Achieving efficient end-to-end file transfer is challenging in a narrow-band communication environment with high latency and high packet loss rate. The traditional TCP-based scheme and the UDP-based automatic retransmission scheme have defects in the transmission performance, which cannot meet the increasing user demands. This paper proposes a high-efficiency file transfer scheme based on random linear network coding and the Kalman filtering algorithm to implement efficient end-to-end file transfer in narrow-band environment. The scheme predicts the link quality of file transmission through the Kalman filter algorithm and designs an adaptive coding strategy for file transfer through random linear network coding. Experimental results show that the proposed method outperforms traditional file transfer schemes.

Sharing content, such as video, with others via personal mobile devices has become more and more popular. However, it tends to incur extremely high traffic fee to share large files in commercial networks. In this paper, we propose an efficient network-coding-based content sharing scheme (NCCSS) for mobile devices via WiFi Direct. When the file owner wants to share a file to others, it equally splits the file into multiple pieces, and then linearly encodes the pieces into segments with random linear network coding (RLNC). After that, it switches itself to an access point (AP), and waits to accept request from other devices. For each device in the network, it connects to the AP, and requests linearly independent segments. After it has received a fixed number of encoded segments, it switches itself to a new AP to enlarge the coverage of sharing. By strategically switching devices between the AP mode and ordinary mode, all devices could receive sufficient segments and recover the original file. NCCSS was evaluated in a real-world testbed consisting of 20 mobile devices. The experimental results show that compared to the traditional replication-based transmission scheme and erasure-coding-based transmission scheme, NCCSS could provide higher sharing rate.

Lithium iron phosphate batteries have become the main choice for energy storage units in electrochemical energy storage due to their high safety, excellent electrochemical performance, long cycle life, and environmental friendliness. However, lithium-ion batteries inherently have safety risks. The thermal runaway of a single battery in a closed space may cause a chain reaction of surrounding batteries, and may ignite the generated combustible gas, causing serious explosion accidents. In this paper, the explosion characteristics under different initiation points of pressure relief plates are studied. The results show that the peak overpressure variation range of different detonation points in the prefabricated chamber is 1∼1.6 times the hatch opening pressure, where the peak overpressure of the detonation at the near end of the hatch is lower than that of the detonation at the distal end, reflecting the role of the detonation when the explosion energy is released to the outside of the chamber earlier. The above study can provide a reference basis for the safe operation of prefabricated cabin type energy storage power plant and the promotion of its application.

为了提高电网作业安全管理能力,提出基于数据挖掘的电网作业安全管理系统设计方法.构建电网作业安全管理的信息化参数分析模型,构建电网作业安全管理的约束参数分析模型,以电网作业安全管理过程中的次日计划、历史小时输电数据、用户类型等参数为自变量,分析电网作业安全管理的控制约束参数模型,通过数据挖掘和大数据信息融合的方法,实现对电网作业安全管理的自适应调度和特征融合处理,提取电网作业安全管理的可靠性特征参量,采用嵌入式的数据库和模型库设计,实现对电网作业安全管理系统的优化设计.仿真结果表明,采用该方法进行电网作业安全管理的输出稳定性较高,电网作业安全管理的智能性和信息化水平较好.

When the AC fault occurs in the power grid,the protection of unified power flow controller (UPFC) would trip to make the UPFC out of operation.It would cause the electrical quantities in the power grid change suddenly once again.Subsequently,the competition between the disturbance caused by AC fault and that caused by the trip of UPFC protection would have adverse influence on the transmission line pilot protection.The demonstrative project of UPFC in the western Nanjing grid is introduced.Moreover,based on the discussion about the UPFC protection system,the impacts of UPFC on the performances of pilot zero-sequence protection,pilot distance protection and superimposed component direction protection are studied with theoretical analysis and simulation study.It points out that the mal-operation or fail-to-trip of the superimposed component direction protection would oceur due to the impact of UPFC,and it is necessary to improve the relevant protection schemes.

In this paper, the structure and the fast fault isolation technique of UPFC is introduced firstly, and then a coordination strategy of UPFC control protection system and power grid protection is put forward for improving fault ride-through capability. Based on comprehensively analyzing UPFC control protection system operation, AC protection operation, power gird status and switch position, the most appropriate operation mode of UPFC such as shutdown, switching mode or restarting to the original mode is determined, and that is executed coordinating with AC protection operating by the strategy. As the part of the strategy, the discrimination principle and implementation method of the strategy are represented in detail. The strategy is verified in system commissioning and operation of Western Nanjing 220kV power grid UPFC project and closing-loop test for control protection system of Southern Suzhou 500kV power grid UPFC project. The result shows that the strategy can further improve UPFC fault ride through capability.

