A Simple and Effective Surface Defect Detection Method of Power Line Insulators for Difficult Small Objects

Insulator defect detection plays a vital role in maintaining the secure operation of power systems.To address the issues of the difficulty of detecting small objects and missing objects due to the small scale,variable scale,and fuzzy edge morphology of insulator defects,we construct an insulator dataset with 1600 samples containing flashovers and breakages.Then a simple and effective surface defect detection method of power line insulators for difficult small objects is proposed.Firstly,a high-resolution featuremap is introduced and a small object prediction layer is added so that the model can detect tiny objects.Secondly,a simplified adaptive spatial feature fusion(SASFF)module is introduced to perform cross-scale spatial fusion to improve adaptability to variable multi-scale features.Finally,we propose an enhanced deformable attention mechanism(EDAM)module.By integrating a gating activation function,the model is further inspired to learn a small number of critical sampling points near reference points.And the module can improve the perception of object morphology.The experimental results indicate that concerning the dataset of flashover and breakage defects,this method improves the performance of YOLOv5,YOLOv7,and YOLOv8.In practical application,it can simply and effectively improve the precision of power line insulator defect detection and reduce missing detection for difficult small objects.

An Oscillating Wave Energy Converter with Nonlinear Snap-Through Power-Take-Off Systems in Regular Waves

Floating oscillating bodies constitute a large class of wave energy converters, especially for offshore deployment. Usually the Power-Take-Off（PTO） system is a directly linear electric generator or a hydraulic motor that drives an electric generator. The PTO system is simplified as a linear spring and a linear damper. However the conversion is less powerful with wave periods off resonance. Thus, a nonlinear snap-through mechanism with two symmetrically oblique springs and a linear damper is applied in the PTO system. The nonlinear snap-through mechanism is characteristics of negative stiffness and double-well potential. An important nonlinear parameter γ is defined as the ratio of half of the horizontal distance between the two springs to the original length of both springs. Time domain method is applied to the dynamics of wave energy converter in regular waves. And the state space model is used to replace the convolution terms in the time domain equation. The results show that the energy harvested by the nonlinear PTO system is larger than that by linear system for low frequency input. While the power captured by nonlinear converters is slightly smaller than that by linear converters for high frequency input. The wave amplitude, damping coefficient of PTO systems and the nonlinear parameter γ affect power capture performance of nonlinear converters. The oscillation of nonlinear wave energy converters may be local or periodically inter well for certain values of the incident wave frequency and the nonlinear parameter γ, which is different from linear converters characteristics of sinusoidal response in regular waves.

Performance Evaluation for Medium Voltage MIMO-OFDM Power Line Communication System

Power line communication(PLC)provides intelligent electrical functions such as power quality measurement,fault surveys,and remote control of electrical network.Most of research works have been done in low voltage(LV)scenario due to the fast development of in-home PLC.The aim of this paper is to evaluate the link-level performance of a medium voltage(MV)MIMO-OFDM communication system based on transmission link under underground power line channel.The MIMO channel is modeled as a modified multipath model in the presence of impulsive noise and background noise.We first perform a measurement on the practical MV MIMO channel parameters for a section of buried cable of 1 km long in Ganzhou city,Jiangxi province,China.Based on the measured channel,we design the frame structure based on an IEEE standard for broadband over power line networks[1]to support MV MIMO-OFDM transmission.According to designed frame structure,we design an encoder and a decoder for a dual binary tail-biting turbo code and optimize some key decoder parameters for low bit error rate performance.Finally,the link-level performance for both spatial multiplexing and spatial diversity are evaluated.Numeral results show that MV MIMO-OFDM is a promising approach to provide both high data rate and link reliability for PLC.

High Precision Ultrasonic Guided Wave Technique for Inspection of Power Transmission Line

Due to the merits of high inspection speed and long detecting distance, Ultrasonic Guided Wave（UGW） method has been commonly applied to the on-line maintenance of power transmission line. However, the guided wave propagation in this structure is very complicated, leading to the unfavorable defect localization accuracy. Aiming at this situation, a high precision UGW technique for inspection of local surface defect in power transmission line is proposed. The technique is realized by adopting a novel segmental piezoelectric ring transducer and transducer mounting scheme, combining with the comprehensive characterization of wave propagation and circumferential defect positioning with multiple piezoelectric elements. Firstly, the propagation path of guided waves in the multi-wires of transmission line under the proposed technique condition is investigated experimentally. Next, the wave velocities are calculated by dispersion curves and experiment test respectively, and from comparing of the two results, the guided wave mode propagated in transmission line is confirmed to be F（1,1） mode. Finally, the axial and circumferential positioning of local defective wires in transmission line are both achieved, by using multiple piezoelectric elements to surround the stands and send elastic waves into every single wire. The proposed research can play a role of guiding the development of highly effective UGW method and detecting system for multi-wire transmission line.

