DC Interference Research Articles

Quantifying Photovoltaic DC Interference on Buried Pipelines: Exploring Theory, Conducting Experiments, and Field Testing

Quantifying Photovoltaic DC Interference on Buried Pipelines: Exploring Theory, Conducting Experiments, and Field Testing

Theoretical Analysis of a Magnetic Shielding System Combining Active and Passive Modes.

Considering the magnetic shielding requirements of both geomagnetic field and 50 Hz power-line frequency in the complex working conditions of the power grid, an electromagnetic shielding system combining active and passive modes is proposed in this article. A three-dimensional Helmholtz coil with a magnetic shielding barrel nested inside is established by the COMSOL simulation tool, and the magnetic shielding efficiency of the system is analyzed. Comparing different materials, the simulation results indicate that permalloy alloy exhibits better shielding performance than pure iron and nickel materials. Additionally, the overall shielding efficiency of the shielding barrel increases linearly with the number of multiple layers. Under the combined active and passive electromagnetic shielding conditions, the system achieves a shielding efficiency of SE = 113.98 dB, demonstrating excellent performance in shielding both AC and DC interference magnetic fields. This study provides theoretical guidance for the construction of magnetic shielding systems in electromagnetic interference environment.

The formation of pitting under dynamic DC interference: Corrosion product film defects or passive film induction

The cause of pitting under dynamic DC interference is unclear. This paper studies the mechanisms of pitting in simulated solutions under neutral and alkaline conditions using weight loss, electrochemical testing, and microscopic characterization. The results indicate that the metal mainly undergoes active corrosion in the neutral solution, and the formation of millimeter-scale pits is due to local defects in corrosion products. Metals in the alkaline solution undergo passive corrosion, resulting in micro-scale pits. Initially, stable pits form at damaged areas of the passivation film. Then, pits can grow rapidly under self-catalysis, with the growth rate surpassing other surface locations.

Mitigating AC and DC Interference in Multi-ToF-Camera Environments.

Multi-camera interference (MCI) is an important challenge faced by continuous-wave time-of-flight (C-ToF) cameras. In the presence of other cameras, a C-ToF camera may receive light from other cameras' sources, resulting in potentially large depth errors. We propose stochastic exposure coding (SEC), a novel approach to mitigate MCI. In SEC, the camera integration time is divided into multiple time slots. Each camera is turned on during a slot with an optimal probability to avoid interference while maintaining high signal-to-noise ratio (SNR). The proposed approach has the following benefits. First, SEC can filter out both the AC and DC components of interfering signals effectively, which simultaneously achieves high SNR and mitigates depth errors. Second, time-slotting in SEC enables 3D imaging without saturation in the high photon flux regime. Third, the energy savings due to camera turning on during only a fraction of integration time can be utilized to amplify the source peak power, which increases the robustness of SEC to ambient light. Lastly, SEC can be implemented without modifying the C-ToF camera's coding functions, and thus, can be used with a wide range of cameras with minimal changes. We demonstrate the performance benefits of SEC with thorough theoretical analysis, simulations and real experiments, across a wide range of imaging scenarios.

Effect of direct current on hydrogen permeation behavior of X80 pipeline steel in Shanghai soil solution

Dynamic direct current may cause hydrogen damage and corrosion in buried pipelines. In this study, the hydrogen permeation behavior of X80 steel in a simulated solution of Shanghai soil under dynamic DC interference was investigated using electrochemical hydrogen permeation testing and surface pH detection, combined with surface morphological observation and numerical simulation methods. The results show that the dynamic direct current causes alternating reduction (hydrogen precipitation) and oxidation reactions on the surface of the specimen and affects hydrogen permeation. At the same amplitude, the diffusible hydrogen concentration of square wave hydrogen permeation is greater than that of triangular wave. With the negative shift of the wave peak potential, the diffusible hydrogen concentration increases for both square and triangular wave hydrogen permeation. The specimens cycle between the generation and rupture of corrosion product films and cause pitting, which may increase the risk of localized hydrogen damage.

