scholarly journals Grounding Fault Model of Low Voltage Direct Current Supply and Utilization System for Analyzing the System Grounding Fault Characteristics

Symmetry ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1795
Author(s):  
Jie Liu ◽  
Kaiqi Sun ◽  
Zhao Ma ◽  
Zhijie Liu ◽  
Kejun Li
Keyword(s):  
Direct Current ◽  
Low Voltage ◽  
Fault Model ◽  
Solution Algorithm ◽  
Fault Analysis ◽  
Assessment Model ◽  
Fault Current ◽  
System State ◽  
Grounding Resistance ◽  
Proposed Model

Grounding fault analysis is of vital importance for low voltage direct current (LVDC) supply and utilization systems. However, the existing DC grounding fault model is inappropriate for LVDC supply and utilization system. In order to provide an appropriate assessment model for the DC grounding fault impact on the LVDC supply and utilization system, an LVDC supply and utilization system grounding fault model is proposed in this paper. Firstly, the model is derived by utilizing capacitor current and voltage as the system state variable, which considers the impact of the converter switch state on the topology of the fault circuit. The variation of system state parameters under various fault conditions can be easily obtained by inputting system state data in normal conditions as the initial value. Then, a model solution algorithm for the proposed model is utilized to calculated the maximum fault current, the system maximum fault current with different grounding resistance is simple to acquired based on the solution algorithm. The calculation results demonstrate that grounding resistance and structure of LVDC supply and utilization system have remarkable impacts on the transient current. The effectiveness of the proposed model is verified in PSCAD/EMTDC. The simulation results indicate that the proposed method is appropriate for the system fault analysis under various fault conditions with different grounding resistance and the proposed model can offer theoretical guidance for system fault protection.

scholarly journals Study on Operational Characteristics of Protection Relay with Fault Current Limiters in an LVDC System

Electronics ◽  
2020 ◽  
Vol 9 (2) ◽  
pp. 322
Author(s):  
Hyeong-Jin Lee ◽  
Jin-Seok Kim ◽  
Jae-Chul Kim ◽  
Sang-Yun Yun ◽  
Sung-Min Cho
Keyword(s):  
Direct Current ◽  
Distribution System ◽  
Low Voltage ◽  
Current System ◽  
Fault Analysis ◽  
Fault Current ◽  
Fault Current Limiter ◽  
Superconducting Fault Current Limiter ◽  
Protection Relay ◽  
Current Limiter

As the application of low-voltage-direct-current system increases, fault analysis in the low-voltage-direct-current system has essential because the fault response has different from the conventional AC distribution system. Especially, the fault current by the discharge current of the capacitor in the low-voltage-direct-current distribution system has very large compared with the conventional AC distribution system. Therefore, this paper proposed the application of the superconducting fault current limiter for limiting the fault current on the low-voltage-direct-current system. As one of the protected methods against fault current, the superconducting fault current limiter which could quickly limit the fault current has been noticed as an attractive method. However, the protection relay may malfunction such as over current relay, selective protection relay due to limiting fault current by applying superconducting fault current limiter. Therefore, in this paper proposed a solution to malfunction problem of the protection relay using the voltage components of the high temperature superconductivity. This paper verified the effect of the proposed method through test modelling and PSCAD/EMTDC.

Simplified and Automated Fault-Current Calculation for Fault Protection System of Grid-Connected Low-Voltage AC Microgrids

2017 ◽  
Vol 18 (2) ◽  
Author(s):  
Duong Minh Bui
Keyword(s):  
Low Voltage ◽  
Operation Mode ◽  
Distribution Coefficients ◽  
Fault Analysis ◽  
Fault Current ◽  
Analysis Method ◽  
Distributed Generators ◽  
Overcurrent Relays ◽  
Current Calculation ◽  
Ac Microgrid

Abstract Fault currents inside a grid-connected AC microgrid are significantly varied because fault current contributions of the main grid and DG units are different from each other due to various fault locations, fault types, and high penetration of inverter-based distributed generators (IBDGs) and rotating-based distributed generators (RBDGs). A traditional fault-analysis method cannot be sufficiently applicable for AC microgrids with the presence of both rotating-based distributed generators and inverter-based distributed generators. From the above viewpoint, this paper proposes a simplified and automated fault-current calculation approach for grid-connected AC microgrids to quickly and accurately calculate fault-current contributions from IBDGs and RBDGs as well as the grid fault-current contribution to any faulted microgrid sections. The simplified and automated fault-current calculation approach is mainly focused on grid-connected and small-sized low-voltage AC microgrids with the support of communication system. Under the grid-connected microgrid operation mode, fault-tripping current-thresholds of adaptive overcurrent relays are properly adjusted thanks to the proposed fault analysis method. Relying on fault-current distribution-coefficients of IBDGs, RBDGs, and the utility grid, the setting values of adaptive overcurrent relays in a low-voltage AC microgrid are effectively self-adjusted according to various microgrid configurations and the operation status of DG units during the grid-connected mode.

