Research On Field Test Method For Broadband Characteristics Of DC Engineering Electronic Transformer

The DC electronic transformer is the data source to which the DC system measurement,control and protection devices comply.In addition to the voltage and current sensors directly connected to the primary line,its entire transmission link also includes remote modules,analog digital conversion and merging units and other units with different functions,In addition,the principle of signal transmission and the characteristic waveform signal acting on its primary side are different from the traditional electromagnetic transformer or the electronic transformer used in intelligent substations,and its broadband signal measurement performance and delay time and other technical indicators have always been concerned,but there are no complete international and national standards to carry out broadband characteristic field test methods and test devices The technical specification system can be used for reference to guide the project site work.Therefore,this thesis focuses on the field test of broadband characteristics of electronic transformers in DC projects to carry out theoretical methods,key technology research and device development.Through the field application of actual DC projects,the feasibility and practicality of the proposed method are verified.The details are as follows:First,based on the establishment of a DC transformer broadband equivalent circuit covering the parameters of passive components such as primary sensors and low-pass filters,the idea of on-site equivalent test of DC transformer broadband characteristics is proposed.The influence of time delay characteristic on DC control and protection system is emphatically analyzed,and the difference of characteristic waveform of DC transformer under different time scales is discussed.Then,according to the on-site requirements of the transient test power supply,such as compactness,miniaturization and long pulse width waveform with fast leading edge,a step voltage source for flexible DC engineering based on solid state switch is proposed,and the optimal electrical parameters of the pulse forming circuit are solved by the non dominated solution sequencing genetic algorithm with elite strategy.A design idea of "building block" IGBT switch is proposed,which realizes accurate control of steep rising edge and long pulse width step voltage waveform.A miniaturized transient step and high frequency current source design circuit based on digital physical simulation is proposed.Modular parallel connection and built-in standard waveform traceability regulation technology are used to realize the transient step large current with fast leading edge and long pulse width and the complex current characteristic waveform of multi state sequence.Secondly,a field verification method of DC transformer broadband characteristics based on absolute delay is proposed.Aiming at the high accuracy synchronous analysis and extraction problem of different types of standard photoelectric signals,a digital message receiving and processing method with high fault tolerance is proposed,which greatly improves the fault tolerance of FT3 signals against accidental exceptions.A method for extracting the key parameters of step response based on waveform characteristics is proposed.The step steady-state value is accurately calculated through modulus maxima and mathematical morphology,which effectively solves the problem that the sampling frequency of standard signal and test sample signal is inconsistent,resulting in deviation in parameter extraction.Thirdly,according to the requirement of DC grounding pole line control protection for accurate measurement of transient current,a field equivalent test method of DC grounding pole current transformer transient characteristics is proposed.The equivalent analysis model of the primary circuit of the on-site broadband test is established,and two feasible schemes to reduce the circuit area are proposed.The relationship between the rise time of step current and the sampling frequency of the merging unit of the tested object in the delay characteristic equivalence test is discussed,and the delay characteristics under different characteristic waveforms are verified.For the three types of ECT widely used in DC projects,the harmonic characteristics and frequency aliasing under high-frequency signals are tested,and their advantages and disadvantages are analyzed.A transient characteristic detection method for ECT based on analog fault signal is proposed,and the transmission capability of decaying DC component under different integral processing algorithms is analyzed,which provides a basis for the upgrading of ECT products and the application of relay protection.Finally,the topology and mathematical model of DC voltage transformer transient characteristic operation test are proposed,which can reproduce the step voltage waveform of the operation state under the actual working condition.Combined with the safety and efficiency of field test,a delay equivalent test method based on transient and steady state signals is proposed,which realizes the accurate measurement of absolute delay without disassembling the tubular bus.The above methods and technologies have been verified in the actual DC project converter station.Aiming at solving the field test method of wide frequency characteristics of DC project electronic transformer,this dissertation focuses on the equivalent test technology of wide frequency transmission characteristics and delay characteristics,and proposes a wide frequency detection technology and test system for DC transformer from DC to step on site.The research results have a good guiding significance for the field test of DC transformer in practical DC projects,wide frequency test and operation state evaluation.