Half-wavelength Transmission Lines Research Articles

Enhanced pilot protection scheme for half-wavelength transmission line based on the conservation of traveling wave energy

The half-wavelength transmission system is a viable technology for long-distance and large-capacity power transmission. It can safely and efficiently transmit a large amount of clean energy to remote load centers. However, the traditional traveling wave protection methods have reliability and speed limitations for HWTL lines. To overcome these limitations, this paper proposes a novel and robust pilot protection scheme based on the conservation of traveling wave energy at the protection installation. The proposed scheme uses the constant equation relationship between fault-traveling waves, reflected waves and refracted waves at the measurement end to significantly improve the reliability and effectiveness of the protection mechanism. The blocking protection operation logic constructed by the inequality directional element is used to improve the rapidity of the pilot protection scheme. The theoretical analysis and real-time digital simulator (RTDS) digital-analog hybrid test demonstrate that the action equation of the proposed protection scheme is explicit to the operating value. The novel scheme exhibits enhanced resilience against high transition resistance and the impact of impulse corona while ensuring both reliability and rapidity.© 2017 Elsevier Inc. All rights reserved.

Backup protection method for half-wavelength transmission lines based on inverse-time characteristic

The advantages of ultra-high voltage (UHV) Half-wavelength AC transmission (HWACT) technology are achieving full-line reactive power self-balancing without the need for reactive power compensation equipment along the line and avoiding the Ferranti effect. Recently, this technology has gained considerable attention worldwide. While numerous main protection methods that were tailored to the unique operational characteristics of HWACT lines have been proposed, backup protection for HWACT has been overlooked relatively. As a transmission line requires both main and backup protection for safe and reliable operation, this paper analyzes the necessity of backup protection for HWACT lines and proposes a method based on inverse-time backup protection. This method relies on the rate of change of current (RCC), determines faults by calculating the initial value of the change rate of the fault current, and applies inverse-time characteristics to remove faults. This protection method demonstrates good quick-acting properties by adopting the RCC in the initial phase of a single-end fault without the need for dual-end communication. A large number of simulation results validated that this method was smaller affected by fault distance, initial fault phase angle, transition resistance and fault type, making it an effective protection approach for main protection failures.

A bandwidth-tunable balanced filter with a broad tuning range and a wide minimum bandwidth

A bandwidth-tunable balanced filter (BTBF) is proposed, which utilizes the quarter-wavelength coupled lines with multi-point loaded varactors and half-wavelength transmission lines. The varactor-loaded coupled lines combined with the pair of the half-wavelength transmission lines provide the basic wideband differential-mode (DM) passband and common-mode (CM) suppression, and the loaded varactors can tune the lower edge, the upper edge and the impedance matching (IM) of the passband. Thus, tunable bandwidth with almost constant center frequency can be achieved by controlling the bridged varactor C v1 and the series varactors C v2 and C v3. Compared to the state-of-the-art designs, the proposed design offers significant advantages of broad tuning range of DM bandwidth, wide minimum DM bandwidth, low insertion loss, and simple structure. For demonstration, a prototype is designed with the DM bandwidth tuning range of 24.7%, the minimum DM fractional bandwidth (FBW) of 46.5%, the maximum insertion loss inside the IM bandwidth of 2.3 dB.

Pilot protection based on the quasi-directional element of LCL-tuned half-wavelength transmission line

To create HWTL characteristics, the electrical distance of AC transmission lines is compensated to half the power frequency wavelength by utilizing tuned circuits. The LCL-tuned circuit exhibits low-pass filtering characteristics, blocking the transmission of high-frequency signals. Measurement devices were installed on both sides of the tuned circuit to assess its filtering characteristics. Based on these characteristics and by employing wavelet transformation to extract the high-frequency energy of the voltage signal on both sides of the tuned circuit as the directional protection criterion, a quasi-directional element was developed. It was determined that, if the high-frequency wavelet energy ratio exceeds one, the fault occurs in the forward direction of the tuned circuit, and if the ratio is less than one, the fault occurs in the reverse direction. Consequently, a pilot protection algorithm was formulated. The directional protection element was integrated with the tuned circuit differential protection to establish the LCL-tuned half-wavelength transmission line pilot protection scheme. This scheme mitigates the need for extensive data synchronization between both sides, and numerous simulations have demonstrated its effectiveness throughout the entire line length, regardless of transition resistance, fault type, noise and outgoing line.

