Number Of Transmission Lines Research Articles

A tight compact quadratically constrained convex relaxation of the Optimal Power Flow problem

In this paper, we consider the Optimal Power Flow (OPF) problem which consists in determining the power production at each bus of an electric network by minimizing the production cost. Our contribution is an exact solution algorithm for the OPF problem. It consists in a spatial branch-and-bound algorithm based on a compact quadratically-constrained convex relaxation. It is computed by solving the semidefinite rank relaxation of OPF once at the root node of the algorithm. An important result is that the optimal value of our compact relaxation is equal to the rank relaxation value. Then, at every sub-nodes of our branch-and-bound, the lower bound is obtained by solving a quadratic convex problem instead of an SDP. Another contribution is that we add only O(n+m) variables that model the squares of the initial variables, where n is the number of buses in the power system and m the number of transmission lines, to construct our relaxation. Then, since the relations between the initial and auxiliary variables are non-convex, we relax them to get a quadratic convex relaxation. Finally, in our branch-and-bound algorithm, we only have to force a reduced number of equalities to prove global optimality. This quadratic convex relaxation approach is here tailored to the OPF problem, but it can address any application whose formulation is a quadratic optimization problem subject to quadratic equalities and ring constraints. Our first experiments on instances of the OPF problem show that our new algorithm Compact OPF (COPF) is more efficient than the standard solvers and other quadratic convex relaxation based methods we compare it with.

Fault location observability rules for impedance-based fault location algorithms

Various impedance-based fault location algorithms have been presented in the related studies. The algorithms need some phasor data of the power system provided by phasor measurement units (PMUs), implying the necessity of PMU placement to attain fault location observability. This paper develops fault location observability rules associated with some important impedance-based fault location algorithms based on known state observability theories. The algorithms include two-ends measurements, one-end measurements, one bus space, only synchronized voltage measurements, and wide-area measurements. The developed rules are used to obtain an index that indicates the number of transmission lines that fault location on them is not possible. The index forms a main constraint or a part of the objective function for the defined PMU placement problem to determine the optimal placement of PMUs for state estimation observability and fault location observability. The proposed rules and optimization problem are applied to IEEE 14, 30, 39, and 57 buses test networks to study different scenarios.

영동권 실 계통 PMU 측정정보를 활용한 울진, 삼척 산불 시 SSR 위험성 검토

The role of the power grid in the power system is to transmit the power produced at the power generation sites to the demand sites without interruption. When a new power source plan is established, a new power grid plan is also established so that necessary power grid construction is carried out at an appropriate time. However, the construction of a new power grid is not easy due to the problem of location selection and economic reasons. For this reason, efforts have been made for a long time to find ways to increase the capacity of the grid to avoid the construction of the new grid. A typical one of them is a method of increasing power transmission capacity by compensating the series capacitive impedance of the power transmission network. Therefore, KEPCO, in response to the delay in the construction of a new power grid for the construction of a large-scale power generation complex in the Yeongdong area, it was decided to increase the power transmission capacity of the existing power grid through series capacitive impedance. However, there is a risk that such an increase in transmission capacity through impedance compensation may cause problems such as sub synchronus resonance (SSR). In case of SSR, occured when the resonance frequency of the impedance-compensated power grid coincides with the mechanical resonance frequency of the nearby generator, and if a mechanical burden is accumulated on the generator shaft, the shaft may break. For this reason, the power authorities reviewed the risk of SSR and installed thyristor controlled series capacitor (TCSC) based on the results to avoid dangerous frequency bands by adjusting the apparent impedance of the impedance-compensated transmission line. In this way, the risk of SSR was responded to through sufficient preparation for impedance compensation. However, in the case of wild fires in Uljin and Samcheok, which occurred in March 2022, a number of transmission lines were opened, and the network topology between the compensation line and the nearby generator approached the condition of SSR, increasing the risk of resonance. This paper analyzes the risk of actual SSR based on the system configuration during wildfires in Uljin and Samcheok and the system operation information obtained through the Phase Measurement Unit (PMU) located nearby sites.

