According to the relevant requirements in GB13955-2005 "Installation and Operation of Residual Current Action Protection Device", this paper analyzes and summarizes the importance and necessity of installing residual current grading protection distribution box in rural low-voltage power grid, and puts forward the installation and operation requirements of using residual current grading protection distribution box in combination with the actual use situation on site, and summarizes the use experience.
1. Importance of residual current classification protection in rural low-voltage power grid.
GB13955-2005 "Installation and Operation of Residual Current Action Protection Device" clearly stipulates: "Installing Residual Current Protection Device in low-voltage distribution system is one of the effective measures to prevent direct contact electric shock accidents and indirect contact electric shock accidents, and it is also a technical measure to prevent electrical fires and electrical equipment damage accidents caused by grounding faults of electrical lines or electrical equipment." "In the low-voltage power supply and consumption system, in order to reduce the power outage range caused by personal electric shock accident and ground fault when the power supply is cut off, the residual current protection device should adopt hierarchical protection, and the hierarchical protection should be based on terminal protection."
In rural low-voltage distribution system, the power consumption of end users is complicated. Taking the suburbs of Beijing as an example, the capacity of each distribution transformer is different, with a large capacity of 315kVA and a small capacity of 30kVA；; The number of low-voltage output circuits of each distribution transformer is also different, some have only one output, and some have two or three outputs; The residual current of each output is also different, some are only tens of milliamps, and some reach hundreds of milliamps; On the same day, in each loop, the change of residual current in each time period is different, which may be only tens of milliamps or even a few milliamps during the day. But at the peak of electricity consumption at night, it will reach hundreds of milliamps or even hundreds of milliamps. For these reasons, it is undoubtedly very difficult to install 1 ~ 2 specifications of residual current protection devices in the station area.
In the Technical Specification for Rural Low-voltage Power, it is clearly pointed out that TT system should be adopted in rural low-voltage power network, and it is stipulated that residual current protection must be implemented. Reducing the number of unnecessary trips and reducing the scope of power failure is one of the effective measures to improve the operation rate of residual current protection devices. The classified protection of residual current is an effective method, which has the following five advantages: "reducing the power outage range caused by personal electric shock accident and grounding fault when cutting off the power supply"; Because the scope of residual current protection device is reduced, it is convenient to check and find the cause of tripping; Improve the operation rate of the total residual current protection device; Avoid large-scale power failure and reduce the losses caused by power failure; It is convenient for the management of rural low-voltage power grid and the implementation of management responsibilities at all levels.