The medium voltage distribution network is located downstream of the system power grid and is a bridge connecting the terminal power users to the large power grid, which is directly related to the user's power quality and power supply reliability. In the planning and design of distribution network, the choice of grid grid structure will directly determine the economics of the project and the reliability of grid power supply. In the following, Xiaozhi briefly analyzes the failure analysis, power supply reliability and line utilization of various typical grid structures to provide reference for the planning and construction of distribution networks.
Radiant
Single radiation: After the line is taken out of the substation bus, only the sectional switch is used for load segmentation and fault isolation, and there is no other power source that can contact the transfer. The line has the advantages of simple structure, small engineering investment, easy operation and maintenance, but it can not meet the "N-1" fault operation requirements, and the power supply reliability is poor. Applicable to the new power supply layout, to meet the new load power supply requirements or remote pastoral areas and rural basic power supply needs.
Figure 1. Schematic diagram of single radiating line wiring
Table 1. Analysis of single radiated line fault operation mode
Remark: The fault power failure range indicates the expected value of the power failure range after the fault is turned off, and the line failure rate is not included.
Double radiation: Two lines are allocated by different busbars of the same substation, and the double-circuit erection method is adopted for the same pole. For users with higher reliability requirements, dual-loop power supply is adopted. When any line accident or maintenance power failure occurs, another circuit can be used. powered by. The overhead double radiation is different from the double shot of the cable. For the personal safety in the state of maintenance, it is necessary to power off the same line with 2 times, and the reliability of power supply is relatively poor.
Figure 2. Schematic diagram of double radiating line wiring
Table 2. Analysis of fault operation modes of dual radiating lines
Segmented contact
Multi-segment moderate contact: Under fault shutdown or planned maintenance, the line load can be transferred from the opposite communication line, and the line utilization rate can be up to (n-1)/n (n is the number of contacts). In order to improve the actual transferable capacity, the contact point generally needs to be at the load equal point, and the networking is difficult; the actual transferable capacity is greatly affected by the load distribution, and the actual line utilization is difficult to reach (n-1)/n.
Figure 3. Schematic diagram of multi-segment single contact line wiring
Figure 4. Schematic diagram of multi-segmented moderate contact wiring
Table 3. Analysis of fault operation mode of segmented contact line
Ring network
Ring network type: The ring line is formed by different substations or different bus lines of the same substation, and the closed loop design is used for open loop operation. The double-ring network frame structure can meet the requirements of N-1-1, and the investment is relatively high. It is recommended to load-intensive area configuration.
Figure 5. Schematic diagram of single-ring network wiring
Figure 6. Schematic diagram of double-ring network wiring
Table 4. Analysis of ring network fault operation mode
N for 1 preparation
Normally, the N main power supply is used for power supply, and there is another backup power supply. When the main power supply is cut off, the backup power supply can be used. The backup power supply can bear all the power supply load (when fully available in full standby mode) or part of the power supply load.
Figure 7. Schematic diagram of 2 supply and 1 line wiring
Figure 8. Schematic diagram of 3 supply and 1 line wiring
Table 5. Analysis of fault operation mode of N supply and standby lines
Petal
The wiring method consists of two "petals", each of which comes from the same busbar of the same substation, forming a "petal" of the ring circuit. The switch station segment switches connected between the "double petals" are open-loop and alternate with each other.
Figure 9. Schematic diagram of petal (partition) wiring
Figure 10. Schematic diagram of petal (complementary) wiring
Table 6. Analysis of the operation mode of petal line faults
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