reference for the optimisation of the external insulation configuration.

Simulation research on magnetic pole erosion of Hall thrusters

It is shown from the experimental results of existing Hall thrusters that erosion phenomena occur in the magnetic poles when the maximum magnetic field is located in the plume region. The developed Particle-in-Cell model is used in this paper for simulation research on magnetic pole erosion of Hall thrusters. The simulation results show that when the maximum magnetic field is located in the plume region, there is a large potential drop between the channel outlet and the magnetic pole. Therefore, low-energy ions close to the outlet plane are accelerated to bombard the magnetic pole surface, which is an important reason for the magnetic pole erosion. Moreover, the ion flux and energy bombarded on the magnetic pole under two conditions (magnetic pole grounding and floating) are calculated and compared. It is shown from the simulation results that grounding the magnetic pole can reduce the potential drop between the channel outlet and magnetic pole, thereby reducing the ion energy and flux bombarded on the magnetic pole and effectively alleviating the erosion of the magnetic pole.

A decoupled circuital model methodology for calculating DC currents in AC grids induced by HVDC grounding current.

Large currents are injected into the earth from grounding poles of HVDC systems under monopole ground return mode. The currents change the earth surface potential and result in DC currents in AC systems. This paper proposes a computationally efficient decoupled circuital calculation method for assessing the unwanted DC currents in AC grids. Firstly, the earth resistive network is acquired by simulating the DC grounding current distribution using Finite Element Method (FEM). Secondly, the earth resistive network and AC grid are combined to develop a decoupled circuital model of the overall system. The acquired model is used to calculate the DC currents in AC grids by solving a set of linear equations. The proposed method is computationally more efficient as compared to field-circuit coupled methods. In addition, its accuracy is proved by showing a close agreement between our results and field-circuit coupled model as well as the actual measurements. Finally, in Shanghai area power grid the DC currents are calculated using the proposed technique. Based on these calculations, remedial measures for reducing the DC currents in AC grid are suggested. Our research results indicate that DC currents in AC systems can be reduced by operating the two HVDC projects with opposite polarities.

DC Biasing Treatment Scheme for Zha-Qing ±800kV Project Zhalute Power Grid

The rated operating current of ±800kV UHVDC transmission (UHVDC) is large, and the influence of grounding pole ground current on the transmission and reception network and its treatment is a subject to be studied. Combining with the construction of Zha-Qing (±800kV) project and using the historical magnetotelluric data, the three-dimensional resistivity model and the magnetic bias current model of Zhalute power grid are established. The calculation of magnetic bias current of Zhalute power grid is completed and the control scheme of DC magnetic bias is proposed. The theoretical analysis of governance effects and the test results after the implementation of the governance project show that the proposed model and algorithm are accurate and the proposed governance scheme is correct and effective; Finally, according to the problems found in the calculation of DC bias current and the treatment plan of Zhalute Power Grid in Zhaqing, the suggestions for grounding site selection and treatment methods are proposed.

Adaptive differential relay coordination for PV DC microgrid using a new kernel based time-frequency transform

A discrete differential current based unit protection and fault distance estimation is proposed for a 100 kW Photovoltaic (PV) based Multi-Terminal Direct Current (MTDC) microgrid. Relay coordination and adaptive relay settings are presented in terms of PV arc and DC cable faults. To distinguish PV arc and DC cable faults without nuisance tripping event, an improved energy density based time-frequency transform is presented in this paper. A new frequency filtering Kernel based Discrete Time Frequency Transform (KDTFT) is proposed for effective fault detection. DC microgrid protection is essential area to be research focus due to lack of precise grid codes/standards. Pole-pole (PP) and pole-ground (PG): positive/negative faults are the most counted operational threats for DC microgrids. As PV is considered to be integrated as primary DG via DC cables, highly resistive DC arc faults (series, parallel: cross-string, intra-string) are also focused in this paper. The independent PV arc protection is designed as backup to arc-fault circuit interrupters (AFCIs). The efficacy of proposed protection measure is considered in terms of percentage error for fault distance estimation and Circuit Breakers trip time (Ts). The adequacy study is presented while considering DC load diversity.

Rancang Bangun Antena Mikrostrip dengan Metamaterial CSRR untuk Penerima TV Digital

Digital television technology has more benefit than analog television, for example several TV channel may included in one frequency channel. The changing from analog to digital televisions system require more innovative antenna parameter such as working frequency, bandwidth, return loss, VSWR, and gain. In other hand, the size of the antenna must be minimalized, so it can be integrated inside digital television.
 This research used metamaterial element of Complementary Split Ring Resonator (CSSR) method with negative permittivity that manufactured in the patch and Double Pole Ground Plane in the ground side. The antenna ad 478-694 operating frequency. Antenna design and simulation using CST (Computer Simulation Technology) Microwave Studio 2012.
 The result show that return-loss value < -10 dB, and VSWR = 2 at 478-625 MHz range of frequency. Te value of gain is 3.27 dBi, it has 147 MHz bandwidth, and omnidirectional radiation pattern.

