Adaptive restart scheme based on active injection current ratio for half-bridge MMC-HVDC with overhead transmission lines

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jingru Zhang ◽  
Baina He ◽  
Renzhuo Jiang ◽  
Xingmin He ◽  
Yanchen Dong ◽  
...  
Keyword(s):  
Transmission Lines ◽  
Short Circuit ◽  
Stable Operation ◽  
Multilevel Converter ◽  
Dc System ◽  
Critical Segment ◽  
Protection Devices ◽  
Suppression Strategy ◽  
Auxiliary Module ◽  
Action Decision

Abstract Modular multilevel converter for high voltage DC system has great potential as the key role in global energy interconnection. Adaptive reclosing or restarting after suffering from short-circuit faults is a critical segment to realize safe and stable operation. An adaptive restart scheme for the half-bridge sub-module transmission system is proposed, which is based on the active current injection of the auxiliary fault discriminate module. Combined with the engineering experience, the transient characteristics of the line current during the fault restart stage are analyzed. The ratio of the current peaks at both ends of the fault point is used as the criterion. Moreover, the restart current suppression strategy is introduced into the adaptive restart scheme. It provides a decision-making basis for discriminate the property of the fault and improves the success rate of fault restart. The simulation results show that after the external auxiliary module is introduced into the adaptive restart stage, the restart current does not exceed the rated value. Finally, The permanent fault and the transient fault can be successfully distinguished, providing a reliable guarantee for the subsequent action decision of the protection devices.

scholarly journals Short circuit fire risk assessment in investigating and examining fires caused by emergency modes in overhead transmission lines

2022 ◽  
Vol 6 (4) ◽  
pp. 363-368
Author(s):  
Yu. S. Kozlova
Keyword(s):  
Transmission Lines ◽  
Fire Hazard ◽  
Short Circuit ◽  
Electric Power System ◽  
Ignition Source ◽  
Electrical Network ◽  
Fuel Load ◽  
Overhead Transmission Lines ◽  
Protection Devices ◽  
Short Circuits

Emergency modes (short circuits) in electric power system and equipment are the main technical cause of fires. However, it is not always possible to prove the involvement of a particular operating mode in a fire. The fire hazard can be due to three components: a fuel load, an oxidizer and an ignition source. Since overhead transmission lines are used in an open space, they are oxidized. The presence of a fuel load is confirmed by a fire. The source of ignition should be identified. The aim of the study is to develop an algorithm for assessing the fire hazard for short circuits in overhead transmission lines with 1000 V. The study was conducted using scientific analysis, physical experiment and simulation. The ignition source is due to the appearance of an energy source with parameters sufficient to ignite a fuel load. The probability of ignition in overhead line wires depends on the probability of occurrence of the short circuit itself  ( Qi (v1) ) , the probability of failure of protection devices  ( Qi (v2) ), and the probability that the electric current value in the event of a fault is in the range of fire hazard values (Qi(z)). The values of the first two components are determined on the basis of statistical data, taking into account the theory of reliability. The third component is based on the experiment results. The experimental studies made it possible to establish the ranges of fire hazard values for uninsulated aluminum wires of various cross-sections, thereby providing the possibility of calculating ( Qi (z). Using the data obtained and information about the nature of changes in short-circuit currents and performance characteristics of protection devices, depending on the line length, an algorithm for assessing the fire hazard for a short circuit was developed. The results make it possible to assess the fire hazard for short circuits in various sections of the electrical network, made by overhead transmission lines, and to establish the involvement of sparks generated by short circuits in a fire

scholarly journals Short-Circuit Fault Current Calculation Method for the Multi-Terminal DC Grid Considering the DC Circuit Breaker

Energies ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1347
Author(s):  
Haipeng Jia ◽  
Jingyuan Yin ◽  
Tongzhen Wei ◽  
Qunhai Huo ◽  
Jinke Li ◽  
...  
Keyword(s):  
Calculation Method ◽  
Short Circuit ◽  
Circuit Breaker ◽  
Fault Current ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Dc System ◽  
Short Circuit Calculation ◽  
Dc Circuit Breaker ◽  
Short Circuit Fault

The analysis and calculation of the short-circuit fault current in the DC grid is of great significance to the design and configuration of the converter station and DC circuit breaker parameters. The existing flexible DC system not only includes the modular multilevel converter (MMC) converter, but also needs power equipment such as the fault current limiter and DC circuit breaker. Therefore, the system modeling and short circuit calculation of the multi-terminal DC system after adding the DC circuit breaker are also of great significance for the design of DC power system parameters and the grid troubleshooting ability. In this paper, firstly, the parameters of the four-terminal DC system of the modular multilevel converter (MMC) are simplified, and the analytical solution of the short circuit fault current of the multi-terminal DC system is given. Then, the external characteristics of the cascaded hybrid DC circuit breaker are modeled. Based on the equivalent circuit of the fault current in different stages, the short circuit calculation method of four-terminal MMC system with DC circuit breaker is obtained. This method can effectively describe the overall trend of fault current and provide the basis for the configuration of DC line protection settings and DC circuit breaker related parameters.

