Research On Non-contact Voltage Measurement Method Of Distribution Network

In the electrical system,a relatively mature scheme has been proposed in the field of distribution network current measurement,the measurement process is safe and convenient,and the practical research degree is high.However,in the field of voltage measurement of distribution network,especially at 220/380 V voltage level of low-voltage distribution network,the contact measuring device has some limitations,such as the measuring probe must destroy the insulation layer of the line to be tested and directly contact with the metal part.In view of the above problems,combined with the domestic and foreign research status,this paper developed a new type of non-contact voltage measurement device for distribution network,allowing real-time measurement of line voltage without any electrical contact,and realizing the development of weak coupling sensing measurement device.In this paper,the overall architecture design and implementation details of a contactless voltage acquisition device based on the principle of line near-field coupling are proposed and further experimental characterization is carried out.The device consists of a new capacitive probe,an analog measurement front end and a digital signal processing module based on a microcontroller.Combined with each module,the topology design of the new contact-free voltage measuring device was realized.After selecting suitable components and parameters,the hardware development was completed,and a prototype was built for physical test.A U-shaped double flexible electrode probe is proposed for external stray electric field interference,and its advantages in measuring accuracy and space of ring plate are verified by linear fitting analysis.Aiming at the unknown coupling capacitance between the line and the probe,the mathematical model of the module circuit in Ltspice is established,and the simulation is consistent with the hardware implementation.The calibration link is designed to solve the parasitic capacitance interference between chips.The transfer function is listed by controlling whether the signal excitation is connected to the measuring circuit,and the specific value of the coupling capacitance and the voltage to be measured are simultaneously solved.At the same time,the permittivity of the main polymer materials of the contact and shell is analyzed to provide data support for product application research.Aiming at the optimization of filtering algorithm,FIR genetic algorithm is selected by FFT comparison to solve low input noise and low frequency distortion and realize signal low pass processing.In the test section of the device,different lines to be tested were selected to measure the 50 Hz fixed frequency 0～500 V AC voltage.The output voltage was reconstructed after digital filtering processing and calculation by the induction probe and signal processing module MCU,and compared with the actual voltage waveform to be tested.The results show that the device can effectively filter the high-frequency noise.The specific value of the coupling capacitance between the line and the probe is calculated accurately,and the instantaneous error accuracy is less than 3 % in the range of 100～500 V.The higher test linearity and measurement accuracy within 5 % can also be guaranteed below 100 V.It proves the feasibility of the non-contact voltage measurement method studied in this paper.