Research On Distance Protection Of Transmission Lines With Series Compensation Capacitor

Series compensation capacitor can shorten the electrical distance of transmission lines; improve the stability of power system. Whereas, the introduction of series compensation capacitor brings new following issues and enhance the difficulty and complexity of fault judgment in the power system relay protection. The work of this paper is to analyze the influence the series compensation capacitor brings to impedance distance protection, zero-sequence distance protection and power-frequency distance protection, bring forward the solution scheme. At the same time, this paper advances the new method which using least-square method to calculate compensation degree and fault position when series compensation capacitor installed in the middle of lines.Firstly, the paper analyze the fault that exists in the series compensation capacitor lines. After analyzing the relationship among frequency characteristic which series compensation capacitor arise, compensation and fault position, we find that resonance frequency in the transient low-frequency component induced by the series compensation capacitor is calculated by the following equationω=ω₀(?) . And then, we analyze the relationship between the metrical impedance in tradition distance protection and equivalent impedance measured from the port. Due to the metrical impedance is calculatedas Z_J(t) = [u^*(?)(t)]/[i^*(?)(t)]and the equivalent impedance is calculated as Z(t) = L^-1[Z (s)], we can deduce that the time-domain characteristic of metrical impedance depends on waveform of current and voltage. At the end, the author analyzes the wave process of series compensation capacitor and deduces the reflected system and transmission system. According to the analysis of frequency-domain characteristic, we find that transmission wave shows high-frequency character, while the reflected wave shows low-frequency smooth character.Secondly, this paper detailedly analyzes the influence series compensation capacitor brings to distance protection, separately analyze the different situation including the install position and compensation degree occurred in the impedance distance protection, zero-sequence distance protection and power-frequency distance protection. To the direction impedance distance relay and power-frequency variation distance relay , we conclude that, the impact of series compensation capacitor installed on the two sides is very small, when the series compensation capacitor installed in the middle of lines, we have to identify the fault occurred before or after the series compensation capacitor. To the zero-sequence reactance relay, when the series compensation capacitor installed at the end of lines, it would affect the phase relationship of between measured zero-sequence current and fault branch zero-sequence current, therefore, it would induce the mis-operation or refuse operation.Finally, the paper brings forward least-square method parameter estimation principle, and introduces a novel fault position identification which can avoid the influence series compensation capacitor and its compensation degree. The novel scheme can not only calculate the component coefficient which can certain the fault occurred before or after the series compensation capacitor, but also deduce the metrical impedance and the fault distance. Theory analysis and EMTP simulation results show that this method has a high reliability, veracity and practical value.