Dynamic Balance Control Based on an Adaptive Gain-scheduled Backstepping Scheme for Power-line Inspection Robots

This paper presents an adaptive gain-scheduled backstepping control(AGSBC) scheme for the balance control of an underactuated mechanical power-line inspection(PLI) robotic system with two degrees of freedom and a single control input.First, a nonlinear dynamic model of the balance adjustment process of the PLI robot is constructed, and then the model is linearized at a nominal equilibrium point to overcome the computational infeasibility of the conventional backstepping technique. Second, to solve generalized stabilization control issue for underactuated systems with multiple equilibrium points,an equilibrium manifold linearized model is developed using a scheduling variable, and then a gain-scheduled backstepping control(GSBC) scheme for expanding the operational area of the controlled system is constructed. Finally, an adaptive mechanism is proposed to counteract the impact of external disturbances. The robust stability of the closed-loop system is ensured by Lyapunov theorem. Simulation results demonstrate the effectiveness and high performance of the proposed scheme compared with other control schemes.

The design of monitoring communication system Based on Power line carrier

The design of the power line carrier communication system was introduced in this paper,DSP was adopted as the hardware platform to complete the core task.DSP sending terminal delivered the collecting data to the DSP receiving terminal through the power line carrier, and the DSP receiving terminal send the data to PC through a serial port.The design improved the power line carrier communication system and the data transmission became faster and more reliable.The experiment results showed that the PER of the receiving data is less than 0.4%, which satisfied the power line carrier communication requirement Our design is feasible and effective.

The changing process and trend of ground temperature around tower foundations of Qinghai-Tibet Power Transmission line

After the construction of Qinghai-Tibet Highway and Railway, the Qinghai-Tibet Power Transmission(QTPT) line is another major permafrost engineering project with new types of engineering structures. The changing process and trend of ground temperature around tower foundations are crucial for the stability of QTPT. We analyzed the change characteristics and tendencies of the ground temperature based on field monitoring data from 2010 to 2014. The results reveal that soil around the tower foundations froze and connected with the artificial permafrost induced during the construction of footings after the first freezing period, and the soil below the original permafrost table kept freezing in subsequent thawing periods. The ground temperature lowered to that of natural fields, fast or slowly for tower foundations with thermosyphons,while for tower foundations without thermosyphons, the increase in ground temperature resulted in higher temperature than that of natural fields. Also, the permafrost temperature and ice content are significant factors that influence the ground temperature around tower foundations. Specifically, the ground temperature around tower foundations in warm and ice-rich permafrost regions decreased slowly, while that in cold and ice poor permafrost regions cooled faster. Moreover, foundations types impacted the ground temperature, which consisted of different technical processes during construction and variant of tower footing structures. The revealed changing process and trend of the ground temperature is beneficial for evaluating the thermal regime evolution around tower foundations in the context of climate change.

Reduction of electric field strength by two species of trees under power transmission lines

Electrical pollution is a worldwide concern,because it is potentially harmful to human health.Trees not only play a significant role in moderating the climate,but also can be used as shields against electrical pollution.Shielding effects on the electric field strength under transmission lines by two tree species,Populus alba and Larix gmelinii,were examined in this study.The electrical resistivity at different heights of trees was measured using a PiCUS sonic tomograph,which can image the electrical impedance for trees.The electric field strength around the trees was measured with an elf field strength measurement system,HI-3604,and combined with tree resistivity to develop a model for calculating the electric field intensity around trees using the finite element method.In addition,the feasibility of the finite element method was confirmed by comparing the calculated results and experimental data.The results showed that the trees did reduce the electric field strength.The electric field intensity was reduced by 95.6%,and P.alba was better than L.gmelinii at shielding.

