Research On Ultrasonic Measurement Method Of Oil Velocity Based On Time Difference Technology

As one of the key equipment in the power system,the long-term safe and reliable operation of power transformer is crucial to the safety of the power system and the construction of the energy Internet,especially the large power transformers of 110kV and above,which are expensive and complex in structure.Once they fail Will cause huge economic losses.Therefore,it is very urgent to realize the transparency of the transformer status.The transparency of the transformer status is a comprehensive monitoring of the operating state parameters of the transformer equipment.Among them,the oil flow change is a non-electricity parameter of the transformer.Limited by its baffle-type mechanical structure,it can only sense a single flow velocity threshold,and cannot realize the range sensing and change process sensing of the flow velocity.At the same time,the Buchholz relay has a slow response speed and low accuracy.In recent years,transformer explosions and fuel injection accidents caused by its untimely action have still occurred from time to time.In order to effectively and quickly sense the change of flow velocity at the connecting pipe of the transformer,this research carried out the research of the digital transformer oil flow velocity sensing method based on the ultrasonic method.In this study,the time difference method was used to measure the flow velocity,and the overall information of the waveform was used to obtain the propagation time through the cross-correlation algorithm.The reflected echo was used as the initial reference wave to obtain the starting point of the waveform.An ultrasonic transducer with good waveform characteristics in the transformer oil was selected.Compared with the attenuation coefficient of the probe,the beam angle has a greater impact on the amplitude of the reflected echo signal,and the influencing factors of ultrasonic measurement are analyzed,which lays the foundation for the measurement of the transformer oil flow rate.Aiming at the elbow structure of the transformer connecting pipe that affects the measurement accuracy,the flow field simulation method is used to carry out the flow field distribution research of the connecting pipe.It is found that the asymmetric distribution of the flow field is serious under the action of centrifugal force when passing through the elbow.Realize high-precision measurement under the condition that the existing rectifier cannot directly improve the flow field distortion at the connecting pipe,According to the characteristics of the flow field distribution after the elbow,an improved vane conditioner is proposed.Under the conditions of steady state,transient state and different dynamic viscosity,its performance is described and the location of ultrasonic sensing is explored.the improved flow conditioner can effectively improve the asymmetric distribution of the flow field while the local resistance coefficient is small and provide a favorable flow field environment for the digital measurement of the flow velocity of the transformer connecting pipe.In the hardware design,FPGA is used as the control and data processing device,and the delay information is effectively extracted through interpolation and fitting algorithms.The accuracy of the parallelized data processing used is basically the same as that of matlab through simulation.The measurement time can be achieved at the ms level.Finally,an oil circulation loop is built,and the flow rate measurement experiment is carried out.In view of the uncertain impact of temperature,the flow rate is corrected by the quadric surface fitting method,and the flow rate under different temperature conditions is corrected.The measurement results show that the relative error of the flow rate measurement is about 4%.