Ground Currents Research Articles

Estimation and Utilization of Ground Effects on Conformal Dielectric Resonator Antennas

Ground effects on arc-shaped conformal dielectric resonator antennas (DRAs) working in the TE $^{\mathrm {z}}_{11 \delta }$ mode are investigated and utilized to attain various radiation performances. Manipulation of directivity patterns are achieved with the help of the three-dimensional curved metal ground. The backlobe, beamwidth, broadside gain, backscattering, and cross-polarization level of the antenna are all readily controllable. The geometric theory of diffraction is applied to provide an intuitional explanation for the radiation changes. Detailed analysis is then conducted from the perspective of ground current. It is found that the current distribution is affected by configurations of both the arc DRA and ground plane. Based on this, analytical methods are developed to calculate the ground effects exclusively for conformal arc-shaped DRAs. Next, the design theory of arc DRAs with curved ground is proposed. To demonstrate it, two conformal DRAs owning directional and wide beams, respectively, are designed as paradigms. At last, a prototype is fabricated and measured for validation.

Single-Phase-to-Ground Fault Location Method Based on SOGI

Most fault location methods depend on the exact extraction of fault transient feature. However, due to the weak grounding current, arc grounding and intermittent problems, it is difficult to extract the fault transient feature. Based on second-order generalized integrator (SOGI), a single-phase-to-ground fault section location method for neutral point ungrounded system is proposed to address this problem in this paper, which avoids the extraction of fault transient feature. Firstly, the fundamental wave phases of zero sequence voltage and zero sequence current are extracted by second-order generalized integrator. Then, the fault position is located based on their phase difference. Finally, the proposed strategy is tested by the simulation data and the field data. The test results show that the method proposed in this paper can accurately locate fault position. Moreover, the phase extraction method based on SOGI is more accurate than traditional Euler method.

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.

Temperature Rise Characteristics of Vertical Grounding Electrodes of Ultra-High Voltage DC ± 800 kV Pu’er Converter Station

The vertical grounding electrode (VGE) is a new type of grounding design of ultra-high voltage direct current (UHVDC) power transmission project, which can greatly reduce the grounding area. The main structure of VGE is several or dozens of vertical electrode wells connected with each other by cables to form a conductor system. However, the ends of the VGE temperature may rise severely due to the non-uniform grounding current of each electrode. In serious cases, cable failures or other accidents may occur. In order to investigate the VGE temperature rise characteristics of the UHV ±800kV Pu’er Converter Station in China, firstly a single VGE was simulated in the laboratory. Measurements of the single VGE temperature rise were compared with the calculations by finite element method (FEM) to verify the validity of the algorithm. Then the calculation model was utilized to compute the current distribution of each VGE of Pu’er Converter Station, and a current balance design was proposed in this paper. Calculations demonstrated that the maximal temperature rise of the VGE was 31 °C, which was lower than the design limit. This paper may provide some useful reference for the design and operation of the UHVDC vertical ground electrodes.

MoM-Based Ground Current Reconstruction in RFI Application

A method of moment (MoM)-based current reconstruction method is proposed to estimate the surface current density on the ground plane. Current continuity property is automatically enforced with Rao–Wilton–Glisson basis function. Both the least square method and the optimization method are utilized to solve the inverse problem and obtain the ground current. The proposed optimization method is successfully validated with numeric simulations and also a real-world measurement example. The reconstructed current distribution on the ground plane is further used in a typical radio frequency interference (RFI) example to perform RFI estimation and provide guidelines for RFI design. The proposed MoM-based ground current reconstruction method can be valuable to estimate and debug RFI issues in early design stage.

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.

Ground Harmonic Current Compensation Based on Cerebellar Model Articulation Controller

Widespread application of microgrid technology and clean energy in recent years has brought people a challenge of how to eliminate the faults caused by ground harmonic currents for multi-type non-linear loads and cable lines or local distributed power generation systems. As the harmonic components of the ground current are complex, there is no clue to the different types of ground faults and fault locations. In the case that the fault data cannot be processed in advance, this paper proposes a model integrated with the CMAC (Cerebellar Model Articulation Controller) and the constraint conditions to tackle this mess of the ground harmonic current detection and compensation. Here is a network design defined in this way that CMAC is used to detect harmonic current. Next, an example of concrete microgrid earth fault is cited for the network training. Experimental results reveal that the CMAC can effectively analyze and estimate the ground harmonic components.

A detailed network model for distribution systems with high penetration of renewable generation sources

One of the most important aspects that characterizes smart grids is the widespread integration of loads and renewable-based generators connected to the distribution network. In general, sequence or phase based network models have included the effect of ground return on equivalent phase and neutral impedances using the Kron's reduction and Carson equations. Under unbalanced grid operation, these traditional models can produce inexact results being inadequate for advanced grid analysis and optimization. This paper presents a detailed and compact formulation for the analysis of multi-grounded distribution systems. The key contribution of the paper is to introduce a detailed representation of the ground loops in the distribution system model suitable to be applied under different analysis methods as power flow, optimal power flow, state estimation and network pricing in an integrated manner. This contribution is meaningful since it allows to analyze future electrical systems with severe unbalanced operation due to high penetration of single-phase renewable and load sources. The ground parameters can be adjusted in the context of a state estimator that integrates ground voltages and currents. The proposed model is tested using illustrative and real-world large-scale test cases. Results reveal significant differences when compared with system analyses using standard three phase network model approach.