Mechanisms of High Efficiency and Stabilization of Baffled Constructed Wetland in Treatment of Domestic Sewage

2013 ◽  
Vol 295-298 ◽  
pp. 1057-1061 ◽  
Author(s):  
Chang Bing Ye ◽  
Zhi Ming Zhou ◽  
Ke Zhao ◽  
Qin Liu
Keyword(s):  
Constructed Wetland ◽  
Removal Rate ◽  
Short Circuit ◽  
Domestic Sewage ◽  
Wetland Plants ◽  
Stable Operation ◽  
Removal Rates ◽  
Operational Life ◽  
High Efficient ◽  
Hydraulic Load

To solve the problem of short-circuit of individual current constructed wetland, a baffled constructed wetland was designed and applied to treat domestic sewage by our research group. The wetland plants were composed of Eichhormia crassipes, Oenanthe javanica, Cyperusalternifolius, Phragmites communis and Aquatic. The results of 18 month indicated that the optimal hydraulic load of baffled constructed wetland was 2.0~2.2 m3/(m2•d). At the hydraulic load of 2.0m3/(m2•d), the COD, TN and TP removal rates of baffled constructed wetland could be over 76.40%, 76.12%, 65.37%, respectively, at 24°C. When the temperature decreased to 12°C, the COD, TN, TP removal rates of system decreased to 67.56%、62.75% and 61.33%, respectively; The SS removal rate of the first 6 compartments was about 79.5% and that of system could maintain 87.18% during the operation of system. Based on the results of trial, the mechanisms of extending the baffled constructed wetland's operational life was owed to high efficient SS removal rate of the first 6 compartments which was used as constructed wetland and anaerobic baffled reactor (ABR). As a result, the long-term stable operation of system in treatment of domestic sewage was explained with extending about 5 times service life than that of individual current constructed wetland. The mechanisms of higher efficiency of baffled constructed wetland in treatment of domestic sewage were owed to the longer flow line of system and the up-down flow of domestic sewage makes pollutant more intimate contact with roots of wetland plants.

Normalization of Capacitor-Discharge I2t by Short-Circuit Fault in VSC-based DC System

2021 ◽  
pp. 1-1
Author(s):  
Seong-Yong Lee ◽  
Young-kwang Son ◽  
Hyung-June Cho ◽  
Seung-Ki Sul AE
Keyword(s):  
Short Circuit ◽  
Capacitor Discharge ◽  
Dc System ◽  
Short Circuit Fault

scholarly journals Probabilistic Vulnerability Assessment of Transmission Lines Considering Cascading Failures

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1994
Author(s):  
Yanchen Liu ◽  
Minfang Peng ◽  
Xingle Gao ◽  
Haiyan Zhang
Keyword(s):  
Transmission Lines ◽  
Large Scale ◽  
Failure Process ◽  
Power Grids ◽  
Weak Links ◽  
Cascading Failure ◽  
Cascading Failures ◽  
Stable Operation ◽  
Chain Model ◽  
Systems Research

The prevention of cascading failures and large-scale power outages of power grids by identifying weak links has become one of the key topics in power systems research. In this paper, a vulnerability radius index is proposed to identify the initial fault, and a fault chain model of cascading failure is developed with probabilistic attributes to identify the set of fault chains that have a significant impact on the safe and stable operation of power grids. On this basis, a method for evaluating the vulnerability of transmission lines based on a multi-criteria decision analysis is proposed, which can quickly identify critical transmission lines in the process of cascading failure. Finally, the proposed model and method for identifying vulnerable lines during the cascading failure process is demonstrated on the IEEE-118 bus system.

scholarly journals Theory and Design of a Flexible Two-Stage Wideband Wilkinson Power Divider

Electronics ◽  
2021 ◽  
Vol 10 (17) ◽  
pp. 2168
Author(s):  
Antra Saxena ◽  
Mohammad Hashmi ◽  
Deepayan Banerjee ◽  
Muhammad Akmal Chaudhary
Keyword(s):  
Transfer Function ◽  
Transmission Lines ◽  
Short Circuit ◽  
Wide Band ◽  
Power Divider ◽  
Design Parameters ◽  
Two Stage ◽  
Quarter Wave ◽  
Band Pass ◽  
Wilkinson Power Divider

This article presents the design scheme of a wideband Wilkinson Power Divider (WPD) with two-stage architecture utilizing quarter-wave transmission lines and short-circuit stubs. The bandwidth of the proposed WPD is flexible and can be controlled using the design parameters. The proposed design achieves excellent isolation between output ports in addition good in-band performance. The analysis of the proposed circuit results in a simplified transfer function which is then equated with a standard band-pass transfer function to determine the parameters of transmission lines, stub’s impedances, and the value of the isolation resistors. Furthermore, it is also demonstrated that a simple alteration in the proposed circuit enables the design of a wideband DC isolated WPD that maintains a good in-band and isolation performance. A number of case studies have been included to highlight the flexibility of the proposed design. Two distinct prototypes are developed on different boards to demonstrate the wideband performance of the proposed design. An excellent agreement between the experimental and measured results for both the designs over a wide band including very good isolation between ports validate the proposed design.

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