| Nowadays, in the age of electricity, electric energy is widely used in various fields, as an important source of energy. Electric energy is the indispensable force of national economic development and social progress. The most important, it is the main signs of a country’s development level. With the development of society, national’s demand of electric energy is sharp increasing. More and more power quality problems are followed up. Power quality problems are voltage and current waveform distortion problems, caused by nonlinear and nonstationary electrical equipment. It has a tremendous impact on the safe operation of power system, and brings significant economic losses. Analyzing power quality parameters accurately and timely, determining the source of power system faults and the order of occurrence are the prerequisite for governing and improving power quality problems.This article describes the research and development of monitoring device for power quality. The hardware part of this device is composed of hall voltage and current sensors, A/D acquisition module and industrial touch computer. This structure is simple and easy to implement. In the software part, with the thinking of virtual instrument, the PC software is written in Lab VIEW, greatly improving the programming efficiency. The device working principle: first, high voltage and current is converted to small amplitude signal by three-phase voltage and current hall sensors. Second, the signal is accessed to six-channel A/D synchronous acquisition module. Third, analog signals are converted to digital signals by A/D synchronous acquisition module, and the digital signals are transmitted to industrial touch computer via parallel data transmission module. At last, industrial touch computer stores and analyzes the digital data. This device can acquire three-phase voltage and current, continuously and uninterrupted. In this way, it can monitor power quality parameters accurately, for example power network, harmonics, virtual value, active power, reactive power, three-phase unbalance, flicker, voltage surges and sags.This device designs a high precision A/D acquisition module, to ensure measurement accuracy. The A/D acquisition module has six-channel synchronous analog input and 25-bit parallel digital signal input. The A/D conversion bit is 16 bits, and sampling rates is up to 200 k Hz. In order to determine the source and generation order of power quality problems, we need to simultaneous detection and synchronous acquisition for a plurality of nodes in the power network. This device is designed with a GPS synchronization module. The synchronization signal generated by GPS synchronization module started A/D acquisition module. In this way, it can achieve high precision synchronization acquisition in each node and analyze the source and generation order of power quality problems accurately. In order to playback various power quality parameters, power quality data need to be stored in industrial touch computer efficiently. In order to save storage space and store the data as long as possible, the converted 16-bit A/D data are stored in the form of binary files, and the files are stored every five minutes. The files are named as the time gotten from GPS module. When the hard disk of industrial touch computer is full, it is refreshed in the manner of FIFO(first in first out). In this way, it can achieve effective management for power quality data. Meanwhile, the monitoring terminal is equipped with network interface for data transmission module. The original power quality data can be transmitted to the master station quickly via Internet, achieving real-time monitoring purposes.Finally, we have an on-site testing to the power quality monitoring terminal device. And the sampling precision and the other index of the device can meet the design requirements, reference to the latest national standards for power quality. |
