Closed-loop Distribution Network Research Articles

Single-phase grounding line selection method for closed-loop distribution network adapted to medium voltage microgrid access

Aim: The access of the medium-voltage (MV) microgrid changes the radial structure of traditional distribution networks, causing the distribution network to operate in a closed-loop manner. The closed-loop operation complicates the fault characteristics of the distribution network, and the traditional single-phase grounding (SPG) line selection method is no longer applicable. Therefore, it is necessary to propose a new targeted SPG line selection method. Methods: This paper analyzes the network structure of MV microgrids and MV distribution networks and establishes a multi-level closed-loop operation distribution network model with MV microgrid access. Then, the SPG fault characteristics of the closed-loop operation distribution system under the small current grounding mode are analyzed from the perspective of two-level bus nodes. Furthermore, based on the analysis of fault characteristics, a closed-loop operation distribution network line selection method suitable for microgrid access is proposed, and a detailed design is carried out in terms of equipment configuration and communication schemes, forming a relatively complete automatic line selection system. At the same time, the proposed line selection scheme is based on the two-level bus nodes, which can be analogously applied to the multi-level closed-loop operation distribution network. Results: The simulation results show that the proposed line selection scheme can be effectively applied to the closed-loop operation distribution network with MV microgrid access. Conclusion: The traditional SPG line selection method will have misjudgment problems after the MV microgrid is integrated into the distribution network, but the line selection method proposed in this paper has good adaptability.

Research on real-time power flow calculation method in closed-loop distribution networks

It is less intelligent to calculate the closed-loop power flow of the distribution network by manually inputting the closed-loop power flow parameters. Therefore, it is necessary to study the real-time calculation method of the loop power flow in the distribution network. In this paper, a real-time calculation method is put forward based on the Thévenin’s Theorem. Forward/backward sweep algorithm is used to calculate the power flow of the closed-loop distribution network with the aid of the equivalent impedance and the maximum inrush current. A real-time automatic analysis tool for the closed-loop power flow is developed as well, based on the autonomous decentralized concept. The closed-loop power flow calculation is embedded in the DSCADA system to evaluate the feasibility of the loop-closing operation. Test results show that the proposed method can effectively identify the limit violation conditions within the distribution network, and that the calculation error in closed-loop power flow is small.

Current-phase-comparison-based pilot protection for normally closed-loop distribution network with underground cable

Current-phase-comparison-based pilot protection for normally closed-loop distribution network with underground cable

Positive-sequence-fault-component-based blocking pilot protection for closed-loop distribution network with underground cable

Closed-loop operation of distribution network has attracted more attention recently to improve supply reliability and adopt Distributed Energy Resources (DERs) friendly. Its protection is usually independent of distribution automation system (DAS). This article presents a blocking pilot protection method for closed-loop distribution network with underground cable, that can be accomplished by remote terminal units (RTUs) in DAS. First, operation value of RTUs is designed on the current variation after fault and the RTUs are synchronized automatically based on fault signal. Second, the power direction characteristic of positive-sequence fault component is analyzed when various short circuit fault occurs at different locations. Based on that, the state of Ring Network Cabinet (RNC) are classified into five types and uniform blocking signal exchanging rule between adjacent RTUs is designed. The fault can be located and isolated directly by cooperation of adjacent RTUs. The setting principle and the operation logic for the pilot protection is given and its performance is analyzed. Finally, simulation model based on PSCAD is constructed. The simulation results prove that this protection can locate and isolate faults timely on the premise of high sensitivity. It has strong ability of enduring fault resistance and it can fit closed and open operation mode.

Facility location for a closed-loop distribution network: a hybrid approach

PurposeThe purpose of this paper is to find a sustainable facility location solution for a closed-loop distribution network in the uncertain environment created by of high levels of product returns from online retailing coupled with growing pressure to reduce carbon emissions.Design/methodology/approachA case study approach attempts to optimize the distribution centre (DC) location decision for single and double hub scenarios. A hybrid approach combining centre of gravity and mixed integer programming is established for the un-capacitated multiple allocation facility location problem. Empirical data from a major national UK retail distributor network is used to validate the model.FindingsThe paper develops a contemporary model that can take into account multiple factors (e.g. operational and transportation costs and supply chain (SC) risks) while improving performance on environmental sustainability.Practical implicationsBased on varying product return rates, SC managers can decide whether to choose a single or a double hub solution to meet their needs. The study recommends a two hub facility location approach to mitigate emergent SC risks and disruptions.Originality/valueA two-stage hybrid approach outlines a unique technique to generate candidate locations under twenty-first century conditions for new DCs.

Closed-Loop Distribution Network by a Midvoltage Flexible HTS DC System

A scheme of closed-loop distribution network by a midvoltage flexible high-temperature superconducting (HTS) dc system is proposed and analyzed. This midvoltage (10-kV) scheme is compared, in terms of capital costs, with that of the closed-loop distribution network by a high-voltage (110-kV) flexible conventional dc system. Based on the HTS cables that are made of the first-generation Bi2223 tapes with a length of 2.5 km, the total investment cost of the 10-kV flexible superconducting dc system with a power capacity of 42 MVA is estimated about 1% lower than that of the 110-kV flexible conventional dc system with the same power capacity, owing to the substantial cost reduction of the voltage-source converter stations with the reduced voltage level. According to the “N - 1” principle of distribution networks, with the interconnecting flexible HTS dc system of 42 MVA, the total power to supply loads of the connected substations can be increased by the same power capacity of the interconnecting system. The simulation results of a three-phase short-circuit fault reveal that the voltage recovery time of the critical loads in the closed-loop distribution network can be reduced to less than 0.1 s, which is much faster than that in open-loop distribution networks.