Due to the special topology and interconnection mode to the power network, the start-up testing method for conventional transformer will be not fit to series transformer in UPFC project. For the construction of a practical UPFC project, a feasible method for series transformer starting is proposed in this paper, and its implementation step is designed. With this method, series transformer energizing and switching, phase sequence verifying, protection testing and thyristor by-pass switch (TBS) checking can be accomplished in the system testing stage of UPFC. More, the temporary protection configuration scheme is provide. Finally, the electromagnetic transient simulation is carried out for the above test procedure to verify the practicability and safety of the method.

Due to the limited land resource, T-connection lines whose rated voltage are not larger than 110kV are more and more popular in the distribution network. However, it is found that the quickness and selectivity of the conventional relay protection cannot be both satisfied when it is employed in the T-connection lines. Based on the detailed analysis on the existing protection configuration, the optimized protection configuration scheme of the T-connection lines is proposed, which includes the unidirectional blocking based pilot protection principle and the inter-substation communication solution. Subsequently, the novel protection device is developed, and the functions and performance are tested with the closed loop test system built in the environment of RTDS. The test results validate the excellent performance and reliability of the novel protection device.

保护用电流互感器(TA)的性能优劣直接影响保护装置的动作行为和电力系统的运行安全,而检验其性能是否满足运行要求的最有效方法是对保护用电流互感器开展励磁特性试验.文中介绍了工频法、变频法和直流法等几种常用的励磁特性试验方法及其优缺点,并指出需采用变频法对1000 kV套管电流互感器进行励磁特性试验.最后介绍了特高压输变电工程中1000 kV套管电流互感器的励磁特性试验方案,并以1000 kV气体绝缘全封闭组合电器的套管电流互感器的励磁特性试验为例,对现场试验数据和被测电流互感器的性能进行了分析.

The wide application of power electronic equipment results in severe non-sinusoidal phenomena, making the conventional steady-state reactive power theory no more applicable. In order to deal with the harmonic compensation and power factor correction under the non-sinusoidal condition, scholars have carried out lots of research works. This paper discusses and compares several commonly used instantaneous reactive power theories, and pointes out the relationships and differences of them. The work of this paper contributes to better understanding of the instantaneous reactive power theories.

Upon grid fault, controller's reference signals of photovoltaic (PV) grid-connected inverter change abruptly, causing controller to operate in non-linear area. Consequently, the fault current transient features of PV power generator are very complicated. On condition that controller operates in both linear or non-linear areas, fault current transient features of PV power generator and their impact factors are studied in this paper. Based on it, applicability of treatment approach of equivalently replacing PV power generator with its steady-state fault current model for fault analysis is pointed out.

概述了南京西环网统一潮流控制器(UPFC)继电保护配置情况及动作策略,在分析UPFC接入后对交流保护影响的基础上,优化了南京西环网UPFC线路保护配置.分析了UPFC保护与交流保护配合策略,并阐述了南京西环网UPFC保护与各类交流保护动作配合原则.作为国内首套UPFC工程,南京西环网UPFC的保护系统配置与动作策略为后续柔性输电系统保护的研究和应用提供了指导与借鉴.

For the Y/Δ converter transformer in the converter station, the transformer has only two windings, and the on load test cannot be implemented to test the polarities of current transformers' (CTs') secondary loops. In order to fill this gap, a novel polarity determination method for the CTs of the Y/Δ converter transformer is presented in this paper. Firstly, the configurations of CTs and relay protections for converter transformer are introduced. Besides, the characteristics of the inrush currents caused by charging the converter transformer is also analyzed. Based on that, a polarity determination method of CTs is proposed. The impact of harmonics on the on-load test data of the converter transformer can be effectively avoided with the proposed method. The proposed approach is validated with the on-load test data of the practical converter transformer.

