Study On Non-contact Detecting Technology For Electric Power Line-Voltage And Current

The voltage and current detecting technology is one of the key technologies to support the smart grid.The healthy operation,security protection,analysis&decision of power system must be achieved through the measurement of information about voltage,current,and so on,so the study of current,voltage detecting technology is of great significance to the development of power system.The non-contact measurement technologies of wire voltage and current avoid the direct electrical connection with the power system,and have the advantages of high insulation and less impact on the existing power network,which have become important research contents in the intelligent sensing of power system.Based on the analysis of existing non-contact voltage and current measurement technology,this paper finds that the existing electric field sensor driven by electrostatic,thermal,or piezoelectric force requires a large drive voltage,so the voltage noise signal interference is large;the existing current sensor based on magnetoelectric?ME?transducer needs external DC bias,and is hard to measure DC current directly.Therefore,this work financially supported by The National Natural Science Foundation of China?NSFC?carries out the research on electric field sensors based on vibrating capacitator and magnetoelectric current sensors from both of the theoretical and experimental aspects;non-contact voltage sensors and current sensors based on cantilever structure are put forward respectively,for the cantilever structure has the advantages of mechanical energy accumulationand displacement amplification at its resonant frequency.The main work of this dissertation is summarized as follows:?1?A magnetically driven electric-field sensor is proposed.The electric field sensor mainly consists of an elastic beryllium bronze cantilever beam,a cylindrical NdFeB magnet,a small solenoid under the magnet and a rectangular sensing copper electrode.The sensor structure,measurement principle and signal detection circuit of the electric field sensor are analyzed in detail.The theoretical relationship between the excitation current,the sensor size parameters,the measured DC voltage and the sensor output is established.The proposed electric field sensor is used for the non-contact DC voltage measurement experiments.The resonant frequency,sensitivity and resolution of the sensor are tested and analyzed.The experiments show that the total power consumption of the electric field sensor can be as low as 17.75 mW.The electric field sensor has an electric field sensitivity of 9.87?V/?V/m?,a resolution up to 10.13 V/m,which means the proposed magnetic drive electric field sensor is a new kind of electric field sensing device with high sensitivity,high resolution,and good linearity.?2?An acoustic-energy-driven electric field sensor is proposed,which is composed of the Helmholtz cavity with an elastic wall and cantilever vibration mechanism.The acoustic-machine conversion principle of the electric-field sensor is analyzed in detail.The acoustic behavior of the Helmholtz cavity and the mechanical behavior of the elastic wall are unified into the equivalent force-acoustic coupling circuit by means of the electro-mechanic-acoustic analogy method,the vibration speed,acceleration of the elastic wall's center and other parameters can be obtained by the equivalent circuit.According to the above theoretical analysis,the design of the sensor structure parameters can be optimized.To achieve the maximum conversion of sound-machine energy,the resonant frequencies of the Helmholtz cavity,elastic wall,and cantilever are adjusted to the same.The proposed acoustic-energy-driven electric field sensor is used for non-contact DC voltage measurement.The experimental results show that the electric field sensor achieves resonance under the excitation of 161Hz acoustic wave.In the range of 0.2¹ Pa incident acoustic pressure,the output of the electric field sensor increases linearly with the incident sound pressure,the voltage sensitivity at 1Pa reaches302?V/V,the correspond electric field sensitivity is 13.16?V/?V/m?.The electric field sensor can completely avoid the electrical signal noise interference caused by the excitation signal in other electric field sensors,which is a new type of electric field sensor with potential application value.?3?the soft magnetic material FeCuNbSiB and the transition metal cobalt?Co?is used to construct the gradient laminated magnetostrictive phase FeCuNbSiB/Co.The FeCuNbSiB/Co/PZT/Co/FeCuNbSiB ME transducer is fabricated by magnetostrictive phase FeCuNbSiB/Co and piezoelectric phase PZT-8.the mathematical expression of the built-in magnetic field of FeCuNbSiB/Co is establishedaccording to the magnetic charge theory.The influence of the two kinds of magnetostrictive materials on the magnetoelectric coefficient of the composite ME structure is explained and expressed mathematically.The ME voltage coefficient expression of the proposed ME structure is deduced by the nonlinear constitutive relations of the magnetostrictive materials and the equivalent circuit method.The ME transducer is tested,and the experimental results show that the self-bias resonant magnetoelectric voltage coefficient of the magnetic gradient laminated ME transducer reaches 42.32 V/cm Oe,and this ME transducer can clearly distinguish 2.76×10^-8 T magnetic field at its resonant frequency.At the same time,the self-bias magnetoelectric current sensor was fabricated by Fe CuNbSi B/Co/PZT.The sensor can be used for non-contact current measurement without external DC bias,and the current sensitivity was 370 mV/A at the resonant frequency.Experiments show that the sensor has a good linearity within 10 A,and the current sensitivity at the resonant frequency is 370 mV/A.When the resonant frequency of the cantilever beam is adjusted to 50Hz by additional tip mass on the cantilever,the sensor still has a high sensitivity of 246.9 mV/A for 50 Hz AC current.The current resolution reaches up to0.004 A or more.?4?A DC magnetoelectric sensor based on coil/cantilever/piezoelectric composite is proposed,which comprises electromagnetic structure,ferroelastic material and ferroelectric material.The DC magnetoelectric sensor achieves magnetic-mechanical-electrical signal conversion by external ME structure.The theoretical analysis of the magnetic-mechanical-electrical conversion process of the sensor is carried out in detail.The experiments on DC magnetic field and the DC current measurement are carried out.The experimental results show that in the reference current of 60¹80mA,the sensitivity of the DC magnetic field increases linearly with the increase of the reference ac current amplitude.When the reference AC current is 180 mA,the DC magnetic field has a measurement sensitivity of 40.36 mV/Oe,and the DC magnetic field sensitivity per unit reference current is 230 mV/Oe/A.A high permeability C-shaped magnetic flux concentrator is introduced in the experiment of non-contact DC current measurement,which effectively converges the current toroidal magnetic field at the notch.The experimental results show that the DC current measurement sensitivity is 32.4 mV/A at180 mA reference AC current.The DC current resolution is above 0.03 A.The sensor has the ability to measure DC magnetic field and DC conductor current stably and accurately.