Optimal uni-local virtual quantum broadcasting

Quantum broadcasting is a cornerstone in the realm of quantum information processing and characterizes the correlations within quantum states. Nonetheless, traditional quantum broadcasting encounters inherent limitations dictated by the principles of quantum mechanics. In this work, we introduce a novel protocol known as \textit{virtual quantum broadcasting} which focuses on broadcasting measurement statistics of a target state rather than the state itself. First, we propose a universal unilocal protocol enabling multiple parties to share the expectation value for any observable in any target bipartite state. Second, we formalize the simulation cost of a virtual quantum broadcasting protocol into a semidefinite programming problem. Notably, we propose a specific protocol with optimal simulation cost for the 2-broadcasting scenario, revealing an explicit relationship between simulation cost and the quantum system's dimension. Moreover, we establish upper and lower bounds on the simulation cost of the virtual $n$-broadcasting protocol and demonstrate the convergence of the lower bound to the upper bound as the quantum system's dimension increases. Our work paves the way for new approaches to distributing quantum information, potentially advancing quantum communication and computing technologies.Comment: 11 page

Characteristics of very fast transient currents in ultra high-voltage power system with hybrid reactive power compensation

Hybrid reactive power compensation (HRPC) consists of a stepped controlled shunt reactor (SCSR) and a series compensation (SC), which will find applications in future ultra high-voltage (UHV) power grids to resolve the problems due to the frequent change of reactive power and bulk power transmission. However, very fast transient currents (VFTCs) are inevitably generated during switching, which would lead to insulation breakdown. In the present work, we first develop the equivalent model for HRPC, following which we deduce the expression of VFTCs in the time domain by using an inverse Laplace transform. The analysis indicates that the amplitude and frequency of VFTCs are both affected by the capacitance of the SCSR and of the SC, as well as the line length, stray capacitance, etc. The oscillating frequency, peak, and amplitude of the main frequency of the VFTCs in the substation can be modified by adjusting the silicon-controlled rectifiers in the SCSR when the disconnecting switch in gas-insulated switchgear is switched on. When the disconnecting switch in the SC is switched on, the VFTC oscillation frequency in SCSR decreases with increasing stray capacitance of SC, but the frequency and peak of the VFTC remains quite large. Increasing the line length between the SC and the SCSR suppresses the VFTC in UHV power systems. These results lay the foundation for developing HRPC methods to suppress VFTCs in UHV substations

The generation and migration of bubbles in oil-pressboard insulation needle-plate system

Bubbles in transformer oil can easily lead to partial discharge, which can deteriorate the transformer oil and even breakdown the transformer insulation. To clarify the migration process and the characteristics of bubbles generated in an oil-immersed power transformer exposed to an extremely uneven electric field, we experimentally monitor these phenomena under an extremely nonuniform AC electric field and numerically simulate the migration distance and the migration speed of bubbles with different initial positions and sizes. The results show that the streamer discharge channel formed by a partial discharge in oil is gasified into a bubble channel. After it collides with the surface of the pressboard, its morphology is transformed into approximately spherical bubbles due to the surface tension of the gas-liquid interface. After bubbles are generated in the oil, they move away from areas with a strong electric field due to the electric-field force and gradually approach the oil surface due to the buoyancy force. The experimental results are consistent with the simulation results, which verify the rationality of the simulation model

Study on the breakdown characteristics of multiple-reignition secondary arcs on EHV/UHV transmission lines

A long-gap AC arc with a length of more than ten meters (secondary arc) are normally generated at the short-circuit arc channel after a single-phase-to-ground fault. In previous studies, arc breakdowns of secondary arcs have mainly been considered as electrical breakdowns, ignoring the role of heat in the arc channel. Besides, the extinction-reignition theory of secondary arc, i.e., dielectric strength recovery theory, still lack the support of experimental data. In this study, based on the equivalent experiments performed in the laboratory, the influences of compensation degree of transmission lines, initial recovery voltage gradient of air gap, test current, wind speed, and wind direction on the breakdown characteristics of secondary arcs are studied and statistically analyzed. The laws of the transient recovery voltage (TRV) and of the rate of rise of recovery voltage (RRRV) also studied by considering the influencing factors mentioned above. The results of this study will provide a more complete experimental basis for the theory of extinction–reignition of secondary arcs and a deeper understanding of the transient characteristics of arc breakdow

