Brief Introduction of Distribution Network N-1 Safety Verification Method for Distributed Power Supply

The "N-1" safety standard is a crucial criterion in the planning of distribution networks. N-1 safety ensures that, even after an outage occurs in the main transformer or feeder, the power supply to the affected load remains secure through load redistribution. This concept is essential for maintaining reliability and continuity in power delivery. Research indicates that the integration of distributed energy resources (DERs) significantly enhances the security and resilience of distribution networks. When the capacity and location of these sources are appropriately planned, they can improve the overall reliability and safety of the network. As distribution networks evolve, it becomes increasingly important to account for the impact of DERs during planning. The N-1 safety verification process plays a vital role in this context. However, the challenge of ensuring N-1 security in a network with integrated DERs remains unresolved, making it a critical area for future research and development in distribution network planning and safety assessment. To address this issue, this paper proposes a new method for N-1 security verification in distribution networks that incorporate distributed generation. This approach provides foundational tools and methodologies for the planning and operation of distribution systems with DERs. ### 1. Processing Method of DG After Distribution Network N-1 #### 1.1 Classification of DG Related to Distribution Network N-1 Distributed generation (DG) can act as a backup power source when an N-1 fault occurs in the distribution network. Based on this function, DG can be categorized into two types: standby DG and non-standby DG. Standby DG typically has controllable output, such as generator sets, microturbines, fuel cells, wind turbines with energy storage, and photovoltaic systems equipped with storage. On the other hand, non-standby DG has intermittent and variable output, often influenced by weather conditions, such as solar panels or wind turbines without storage. Additionally, DG can be classified as grid-connected or off-grid based on whether it remains connected to the main grid after an N-1 fault. Grid-connected DG continues to operate in synchronization with the main grid, while off-grid DG includes three types: DG used as a backup during normal operation but disconnected from the grid, non-standby DG that disconnects immediately after a fault, and DG that forms an island after a fault. DG can also be divided into fault zone DG and non-fault zone DG depending on whether it is located in the power-off area caused by the N-1 fault. Fault zone DG is located in the affected area, whereas non-fault zone DG remains in the unaffected region. It’s important to note that these classifications are not absolute. As the fault recovery process progresses, DG may transition between different states and roles. #### 1.2 Processing of DG After Distribution Network N-1 When an N-1 fault occurs, the handling of DG depends on its type. For standby DG that can form an island, it should be utilized to serve more users if possible, expanding the power supply range and improving the reliability of the network. These DG units can be modeled as PQ nodes in power flow calculations. ### 2. N-1 Safety Verification Process for DG-Integrated Distribution Networks Based on the fault recovery process in a distribution network with DG, the N-1 safety verification process is as follows: 1) Assume an N-1 fault occurs at a main transformer or feeder outlet. Identify the fault area. If non-standby DG exists in the fault area, it should be disconnected. If standby DG (including both grid-connected and off-grid DG) is present, attempt to form a multi-user island operation to maximize power supply to local users. 2) Locate the tie lines between the faulty and non-faulty areas. Perform power flow analysis on each non-faulty area connected to the faulted zone to determine the available capacity margin and node voltage levels. 3) Use the feeder with the highest capacity margin and stable voltage to restore power to the faulted area. Gradually restore power to a certain number of loads and perform power flow calculations. If no overloads or voltage violations occur, continue the restoration; otherwise, stop the process. During restoration, if the isolated island formed by the fault can reconnect to the grid, it should do so. Otherwise, continue operating in island mode. Throughout the restoration process, the following constraints must be met: - Node voltage must remain within acceptable limits. - Branch flows must not exceed the capacity of the feeders. - The total load on the outgoing feeders of the main transformer must not exceed its rated capacity. - The network must maintain a radial configuration during power restoration, regardless of the presence of DG. 4) After restoring power to the faulted area using a healthy feeder, re-evaluate the system to identify any remaining faulted zones. Repeat steps 2 and 3 until all areas are restored or no further restoration is possible due to lack of healthy feeders.

Solar Panel Cleaning Tools

Solar Panel Cleaning Tools,Solar Cleaning Brush,Solar Panel Cleaning Machine,Solar Panel Cleaning System Tools

GuangZhou HanFong New Energy Technology Co. , Ltd. , https://www.gzinverter.com