THE Simulation Study of DC Grounding Electrode Based on CDEGS and ANSYS

When the UHVDC project was put into operation, grounding electrode grounding current may affect the transformer in the substation near the pole, it will cause transformer DC bias saturation, which leads to higher transformer temperature rise, too high harmonic and reactive power consumption, which will cause transformer damage or power grid blackout. The earth resistivity model of grounding pole is not accurate enough and the calculation of surface potential distribution is not accurate enough, which will cause the deviation between the evaluation and actual damage degree before and after the project put into operation. In order to simulate the grounding potential distribution directly after grounding, the simulation analysis with different methods can be checked with each other, and the related design units used CDEGS to simulate the earth potential rise. In this paper, the influence of DC transmission grounding electrode on the distribution of ground surface potential is analyzed, and the calculation method of DC grounding electrode current field is deduced. The 6 layers earth soil model was established. CDEGS and ANSYS were applied. The earth potential rise distribution in the 0~100 km radius of the earth electrode was calculated respectively. In this paper, the results of the earth potential distribution in the 0-50 km range of the two schemes were compared and analyzed. The results show that the calculation results of ANSYS were slightly smaller than those calculated by CDEGS, and the difference was about 0.6 V. The calculation results of the two schemes could provide reference for field practical monopole operation and commissioning.

Comprehensive Fault Type Discrimination Concept for Bipolar Full-Bridge-Based MMC HVDC Systems with Dedicated Metallic Return

Bipolar HVDC transmission systems typically offer up to 50% transmission redundancy in case of single pole-to-ground line faults. Continuous operation during permanent multiconductor faults, however, is not permitted, emphasizing the need for accurate fault type discrimination in such applications. For bipolar schemes with a dedicated metallic return (DMR) conductor, discrimination of pole–ground faults and pole–DMR faults represents a challenging task due to their similar electrical characteristics. In this paper, several approaches to detect DMR fault involvement are identified and analyzed, comprising both noninvasive methods based on measurement data and invasive methods based on DC current control strategies of full-bridge VSC-MMC stations (Modular Multilevel Converter based on Voltage Source Converter technology). An exemplified point-to-point HVDC system is modeled in PSCAD/EMTDC and extensive simulation studies are carried out. Based on the obtained results, a comprehensive fault type discrimination concept for permanent line faults is developed, which can be incorporated into fault handling schemes. Thus, successful fault type discrimination can be performed for all relevant fault types, even under exceptional fault conditions.

A Novel Hybrid-Arm Bipolar MMC Topology With DC Fault Ride-Through Capability

This paper proposes a novel bipolar modular multilevel converter (MMC) topology with dc fault ride-through capability. The proposed bipolar MMC topology is a hybrid of two types of arms: the half-bridge submodule (HBSM)-based arms (HBSM-arms) which are connected to the ground pole, and the unipolar-voltage full-bridge submodule (UFBSM)-based arms (UFBSM-arms) which are connected to the positive or negative pole. During a pole-to-ground or pole-to-pole dc fault, the hybrid-arm design offers the proposed UFBSM-based hybrid-arm bipolar MMC (UHA-BMMC) the capability to provide additional reactive power to support the ac grid while blocking the dc fault current. The topology, operation principle, dc fault mechanisms, and dc fault ride-through scheme of the UHAB-MMC are presented in this paper. Compared with other possible bipolar MMC topologies, the UHA-BMMC provides good dc fault ride-through capability with a small cost of power-electronic devices. The validity and features of the proposed UHA-BMMC are verified by simulation results conducted in PSCAD/EMTDC.

Approximate model for ground inhomogeneity with rectangular cross section: application to analysis of grounding systems

A procedure for characterization of lighting pole grounding systems placed inside and/or outside the road is presented in the paper. The road is treated as ground inhomogeneity of parallelepiped shape. Using an estimation method, the road is approximated by a domain having a semi-circular cross section. The analysis includes application of the quasi-stationary image theory, and Green‘s function for the point source placed inside/outside the cylinder of semi-circular cross section. Leakage current distributions are obtained applying the Method of Moments. Afterwards, the grounding system characteristics are determined. The results are compared to the ones obtained by the COMSOL software package.

Thévenin Equivalent of Voltage-Source Converters for DC Fault Studies

This paper presents a simple modulation index-dependent Thevenin equivalent circuit model of the voltage-source converters (VSCs) and the associated anti-parallel diode rectifier. The model derivation uses orthogonal transformation and a transformer analogy to transfer impedances to the dc side of the converter. The paper proposes a switched equivalent representation of a three-phase diode rectifier formed due to the antiparallel diodes when VSC switching is inhibited. The proposed model is implemented in Alternate Transients Program–Electromagnetic Transients Program and simulation results are compared with the switched model. The proposed model is shown to under predict the fault currents for pole-ground (PG) faults and to provide a nearly exact match for pole-pole faults. The rectifier equivalent provides increased accuracy in the transient region with the inclusion of the source inductance. A multiterminal dc (MTDC) system model is used to study effects of aggregation which gives increased accuracy of the equivalent circuit. It is shown that the MTDC system simulation with the proposed Thevenin equivalent is about 3 times faster than full-switched circuit simulation for a time step of 5 $\mu$ s. The MTDC system simulation with the Thevenin equivalent circuit is still accurate and 126 times faster when the time step is increased to 750 $\mu$ s.

204 大気圧低温プラズマ支援燃焼に関する研究(OS1 燃焼,エネルギー変換,熱利用(3),研究討論セッション)

Plasma assisted combustion is one of the hot topics in combustion engineering. Fuel gas at room temperature can be radicalized by plasma produced in the fuel gas stream by dielectric barrier discharge. Fuels used in this study are pure methane and hydrogen, and a mixed gas imitating bio-mass gas consisting of methane, hydrogen, nitrogen, and small amount of ammonium. Flame propagation, temperature, and NOx concentration are measured on various conditions. The obtained results are as follows. (1) The flame propagation velocity is increased by plasma, near the ground pole of discharge. (2) In premixed flame, NOx concentration is increased by plasma. It is considered that reaction between oxygen and nitrogen is enhanced by discharge. (3) When ammonium is doped into fuel, fuel NOx is generated. (4) In diffusion flame, when ammonium is added into fuel, fuel NOx concentration is increased by plasma.