Lightning Protection of the Explosion Airflow Arc-Quenching Gap for 110 kV Transmission Lines

With the increase in the voltage level and number of transmission lines, the probability of lightning strikes on transmission lines is significantly increased, while lightning breakage accidents occur frequently. Therefore, an explosion airflow arc-quenching gap for 110 kV transmission lines was developed based on the idea of rapid extinction. A mathematical model of the detonation wave based on the CJ (Chapman–Jouget) detonation wave theory was developed to calculate the detonation air pressure and analyze its influencing factors. ANSYS software and the magnetohydrodynamic (MHD) model were used to simulate the process of detonation airflow coupled with an arc, and the simulation results indicated that the power frequency arc was evidently suppressed with the influence of airflow, which can effectively prevent arcing. A combined impulse and power frequency test and arc-quenching tests were performed to verify the effectiveness of the arc-quenching gap. The results of the combined test indicated that the arc burn time was 0.1 ms and that no power frequency continuous current was displayed. The results ensured the accuracy of the simulation model. The results of the arc-quenching tests proved that the explosion airflow can extinguish a power frequency arc with an amplitude of 40 kA in half of a power frequency arc cycle.

ПОРІВНЯННЯ СТРУМІВ КОРОТКОГО ЗАМИКАННЯ ЕЛЕКТРИЧНОЇ МЕРЕЖІ 6(10) кВ та 20 кВ

The reasons for such violations are various: aging of insulation, breakages of wires of overhead transmission lines, mechanical damages of isolation of cable lines at ground works, lightning strikes in the transmission line and others. Most often, short-circuits occur through transient resistance, such as through the resistance of an electric arc that occurs at the point of damage to the insulation. Sometimes there are metallic short circuits in which the resistance of the electric arc is very small. The study of short circuits in the power grid is a major step in the design of modern electrical networks. The research is conducted using computer software, first by modeling the system and then simulating errors. A malfunction usually leads to an increase in the current flowing in the lines, and failure to provide reliable protection can result in damage to the power unit. Thus, short-circuit calculations are the primary consideration when designing, upgrading, or expanding a power system. The three-phase short circuit is the least likely. However, in many cases, the three-phase short circuit is associated with the most severe consequences, as it causes the highest power imbalances on the shafts of the generators. The study of transients begins with the mode of three-phase closure due to its relative simplicity in comparison with other types of asymmetry. In most cases, the analysis and calculation of the transient regime of the electrical system involves the preparation of a calculated scheme of substitution, in which the parameters of its elements are determined in named or relative units. The electrical substitution circuitry is used to further study the transients in the power system. The definition of electrical and electromagnetic quantities in relative units is widely used in the theory of electric machines. This is because it significantly simplifies the theoretical calculations and gives the results a generalized view in the practical calculations of currents and residual voltages at the short circuit. By the relative value of any value is understood as its relation to another value of the same name, taken as the base. So, before presenting any quantities in relative units, we need to choose the basic units. In the electrical system with increased voltages, the overall load capacity of the network increases, which in turn makes it possible to supply high-quality electrical energy over a greater distance. In the process of comparing the type of transmission lines, it should be noted that the advantages of the cable transmission line. According to the results of the calculation of short-circuit currents, it can be concluded that in networks with a larger line cross-section and a higher voltage, the short-circuit currents are larger. Thus, during the transition of the electric networks to the higher voltage class of 20 kV, the currents of the KZ increased by 43% compared to the 6 kV electric network. This analysis shows that the importance of reliable power supply in the power supply system for high voltage classes must be high and have equipment to prevent emergencies. In the future, it is planned to develop a systematic calculation of short-circuit currents for a number of transmission lines and to conduct mathematical modeling in the system of applications for the study of transient processes at short circuits

Worst-Case Load Shedding in Electric Power Networks

We consider the worst-case load-shedding problem in electric power networks where a number of transmission lines are to be taken out of service. The objective is to identify a prespecified number of line outages that lead to the maximum interruption of power generation and load at the transmission level, subject to the active power-flow model, the load and generation capacity of the buses, and the phase-angle limit across the transmission lines. For this nonlinear model with binary constraints, we show that all decision variables are separable except for the nonlinear power-flow equations. We develop an iterative decomposition algorithm, which converts the worst-case load-shedding problem into a sequence of small subproblems. We show that the subproblems are either convex problems that can be solved efficiently or nonconvex problems that have closed-form solutions. Consequently, our approach is scalable for large networks. Furthermore, we prove convergence of our algorithm to a critical point, and the objective value is guaranteed to decrease throughout the iterations. Numerical experiments with IEEE test cases demonstrate the effectiveness of the developed approach.

