introduction
In recent years, with the rapid development of the power industry and the continuous expansion of the power system capacity, various distributed power generation units are gradually connected to the power grid, and the use of various non-linear loads is also increasing, resulting in the deterioration of the power quality of the public power grid. The equipment's sensitivity to voltage disturbances is increasing. Therefore, the requirements for power operation on the level of automation and safety of power dispatching are getting higher and higher. Power dispatching requires various power detection instruments with more complete functions and easier operation to detect, locate, and classify power quality disturbances for timely management. With the gradual establishment of China's power market, electricity is gradually priced according to quality, and power users also require high-quality electricity to ensure the normal operation of their equipment, instruments and systems.
Traditional power quality monitoring instruments mostly use RS-485, optical fiber, modem dialing and other wired transmission methods. The monitoring points are scattered in remote areas and the environment is harsh. It involves a series of problems such as wiring construction, construction cost, safety and reliability. Therefore, in recent years, wireless transmission methods have been used. At present, most power grid monitoring instruments use GSM short message to communicate with the host computer. The GSM short message communication method is a half-duplex communication method. It cannot send and receive data in both directions at the same time. The real-time performance is not strong, and the cost is high in the case of large communication traffic. GPRS (General Packet Radio Service) uses packet switching technology, supports applications based on standard data communication protocols, and can be interconnected with IP networks and X.25 networks to achieve billing functions based on data traffic, business type, and service quality level. The billing method is more reasonable, and on the premise of ensuring timely and accurate data transmission, the system operating costs are also reduced to a minimum.
This paper designs a power quality online monitoring system based on GPRS communication technology to meet the real-time requirements of power quality monitoring and monitor various indicators of power quality in real time.
1 System design
1. 1 overall design
In terms of power grid operation, current power quality problems can be divided into two categories: transient power quality problems and steady-state power quality problems. Transient power quality problems are usually characterized by frequency spectrum and duration, and are divided into two categories: pulse transient and oscillating transient. The main performance indicators are voltage fluctuation and flicker, voltage sag and transient voltage interruption. Among them, the voltage sag The impact is most common. The steady-state power quality is characterized by waveform distortion, which lasts for a long time. Its main performance indicators are harmonic voltage, harmonic current, three-phase voltage unbalance, and voltage deviation. Steady-state power quality parameters are the main targets for power quality monitoring.
The power quality monitoring system is composed of three parts: monitoring main station, GPRS communication network and monitoring terminal, as shown in Figure 1.
Figure 1 Structure diagram of power quality monitoring system
1. 2 System working principle
The monitoring terminal accesses the GPRS network through its own GPRS wireless module (GPRS DTU), and then connects to the Internet public data network through the GPRS wireless network, and then connects to the monitoring master station, and sends the data to the monitoring master station for further analysis and processing.
According to the actual needs of power grid power quality supervision and management, determine the number of monitoring units and installation locations.
The GPRS module (GPRS DTU) of the monitoring terminal is embedded with TCP / IP protocol, each module has a unique ID number that can be set and modified at any time, and saves the IP address of the master station. The GPRS DTU is initialized after power-on, set the corresponding communication parameters, the terminal actively sends a connection request to the master station according to the set parameters, the SGSN of the GPRS network processes the request, and assigns a dynamic IP address to it; after the terminal establishes a connection with the master station , The main station reports its own terminal address, and the main station adds it to the dynamic address database after receiving it, and then completes the active upload of tasks and warnings according to the settings of the administrator. If the terminal cannot establish an effective TCP connection with the master station, it will compress and store the real-time data and send it to the master station after the connection is established.
The monitoring main station is a computer system, which can realize monitoring and information management of the monitoring terminal, and realize statistics, analysis and processing of various collected power quality information through background software to realize long-term data storage and management. It has a fixed IP address and opens the corresponding listening port to the terminal; receives the GPRS DTU connection request, and sends parameters and commands to the terminal. Because the system data flows through the public network, in order to ensure the security of the system, the data can be encrypted before transmission to the GPRS DTU, and after the database server of the remote monitoring master station receives the data, the data is decrypted and verified by the special processing software .
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