Circuit Breaker Rate-of-Rise Recovery Voltage in Ultra-High Voltage Lines with Hybrid Reactive Power Compensation

With the development of ultra-high voltage (UHV) technology, hybrid reactive power compensation (HRPC) will be widely applied in the future. To study the mechanism by which HRPC influences the characteristics of circuit breakers in UHV transmission lines, this paper establishes an improved electromagnetic coupling transmission line model for out-of-phase and short-line faults. Based on the HRPC equivalent model, a simulation analysis was performed on the characteristics of the circuit breaker when a fault occurs. Using an equivalent lumped parameter circuit, the rate-of-rise of recovery voltage (RRRV) computational formula was deduced and computed. The RRRV variation in the circuit breakers in the system, with and without HRPC, was obtained. Given the circuit breaker interruption characteristics, the research results provide an analysis foundation and a theoretical basis for optimizing the HRPC parameters and selecting the arrangements of circuit breakers in an UHV transmission line

Impact of the inductive FCL on the interrupting characteristics of high-voltage CB's during out-of-phase faults

With respect to power systems installed with inductive fault current limiters (FCLs), the impact of an FCL on the out-of-phase fault current level was first analyzed, and thereby a method for determining the critical length of the power transmission tie lines was also given. Based on theoretical analysis and deduction, strict mathematical formulas were obtained to properly describe the relationship between the current limit factor and the recovery voltage of a circuit breaker (CB) as well as the rate of rise of recovery voltage (RRRV). Further, the concrete impacts of an FCL on the maximum and the RRRV of the recovery voltage were analyzed. Regarding out-of-phase faults, a conception of interruption severity as well as its quantitative expression for CBs was introduced, and a formula was established to incorporate the influence from the current limit factor and stray capacitance on the interruption severity of CBs, subsequently followed by detailed investigations. The aforementioned proposed research presents analytical methodology and practical reference for the parameter optimization of the inductive FCL and reliable selection of the interrupting characteristics of the high-voltage CBs

Analysis and simulation of the PMFCL based on coupled-field circuit modeling methodology

Fault current limiter based on permanent magnet biased saturation (PMFCL) is believed to foresee considerable application potentials in power systems due to its obvious advantages both technically and economically. In this paper, a new equivalent model of the PMFCL is presented based on a coupled field-circuit modeling methodology. Firstly, the governing equations of the PMFCL are obtained based on equivalent magnetic circuit analysis. Then the analysis of magnetic field of the PMFCL is done by FEM. Finally, a coupled equation for the PMFCL is presented to be solved. The simulation results compared with that of prototype experiments indicate that, the proposed modeling scheme provides theoretical basis for further comprehensive optimization of the PMFCL

Natural Contamination and Surface Flashover on Silicone Rubber Surface under Haze–Fog Environment

Anti-pollution flashover of insulator is important for power systems. In recent years, haze-fog weather occurs frequently, which makes discharge occurs easily on the insulator surface and accelerates insulation aging of insulator. In order to study the influence of haze-fog on the surface discharge of room temperature vulcanized silicone rubber, an artificial haze-fog lab was established. Based on four consecutive years of insulator contamination accumulation and atmospheric sampling in haze-fog environment, the contamination configuration appropriate for RTV-coated surface discharge test under simulation environment of haze-fog was put forward. ANSYS Maxwell was used to analyze the influence of room temperature vulcanized silicone rubber surface attachments on electric field distribution. The changes of droplet on the polluted room temperature vulcanized silicone rubber surface and the corresponding surface flashover voltage under alternating current (AC), direct current (DC) positive polar (+), and DC negative polar (−) power source were recorded by a high speed camera. The results are as follows: The main ion components from haze-fog atmospheric particles are NO3−, SO42−, NH4+, and Ca2+. In haze-fog environment, both the equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) of insulators are higher than that under general environment. The amount of large particles on the AC transmission line is greater than that of the DC transmission line. The influence of DC polarity power source on the distribution of contamination particle size is not significant. After the deposition of haze-fog, the local conductivity of the room temperature vulcanized silicone rubber surface increased, which caused the flashover voltage reduce. Discharge is liable to occur at the triple junction point of droplet, air, and room temperature vulcanized silicone rubber surface. After the deformation or movement of droplets, a new triple junction point would be formed, which would seriously reduce the dielectric strength of room temperature vulcanized silicone rubber