Near-lossless compression/decompression algorithms for digital data transmitted over fronthaul in C-RAN

The cloud radio access network (C-RAN) is not only a very important deployment solution for the future RAN but is also a core platform for network-centric advanced transmission techniques such as coordinated multi-point transmission and reception and the distributed antenna system. One of the main issues when implementing C-RAN at low cost and high efficiency is the need to reduce the implementation cost of the fronthaul and improve its usage efficiency. In order to achieve this, in this paper, near-lossless compression and decompression algorithms for digital data transported via fronthaul in C-RAN are proposed, where the compression is mainly achieved through the removal of various redundancies in wireless communication signals. Since the proposed algorithms significantly reduce the amount of data that should be transmitted via fronthaul while maintaining negligible in-band distortion in terms of error vector magnitude (EVM), we can actually reduce the number of transmission lines or enhance the utilization of them. In addition, they can be operated with a minimum compression ratio as well as a constant compression ratio; therefore, real-time processing and fronthaul data-muxing can be easily performed. Simulation results and comparisons have been carried out based on the 3rd generation partnership project long-term evolution system and the common public radio interface, which is a publicly available specification that is widely utilized to implement the fronthaul. Simulation results confirm that the proposed schemes can provide remarkable compression performance with a zero uncoded bit error rate and negligible signal distortion. Finally, the proposed schemes have various parameters that can be adjusted to meet given requirements such as latency, the compression ratio, EVM, complexity, and so on, and thus a smooth tradeoff between them can be achieved.

The Comparative Study on Influence on the Northeast China UHV Planning Power Grid Induced by Different Kind Geomagnetic Storms

Along with the UHV construction scheme, China will form a large number of transmission lines which have the characteristics of the ultra-high voltage, large-capacity, long-distance. Because the UHV power grid transmission line parameters and the structure of the grid and the transformer are different from the other power net, Geomagnetic storms will affect the UHV power grid more, the work have important significance to the assessment of the ultra-high voltage power grid level and influence. The impact of different storms on the grid are also different .Based on the power flow mechanism of the GIC, different data and network parameters of geomagnetic storms, the evaluation model of the GIC is established ,we assess the result of the GIC induced by the geomagnetic storms happened on November 2004 and December 2006 in the 2020 planning ultra-high voltage power grid, find out the greatest impact transformer substation and the timing analysis results of the grid compare the different impact of different storm.. The comparison of the analysis results is helpful for understanding the different kind geomagnetic storms and the regional features of GIC.

Fault Current-Division Factor of Substation Grounding Grid in Seasonal Frozen Soil

The determination of the maximum ground fault current, which has a close relation to the maximum hazardous step-and-touch voltage, is essential for the safety of a substation. Seasonal frozen soil changes the grounding resistances of the substation grounding grids and the tower footing devices, which seasonally influences the maximum grid current. This paper first introduces the method to calculate the fault current-division factor, and then discusses the influence of the seasonal frozen soil layer on it by using the proposed method. Based on the cases of two substations connected by the transmission lines and without neutrals or other connection paths, the influence of several factors on the fault current-division factor, including the thickness of seasonal frozen soil, and the number of transmission lines with overhead ground wire connected to the substation grounding grid, is analyzed. It is reasonable to consider the influence of the seasonal frozen soil on the fault current-division factor in grounding grid design. According to the analysis, adding vertical grounding rods to the grounding grid and the tower footing grounding device can almost eliminate this seasonal influence.

Improvement of transient stability by NAS battery system installation on a generator bus

Recently, because of the introduction of renewable energies, the electric power system has become larger and more complex. Under such environment, the number of transmission lines has increased, on which heavy-load currents flow, and as the result, the transient stability has emerged as a significant problem. In this paper, we propose a smart approach in which we use the NAS battery system on a generator bus for improving transient stability, and determine the output of NAS battery system by the LQR control theory. Finally, we verify the effects of the proposed method for the transient stability on the IEEJ EAST 10-machine 47-bus system model.