Pilot protection method of half-wavelength AC transmission lines based on random matrix theory

The fault characteristics of ultra-high voltage (UHV) half-wavelength (HWL) transmission lines exhibit significant differences from those of conventional transmission lines, which renders the conventional relay protection method unsuitable for ensuring the protection of HWL. To solve this problem, a pilot protection method of HWTL based on random matrix theory was proposed. Voltage and current fault components obtained at the protection installation on both sides of the line were used as the input of the random matrix to form the singular value equivalent matrix, and the eigenvalues of the random matrix at both ends were calculated. The faults inside and outside the area were determined according to the distribution of the eigenvalues in the circular plane area. The protection scheme avoids the data synchronization problem at both ends of the line. Real time digital simulation system (RTDS) simulation revealed that the proposed protection method can protect the full length of the line, is suitable for various fault types and fault conditions, and exhibits excellent resistance to transition resistance.

Overvoltages due to line faults on a HWL transmission line: Corona effect and mitigation techniques

In half-wavelength (HWL) transmission lines, severe temporary overvoltages are usually observed during the occurrence of line-to-line faults in specific critical locations, and it is unrealistic to ignore the impact of the corona phenomenon. To represent the corona effect, an accurate Suliciu corona model was adopted and implemented in PSCAD software, and a new technique based on the genetic algorithm (GA) was proposed to fit the model parameters. Furthermore, the paper evaluated the performance of the overvoltage mitigation method based on the installation of two spark gaps (SGs) at strategic points to detune the resonance condition. As shown, the SGs turn the HWL line overvoltage levels similar to those observed in conventional AC lines, and the corona modelling further reduces the severity of the overvoltages.

Power differential protection for half-wavelength transmission lines—Software in the loop analysis

Half-wavelength transmission line protection is a challenge that hinders the implementation of this technology. However, this line is considered an interesting alternative to transmit bulk power blocks over very long distances and to connect wind and photovoltaic generation to an electrical power system. This study introduces a method to protect a half-wavelength transmission line. The proposed complex plane-based protection algorithm uses a differential complex power in the sequence domain to detect faults along the entire line. The embedded spark-gap mitigation device is properly considered because it is a necessary apparatus to remove severe resonant fault conditions. A time-domain analysis shows that the proposed algorithm achieves robust performance for both internal and external faults.

Design of a wideband isolated out-of-phase filtering power divider/combiner with sharp selectivity

AbstractA new isolated out-of-phase filtering power divider/combiner with high selectivity is presented. Based on a single-layer microstrip, required coupling strength and phase difference are achieved by two pairs of three-line coupled feeding structures. To realize desired bandpass responses, a specific resonator is located between the input and output coupled structures. By connecting a half-wavelength transmission line which is centrally loaded with a grounded resistor between two output ports, high port-to-port isolation is attained. Based on the impedance matrix of coupled three-line structure, theoretical filtering responses are predicted with the specified bandwidth and return loss. For demonstration, a prototype is designed, fabricated, and tested. Both simulated and measured results are displayed to verify the design mechanism.

Three-phase adaptive reclosure technology for half-wavelength transmission lines using residual voltage frequency difference to identify fault existence

• The single-phase reclosing technique should not be used in half-wavelength transmission systems. • The residual voltage of half wavelength transmission system can be used to determine the existence of faults. • The frequency difference of residual voltage can be used to determine the existence of faults. • We propose a complete and feasible three-phase adaptive reclosure scheme for half wavelength transmission system. UHV AC transmission lines use adaptive reclosure technology not only to avoid reclosing in the permanent faults, but also effectively prevent the emergence of reclosing overvoltage, adaptive reclosure is of great significance, and its technical principle is based on the study and judgment of the existence of the fault. The reactive power of half-wavelength transmission lines along the line was self-balanced, no shunt reactor equipment, there is no "beat frequency" phenomenon, and very little information is available after the three-phase trip. In this paper, we analyze the fault traveling wave's frequency characteristics and identify the fault's characteristics based on the residual voltage frequency difference of the line after the three-phase trip. After the disappearance of the line fault, the stable frequency difference obtained by CVT reflects the entire length of the line, which is not affected by the system boundary conditions and can complete the reliable identification of the disappearance of the line fault. The two-terminal criterion is given for the short-line dead zone problem, and then a three-phase adaptive reclosure scheme for half-wavelength transmission lines based on the frequency difference to identify fault disappearance is proposed. Extensive RTDS digital-analog hybrid tests show that the method is correct and robust.