Power Line Monitoring Data Transmission Using Wireless Sensor Network

The WSN used in power line monitoring is long chain structure, and the bottleneck near the Sink node is more obvious. In view of this, A Sink nodes’ cooperation mechanism is presented. The Sink nodes from different WSNs are adjacently deployed. Adopting multimode and spatial multiplexing network technology, the network is constructed into multi-mode-level to achieve different levels of data streaming. The network loads are shunted and the network resources are rationally utilized. Through the multi-sink nodes cooperation, the bottlenecks at the Sink node and its near several jump nodes are solved and process the competition of communication between nodes by channel adjustment. Finally, the paper analyzed the method and provided simulation experiment results. Simulation results show that the method can solve the funnel effect of the sink node, and get a good QoS.

Steady-state voltage-control method considering large-scale wind-power transmission using half-wavelength transmission lines

Half-wavelength transmission can transmit large-scale renewable energy over very long distances.This paper proposes an improved steady-state voltage-control method for half-wavelength transmission systems considering largescale wind-power transmission.First,the unique voltage characteristics of half-wavelength lines are deduced based on the distributed parameter model.In the secondary voltage-control level,reactive power-transmission limits of half-wavelength lines are introduced as another control objective except for tracing the pilot bus voltage reference.Considering the uncertainty and fluctuation of wind power,the overvoltage risk-assessment method of half-wavelength lines is presented to determine specific voltage-control strategies.Simulation results demonstrate that the proposed voltage-control method delivers superior tracking performance according to a voltage reference value and prevents the overvoltage risk of halfwavelength lines effectively in different wind-power penetrations.

A FAST BIT-LOADING ALGORITHM FOR HIGH SPEED POWER LINE COMMUNICATIONS

Adaptive bit-loading is a key technology in high speed power line communications with the Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. According to the real situation of the transmitting power spectrum limited in high speed power line communications, this paper explored the adaptive bit loading algorithm to maximize transmission bit number when transmitting power spectral density and bit error rate are not exceed upper limit. With the characteristics of the power line channel, first of all, it obtains the optimal bit loading algorithm, and then provides the improved algorithm to reduce the computational complexity. Based on the analysis and simulation, it offers a non-iterative bit allocation algorithm, and finally the simulation shows that this new algorithm can greatly reduce the computational complexity, and the actual bit allocation results close to optimal.

Propagation characteristics of power line harmonic radiation in the ionosphere

Theoretical model and solutions on power line harmonic radiation （PLHR） propagating in the ground, air, and anisotropic homogeneous ionosphere are presented, The theoretical model is verified by the PLHR events observed by the DEMETER satellite. Some propagation characteristics of PLHR based on the model are obtained. This paper is bene- ficial to quantitatively interpret the formation mechanism of PLHR phenomenon.

A power divider based on a new kind of composite right/left-handed transmission line (CRLH TL) unit

A new power divider, composed of a novel composite right/left-handed (CRLH) transmission line (TL) unit, is proposed. The properties of the power divider based on four CRLH TL unit cells are investigated theoretically. By adjusting the parameters of the capacitors and the inductors, the power divider shows perfectly symmetric power division at 5.13 GHz, return loss up to ?24 dB, with the transmitted power being close to ?3.1 dB. The phenomena are demonstrated by simulation results. Being compact in size and low-cost, the proposed power divider is very suitable for microwave and millimeter wave integrated circuits.

Power line strikes by Black-necked Cranes and Bar-headed Geese in Tibet Autonomous Region

We investigated collisions with power lines by Black-necked Cranes (Grus nigricollis) and Barheaded Geese (Anser indicus) along the Yarlung Tsangpo River in the Tibet Autonomous Region during two winters.Three segments of a 35 kV transmission line were surveyed each winter for injured and dead birds.Injured birds disappeared within five days of their initial detection; most dead birds encountered had been scavenged.We recorded two dead geese on transects and two injured geese and two dead cranes adjacent to transects.We found a higher incidence of bird strikes along power line segments close to roosting and foraging areas.We recommend that power lines,new or old,located in the flight path from nocturnal roosts,near important foraging areas or crossing the mouths of important agricultural valleys should be marked with colored and/or reflecting devices that have been proven to reduce crane and goose collisions.

Next Generation Narrowband(Under 500 kHz) Power Line Communications(PLC) Standards

In the past decade,several efforts around the world were started with the goal of introducing "smart metering" capabilities into the power grid.These efforts have spurred renewed interest in the design of next generation Narrowband Power Line Communications(NB-PLC) transceivers.In the past few years,ITU-T and IEEE have standardized a family of next generation OFDM-based NB-PLC transceivers some of which are today being considered for massive deployments in Europe and Asia.This paper addresses the important role that PLC has not only for smart metering but also for many other Smart Grid applications,and also gives an overview of the main differences between these next generation NB-PLC standards.