Equivalent for Electromagnetic Transient Calculation in Power System with Multiple Transmission Line

The results of searching of equivalent for electromagnetic transient calculation in power system with the big number of transmission lines are shown. Brief information on the proper transmission line model is given. Comparison of results of simulation in real and reduced system is presented taking into consideration three methods of identification. Some example are examined for different number of transmission lines in reduced system and consequently the recommendation are given for searching of equivalents of systems with many lines.

ECRH-Related Technologies for High-Power and Steady-State Operation in LHD

The electron cyclotron resonance heating (ECRH) system on the Large Helical Device (LHD) has been in stable operation for ~11 yr in numerous plasma experiments. During this time, many upgrades to the system have been made, such as reinforcement of the gyrotron tubes, modification of the power supply depending on gyrotron type, and increase in the number of transmission lines and antennas. These efforts allow the stable injection of millimeter-wave power in excess of 2 MW. In parallel, various transmission components were evaluated, and antenna performance was confirmed at a high power level. The coupling efficiency of the millimeter wave from the gyrotron to the transmission line and the transmission efficiency through the waveguide were further improved in recent years. The feedback control of the wave polarization has also been tried to maximize the efficiency of wave absorption. The gyrotron oscillation frequency was reconsidered in order to extend the flexibility of the magnetic configuration in plasma experiments. The development of 77-GHz gyrotrons with the output of 1 MW per few seconds in a single tube is currently taking place in collaboration with the University of Tsukuba. Two such gyrotron tubes already have been installed and were used for plasma experiments recently. An ECRH system with a capability of the steady operation is required, because the LHD can continuously generate confinement magnetic fields using superconducting magnets. Not only the gyrotron but also the transmission system and components must withstand continuous power operation. Further acceleration of both the power reinforcement and a steady-state capability will allow the sustainment of high-performance plasmas.

Severe Multiple Contingency Screening in Electric Power Systems

We propose a computationally efficient approach to detect severe multiple contingencies. We pose a contingency analysis problem using a nonlinear optimization framework, which enables us to detect the fewest possible transmission line outages resulting in a system failure of specified severity, and to identify the most severe system failure caused by removing a specified number of transmission lines from service. Illustrations using a three-bus system and the IEEE 30-bus system aim to exhibit the effectiveness of the proposed approach.

Phase-Encoding for On-Chip Signalling

A novel self-timed communication protocol is based on the phase-modulation of a reference signal. The reference signal is sent on a number of transmission lines and the data can be recovered observing the sequence of events on the these lines. Employing several lines increases the number of states hence reducing the number of symbols required for a transmission. A new encoding algorithm is described which generates symbol-dependent matrices which are used to control the phase of transmission lines. The protocol concept, the algorithm and analysis of the system, together with simulation results, are presented.

An N‐bit digitally variable ultra‐wideband pulse generator for GPR and UWB applications

AbstractThis paper presents a low‐cost ultra‐wideband (UWB) pulse generator that can vary the pulse duration digitally by using a step‐recovery diode (SRD), microstrip transmission lines, and PIN diodes. First, a sharp edge is generated by using SRD circuitry. Then a pulse is formed from the sharp edge through the use of transmission lines and the PIN diodes. Based on the number of transmission lines (N), the duration of the pulse can be varied in 2N steps. The UWB pulse generator circuits are implemented on an FR‐4 substrate using microstrip‐line technology and UWB pulses with durations of 550 to 2400 psec are measured. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1334–1339, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21620

