The Development Of Rural Digital Power Meter Calibrator Of Intelligent Substation

With the continues development of science and technology in China and the rapid progress of substation automation technology, the construction and monitoring of intelligent substation have been paid more and more attention. As an important part of the power system, the intelligent building for the rural power substation has become an important direction of development. At present, the construction of intelligent substation are mainly based on IEC61850 protocol, including the logic of the intelligent substation layered, system modeling, communication protocol and so on. Logically, digital power meter is the important equipment to the bay layer of the intelligent substation, the communication protocol followed IEC61850-9-1 and IEC61850-9-2 two parts content, yet the traditional power meter calibrator under traditional power metering system is not suitable for the digital power meter. Therefore, there is an significance of designing the calibrator following IEC61850 protocol to realize the calibration for digital power meter of intelligent.Based on the detailed analysis and research of communication protocol and the hierarchical structure characteristics of intelligent substation, the paper introduced the development of the digital power meter calibrator. The IPC containing optic communication interface is used as the main control section of the digital power meter calibrator, and it is connected with A/D module and D/A module of the calibrator via PC/104 bus and dual-port RAM, realizing the function of analogy signal acquisition and digital signal output. The electric energy pulse receiving and sending function is realized by FPGA chip, in order to enhance the anti interference ability of the calibrator, photoelectric isolator is used at the sending and receiving end of the pulse.Receiving and sending the Ethernet packets are implemented in C++ Builder software platform. By transplanting the Winpcap, a capture tool of VC++, C++ Builder software can detect the bottom of the network through controlling the network card, and then complete the sending and receiving Ethernet data packets for communication with the digital power calibrator. In C++ Builder environment, using Winpcap software send data packets according to the format of IEC61850-9-2LE to another computer via Ethernet port, and then use MM Ethereal software to capture and display the data packets. The data packets are parsed out by the MM Ethereal software, and the identification number of is correct. It indicates that the analysis of the Ethernet frame is right.The energy metering section includes measuring frequency, active and reactive power. The measurement algorithm of frequency realizes by combing Fourier transform theory and angle difference of N time window sampling signal. To improve the measurement accuracy, we use frequency correction algorithm to calculate active power, using a different correction factor for the different frequency ranges, which makes the measurement more accurate. Before the calculating of the reactive power measurement, we need to firstly transform the receiving data according to Hilbert transformation, and then combined with the frequency correction algorithm to calculate the reactive power.Finally, with high-precision standard meter and three-phase programmable AC source conducting the test of dissemination of value of quality to check the accuracy of the calibrator. Use the calibrator and three-phase programmable AC source conducting virtual load calibration to check digital power meter. The computer is used to send data, simulating the function of merge unit, and then conducting the on-line testing of digital power meter. The results show that the calibrator function of data packet receiving and sending, decoding and power metering fully meet the requirements.