Ground and phase fault classification for half-wavelength transmission lines relaying purposes

In this work, a new fault classification and phase selection methodology for half-wavelength (HWL) transmission lines is developed. Initially, the basic principles of phase currents transformations are presented. Then, an innovative faulted phase selection methodology based on the variation of those currents is developed. The behavior of the electrical quantities related to short circuits in such long lines is very different when compared to conventional lines. The faulted phase selection method employed in this work is built on the fact that those decoupled currents are expected to not vary or vary less than the others, depending on how many phases are in short circuit. The robustness of the method was analyzed considering different load conditions and fault resistances. Furthermore, different sampling rates were considered for the phase currents. Extensive simulation studies showed that the developed method can accurately identify the fault types and the faulted phase with a relatively low sample rate. Moreover, the simulation results showed that the proposed method is not affected by the presence of inter-harmonics and responds precisely with high-resistance faults. The proposed algorithm presented errors smaller than 0.04%.

A Dual-Band Rectifier Using Half-Wave Transmission Line Matching for 5G and Wi-Fi Bands RFEH/MPT Applications

A dual-band rectifier is presented for RF energy harvesting (RFEH) and microwave power transfer (MPT) applications. Starting with a single-band rectifier, the second band is added by utilizing a half-wavelength transmission line (HWTL) in the matching network (MN). A series diode topology using HSMS-2860 Schottky diode is used for power conversion. The rectifier simultaneously harvests the RF energy with power conversion efficiency (PCE) of 54.9% and 42.3% and output voltage of 1.4 and 1.242 V at 0-dBm input power for 3.5-GHz 5G band and 5.8-GHz Wi-Fi band, respectively.

Identification Method for Pulse Wave Resulted From Fault Transient of Overhead Transmission Line

This paper presents a simple and effective method to extract the identification quantity of transient pulse waveform produced by the overhead transmission line short-circuit fault. This method employs the second-order time harmonic equation of the power frequency component to convert the fault full-wave data. After the conversion, only the identification quantity remains. This method can amplify high-frequency spectral content by the times of the square of the angular frequency, and hence improve the sensitivity of identifying fault transient. Using the identification quantity, one can clearly observe the arrival time and relative intensity of fault transient. A three-phase half wavelength transmission line of 50Hz/3000km is simulated with PSCAD to illuminate the effectiveness of this method. The effects of fault type, soil resistivity, fault resistance, power frequency fluctuation, sampling rate, transposition length,fault inception angle and white noise are analyzed. Calculated results show that this method can distinguish different fault type and can work effectively at low sampling rate down to 10kHz. This method is helpful for improving the performance of the traveling-wave based fault location method.

Balanced-to-Unbalanced Quadrature Couplers With Wide-Band Common-Mode Suppression

In this paper, two types of balanced-to-unbalanced quadrature couplers with six hybrid ports and arbitrary power division ratio are proposed. For Type 1, the quadrature coupler can realize two power division functions, including balanced/unbalanced to balanced-unbalanced-hybrid, and for Type 2, the quadrature coupler contains balanced -to-unbalanced and unbalanced-to-balanced power division functions. To reduce the circuit size, double-sided parallel-strip line (DSPSL) swap structure is used to replace the half-wavelength transmission line, and compact circuit size can be easily achieved. To validate the performance of the quadrature couplers, two types of the balanced-to-unbalanced quadrature couplers centered at 1 GHz with power division ratios 1:1 and 3:1 are fabricated and measured, respectively. The common mode suppression higher than 10 dB (bandwidths over than 176%) can be realized, the isolation and in-band matching level can be also improved.

Performance evaluation of power differential protection applied to half-wavelength transmission lines

The half-wavelength transmission line is considered a feasible alternative to interconnect very distant electrical subsystems, in the range of thousands of kilometers. Despite presenting good economic advantages, this alternative still has some challenges. This kind of line has unique characteristics, which makes it difficult to apply protection methods as practised today. This paper presents an analysis of power differential protection developed for half-wavelength transmission lines. Here, the performance of complex power is analysed. The method uses apparent power in the sequence domain to develop efficient protection. During an external fault, there is a balance between the measured power in both line terminals. However, when an internal fault occurs, this balance is broken. MATLAB simulations show that the method achieved good results, mainly in detecting faults in the central region of the line and external faults. Additionally, the tests considered the spark-gap apparatus to remove severe resonant fault conditions.