Pitting corrosion behavior of X70 steel in weakly alkaline solution under dynamic DC interference

Stray current discharged into the soil when subway trains operate will lead to fluctuation in the pipe-soil potential, which causes severe corrosion. In this work, the pitting corrosion behavior of X70 steel in a weakly alkaline simulated soil solution under different potential fluctuation ranges was studied. The influence of the fluctuation of the pipe-to-soil potential on the passivation film and pitting corrosion was studied using electrochemical measurement and surface characterization. X70 steel has passivation characteristics in the weakly alkaline solution. The passivation film is in a dynamic process of continuous growth or growth-dissolution due to the alternating polarization. The critical factor in inducing pitting corrosion is the failure to produce stable and dense passivation film or the instantaneous polarization potential exceeding the range of passivation potential. The passivation film's density determines the pitting's initiation and development trend. It is preliminarily found that the charge transfer resistance at the initiation stage of pitting has a good exponential function relationship with the pitting rate at the stable development stage, which is of great significance for the qualitative evaluation of the pitting rate.

Research on Pattern Extraction Method of Underwater Acoustic Signal Based on Linear Array

Underwater acoustic signal is an important reference data for marine information research. The research and application of underwater acoustic signal have been widely concerned and valued by countries and enterprises. With the needs of modern military development and the development of marine industry, the research and application of underwater acoustic signal will develop faster and faster. In order to better understand marine information, it is necessary to collect seawater acoustic signal data. Aiming at the purpose of recording underwater acoustic signals placed in the ocean for a long time, this study innovates the calibration and recording of large dynamic range of long-time underwater acoustic signals, improves the circuit setting methods such as receiving, amplification, and sampling, designs a large dynamic series of long-time underwater acoustic signal recording device, and adopts the linear array extraction method, so that it can monitor the underwater acoustic biological sound under the condition of low power. It can also monitor the blasting sound of offshore engineering. Hardware circuit design mainly includes main control chip selection, amplification circuit design, filter circuit design, analog-to-digital conversion circuit design, storage circuit design, and some auxiliary circuit design. The fourth chapter introduces the software development process of large dynamic range underwater acoustic signal recorder and mainly introduces the system development tool, system clock working method, real-time clock module working method, underwater acoustic signal acquisition method, data storage scheme design, and the use of FatFs file system. The underwater acoustic signal data is stored on a MicroSD in the form of TXT file; linear array extraction method is used for feature extraction. Compared to other methods, the transformer will suppress DC and low-frequency interference signals, thus achieving high-pass filtering characteristics. Finally, the performance and experimental results of the whole underwater acoustic signal recording device are analyzed. After testing, the underwater acoustic signal recording device designed in this paper works stably and can record underwater acoustic signals with large dynamic range for a long time in low-power mode.

Complete Method to Assess the DC Corrosion Impact on Pipeline Systems During the Planning and Approval Stages of HVDC Systems With Earth Current Return

The technology of HVDC systems defines the current return process, which can be through a dedicated metallic conductor or through a conducting medium, such as the earth or sea. Although the magnitude of the earth/sea return current is normally specified in local regulations or project specifications, there is no explicit methodology to estimate the intermittent, time duration of this current, over the life-span of a system. However, dc interference/corrosion impacts related to the development of HVDC links are, to a large extent, associated to the time duration of the earth current. In the absence of any explicit methodology, the potential influence of the earth/sea return current on nearby critical infrastructures is often based on unrealistic or on conservative interference impact studies. The purpose of this paper is to firstly provide a methodology to quantify the expected intermittent duration of the earth return current - in point-to-point bipolar HVDC systems, which arises from their partial-availability or the emergency conditions. Subsequently, the proposed methodology is applied in a realistic dc interference/corrosion study of a critical pipeline system that operates near a HVDC link currently being constructed. In essence, the paper describes a top-down complete approach for HVDC dc interference modelling endeavors in an attempt to avoid conservative and costly mitigation measures concerning third-party critical infrastructures in the nearby vicinity.

