Defects of traditional distribution network protection

Active distribution network is a system composed of micro power supply, load, energy storage system and control device.

2. The traditional distribution network is passive, and its operation, control and management modes are passive. The power generated by large power plants flows through the transmission network (high voltage) and is delivered to users through the distribution network (medium voltage and low voltage), so the medium and low voltage (low voltage) distribution network is the "passive" load of the power system, so the distribution network can be called passive distribution network (PDN). Even if distribution automation is adopted, especially in China, its core control idea is still passive, that is, under the condition of no fault, automatic control operation is generally not carried out. The existing distribution network analysis and calculation, regardless of loss, voltage and reliability, are based on the maximum load condition or the average load condition. Therefore, the traditional distributed system is not designed to access a large number of distributed resources. A large number of distributed energy sources connected to the distribution network may bring many impacts. For example, it affects the short-circuit level and equipment selection, reactive power and voltage distribution, protection, distribution automation and fault removal process, and island operation under special circumstances. Therefore, in order to cope with the access of a large number of distributed der and maintain the original reliability, it is necessary to develop into active control and active management.