High-voltage direct-current (HVdc) transmission lines have been implemented in many countries, including Australia, Brazil, China, and Sweden, and the safety concerns as the result of the high electromagnetic-radiation underneath the HVdc lines have garnered increased public attentions. Here, we report on the model, design, and testing of field-mill electric field sensors to measure the electric field at the ground level under the HVdc transmission lines. This study utilized a finite-element analysis method to establish numerical simulation results based on the electrical and mechanical parameters to achieve optimal designs with experimental calibrations. Afterward, these sensors were successfully tested and utilized at the national high-voltage test base.

Model, Design, and Testing of Field Mill Sensors for Measuring Electric Fields Under High-Voltage Direct-Current Power Lines

Optimizing the grounding grid configuration is an effective approach to improve the performance of grounding grid. On the other hand, configuration of grounding grid is necessary for some defect diagnosis method to detect the faults existing in grounding conductors. This paper employs the transient electromagnetic (TEM) method to draw the configuration of a substation grounding grid. The surface magnetic field is recorded by receiver coils above the grounding grid. Based on the regular distribution characteristics of a recorded magnetic field, the grounding conductor is accurately located from the curve of magnetic intensity. The complete process of configuration detection of the grounding grid is described in detail. After fast inversion calculation of the recorded magnetic field, the equivalent resistivity is obtained. The configuration of the grounding grid will be clearly and accurately shown in the contour map and three-dimensional (3-D) surface map of equivalent resistivity. Model study is performed, and a field test is also conducted. The results are in good agreement to demonstrate the effectiveness of TEM method for configuration detection of the substation grounding grid.

Configuration Detection of Substation Grounding Grid Using Transient Electromagnetic Method

Faults of grounding grids are threat to the safety of power system and cause significant economic loss every year in China. Accurate detection of the faults will alleviate these detrimental effects. This paper presents a novel approach using the transient electromagnetic method for fault diagnosis of grounding grids. The induced magnetic intensity is collected by receiver coils in the form of electromotive force. After inversion calculation, the contour map of equivalent resistivity of underground covered by grids is obtained. The faults due to corrosion or break can be accurately located from the distribution characteristics of equivalent resistivity maps. The influence of the fault of different degrees, material of grounding conductor, and soil resistivity on distribution of induced magnetic intensity to fault diagnosis will be analyzed in detail. The effect of the underground pipeline on fault diagnosis of grounding grids is also investigated. Simulation was performed, and a field experiment was conducted to verify the effectiveness of the proposed method.

A Novel Method for Fault Diagnosis of Grounding Grids

A grounding grid of a substation is essential for reducing the ground potential rises inside and outside the substation during a short-circuit event. The performance of a grounding grid is affected by a number of factors, such as the soil conductivity and grounding rod corrosion. Industry always has a strong desire for a reliable and cost-effective method to monitor the condition of a grounding grid to ensure personnel safety and prevent equipments damage. In view of the increased adoption of telecom and sensor technologies in power industry through the smart grid initiative, this paper proposes an online condition monitoring scheme for grounding grids. The scheme monitors touch and step voltages in a substation through a sensor network. The voltages are created by a continuously-injected, controllable test current. The results are transmitted to a database through wireless telecommunication. The database evaluates the grid performance continuously by comparing the newly measured results with the historical data. Many of the limitations of the offline measurement techniques are overcome. Computer simulation studies have shown that the proposed scheme is highly feasible and technically attractive.

Online Monitoring of Substation Grounding Grid Conditions Using Touch and Step Voltage Sensors

Faults in the grounding grid are a hidden danger to the safety of power systems and cause significant economic loss every year. This paper presents a new means to locate faults in grounding grids using the transient electromagnetic imaging method. The method compares the distribution characteristics of the equivalent resistivity of the underground covered by grids for the no-fault case and those with break points. We describe why and how the proposed method can be used for the break-point diagnosis of grounding grids. Simulation was performed using the Ansoft finite-element method package, and a field experiment was conducted to verify the effectiveness of the proposed method. This study provides a practical means for break-point diagnosis with no requirement of power shut down or soil excavation. Moreover, the proposed method does not require the design drawings of grounding grids.

Break-Point Diagnosis of Grounding Grids Using Transient Electromagnetic Apparent Resistivity Imaging

A grounding grid defect diagnosis method of a transformer substation belongs to the field of electric power technology for solving the problems in grounding grid defect diagnosis. The technical proposal of the method comprises the following steps of: firstly, connecting different-frequency sine wave excitation sources between two lower conductors of the grounding grid of a transformer substation,directly injecting excitation current, simultaneously converting a magnetic induction intensity signal excited by the injected current on the ground into an induced voltage signal by a detection coil,measuring the distribution of the magnetic induction intensity on the ground and simulating the ground magnetic induction intensity of the grounding grid under normal condition; then comparing the measurement result with the simulation result and diagnosing the specific position and the degree of corrosive thinning or rupture defects of the grounding grid. The invention has convenient operation and can rapidly and accurately diagnose conductor defect in the grounding grid under the normal operation condition of the transformer substation to meet the requirement of actual field measurement anddiagnosis.

Substation grounding net defect diagnostic method and apparatus

The corridor of the high-voltage direct current transmission lines in China is very complex and there may be buildings near the lines. The conductivity of the building material may influence the electric field in the building. In this paper, based on the upstream FEM, a method is proposed to solve the coupled problem of the ion flow field in the air and the current field in the building model. The numerical results coincide with the analytic results and measurement results. The electric field in and on the building model is analyzed considering different conductivities.

Ion Flow Field Analysis Considering the Finite Conductivity of the Building Near HVDC Transmission Lines

The grounding grid buried in the earth will become a hidden danger to the safety of substations due to some faults of breaks or thinner conductors in corrosion. A novel method to get accurate status of grounding grid was proposed based on measuring magnetic induction intensity. The basic structure of grounding grid without working drawing was concluded, and the positions and the status of faults were diagnosed by this method. The completed detecting system, including hardware device of data measurement, diagnosis, and analysis software, was introduced concisely. The results of simulations and applications show that this method is simple and effective in the practical engineering.

A magnetic detecting and evaluation method of substation’s grounding grids with break and corrosion

The electromagnetic interference (EMI) from the valve hall as an important consideration in the design of high voltage direct current (HVDC) converter stations is analyzed by electromagnetic field numerical method and measurements. By using moment method, the EMI filed strength level as well as radio interference level (RIL) of the valve hall during the normal operation are computed after an antenna model is built for the valve tower. According to the character of EMI obtained, the practical shielding measures for valve hall are discussed to satisfy the relative standards. The test results for the ±500 kV converter station show that both the numerical method and shielding technique used in this paper are practical.

Electromagnetic interference and shielding of valve hall in HVDC converter station

The steel grounding grid buried in earth will corrode and become hidden danger to the safety of power system. It is difficult to get accurate status of corroded ground grid with traditional method. A novel method is presented in order to improve the efficiency and precision of diagnosis. A sine wave exciting current of different power frequency is injected directly into grounding grid by two ground lead wires. At the same time, the distributions of the surface magnetic induction intensities are measured based on the electromagnetic induction theory, then the faults of mesh conductors becoming thin or broken can be diagnosed. The feasibility of the method is demonstrated and the technical way of diagnosis is established by simulation computations using the grounding analysis software package. Combining with the practical EMI environments in substation, the diagnosis system has been designed. Experimental and practical results show that the functions of the system can satisfy the testing needs, this diagnosis method is simple and effective, and it can be used in engineering practice.

Corrosion diagnosis for grounding grids by using electromagnetic induction method

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