Study Of Sensor Theory Centered On Rogowski Coil For Heavy Current Measurement Application

As one of the key technologies for the modern electromagnetic measurement field, heavy current measurement technology is very important to the energy conservation, the safe operation of the power system and the improvement of the quality of products. The development trend of the measurement technology is concluded that the sensor instrumentation with the data acquisition and processing system centered on the computer replaces the one has no capability to communicate directly and easily with the computer. It is increasing demand to properly design and select the sensor theory and methods to satisfy increasing requests of the different kinds of heavy current measurement application. The principle of measuring the current centered on the Rogowski coil has been known since 1912. The coil has many useful features that provide it an advantage over other current transducers or transformers: it has good ability of electric isolation to the conducting current leads; and it owns wide bandwidth that only depends on its type; and its output voltage is low cost; and it has compact structure and is very lightweight; and the coil is linear: the same coil transducer or transformer can be used to measure current in a wide range; what's more, it can connect directly with computer. Due to the coil's unique feathers, it becomes the first choice of the sensing devices applied to measure currents in the region of a few tens of kiloamperes, which are situated in the high voltage environment. In order to give some useful help to solve the problems in the heavy current measurement field of our present situation, theory of Rogowski coil is adopted as the research focus for the dissertation, which is funded by National Nature Science Funds of China (No. 60274037) and Huazhong University of Science & Technology Excerlelent PHD Dissertation Fund. Such important technique issues of the Rogowski coil are proposed to design a proper sensor as construction features, the function of the return wire, selection method of the material of the frame core, and the operation principle, and the equivalent circuit, and shielding measures, and typical experimental methods of the Rogowski coil. Highlights of the dissertation can be concluded that: the computation models, optimum methods and selection criterions of dimension and electromagnetic parameters of the coil are analyzed respectively including their influence characteristics to the performance of the sensor instrumentation; the computation model, operation principle and measurement method of the distributed capacitance of the Rogowski coil are presented including its influences to the dynamic property of the coil sensor set; optimum criterions of the parameter of the terminal resistance of the coil is proposed; typical design methods, basic operation procedures, elimination measures to error and other critical techniques are provided to meet the engineering demands of measuring such heavy currents as transient current, pulsed current, direct current (DC) and so on. A novel self-balancing hybrid DC comparator is proposed by the pioneer adoption of the Rogowski coil functioning as detection winding. In the high voltage adjustable speed drive (ASD), Rogowski coil is creatively used to detect the common-mode current of the power electronics transfer installation. Several typical engineering measurement applications centered on the Rogowski coil are presented to verify the truth of the proposed optimum criterions both of dimension parameters and electromagnetic parameters of the coil and useful measures used to eliminate the test error of the measurement instrumentation. I. e., such typical heavy currents are measured by means of Rogowski coil sensor set as earthing currents and pulse currents both of the preionization loop and the primary discharge loop of the SG III laser source, pulse currents of the type test of the series compensation capacitor, transient current of the abruption test of the cover structure of the power capacitor and switch state currents of the high-speed and high-power RSD (Reversely Switched Dynistor) switch. Construction characteristics, operation performance and design criterions of every kind of sensor instrumentation centered on the Rogowski coil are analyzed in detail. The operation performance and control principle of the conventional saturable reactor (SR) stimulated both by AC (Alternating Current) and DC sources are presented. A novel DC comparator is proposed by adding the detection winding (made of Rogowski coil) and the secondary winding to the SR, which includes four windings, (viz. detection winding, excitation winding, primary winding and secondary winding), single magnetic core and peripheral circuits. The terminal voltage from the detection winding is asymmetric waveform when the SR is stimulated both by AC voltage source and DC biasing magnetic potential. Researches indicate that peak-peak value, full-wave root-mean-square (RMS) and differential RMS between positive and negative half waves of the terminal voltage have direct concerns with the biasing magnetic potential (or the measured current). But the differential RMS is properly adopted as the error signal for the close-loop control structureof the proposed novel DC comparator. Firstly, the differential RMS above is preconditioned and converted current (V/I) and amplified by power circuit. Then, the amplified difference current flows into the secondary winding to balance the biasing magnetic potential to form the zero flux condition (i.e. the primary ampere-turn is equal to that of the secondary) and thus the DC measurement goal is achieved. A discussion on theory, specifications, operational aspects, and construction feature, analysis and selection of the characteristic signals, both control properties of open loop and close-loop, output scope ,static and dynamic performance of the presented novel DC comparator model are analyzed respectively. Simulation and experimental results are presented to verify the truth of the comparator above. The proposed comparator integrates the advantages of the close-loop control principle (i.e. zero-flux technique), merits of MMC (Magnetic Modulator Comparator) and MAC (Magnetic Amplifier Comparator) together with operations of SR core. It is specially called self-balancing hybrid DC comparator. The common-mode voltage will be produced both by rectifier and inverter of the ASD plant. The common-mode voltage that reflects the zero-sequence voltage of the ASD power installation generates the common-mode current, whose spectrum and amplitude are directly dependent on such many factors as the modulating frequency, fundamental frequency and topology of the ASD set and so on. The common-mode current existed in ASD plant belongs to a typical pulse current with high frequency in the amplitude of several amperes, and it gives bad influence to the lifespan of the insulating layer and the bearing of the motor. Principles of the common-mode voltage and common-mode current induced in the ASD both of the conventional PWM inverter and the three-level inverter are analyzed. Rogowski coil is proposed to measure currents passing along each leg of L-R-C filter or each phase current flowing into the motor. The added current of each phase current of L-R-C filter or the motor can be verified to indicate the common-mode current of the ASD set centered on the proposed inverter topology. A 2250kW/6kV motor is presented to simulate and verify the truth of the proposed ASD topology and the test instrumentation centered on the Rogowski coil. The valuable theory is concluded and simulation research results are presented to meet design demands of the high voltage inverter drive plant.