Design and Realization of Power Transmission Line Monitoring System

In order to solve the three major problems of manual adjustment of power transmission lines, which are difficult to observe, record, and calibrate. Through the design of software and hardware, the design realizes the long-term and uninterrupted monitoring of the current, voltage, zero sequence current, power factor, active power, reactive power, apparent power, fundamental wave and harmonic energy in the power transmission line. Monitoring, recording and storage.

0 Preface

In order to solve the three major problems of manual adjustment of power transmission lines, which are difficult to observe, record, and calibrate. Through the design of software and hardware, the design realizes the long-term and uninterrupted monitoring of the current, voltage, zero sequence current, power factor, active power, reactive power, apparent power, fundamental wave and harmonic energy in the power transmission line. Monitoring, recording and storage. The design uses MSP430F135 single-chip microcomputer as the control core, combined with voltage, current transformer, DSP power chip, human-machine interface, sound and light alarm circuit and signal processing circuit to realize the monitoring of power transmission line parameters. The system can be stored in U disk The data collected in the medium and long time is analyzed on the upper computer to provide a scientific and reliable basis for the power sector to adjust the line load.

1 System design scheme

1.1 The choice of DSP power chip

The design uses a DSP power chip, which has seven second-order 16-bit sigma-delta ADCs, reference voltage output, voltage, current sampling, fundamental wave, harmonics and signal processing circuits for energy frequency measurement. It also has an SPI communication interface. It also supports gain and phase correction in the full digital domain. It can automatically calculate active power, reactive power, apparent load power and power factor. There is a voltage monitoring circuit inside, which can ensure normal operation during power-up and power-down.

The design can perform high-precision measurement, input dynamic working range of 1000:1, while ensuring that the non-linear measurement error is within 0.1%. Support gain and phase compensation, low current nonlinear compensation. The accuracy of the effective value of voltage and current is better than 0.5%.

1.2 Single-chip selection

The MSP430 microcontroller is a low-power 16-bit microcontroller with typical SOC characteristics and integrates a large number of peripherals. Especially its internal integrated baud rate trimmer can make the MCU work under any crystal oscillator of no less than 32 768 Hz (but cannot exceed the upper limit required by the MCU for crystal oscillator), and the communication baud rate can be selected without baud rate. The rate factor does not have a decimal limit, that is, a crystal oscillator of any frequency can be used within the allowable range of the baud rate. In addition, because the MSP430 MCU integrates a temperature sensor, the temperature of the pressure sensor used to measure the liquid level can be compensated more conveniently. Moreover, the MSP430 series single-chip microcomputer is composed of various modules for different applications. Due to the low power consumption of the microcontroller used, it can work normally with ordinary batteries to achieve long-term uninterrupted normal use.

2 The overall structure and working principle of the system

As shown in Figure 1, the whole system is mainly composed of MCU host circuit, control circuit, signal measurement, sound and light alarm circuit, button circuit, LCD Chinese character Display circuit, power supply circuit and communication circuit. The P1 port is used as the data line of the system, and the DSP power chip uses P3.0 P3.1 P3.2 port to connect to the MCU to provide input data to the system. The working signal of the sound and light alarm module is output through the P2.5 port to generate an alarm. sound. The keyboard module is connected to the MCU through the P2.0, P2.1 and P2.2 ports to control the 6 keys of the system. The system controls the LCD Display through the P1 port and P5.0 and P5.1. The serial communication is controlled by P3.6 and P3.7 through the communication interface circuit to control the reading and writing of the U disk. The power module of the system generates 3.3 V and +5 V voltage for the system Provide stable working voltage.

Design and Realization of Power Transmission Line Monitoring System
Figure 1 Overall system structure

The system uses voltage and current transformers to input the DSP power chip for signal analysis and processing after differential conversion, and outputs high-precision three-phase voltage values, three-phase current values, zero-sequence current values, active power, reactive power, and Apparent power, power factor, fundamental wave and harmonic energy value and other data, these data read out the data calculated by the DSP energy chip through the SPI communication interface, and then send the data to the LCD for display after data conversion.[4-5]. When the system time runs to the write time specified by the U disk, the system automatically records all the collected data. The user can set the collection time interval through keyboard input as needed. The device number in the system can be set arbitrarily. At the same time, the system can also display the temperature and system time of the working environment in real time.

3 The main hardware circuit design of the system

3.1 Signal differential input circuit design

The signal input adopts the differential input mode. The input current and voltage sensor signals are sampled through the sampling resistor R17, and C5 and C6 are filtered to reduce interference. REFO provides a 16-bit AD standard reference voltage through a 10K current-limiting resistor. The voltage and current signal input circuit diagram is shown in Figure 2.

Design and Realization of Power Transmission Line Monitoring System
Figure 2 Voltage and current signal input circuit

3.2 Communication control circuit

The communication circuit function in this system completes the conversion between TTL level and CMOS level. Passive input does not consume power during the non-communication phase, and only consumes power during communication. This will greatly help the entire system to achieve low power consumption. This is also a feature that the dedicated conversion chip on the market does not have. Its control circuit is shown in Figure 3.

Design and Realization of Power Transmission Line Monitoring System
Figure 3 Communication control circuit

3.3 Sound and light alarm circuit design

The acousto-optic alarm circuit is composed of transistors, light-emitting diodes, resistors, capacitors, buzzer components, etc. When the measured liquid level value is less than the set warning value, the single-chip microcomputer will send an alarm signal to alarm, and light up when the alarm signal is received The diode is lit and the buzzer emits a sound to produce an audible and visual alarm effect.

4 System software design

The system software adopts a modular structure design and is divided into seven modules: system initialization module, LCD display module, key recognition and processing module, SPI analog communication module, serial communication module, U disk read-write module. Time, working environment temperature detection module.

The main function of the initialization module is to set the display buffer, stack pointer, various working units, operation flags and working registers, various I/O ports and CMU working clock module setting, setting system timer module, communication module, DSP power chip module Initialization and system interrupt settings, etc.; the main function of the LCD display module is to display collected data and system working parameters and other data; the keyboard module is responsible for key recognition and key processing, when there is a key action, the corresponding key processing subroutine is called for processing . The system time, storage interval, and device number can be set; the main function of the SPI module communication module is to complete the data exchange between the MCU and the DSP power chip. The serial communication module sends data to the U disk module to prepare for data storage; the function of the U disk read-write module is to write the data transmitted by the MCU into the U disk and store it; the function of the time and working environment temperature detection module is to complete the time Calculate, and collect the temperature of the working environment in real time at the same time.

5 Conclusion

The instrument can be widely used in the fields of electric power, petroleum and chemical industry, real-time detection and recording of various parameters in the power line and timely storage in the U disk, so that technicians can adjust the equipment according to the actual conditions of the line. The instrument has the advantages of stable and reliable performance, small size, low cost, accurate and sensitive measurement and control, easy installation and use, and low power consumption. It has high practical application value.

The Links:   BSM100GD120DLC 6DI50M-050

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