Circulating Net Currents in Meshed DC Distribution Grids: A Challenge for Residual Ground Fault Protection

In dc distribution grids, residual ground current protection is more feasible than in ac distribution grids, where stray capacitance leads to significant ac ground currents. However, when meshing dc distribution grids, circulating net currents can appear that resemble residual ground currents and would trip traditional protection schemes. This letter introduces this phenomenon in both unipolar and bipolar dc distribution grids. Furthermore, worst case net current magnitudes are derived and examples are shown. Implications for measurement and protection devices are discussed.

Evaluation of high‐voltage AC cable grounding systems based on the real‐time monitoring and theoretical calculation of grounding currents

For high-voltage (HV) AC cable transmission systems, the metal sheaths of three separate single-core cables are cross-bonded at each end of the cable section, to suppress the induced voltages in sheaths. The status of HV cable grounding systems is, therefore, an important consideration for power utilities. This study presents the status evaluations of 93 cable grounding systems in Beijing, obtained using the standards established by State Grid Corporation of China. As a result, 13 of these systems were classified as abnormal or defective. Additionally, a theoretical calculation of grounding currents was proposed and these 13 systems are re-evaluated by comparing the calculated and measured values of certain parameters. Based on this work, the authors propose a modified evaluation standards. It is indicated that the absolute value of grounding current (|I|) during a given 24-hr period has no relationship with the status of grounding system, and the ratio of grounding current to load current (K) at the time of maximum load current could be used as a status indicator instead of K at some other time, in order to avoid possible incorrect evaluations due to light load conditions.

MV Generator Ground Fault Arcing Power Damage Assessment

An industrial medium voltage (MV) system usually consists of multiple power sources such as utility tie transformers and generators. These are normally low-resistance grounding as shown in Fig. 1 . When a ground fault occurs at the generator stator, ground currents from its own neutral circuit and external power sources will flow into the fault and cause damages to the stator winding. The IEEE Generator Grounding Working Group issued a guideline for generator grounding practices, which recommends using a hybrid grounding system to minimize the ground fault damage induced by its own neutral grounding source. This paper will evaluate the total ground fault damages based on the arcing power energy to derive a maximum MV system ground current that would limit the ground damage to 1800 kW-cycle or 30 kJ as the minimum arcing power energy damage as suggested by Conrad and Dalasta [10].

A Novel Single-Phase Multilevel Transformerless PV Inverter For Reduced Common-mode current

Transformerless photovoltaic (PV) inverters are vital role in the solar energy market due to reduced cost, weight and high in efficiency. A critical issues and challenges exist in this system such as suppress the ground leakage current, which is harmful to the human with additional ground currents flowing via resonant circuit parameters of the system. In this paper a novel topology introduced with multilevel output voltage using modified sinusoidal multi-carrier based PWM technique for control the inverter. In addition a super junction MOSFETS are consider as main power switches. And the key features of the proposed topology are follows with no reverse recovery issues, operating with high efficiency, low ground current and current distortion is achieved. Finally the proposed topology and its performance evaluation are verified by the simulation results.

Evaluation of Ground Currents in a PV System with High Frequency Modeling

In this work a high frequency model of a photovoltaic (PV) plant is identified and implemented aiming to investigate the common mode (CM) currents circulating through the ground connections of the plant. From the identification of the impedance obtained by frequency response of photovoltaic module and by a suitable of the power conversion unit, an equivalent high frequency circuit representation has been developed. The lumped parameter s circuit model is implemented in PSpice environment to obtain the CM leakage currents.

High‐efficiency PV inverter with SiC technology

A high-efficiency, three-phase, solar photovoltaic (PV) inverter is presented that has low ground current and is suitable for direct connection to the low voltage (LV) grid. The proposed topology includes a three-phase, two-level (2L) voltage source inverter (VSI) and an active common-mode (CM) filter. The VSI utilises silicon (Si) insulated-gate bipolar transistors with silicon carbide (SiC) diodes to reduce switching losses and provide very high efficiency. The active CM filter reduces the high level of CM voltage associated with the three-phase 2L VSI. The active CM filter is controlled so that the PV ground current is reduced to acceptable levels, even when the PV inverter is connected directly to a LV grid with low-impedance grounding. 50 and 100 kW prototypes are presented that demonstrate high efficiency.

Research on the influence of ac current overflowing on grounding electrode corrosion

In the power system, earth electrode is laid in the soil for current overflowing, to ensure secure and stable operation of power grid and electric accessory. Compared with general pipeline laid in the soil, earth electrode is under the circumstance of unbalanced grounding current of neutral point and electric field induced by high-voltage transmission line, so there is current straightly overflowing from electrode surface to the earth. Grounding current density carried by earth electrode is large, with an important effect on electrochemical corrosion of earth electrode in the soil. Based on the established corrosion model, this paper makes research on the influence of AC current overflowing on corrosion potential, current and deformation, without considering the effect of species diffusion. What is more, the relationship between the amount of corrosion deformation and the frequency of ground current is also studied.