Corrosion behavior of HRB400 and HRB400M steel bars in concrete under DC interference

The influence of direct current interference on the corrosion behavior of HRB400 and HRB400M steel bars in simulated concrete solution was studied using methods such as weight loss experiment, electrochemical experiment, surface technology and product analysis. The research results showed that with the increase of DC interference voltage, the corrosion rates of HRB400 and HRB400M steel bars would increase. The corrosion resistance of HRB400M steel bars was better than HRB400 steel bars under the experimental conditions. In addition, direct current interference could cause damage to the corrosion product layer on the surface of HRB400 steel bars and HRB400M steel bars. And the corrosion form and corrosion product types of HRB400 and HRB400M steel bars would be affected by direct current interference. The main corrosion products of HRB400 steel bars included γ-FeOOH and Fe2O3 when it was not interfered by DC. When DC interference was applied, the main corrosion products included Fe3O4 and Fe2O3. The corrosion products on the surface of HRB400M steel bars were mainly Fe3O4 and Fe2O3, and the types of products increased to form Cr2O3 and MnFe2O4.

Research on corrosion assessment model for buried steel pipelines under dynamic DC stray current based on machine learning

AbstractCoupon tests on the pipeline subjected to metro dynamic DC interference were conducted. The pipe‐to‐soil from 78 sites including off‐potentials (Eoff), on‐potentials (Eon), and corrosion rate data were obtained, and then the dynamic fluctuation parameters of pipe‐to‐soil potentials were analyzed statistically. Further, the Pearson correlation between dynamic statistical parameters of pipe‐to‐soil potentials and corrosion rates was analyzed and showed that the statistical parameter of “roff ⩾ −0.85 V” and “mean[Eoff,cmax]” have a greater correlation with corrosion rate than others. Based on the statistical parameters of Eoff and the machine learning method, the optimal feature subset of the corrosion rate model was selected; meanwhile, it is proved that the negative shift of Eoff plays an important role in the prediction of corrosion rate. Finally, the corrosion rate model for buried steel pipeline under dynamic DC interference was established by random forest (rfr) method on 66 training data, then generalization performance of the model was verified on 12 test data. The results show that mean absolute error and R2 are 0.0358 mm/a and 0.56, respectively, on test data.

Effects of non-stationary stray current on carbon steel buried pipelines under cathodic protection

DC stray currents may cause severe corrosion on buried carbon steel pipelines even if in cathodic protection. According to international standard anodic interference is unacceptable if the IR-free potential is more positive than the protection potential (−0.85 V CSE). But, duration and magnitude of the anodic peak is not defined. The criterion appears to be too restrictive if short periods of anodic interference are established. This paper deals with the study of the effects of anodic interference on carbon steel in cathodic protection in soil-simulating environment in the presence of DC interference at varying peak current density and duration.

Research on corrosion rate assessment of buried pipelines under dynamic metro stray current

AbstractTo provide a reference for the evaluation of corrosion rate under dynamic metro stray current, both simulated experiments in laboratory and coupon tests in the field were conducted to explore the corrosion behavior and the relationship between corrosion rates and dynamic DC interference parameters of buried pipelines. The results show that the dynamic period has a significant influence on the corrosion rate and the ratio of actual corrosion rate to the theoretical corrosion rate. The statistical data of pipe to soil potentials or current densities of coupons electrically connected to pipelines obtained from the field in many cities of China show that the dynamic fluctuation periods under metro stray current are within the range of 0–300 s, among which the majority of fluctuation periods distribute from 50 to 200 s. The dynamic fluctuation of pipe to soil potentials and current densities of coupons exhibits symmetric or asymmetric characteristics. Under the situation of symmetric positive and negative current density, the ratio of the actual corrosion rate to the theoretical corrosion rate ranges from about 4% to 22% under the typical dynamic periods range from 50 to 200 s based on the simulated experiments results in the laboratory. Besides, two corrosion rate assessment methods, including the positive shifting and time ratios of off‐potentials and symmetrical or asymmetric characteristics of DC current density of coupons were proposed. In addition, the evaluation of the on‐potential criteria to assess the corrosion risk of time‐variant anodic interference was also discussed in the paper.

