Translated Abstract
The requirements for protective relaying are higher and more urgent than ever as far as the unceasing increasements of power transmission capability, voltage level and system stability. Are concerned. Longitudinal protective relays are widely used as main protection in HV transmission line, their onsite operations are effective and bring on experienced advices and the effects are good as a whole. The paper do research on the protection of HHV/EHV/HV transmission line. As the UHV/EHV/HV transmission lines are characterized by relatively large distributed capacitance, the paper do some research on the new pilot protection principle which is not influenced by the capacitance of the line Distance element plays an important role in the pilot protection which is constructed by distance element and line backup protection, but the distance element is influenced heavily by the swing of the power system, the paper do some research on the theory of swing block and unblock, and do some research on the faulty phase selection during power swing. (1) A novel pilot protection principle base on fault component integrated impedance is proposed in this dissertation, the fault component integrated impedance is difined as the ratio between the sum of two terminals fault component voltage phasor of the transmission line and the sum of two terminals current phasor of the same line. When an outer fault occurr, the fault component integrated impedance reflect the capacitance impedance of the line, its value is large, and when an internal fault occur, the fault component integrated impedance reflect the impedance of the system source and the line, its value is relative small. According to such a characteristic, whether there is fault in the line can be distinguished. The criterion is not influenced by the capacitive current and fault resistance, has inherent ability of phase selection, and can be applied in the line with or without shunt reactor.(2) Because fault component can only be distracted in a short time, so the pilot protection principle based on the fault component integrated impedance can be used only in a short time. In order to protection the line during the whole fault period, pilot protection principle based on the full component integrated impedance is proposed in the paper. The full component integrated impedance is defined as the sum of two terminals voltage phasor of the transmission line and the sum of two terminals current phasor of the same line. When an outer fault occurred, the integrated impedance reflect the capacitance impedance of the line, its imagine part is negative, and the absolute value of its imagine part is large, when an internal fault occurred, the imagine part of the integrated impedance of faulty phase is either a positive figure or a negative figure with small mode, According to such a characteristic, whether there is fault on line or not can be distinguished. The new criterion doesn’t need capacitance current compensation, has inherent fault phase selection ability, can be applied in the line with or without shunt reactor, can resist large fault resistance, and can be used during the whole fault perion..(3) The fault component integrated impedance is influence by the capacitance between phases and the capacitance between the phase and the ground, whose calculation result would be different when the fault type changes. The pilot protection principles based on the fault component positive sequence integrated impedance, on the negative sequence integrated impedance, and on the zero sequence integrated impedance are proposed, these three pilot protection principles don’t need compensating the capacitive current of the line, are not influenced by fault resistance, and the calculation results are steady, the setting rules of which are clear, can be set according to the positive sequence parameters, negative sequence parameters and zero sequence parameters of the line. These three pilot protection principles don’t have ability of phase selection, so they can be used under the conditions which needn’t phase selection, for example, these three pilot protection principles can be used for the high voltage cable or the overhead lines whose voltage level is equal to or less than 110kV. And with the help of the phase selection element, these three pilot protection principles can be used for the situation which need selecting faulty phase. (4) A set of transmission line pilot protection scheme based on integrated impedance is provided, which needn’t compensating the capacitive current, can be used for the line with or without shunt reactor, can provide protection function for the line during the whole fault period, has high sensitivity and certain practical value in the real project. In order to avoid losing protection under the condition when the voltage circuit is abnormal, the differential current protection with high current threshold is used as back up protection for the protection based on integrated impedance. The performance of the protection scheme during different operation condition, including cross country fault scenario, evolve fault scenario, power swing scenario and two phases operation scenario is analyzed, and the scheme is verified by the EMTP data and physical model data, the simulation result shows that validity of the scheme.(5) The current differential protection principle has been widely used for the transmission lines which is influence by the distributed capacitance current of the line, whose sensitivity is relatively low when the fault with high resistance occurs. A novel protection principle based on the resistance component of the differential current is presented in the paper, which can be used with full component differential current protection principle to provide protection for the line with high sensitivity and reliability. The criterion using the resistance component of differential current as operator component, is not influenced by the capacitance current at all, and is independent of shunt reactors. Its sensitivity for single-phase to ground fault with high resistance is very good. (6) Combined with the signal received from the protection at another line terminal, whether there is fault in the line can be distinguished by the distance pilot protection, and the distance element is also used as the back up of the pilot protection widely. But the distance element may be mal-operated during power swing, should be blocked during swing and unblock the distance element when the faults occur in the line. The schemes to block and unblock the distance element used now have much negative influence on the distance element. A power system instability detecting element based on the angle between the voltage of two terminals of the line is presented. Through the voltage and current the protective relay get and the line impedance parameters, the voltage of another terminal can be calculated. By the angle between the phasors of the sampled voltage and the calculated voltage of another terminal, whether the power system begin to swing can be distinguished. This instability detecting element can distinguishes whether the power system is stable or not, block the distance element in time, and is self-adaptive to the swing period.A power system swing unblock criterion of the three-phase faults based on the angle between the voltages of two terminals of the line for the high voltage line protection relay is presented. The angle between the phasors of the sampled voltage and the calculated voltage changes periodically when the power system swing, and when there is a three-phase fault occurring on the line, this value of the angel is 180°and does not change. According to such a character, a new three-phase fault unblock criterion is presented. The criterion can determine the unblock delay by the actual swing period, the time to clear the three phases fault in the line during swing is shorter.It is difficult to select the faulty phase during swing, the methods to select the faulty phase during swing now need to be improved. A novel phase selector based on the relative variation between measured impedance of single phase and measure impedance between phases during power swing is proposed. According to the characteristic that the measured impedance is constant in faulty phase and variable in sound phase, the fault phase can be selected. The proposed phase selector can select the fault phase quickly during power swing.
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