Synchronous sampling data is considered as a basic condition for correct operation of all kinds of differential protections in a substation. It is necessary to test it in the substation commissioning procedure. This paper first addresses the root causes of synchronization problems and the necessity of onsite synchronization test for line differential protections and all distributed sampling differential protections in a smart substation. Then a method based on precise time-setting is proposed to test sampling synchronization of differential protections, which can solve difficulties of on-site synchronization test of distributed electrical data. Specific implementations are given and the causes of error are also analyzed in this paper. In a real 500kV smart substation project, error of data synchronization is controlled under 1.5 ° by testing line differential protections and the whole sampling circuit based on the method, which entirely meets the performance requirements of differential protections.

随着信息技术的发展,电网运行信息、故障信息及一次设备状态监测信息逐步开始融合,为实现基于多数据源信息的故障诊断与应用提供了前提依据,文中提出了一种利用雷电定位信息进行电网故障分析的信息综合处理方法.首先从整体上剖析了现有电网故障信息系统与雷电定位系统的基本构成和数据特征,在此基础上应用分阶段故障分析的思想,设计了使用雷电定位信息进行故障分析的流程,并提出数据融合与处理方法.最后,以某电网220 kV线路实际故障为例,对该故障诊断算法和方法和流程进行说明,并验证其有效性.

With the increasing capacity, decreasing saturation magnetic flux of transformer and remanence produced by DC resistance testing, the ultra-saturation phenomena will be induced in transformers. In this situation, magnetizing inrush current generated by transformer will tend to a sinusoidal waveform. The differential protection based on second harmonic restrained method and principle of dead angle will be no longer applied due to second harmonic component and dead angle is too small. An intelligent adaptively algorithm to identify magnetizing inrush based on the difference between 2 times fundamental wave phase angle and second harmonic phase angle, and aperiodic component is put forward by analyzing the ultra-saturation phenomena in transformers. The algorithm firstly determines whether the current has the character of magnetizing inrush or not intelligently by calculating the difference between 2 times fundamental wave phase angle and second harmonic phase angle. And then, second harmonic component is increased adaptively by aperiodic component to guarantee protection block if the character exists; otherwise, second harmonic component is decreased by another fixed ratio to guarantee protection operation. This algorithm identifies ultra-saturation magnetizing inrush much more quickly and exactly compared with the algorithms in the past. And it can make the protection have a faster operation speed when the transformer has internal fault. Dynamic simulation experiment proves its validity and superiority. The algorithm can block the differential protection reliably even when second harmonic component is less than 8%.

For HVDC converter station, a 12-pulse converter transformer is composed of six single-phase two-wing transformers generally, which are connected as Y0, y and Y0, d11 3-phase structure respectively. The two 3-phase transformers are parallel accessed to AC bus. Combined with the building and analyzing on the electric equivalent circuit, the theory researching on mechanism and characteristic of zero-sequence inrush current as 12-pulse converter transformer energizing in detail, and the distribution principle of the zero-sequence inrush current is laid out. With an energizing failure event of converter transformer in Zhengping converter station of ±500kV Three-Gorges HVDC project, the conclusion on zero-sequence inrush current of converter transformer is verified, which can explain the cause of converter transformer protection tripping.

直流系统的可靠对于变电站的安全运行至关重要.文中针对一起区外故障下线路保护动作事件,阐述了该故障分析思路和排查方法,通过对直流监测系统动作信息、保护录波图进行分析,确定故障原因是由于单个蓄电池内部故障引发的故障范围扩大,最后针对存在的缺陷提出了整改和防范措施.

In the testing of commutation station,the polarity and transformation ratio of CT need to be obtained by measuring the current magnitude and phase of the second side of CT.In this paper,calculation method of reactive power when transmitting different active power is inferred,of which the rightness is verified by testing data in the case of Zhengping commutation station.Calculation method of the second side of CT of converter transformer is proposed.Rightness of CT polarity and transformation ratio is confirmed by comparison with current value and calculated value of the second side of CT of testing data when transmitting 10% of nominal active power.

This paper analyzes the process of zero-sequence direction relay mal-operation of a double parallel 500 kV and 220kV lines after a fault occurred at the end of the 500 kV line. The mechanism is studied, which shows that the mal-operation is caused by the zero-sequence mutual inductance between multi-transmission lines. In the case of grounding fault occurred at one of parallel line, the existence of zero-sequence mutual inductance would activate the zero-sequence direction relay of the other line. The conclusion of this paper will provide a valuable reference for similar faults analysis.