Research On The Principle Of An Adjustable Reactance Based On Magnetic Control And Its Application In Arc-suppression Coils

In this dissertation, an adjustable reactor, which works on the principle of magnetic flux control, is deeply analyzed theoretically and technically on the basis of comprehensively summarizing the present development in adjustable reactors at home and abroad, especially, the study on the application of this reactor to the arc-suppression coil is emphasized in the paper. First, a mathematic model of adjustable reactors based on the magnetic flux control is established and a deep analysis is made. The realization of the adjustable reactance depends on the decoupling between the current and voltage in the primary winding and the secondary winding of a transformer working as a adjustable reactor, and the decoupling must be based on a feasible control strategy. So we develop a feasible control strategy, including the model and some corresponding control methods, etc. Second, four practical control methods of adjustable reactors with high voltage and large capacity are studied in the paper while reducing production cost and restraining harmonic waves are taken into account. The first is the compensation technology by injecting current into the multiple branches of the reactor secondary. And the second is a method of controlling current available to a power switch devices with low frequency but large power or high frequency but small power. The third is the method for cascaded-inverters based converter, and the last is with phase-shifted SPWM. And then, by researching the compensation principle of resonant earthed neutral systems and referring to the excellent characteristic of such adjustable reactor, an automatic resonant arc-suppressing coil system based on magnetic flux control is proposed here. A method of measuring the grounding capacitance, based on resonance principle and frequency scan, is developed by injecting a current of scanning frequency into the secondary winding of the arc-suppressing coil. The mechanism of automatic resonance and compensation of the system in the period of a single-phase earth fault is also analyzed. Especially, a novel impedance-adjustable device based on magnetic flux control is proposed. Its impedance consists of an equivalent resistance and reactance. They can be adjusted by changing the current in the windings for controlling resistance and the current in the windings for controlling reactance, respectively. In terms of the principle, an improvement on an arc-suppression coil based on magnetic flux control is made. As a result, we develop an excellent device for compensating single-phase earth fault current, which can also compensate the resistive component of the current flowing towards single-phase earth fault point except the capacitive component. The system overcomes the limitation of the present arc-suppression coils that only the capacitive part of single-phase earth fault current can be compensated. Finally, It is verified by the results of theoretical analysis and experiment that its reactance of an adjustable reactor based on magnetic flux control is linearly changed with the compensation ratio of the current in the secondary to the one in the primary, and it produce no lower order harmonics. A practical application of adjustable reactor based on magnetic flux control is that we successively developed a capacity of 180 KVA automatic resonant arc-suppressing coil for the first time. It exhibits a series of excellent performances as we expected, such as automatic resonance tuning, fast dynamic response, absence of lower order harmonics, and easy realization of the system, and etc.. From the simulation it follows that the improved arc-suppression coil do compensate both the resistive component and capacitive component of the current flowing towards single-phase earth fault point.