Multiple-sample probe for solid-state NMR studies of pharmaceuticals

Solid-state NMR spectroscopy (SSNMR) is an extremely powerful technique for the analysis of pharmaceutical dosage forms. A major limitation of SSNMR is the number of samples that can be analyzed in a given period of time. A solid-state magic-angle spinning (MAS) probe that can simultaneously acquire up to seven SSNMR spectra is being developed to increase throughput/signal-to-noise ratios. A prototype probe incorporating two MAS modules has been developed and spectra of ibuprofen and aspirin have been acquired simultaneously. This version is limited to being a two-module probe due to large amounts of space required for the tuning elements located next to the MAS modules. A new probe design incorporating coaxial transmission lines and smaller MAS modules has been constructed. This probe allows for close proximity of the MAS modules (within 3 cm), adequate proton decoupling power (>50 kHz), and the capability of remote tuning and sample changing. Spectra of hexamethylbenzene (HMB) have been acquired and show signal-to-noise ratios comparable to existing SSNMR probes. Adamantane line widths are also comparable to conventional probe technology. Decoupling powers of 70 kHz have been achieved using a MAS module suitable for 3 cm spacing between modules. Remote tuning has also been achieved with this new coaxial transmission line design. This probe design can be easily scaled to incorporate multiple MAS modules, which is a limitation of the previous design. The number of modules that can be incorporated is only limited by the number of transmission lines that will fit in a cross-sectional diameter of the bore and the axial field length of the magnet.

Calculation of the loss‐minimum configuration in the IEEJ local power system model

AbstractIn Japan, local power systems (77 kV) are served from the 275‐ or 154‐kV substations. For enhancement of power supply reliability, the transmission lines are connected to several substations, and the operational configuration is radial. The local power system's configuration is determined by connecting and disconnecting transmission lines so as to keep the radial structure and satisfy the operation constraints. When a local power system has a number of transmission lines, many configuration candidates occur. Recently, an IEEJ committee made a practical scale local system model (IEEJ Local System Model). Since the IEEJ Local System Model has 76 transmission lines, the total number of configuration candidates is 276 (approximately 7.5 × 1022). In this paper, the authors try to strictly obtain the loss‐minimum configuration under constraints such as substation capacity, line capacity, and radial structure in the IEEJ Local System Model. In order to obtain the optimal configuration, a new computation algorithm is proposed. In the proposed algorithm, the configuration determination problem is replaced as two combinatorial optimization problems based on the operational constraints [(1) substation capacity, (2) line capacity, and (3) radial structure]. One combinatorial optimization problem (subproblem 1) is to pick up all partial configurations so as to minimize total line loss under the substation capacity constraint. By using the enumeration method, subproblem 1 is solved. Subproblem 2 is solved by using the reduced ordered binary decision diagram (ROBDD). Since the proposed method is based on enumeration and Boolean function, the optimality of obtained solution is guaranteed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 34–42, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10226

Multi Objective Evaluation for Local Power System Configuration Based on Deterministic and Probabilistic Approaches

Local power systems (66kV) are served from the 275kV or 154kV substations. In order to maintain power supply reliability, the transmission lines are connected to several substations, and the operational configuration is radial. Since practical local power system has a number of transmission lines, many configuration candidates occur. It is expected to effectively evaluate these configuration candidates from various viewpoints such as reliability of power supply, transmission loss and so on. In this paper, the authors propose a multi objective evaluation method by using deterministic and probabilistic approaches for local power system configuration. In the proposed multi objective evaluation method, after selecting system configuration candidates which satisfy N-1 security by using an optimization method based on Boolean function, these candidates are evaluated from viewpoints of expected outage time, transmission loss and facility operation rate. In order to check the validity of the proposed method, numerical results are shown for a practical local system model with about 39 × 1027 configuration

A pulse voltage multiplier

A pulse voltage multiplier is presented. The device consists of a set of transmission lines connected in parallel at the entry and connected in series at the end. The multiplication factor can become equal to twice the number of transmission lines, depending on the conditions at the entry of the device.

Order-recursive Gaussian elimination (ORGE) and efficient CAD of microwave circuits

Planar circuit elements in millimeter-wave integrated circuits (MMIC's) typically consist of one or more discontinuities (e.g. stubs) connected to a number of transmission lines. In the computer-aided design (CAD) and optimization of such passive elements using the method of moments, it is necessary to iteratively simulate many subproblems involving dimensional changes to various parts of the circuit. On examining the simulation problem closely, it can be seen that there is a considerable overlap of data in various subproblems. In practice, each subproblem is solved independent of others, without taking into account the duplication of data. This leads to an inefficient design technique. In this paper, we present a design technique that effectively exploits the duplication of data by employing a recursive variant of Gaussian elimination, called order-recursive Gaussian elimination (ORGE). The potential utility of ORGE in microwave circuit simulation and CAD is demonstrated by applying it to the design of a microstrip filter.