Keywords: distribution network automation control
China Library Classification Number: TM7 Document Identification Number: A Document Number:1672-3791(2012) 07 (b)-0018-01.
Capacitive reactive power optimization compensation of electrostatic capacitor distribution network is used to compensate reactive power flowing in the power grid, which can improve the power factor of the power grid. Substation dispatching automation system is used to provide line operation parameters, compensate the operating voltage of capacitors and automatically control the switching of capacitors. Below we analyze and study the application of distribution network optimization automatic control system, and realize the optimization goal of distribution network automatic control system, hoping to help readers.
1 Switching control of compensation capacitor
In order to ensure the normal operation of the distribution network, it is necessary to analyze the power factor and voltage stability of the feeder head end, install compensation capacitors at corresponding positions, require the compensation capacitors to have automatic switching function, analyze the operation of the line, analyze the power factor and voltage of the feeder head end, and achieve the purpose of optimizing the control of the power grid by dynamically controlling the switching of the compensation capacitors. 10kv line is used to provide voltage for the controller to control the automatic switching of the capacitor, and the correct capacitor excitation voltage can be obtained through the operation of the controller.
2 distribution network optimization automation system framework
The upper computer optimization automation control system is the core of the distribution network optimization automation control system. The upper computer can realize the comprehensive and coordinated remote switching control of the compensator. When each feeder of a substation is equipped with multiple compensators at the same time, these compensators all operate independently, so the upper computer optimization automatic control system can coordinate and control the normal operation of each compensator. In the substation dispatching automation system, the running state of distribution network and the outlet parameters of feeder can be observed and managed at any time. When the substation is running, data is transmitted from the external network through the network server. The optimized automatic control system can obtain the head-end parameters of each feeder through the TCP/TP protocol interface of substation dispatching automation system, and can effectively control each compensator to make it run normally.
The automatic control system for distribution network optimization should be a variable system [1], because the structure of distribution network often changes, and the change of distribution network structure leads to the change of compensator's capacity, parameters and position, so the automatic control system for distribution network optimization will also be flexibly adjusted with the change of compensator. The optimized automatic control system has powerful database information storage and calling functions, which can store all topological network structure information, capacitance information and control information of distribution network. When the system is connected to the database, it can call the information in the database.
3 switching control strategy
Through the interconnection and communication between the optimized automatic control system and the substation dispatching automation system (SCADA), the active power, reactive power and power factor of the head-end parameters of each compensation line are detected. If it is found that the parameters are different from the established switching control parameters, the upper computer automation control system will send a switching command to the compensator of the faulty line to ensure safety.
3. 1 Input control strategy
Judge the power factor. If the power factor is less than the compensation lower limit set by the current situation, put the current line special capacitor to compensate the reactive power. According to the topological structure between the line and the capacitor, the capacitor can be put into operation in the way of decreasing capacitor capacity. When capacitors with the same capacity are encountered, they are put into operation in descending order. The capacitor put into operation for the first time cannot meet the reactive power optimization state and needs to be compensated again. When the optimization automation system automatically detects the unsatisfied state, it will automatically select a new capacitor to put into operation, and so on. After repeated detection and input compensation, the power grid lines will eventually reach the state of reactive power optimization.
3.2 Excision control strategy
When the reactive power is less than 0, the reactive power is sent back, indicating that the reactive power compensation of the line is too much, causing overcompensation, and the capacitor that has been put into operation must be removed in time. The capacitor removal strategy is to remove the capacitor closest to the reactive power value first. Input capacitors are sorted according to the principle of increasing capacity and serial number, and the capacitor closest to reactive power is selected to start switching [2]. When the optimization automation system automatically detects that there is still compensation, the capacitor will be cut off again in the next detection cycle, and so on. After many times of detection and removal, the power grid lines will eventually reach the non-overcompensation state.
3.3 The controller switches the control mode
The controller is provided with a setting window, and the upper and lower limits can be set as set values as required. If the controller detects that the voltage is higher than the set value, the capacitor is cut off, and if the detected voltage is lower than the set value, the capacitor is put into operation. Execute the command of the upper computer. When the command is input, the setting window moves up and the setting value is higher than the actual voltage. When the command is cut off, the setting window moves down, and the set value is lower than the actual voltage, thus adjusting the setting window to the best optimization. The controller communicates with the upper computer through GPRS. If the connection confirmation packet sent by the upper computer does not get the feedback information from the controller, the controller will work independently, automatically turn on and off the machine, and be controlled again after contacting the upper computer.
4 communication protocol stipulates that
According to the requirements of communication protocol, the meaning of the data packet between the upper computer and the controller of the optimization automation control system must be clear. Every time a data packet is transmitted, the event command of the upper computer can be clearly expressed, and the controller can easily analyze the data packet command and execute the command operation.
The types of data packets transmitted between the upper computer and the lower computer are as follows.
4. 1 Confirmation package for connection between upper computer and controller
The host sends a connection confirmation packet to the remote controller, and the controller receives the instructions from the host and replies, indicating that the communication is normal. If the host computer sends the connection confirmation data packet [3] for three consecutive times, but no reply is received, the communication connection fails and the controller works independently. After testing the system, the controller can reply to the connection confirmation instruction of the upper computer, indicating that the communication is connected.
4.2 Input and Excision Control
The upper computer sends the switching control command data packet, and the lower computer obtains the switching action command data packet. Because the command is issued in multi-thread asynchronous execution mode, the data packet fed back by the lower computer needs to be in a state, so that the upper computer can clearly know the feedback information and the operation of controlling the command execution.
4.3 Recovery of capacitor operation parameters
The control system of the upper computer needs to obtain the running state and excitation voltage of the capacitor in real time, and the upper computer needs to send a state parameter request. After receiving the request, the controller packages the real-time state parameter information and sends it to the upper computer.
5 automation control system software
5. 1 architecture
The automatic control system of distribution network optimization is constructed by using multi-thread technology and modularization. The communication synchronization between the upper computer and the lower computer is realized through GPRS communication. The upper computer receives data packets from the remote controller through the central module and sends control instruction data packets to the controller. The controller executes the feedback data packet of the switching event and records and reads it through the database.
5.2 Control Entity and Status Identification
The logical turnover center of automatic control system is controller agent and capacitor agent [4]. The upper computer control decision-making module sends out control instructions according to the switching information of the controller agent and the capacitor agent, and the lower computer realizes switching operation according to the switching information and feeds back the state to the upper computer.
5.3 Software implementation
The design of the software is realized in C++ language, and the compensator is controlled to run according to the compensation strategy, and the communication network on the controller is ensured to be normal under the switching control instruction [5]. The designed software correctly shows the running state of the lower computer.
4 conclusion
Through the application analysis of the optimized distribution network automatic control system, it can ensure the stability of transmission voltage, ensure the quality of power supply, reduce the power loss, and be scientific and environmentally friendly. It needs continuous innovation and development in actual design and use, so that the optimized automatic control system can be expanded and improved.
refer to
[1] Zhou Yuncheng, et al./design of reactive power optimization automation control system for kloc-0/0kv distribution network [J]. power system protection and control, 20 1 1(39).
[2] Lv Weiwei. Analysis of distribution system automation [J]. Private Science and Technology, 20 10(7).