| The resources shortage, environmental pollution and climate change are the great challenges in the world wide, because of the overuse of a large number of fossil energy. Therefore, it is important to promote the energy revolution, the energy saving, and emission reduction to achieve the coordinated development of the economy, society and the environment. The Global Energy Interconnection is an important platform to optimize the allocation of global resources and promote the use of clean energy. The modern high voltage power grid is the important composition of the Global Energy Interconnection. To ensure the stable and safe operation is of the vital significance to ensure the national energy security and promote the progress of global energy. The Ultra High Voltage and the Extra High Voltage transmission are the key technology of the modern high voltage power grid. By using of series compensation and multiple circuits on the same tower is conductive to further increase the transmission capacity of Ultra High Voltage and Extra High Voltage power grid and make full use of the transmission corridor and save investment. In this paper, the key problems existing in the relay protection of the series compensation and multiple circuits on the same tower are analyzed. The research work mainly includes the following aspects:(1) A compensation method to reduce the secondary arc current for separately and completely transposed four-circuit transmission lines on the same tower is proposed. Firstly, the average values of the line to ground capacitances, inter-phase capacitance, and zero sequence mutual capacitance are converted to sequence value through the transformation matrix. Secondly, the inductance compensation scheme is converted to the sequence component. The sequence component of the inductance can be converted to the same form as the positive capacitance, inter-phase capacitance and zero sequence mutual capacitance. Finally, the compensation reactance is calculated according to the requirement of the compensation degree. The neutral point reactance is also optimized about various maintenance conditions. The simulation results show that this compensation scheme can decrease the value of secondary arc current and recovery voltage in the single-phase to ground fault and the cross country fault with same or different phases in the four-circuit transmission lines.(2) A distance protection algorithm for single-phase to ground fault in the four-circuit transmission lines on the same tower based on optimal equivalent zero sequence mutual inductance compensation coefficient and single circuit electrical data in one end is proposed. Firstly, by using the relationship between the zero sequence current and zero sequence impedance, the health circuit zero sequence current can be calculated by the fault circuit zero sequence current. Secondly, the optimal compensation coefficient of zone-I distance protection is selected based on the calculated zero sequence mutual inductance compensation coefficient under different operation modes in the protection side. The optimization method of zero sequence mutual inductance compensation coefficient for maintenance state is also proposed. The simulation results show that the proposed algorithm is not affected by the zero sequence mutual inductance in the four-circuit transmission lines and it is superior to the traditional distance protection algorithm.(3) A distance protection time domain integral algorithm is proposed for a single-circuit series compensated line. According to the fault current, the series compensation capacitors have three types of operation condition. a) Metal Oxide Varistor (MOV) and air gap (GAP) do not bypass the series compensation capacitor. b) the MOV bypasses the series compensation capacitor and the GAP does not conduct. c) the GAP conducts and bypasses the MOV and series compensation capacitor. The time domain equation of fault circuit based on the condition of series compensation capacitor and the equivalent circuit is utilized in this algorithm. The unknown parameters of the equation include fault circuit equivalent resistance, fault circuit inductance, series compensation capacitor and initial voltage of the series compensation capacitor. The known parameters include instantaneous voltage and current measured by the relay protection. In the traditional distance protection algorithm, if the state of the series compensation capacitor is assumed during the fault, while series compensation capacitor is different from the assumption of state action, the relay protection maybe mal-operation. In the proposed algorithm, the series compensation capacitor is set as an unknown parameter to solve the equation without the necessary to determine the state of the series compensated capacitor in advance. Simulation shows that in the single-phase to ground fault and phase-to-phase fault, the proposed algorithm can accurately calculate the fault distance in these cases: the MOV/GAP conduct; MOV conducts; GAP conducts.(4) A distance protection integral algorithm for double-circuit series compensated lines is proposed. Due to the influence of zero sequence mutual inductance existing in the parallel double-circuit transmission lines, the unknown parameters of the time domain equations for the fault circuit include fault circuit equivalent resistance, fault circuit inductance, zero sequence mutual inductance, series compensation capacitor and initial voltage of the series compensation capacitor. The known parameters are instantaneous values of voltage and current measured by the relay protection. The time domain equation for the fault circuit is solved after the integration of time. Simulation shows that the proposed algorithm, which is not affected by the zero sequence mutual inductance, can accurately calculate the fault distance in these cases:the MOV/GAP conduct; MOV conducts; GAP conducts.(5) A distance protection algorithm is proposed for Ultra High Voltage double-circuit transmission lines with high fault resistance. Firstly, the Fourier transform is used for the fault phase voltage and current and adjacent circuit zero sequence current. Secondly, with the principle that the voltage and current at the fault point have the same phase the fault distance can be calculated through the equation about the ratio of the real and imaginary part of the increment of positive and negative sequence current and the voltage at fault point. The angle of Ultra High Voltage system impedance is very high. The simulation results of the algorithm are very well in Ultra High Voltage transmission lines. The simulation shows that the proposed algorithm is better than the traditional algorithm with high resistance fault. It is not affected by the zero sequence mutual inductance and load current. The algorithm also presents good performance when one of the two circuits is in maintenance state or two lines are in split operation.This paper is mainly to solve the five key problems existing in the construction of the modern high voltage power grid. Therefore, this paper has high engineering application value and research significance... |
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