Experimental and simulation results of a symmetrical pad to reduce a stray ground current in superconducting integrated circuits

The method of extracting bias current is widely used in large scale SFQ circuits to avoid harmful effect by spreading the bias return current on a ground plane, which causes malfunction or degrading the operating margin by the stray magnetic field. Although extracting the bias current is effective, we found that the extraction using a normal pad structure with a bias pad and a current extracting pad still produces a large stray ground current (magnetic field) for its asymmetric structure. We proposed a bilaterally symmetrical pad structure, which can reduce the stray ground current significantly in superconducting circuits. The bias current is extracted from a nearby ground pad of a bias pad in usual method, whereas the bias current is extracted from two of the symmetrical ground pads which are arranged both sides of the bias pad in the symmetrical structure. Then, the bias current is extracted on halves from each of the two pads symmetrically, reducing the stray ground current. First, we have simulated the ground current by using FastHenry program. The results showed that the symmetrical pad structure outside of ground plane reduced spread of the ground return current significantly. Next, we have designed a test chip and confirmed the effectiveness of the symmetrical structure experimentally.

A Capacitance-Minimized, Doubly Grounded Transformer less Photovoltaic Inverter With Inherent Active-Power Decoupling

Two major challenges in the transformerless photovoltaic (PV) inverters are the presence of common-mode leakage currents, and as in most single-phase converters the need for reliable and compact double-line-frequency power decoupling. In the proposed doubly grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the capacitive-coupled common-mode ground currents. The decoupling capacitance requirement is minimized by a dynamically variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The topology uses only four switches and potentially enables a high power density solution. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100/75 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output with a wide range of power factor has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. Extensive experimental results from the prototype are presented to validate the concept, design, and superior performance of the proposed topology.

Cabling design of booster and storage ring construction progress of TPS

The 2012 Taiwan Photon Source (TPS) cable construction project started after 10 months to complete the cable laying and installation of power supply. The circumference of the booster ring (BR) is 496.8 m, whereas that of the storage ring (SR) is 518.4 m. Beam current is set to 500 mA at 3.3 GeV. The paper on grounding systems discusses the design of the ground wire (< 0.2 Ω) with low impedance, power supply of the accelerator and cabling tray. The flow and size of the ground current are carefully evaluated to avoid grounded current from flowing everywhere, which causes interference problems. In the design of the TPS, special shielding will be established to isolate the effects of electromagnetic interference on the magnet and ground current. Booster ring dipoles are connected by a series of 54-magnet bending dipole; the cable size of its stranded wire measures 250 mm2, with a total length of 5000 m. Booster ring and storage ring quadrupoles have 150 magnets; the cable size of their stranded wire is 250 mm2, with a total length of 17000 m. Storage ring dipole consists of 48 magnets; the cable size of its stranded wire is 325 mm2, with a total length of 6000 m. This study discusses the power supply cabling design of the storage ring and booster ring construction progress of TPS. The sections of this paper are divided into discussions of the construction of the control and instrument area, cabling layout of booster ring and storage ring, as well as the installation and commission machine. This study also discusses the use of a high-impedance meter to determine the effect of cabling insulation and TPS power supply machine on energy transfer to ensure the use of safe and correct magnet.

Spectral scaling technique to determine extreme Carrington‐level geomagnetically induced currents effects

AbstractSpace weather events produce variations in the electric current in the Earth's magnetosphere and ionosphere. From these high‐altitude atmospheric regions, resulting geomagnetically induced currents (GICs) can lead to fluctuations in ground currents that affect the electric power grid and potentially overload transformers during extreme storms. The most extreme geomagnetic storm on record, known as the 1859 Carrington event, was so intense that ground‐based magnetometers were saturated at high magnetic latitudes. The most reliable, unsaturated observation is the hour resolution data from the Colaba Magnetic Observatory in India. However, higher‐frequency components—fluctuations at second through minute time cadence—to the magnetic field can play a significant role in GIC‐related effects. We present a new method for scaling higher‐frequency observations to create a realistic Carrington‐like event magnetic field model, using modern magnetometer observations. Using the magnetic field model and ground conductivity models, we produce an electric field model. This method can be applied to create similar magnetic and electric field models for studies of GIC effects on power grids.

Protection Method of Biological Lightning Safety around Power Grid Based on Grounding Electrode Structure

Aimed at the actual situation of fish death in fish ponds near the power transmission line towers after the thunderstorm happened in Guangdong Province in China, this paper studied the influence of the ground current on fish in the pond. Firstly, This paper studied the current density of the fish without protection. On this basis, paper studied the horizontal pole with full-shielded, the vertical pole with half-shielded, the horizontal pole with extension three kinds of protective measures and effects. Finally an effective protection scheme was put forward according to the engineering practice. The results can provide some engineering guidance and quantitative basis for the design and modification of grounding devices when the tower is adjacent to the fish ponds in southern China.