Fault classification and phase selector algorithm for half-wavelength transmission lines

This study presents a new phase selector algorithm and fault type classification for very long transmission lines, known as the half-wavelength lines (HWL). For this work, the Clarke components variation rate method applied to current magnitudes was used. The method was implemented in a real-time digital simulation hardware-in-the-loop (HIL) test environment. We applied different fault types at each 5% line length, obtaining Clarke component current phasors. The proposed algorithm is stable for the native behavior of the half-wavelength line, including the resonance zones and their mitigation procedures. In addition, the algorithm is immune to the fault insertion angle, fault resistance, and line loading level. Finally, the algorithm could be applied in commercial microprocessor-based relays or could be used as a post-fault analysis tool.

Grid-connected resonance analysis of half-wavelength transmission system with wind power and photovoltaic power supply

New energy centers such as wind power and photovoltaic power generation are generally too far away from the load center. Half wavelength AC transmission technology can solve this problem. However, harmonics may be generated when new energy is connected to half wavelength transmission system. Harmonics will do harm to the normal operation of power grid. Therefore, this harmonic resonance problem is studied in this paper. Firstly, this paper expounds the principles of classical resonance analysis method and modal analysis method, and explains the advantages of modal analysis method through analysis and calculation. Then, the grid connected resonance of large-scale wind farm and photovoltaic power station connected to half wavelength transmission system is studied by modal analysis method. The effects of transmission line length, the number of groups of wind power and photovoltaic inverters on typical modal harmonic resonance are analyzed. The results show that the length of half wavelength transmission line and outgoing line only affect the low-frequency harmonic resonance of some modes; The length of collector cable has an effect on the harmonic resonance of each typical mode; The number of wind power and photovoltaic inverter groups has an impact on the harmonic resonance of some modes, but will not change the location of resonance.

Compensation circuit design for tuned half-wavelength transmission lines based on Bessel filter

Compensation circuit, which can increase electrical length, is the most feasible solution for flexible applications of half-wavelength transmission lines (HWTL). In previous studies, it is always assumed that the compensation circuit is structured by passive components with identical parameters to represent the distribution parameter of transmission lines. However, the structure of the traditional compensation circuit is actually equivalent to that of the constant k filter, which concludes that the compensation circuit is fundamentally a low-pass filter. In consideration of basic requirements for tuned HWTL, the Bessel filter, which has smooth group delays without waveform distortion, is selected for the calculation of compensation circuit parameters in this paper. Lastly, the Bessel-based compensation circuit is compared to natural HWTL and tuned HWTL with Butterworth filter-based and traditional compensation circuits. Comprehensive cases simulated by PSCAD are undertaken, which validate that the voltage distribution of Bessel-based compensation circuits is quite similar to that of traditional compensation circuits. Moreover, electromagnetic transients can induce significant high-frequency oscillations in tuned HWTL with traditional compensation circuits, but high-frequency oscillation is significantly reduced by Bessel-based compensation circuits. Therefore, the Bessel-based compensation circuit is verified to be a better solution for tuned HWTL.

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 large- scale 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 half- wavelength lines effectively in different wind-power penetrations.

Fault impedance analysis and non-conventional distance protection settings for half-wavelength transmission line applications

This paper presents an analysis of fault phase impedance and its dynamic response for half-wavelength (HWL) transmission lines. One important issue of this technology is fault protection as distance protection elements are based on impedance for conventional AC lines. HWL line has very long length, preventing the direct application of classical impedance method because the capacitance effect produces different impedance behavior. This paper analyzes and characterizes the phase impedance response, and proposes alternative distance protection settings focusing on solving the problem of line-to-line fault detection. It is proven that the algorithm covers 84% of the line length. However, faults in the central region have a high resistance characteristic and cannot be detected with the proposed method. The paper takes into account the influence of line transpositions that further affects the protection performance near central region. Transient analysis and software in the loop tests were performed with PSCAD/EMTDC.

Directional element evaluation applied to half-wavelength transmission lines

In this paper, a careful analysis of directional element behavior applied to a half-wavelength transmission line (HWL) is presented. Single line-to-ground (SLG) faults were applied, varying loading conditions and fault resistance. A commercial relay was used. Two directional elements were considered: 32QG and 32V. With the aim of obtaining directional element setting parameters, a Python program based on two-port network theory was developed. The simulations were also performed in a hardware-in-the-loop (HIL) environment. It was observed that only the element 32V operated properly throughout the system during SLG fault conditions. It can be concluded that the conventional directional element algorithm can be applied to a system with a half-wavelength transmission line under the above-mentioned fault condition.