scholarly journals Tansient fault analysis of a VSC-based multi-terminal HVDC scheme

2020 ◽  
Author(s):  
◽  
Sindisiwe Cindy Malanda
Keyword(s):  
High Voltage ◽  
Direct Current ◽  
Reactive Power ◽  
Short Circuit ◽  
Critical Time ◽  
Fault Analysis ◽  
Fault Current ◽  
Dc Voltage ◽  
High Voltage Direct Current ◽  
Ground Fault

A multiterminal HVDC system includes the connection of different HVDC terminals to a common grid. Most of the MTDC networks are realized in voltage source converter (VSC) high voltage direct current (HVDC). Over long distances, HVDC transmission is preferred to high voltage direct current (HVAC). Furthermore, HVDC is subjected to minimal harmonics oscillation problems due to the absence of frequency. HVDC enables the interconnection of systems at different frequencies, and the system becomes free of angular stability problems. VSCs employ insulated gate bipolar transistors (IGBTs) switches, and High-frequency pulse width modulation is used to operate the IGBTs in order to achieve high-speed control of active and reactive power. The growth of MTDC networks may require a new type of VSCs topology, which is resilient and efficient to dc and ac network fault. This research investigation focuses on the transient dc-side fault analysis in a two-level Monopolar VSC- Based Multi-Terminal HVDC Scheme consisting of four asynchronous terminals sharing a rated 400kV DC-grid was carried out in PSCAD software. During dc-side fault analysis, a pole-to-ground fault was taken into consideration as it’s more likely to occur, although it is less severe compared to pole-to-pole. The converters are interconnected through 100 km dc cables placed 0.5 gm apart and at a depth of 1.5 m underground. It was observed that during the steady-state analysis, the dc voltage in the grid was maintained at the rated value 400 kV, the currents measured at the converters bus was 0.5 kA, and the current flowing through the cables was 0.25 kA. Under the fault condition, the dc voltage drop needs to be maintained to a closed range to avoid the grid to collapse. The voltage droop technique was incorporated in the dc voltage controller to keep the dc voltage at the narrow range. Depending on the value and nature of ground fault resistance, the fault current magnitude varies, and distance variation along the cable has a significant contribution in the fault current. It is observed that fault close to the converter (5 km’s measured 9 kA) results in high fault currents compared to fault away from the converter (50 km’s measured 7.8 kA). The protection design of the VSC needs to be able to detect whether its ground fault or short circuit since the location of the fault needs to be identified and repaired. Another observation made when the fault is inserted 50 kms away from the converter, meaning the fault is at the center of the two converters, the outcome results in high currents in both converters. The isolation of the fault should be fast and selective as the critical time is very short. The dc circuit breakers are mostly recommended to be used as primary protection; however, different protection techniques need to be incorporated with dc circuit breaker in order to quickly identify, select and reliable isolate the faulted line. Moreover, the protection should be able to isolate the line before the fault reaches the maximum fault current to avoid the damage in the converter components.

scholarly journals An Approach to Steady-State Power Transformer Modeling Considering Direct Current Resistance Test Measurements

Sensors ◽  
2021 ◽  
Vol 21 (18) ◽  
pp. 6284
Author(s):  
Henrique Pires Corrêa ◽  
Flávio Henrique Teles Vieira
Keyword(s):  
Steady State ◽  
Direct Current ◽  
Low Voltage ◽  
Power Transformer ◽  
Short Circuit ◽  
Load Flow ◽  
Resistance Test ◽  
Model Parameters ◽  
Extended Model ◽  
Proposed Model

Measurements obtained in transformer tests are routinely used for computing associated steady-state model parameters, which can then be used for load flow simulation and other modeling applications. The short circuit and open circuit tests are most commonly performed with this purpose, allowing estimation of series and parallel branch transformer parameters. In this study, an extended model is proposed which does not employ the usually assumed cantilever circuit approximation and explicitly accounts for transformer connection resistance. An estimation of the proposed model parameters is enabled by usage of additional measurements yielded by the direct current (DC) resistance test. The proposed approach is validated by means of an experiment carried out on a real distribution power transformer, whose results demonstrate that the proposed model and parameter computation approach effectively decompose total transformer resistance into winding and contact components. Furthermore, the numerical results show that contact resistance is not negligible especially for low voltage windings, which reinforces the usefulness of the proposed model in providing detailed modeling of transformer resistances.

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