A unipolar thin‐film transistor‐based amplifier with enhanced DC offset suppression

This letter proposes a unipolar thin-film transistor (TFT)-based amplifier design that can provide enhanced DC offset suppression. The amplifier consists of an input AC coupling network and a capacitor bootstrap amplifier. By making the first pole of the input AC-coupling network coincide with that of the capacitor bootstrap amplifier, a DC offset suppression capability of 40 dB/dec, which is 2× higher than that of the prior arts, can be obtained. An implementation is also proposed and a Rensselaer Polytechnic Institute (RPI) TFT model whose parameters are turned to fit the measured data of our metal-oxide TFT is used to simulate the circuit. Simulation results show that the implementation has 31 dB midband gain, 0.5 Hz–5 kHz bandwidth, 300 μW power consumptions, and the expected 40 dB/dec DC offset suppression. This design is suitable for applications that need to block large DC interference, such as sensor readout amplifiers.

Cathodic protection and DC non-stationary anodic interference

DC stray currents may induce corrosion on buried carbon steel pipelines transporting methane even if in cathodic protection. According to international standard, anodic interference is unacceptable if the IR-free potential is more positive than the protection potential (−0.85 V CSE). But, duration and magnitude of the anodic peak is not defined. This paper describes results of laboratory tests performed in soil-simulating environment on cathodically protected carbon steel specimens suffering DC interference at varying peak current density, anodic potential and duration. Measured corrosion rate is always lower than the theoretical value predicted by Faraday Law. Consequently, it is possible to conclude that cathodic protection has a positive effect towards DC interference. A parameter Time Out of Protection has been defined as the period of time during interference where the potential is more positive than −0.85 V CSE; this factor has been correlated to the measured potential during DC interference.

Interference Activity on Pipeline Systems From VSC-Based HVDC Cable Networks With Earth/Sea Return: An Insightful Review

High Voltage Direct Systems (HVDC) are in operation for many years; however, their underlying technology is rapidly advancing. Depending on technology, their operating characteristics can vary under fault and maintenance conditions. Thus, when evaluating the interference activity from such systems, expert knowledge is required with regard to the physical and electrical component aspects of transmitting HVDC electrical power. This paper provides an insightful review, by explicitly elaborating the relevance and importance of such aspects when evaluating their interference activity on collocated pipeline systems. To this end, the paper firstly elaborates on dc interference issues. However, other prevailing interference conditions rely not only on the HVDC steady-state system operation, but also on its transient conditions under dc fault conditions. This is because the transient conditions can exacerbate voltages accumulating on nearby buried pipelines -thus posing safety related concerns. In essence, the paper engages constructively with key source material and provides explicit insights and recommendations that should be considered when addressing the impact of both dc interference and short-term electromagnetic interference on pipeline systems. Exclusive emphasis is given on the operation and fault conditions of VSC-based HVDC cable networks that are using distant, earth or sea electrodes to facilitate the current return process.

On the Mechanism of Cathodic Protection and Its Implications on Criteria Including AC and DC Interference Conditions

In recent years, a wide agreement with respect to the processes associated with cathodic protection (CP) has been reached within the CP industry. The increase of the pH value at the steel surface and the generation of passivating conditions as a result of the CP current are widely accepted as the relevant underlying mechanism. Based on this understanding it was possible to identify the relevant processes with respect to AC and DC interference and explain the empirical observations. This led to the development of ISO 18086 and has significantly influenced the work on ISO/DIS 21857. This paper summarizes present state of knowledge, the more recent developments, and their implications with respect to the CP criteria. It summarizes the relevant aspects in association with interference conditions and highlights possible future approaches with respect to the assessment of the effectiveness of CP.

