The distribution network is the end of the entire power system, directly facing the end user, and the power supply reliability and power quality requirements are getting higher and higher. At present, the domestic distribution network infrastructure and structure are relatively weak; the power supply quality is poor, the voltage level is low, the network loss rate is high; the degree of distribution automation is still low. The overall level of distribution network can no longer meet the increasing power demand of end users, and large-scale distribution network automation transformation and construction is actively developing.
Distribution network automation is based on informationization, integrating distribution network online data and offline data, distribution network data and user data, grid structure and geographic graphics to form a complete automation system to realize distribution network and The normal operation of the equipment and the monitoring, protection, control and automation of power and distribution management in the event of an accident, and finally realize the online and quasi-real-time distribution of the distribution system with the goal of greatly improving the reliability of power supply and improving the quality of power. Closed-loop control. As an important part of the distribution network automation system, the distribution automation terminal requires perfect functions, reliable operation, simple expansion and convenient maintenance.
Based on the analysis of typical distribution automation schemes and the actual operation of distribution network, this paper proposes a distribution automation terminal scheme, in order to solve the actual problems existing in the distribution network.
Analysis of typical distribution automation scheme
Considering the complexity of the distribution network in each place, without loss of generality, the distribution network can be represented by the following topology:
In Figure 1, the 10kV outlet configuration of the substation and the corresponding protection, the main line uses segmented switch segmentation, each branch line uses the configuration of the load switch, all switches have electric split and close function. Since neither the segment switch nor the load switch can break the short-circuit current, no protection is configured. Fault zone discovery, isolation, and recovery of power supply currently have two options:
First, it relies on the automatic switching device to repeatedly cooperate with the action to automatically realize. In the case of fault, the protection of the substation outlet circuit breaker is cut off, and the whole line will be de-energized. Then the sectional switch and the load switch will trip due to the voltage loss, and then the switch of the substation will be closed. The load switch and the sectional switch detect the fault point. Of course, there is also the possibility that the circuit breaker trips again and closes again, causing multiple impacts on the load (especially the transformer), and the power failure time is long.
Second, relying on the FTU distributed on the segmentation switch to collect fault information, uploading and dispatching centralized control through the communication network, and isolating the fault by remote control and restoring the power supply to the non-faulty section. The solution reduces the repeated action of the switch, improves the operation safety of the device, has a high degree of automation, and is highly dependent on the communication system.
The existing distribution network automation solutions are focused on fault isolation and network reconstruction of the distribution network main network. In theory, these solutions are feasible, but many problems are encountered in practical applications, resulting in the system. It can't exert its due effect, such as: communication mode and communication system stability, sensitivity matching of fault identification components, environmental applicability, reliability of power supply, etc., which have more or less problems, and the application effect is not good.
Integrated distribution automation terminal design
According to the statistics of the actual operation of the distribution network system, the fault is generally located on the branch circuit. The probability of failure on the main circuit is not large. The starting point for transforming the distribution network should be able to solve the problem practically. If the fault of the branch line can be quickly removed, It will solve most of the problems of the distribution network, that is, the fault is quickly isolated and the reliability of the power supply is improved.
The power supply quality of the distribution network is poor. The usual way to improve the quality of the power supply is to install a reactive power compensation device on the distribution network. In order to reduce the power loss of each distribution line within the power user and improve the power factor of the distribution network, it is more appropriate to use the distributed reactive power compensation method, that is, to install reactive power on the low-voltage side of the branch line common distribution transformer and the user's power distribution bus. Compensation device.
Taking into account the above situation, the author proposes a branch line configuration set to protect the measurement and control, reactive power compensation, no power supply, multiple communication interface functions in one of the distribution automation terminals.
First, replace the load switch of the branch line with a vacuum circuit breaker to configure special protection for the branch line.
In the case of a branch circuit fault, the fault is removed by the branch line circuit breaker, and fault isolation of the protection level can be achieved. Existing distribution network automation No matter what scheme is adopted, fault isolation can not reach the protection level (that is, it can isolate faults within 1s). The general time is several tens of seconds or several minutes. With this scheme, fault removal can be performed. Reliable completion within 1s greatly shortens the power outage time and improves the reliability of power supply.
The branch line configuration protection greatly simplifies the protection coordination. The protection of all branch circuits is set independently, and does not need to cooperate with other circuits. If there are branches under the branch circuit (such as opening and closing), the protection time of the branch circuit below can be performed. The cooperation on the line can be used. The line outlet protection of the substation only needs to cooperate with the longest delay of all branch circuit protection. There is a certain level difference, and the protection setting and coordination are very simple.
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