Wentao Huang

An Impedance Protection Scheme for Feeders of Active Distribution Networks

Distribution networks (DNs) gradually become more active and flexible with the massive integration of renewable resources. The conventional protection methods are unsuitable for the promising active DNs. This paper proposes a protection scheme on the basis of measured impedance, which includes an impedance differential method and an inverse-time low-impedance method. The former approach identifies fault instant and provides time reference for the exchanged data. As primary protection, it is able to clear different types of faults as soon as possible. The latter method operates in an automatic coordination way with inverse-time characteristic. It can be used as backup protection or provide protection for single-end lines alone. Both of the methods are independent of operation modes and are able to clear faults with high sensitivity. The efficiency of the protection scheme is validated by PSCAD/EMTDC.

An interconnection protection design for the interface of alternating current microgrids

The interface of AC microgrids plays an important part in implementing the flexible operation modes. It always manages the disconnection and reconnection between microgrids and the host distribution networks. This study proposes a new protection design interconnection protection (IP), for the interface of microgrids especially the multiple and large-scale ones. IP is intended to decouple interconnected subsystems to prevent disturbances or faults from damaging the both subsystems. IP can be classified into facility IP, circuit IP, and utility IP corresponding to the microgrid served. The deployments, features, and protection schemes of different IPs are analyzed according to the operation characteristics and requirements of the typical microgrid in IEEE Std 1547.4. Facility IP detects faults and disturbances by monitoring the power quality at the point of common coupling. Circuit IP and utility IP have alternative schemes, for example, current differential protection, distance protection, and overcurrent ...

A novel fault-location method for VSC-MTDC transmission lines based on EMTR

This paper presents a novel method for locating faults on VSC-MTDC transmission lines using electromagnetic time reversal (EMTR) theory. A method named First fault-segment, Second fault-location is proposed. The observed currents are time-reversed and back-injected into the simulation system, which equals to the actual system. In this procedure, a fault is not necessary to be assumed in the simulation system. After fault segment has been screened, the fault location can be verified with minor calculation burden. Moreover, the performances of the EMTR-based technique are discussed under different time-asynchronous cases. The simulation test cases are: a five-terminal VSC-HVDC modified from the China Nan-au demonstration project. Considering the effects of protection and control system, the proposed method presents its straightforward application with low sampling rates and ultra-short time-windows, and robustness against fault type and fault impedance.

A novel pilot protection scheme for MMC-HVDC transmission lines

Overcurrent or overvoltage problems caused by DC line faults endanger the security of modular multilevel converter based high voltage direct current (MMC-HVDC) system. To improve the reliability of fault identification for MMC-HVDC transmission lines, a novel pilot protection scheme based on DC power difference is proposed in this paper. Characteristics of the DC power difference between positive pole DC power at one terminal and negative pole DC power at the other terminal are theoretically analyzed for various faults. The analysis reveals that fault detection and fault line selection can be achieved by calculating the DC power differences. According to that, the proposed protection scheme is constructed. Simulation results in real-time digital simulator (RTDS) demonstrate that the proposed protection scheme can identify and classify MMC-HVDC transmission line faults under different fault conditions accurately.

Distance protection optimization strategy for distribution systems with battery energy storage system

Battery Energy Storage System (BESS) is a type of clean energy, which is able to enhance energy efficiency. However, the connection of the BESS with distribution systems has an impact on the conventional protection. This paper presents the BESS operation characteristics and its impact on distance protection. Optimal strategy of Zone II is analyzed from the perspective of impedance originally. The BESS has three operation statuses which will be studied separately. When a fault occurs at different locations of feeders downstream, the fault current of the BESS increases nonlinearly. By defining two original concepts, critical impedance and maximum protection impedance, the nonlinear output current is classified into two parts. Protect access capacity and protection sensitivity are analyzed under both situations. Modifying value m is presented to solve this protection-related problem. Minimum and maximum values of m are calculated to avoid overreach or blinding operation. After optimized by m, Zone II protection can trip correctly. Analysis and simulation results, based on two practical distribution systems, verified the effectiveness of the optimization strategy.

Protection scheme for active distribution networks using positive-sequence components

Active distribution network is a new pattern for integrating distributed generators (DGs) and smart loads. It features in flexible topologies, plug-and-play functionalities, and active control and management. These features, however, make the conventional protection schemes ineffective in active distribution networks together with the fault-current limiting of inverter-interfaced DGs. This paper proposes protection schemes using positive-sequence components with the aid of the advanced communication techniques. The directional comparison method uses the positive-sequence current fault components to detect solid or low-resistance faults. The impedance differential method using positive-sequence currents and voltages is presented to clear or alarm medium- and large-impedance faults. Both of the protection methods are immune to the varied fault currents and do not require data synchronization between ends of protected feeders. Simulation on a 0.4-kV active distribution network demonstrates the effectiveness of the proposed protection scheme.

A selection strategy for interconnection point of distributed generators

The technologies and application of distributed generators (DGs) are progressing rapidly due to the advantages of DGs. The penetration of renewable resources becomes higher and higher, which brings a lot of problems in distribution networks (DNs). The selection of interconnection point for DGs is required to be solved urgently. In this paper, the factors impacting on the interconnection includes host DN structure, DG characteristics, and DG function, which are analysed in order to provide the constraints for the selection strategy. The objective of the selection strategy is to search the interconnection point with the minimum equipment and operation costs. The IEEE 34-node test bed and a practical project of the building integrated photovoltaic in Shanghai are utilized to demonstrate the effectiveness of the selection strategy.