Modeling of OFDM Based Transceiver for Broadband Powerline Communication

In the recent past power line communication has emerged as an attractive choice for high speed data transfer and is looked upon as inexpensive and reliable media suitable for broadband internet access, home and office automation, in-vehicle data communication etc. In this paper we present an architecture for the physical layer of a PLC transceiver based on Orthogonal Frequency Division Multiplexing (OFDM) and the impact on multipath distortion for PLC transmission in terms of bit error rate. Since there is no standard PLC channel model available, a widely accepted multipath channel model is used for simulation purpose. Simulation results as well as FPGA synthesis verify the effectiveness of the proposed architecture for PLC modem design at 110 Mbps data rate.

A line laser detection screen design and projectile echo power calculation in detection screen area

A line laser with high power as the background light source for the design of a new photoelectric detection target is proposed in this paper, aiming to improve the detection ability of the traditional photoelectric detection target under low background illumination. The laser emitted pulse waveform function and the laser echo pulse response function were used to establish the mathematical model of the reflected echo power of projectile in the detection area and derive the calculation function of minimum detectable echo power in the line laser detection screen, according to information of the line laser emitted power, incident angle of projectile, duration time and detection distance of projectile passing through the line laser detection screen. Calculations and experimental results showed that the design method of line laser detection screen and calculation model of laser echo power are reasonable, and the detection ability of line laser detection screen is obviously higher than that of traditional photoelectric detection screen, especially in low background illumination;at the same time, the designed line laser detection screen was used to combine a six line laser detection screen intersection test system, based on live ammunition for shooting. The test system is stable and able to obtain the dynamic parameters of the flying projectile, verifying that the design of the line laser detection screen in new photoelectric detection target can be suitable for shooting range test applications.

Design of A Hydraulic Power Take-off System for the Wave Energy Device with An Inverse Pendulum

This paper describes a dual-stroke acting hydraulic power take-off （PTO） system employed in the wave energy converter （WEC） with an inverse pendulum. The hydraulic PTO converts slow irregular reciprocating wave motions to relatively smooth, fast rotation of an electrical generator. The design of the hydraulic PTO system and its control are critical to maximize the generated power. A time domain simulation study and the laboratory experiment of the full-scale beach test are presented. The results of the simulation and laboratory experiments including their comparison at full-scale are also presented, which have validated the rationality of the design and the reliability of some key components of the prototype of the WEC with an inverse pendulum with the dual-stroke acting hydraulic PTO system.

Capture Performance of A Multi-Freedom Wave Energy Converter with Different Power Take-off Systems

Among the wave energy converters (WECs), oscillating buoy is a promising type for wave energy development in offshore area. Conventional single-freedom oscillating buoy WECs with linear power take-off (PTO) system are less efficient under off-resonance conditions and have a narrow power capture bandwidth. Thus, a multi-freedom WEC with a nonlinear PTO system is proposed. This study examines a multi-freedom WEC with 3 degrees of freedom: surge, heave and pitch. Three different PTO systems (velocity-square, snap through, and constant PTO systems) and a traditional linear PTO system are applied to the WEC. A time-domain model is established using linear potential theory and Cummins equation. The kinematic equation is numerically calculated with the fourth-order Runge–Kutta method. The optimal average output power of the PTO systems in all degrees of freedom are obtained and compared. Other parameters of snap through PTO are also discussed in detail. Results show that according to the power capture performance, the order of the PTO systems from the best to worst is snap through PTO, constant PTO, linear PTO and velocity-square PTO. The resonant frequency of the WEC can be adjusted to the incident wave frequency by choosing specific parameters of the snap through PTO. Adding more DOFs can make the WEC get a better power performance in more wave frequencies. Both the above two methods can raise the WEC’s power capture performance significantly.

SELECTION OF TRANSMISSION LINE MODELS USED IN POWER SYSTEM TRANSIENT SIMULATIONS

A method used for determining the number of equivalent π sections oftransmission line model according to the frequency range of interest and the model accura-cy defined herein is proposed.Factors influencing the discrepancies between continuous ordistributed parameter and multiple π or lumped parameter models are discussed.Generalconclusions concerning the π section lengths of line models used in transient stability,faulttransient and switching over-voltage studies are drawn.Time-domain simulation resultsconfirm the effectiveness of this method.