All-Pass-Filter-Based PLL for Single-Phase Grid-Connected Converters Under Distorted Grid Conditions

All-pass-filter-based single-phase phase-locked loop (APF-PLL) is a widely used grid synchronization method in grid-connected power converters. However, the performance of APF-PLL degrades under distorted grid conditions and the estimated phase and frequency will contain low-frequency oscillation terms, which is not conducive to practical application. To deal with this problem, this paper proposes two advanced APF-PLLs, which have good ability to suppress harmonics and dc offset interference without sacrificing the dynamic response of the system. In the first one, a band-pass filter (BPF) is used as the prefilter of APF-PLL to process the input voltage signal, and in the second one, the APF-PLL input signal is processed by using a harmonic decoupling network (HDN) and multiple prefilters. In addition, their parameter design procedure is also described in detail and is easy to follow. The experimental results presented in this paper finally verify the superiority and effectiveness of the two proposed methods.

DC Interference Modeling for Assessing the Impact of Sustained DC Ground Faults of Photovoltaic Systems on Third-Party Infrastructure

In grounded photovoltaic (PV) systems, dc leakage to earth is formed by the contribution of the PV modules, inverters, and dc circuitry. Ground faults in such systems occur when there is an unintentional connection between any dc-carrying conductor with a grounded surface or earth. On the occurrence of ground faults, dc leakage will be intensified and will flow through the earth or other conductive paths, before returning back to the source. Thus, it is highly probable that some portion of the dc leakage will attempt to return to the source through any low-resistance paths that exist in the nearby vicinity, for example, through nearby buried pipelines. Therefore, unattended dc leakage may induce stray current corrosion concerns on these pipelines. To this extent, this paper presents a detailed dc interference modeling for assessing the dc leakage activity in PV systems—particularly under undetected fault conditions. First, the modeling carried out embraces the topologically accurate consideration of all sources of dc leakage that are associated with the grounded PV systems. A second feature presented in the paper is the modeling of blind-spot dc faults and their impact on third-party infrastructure.

Evaluation Model for the Scope of DC Interference Generated by Stray Currents in Light Rail Systems

Electrochemical corrosion caused by stray currents reduces the lifespan of buried gas pipelines and the safety of light rail systems. Determining the scope of stray current corrosion will help prevent the corrosion of existing buried pipelines and provide an effective reference for new pipeline siting. In response to this problem, in this paper the surface potential gradient was used to evaluate the scope of stray current corrosion. First, an analytical model for the scope of the stray current corrosion combined with distributed parameters and the electric field generated by a point current source was put forward. Second, exemplary calculations were conducted based on the proposed model. Sensitivity of the potential gradient was analyzed with an example of the transition resistance, and the dynamic distribution of surface potential gradient under different locomotive operation modes was also analyzed in time-domain. Finally, the scope was evaluated at four different intervals with the parameters from the field test to judge whether the protective measures need to be taken in areas with buried pipelines and light rail systems nearby or not.

Wideband Microwave Phase Noise Analyzer Based on an All-Optical Microwave I/Q Mixer

Digital phase demodulation can greatly simplify the calibration of microwave phase noise analyzers (PNAs) based on frequency discriminators, and avoid the use of feedback loops, but the required microwave in-phase and quadrature (I/Q) mixer always has a small operational bandwidth, leading to a limited phase noise measurement frequency range. In this paper, a novel photonic microwave PNA based on digital phase demodulation is proposed and investigated, using an all-optical microwave I/Q mixer that consists of a Mach–Zehnder modulator, a polarization modulator and two polarizers. Different from conventional electrical I/Q mixers, which rely on electrical hybrids to introduce a 90-degree phase difference between the I and Q channels, the all-optical microwave I/Q mixer achieves the 90-degree phase difference by properly setting the polarizers, ensuring a broad operational bandwidth. The major problems associated with the use of the optical mixer in the PNA, i.e., DC interference and I/Q mismatch, are solved by tuning a variable delay-line together with post signal processing. In addition, to improve the phase noise measurement sensitivity, the time delay required in the frequency discriminator is implemented by a span of low-loss fiber. Experimental results show that the I/Q mixer can maintain a good performance within a frequency range from 5 to 40 GHz, and the proposed PNA has a high sensitivity (<-100 dBc/Hz@1 kHz and <-130 dBc/Hz@10 kHz).