An Algorithm Study Of Fault Location For Double Circuit UHV Transmission Lines On The Same Tower

Double circuit UHV transmission lines on the same tower have advantages of long transmission distance, large transmission capacity, low loss, high efficiency, and have become the skeleton of a strong smart grid in our country. The accurate fault location has important significance in assuring the safe and stable operation of UHV power grid. In this paper, an algorithm of fault location for double circuit UHV transmission lines on the same tower are studied.UHV power grid distributed capacitive current is big, transient process is long, aperiodic component attenuation is slow, and contains the whole time and less than a full time harmonic components. In power system protection and control, signal analysis and processing is based on the fundamental component. Therefore,based on the analysis of the ability to extract fundamental wave and the response time delay characteristics of narrow-band filtering algorithm, and combined with the filtering performance of orthogonal filter algorithm, a fast narrow-band filtering algorithm based on orthogonal filter functions for fundamental component extraction is presented in this paper. Two trigonometric functions related with the length of data window are adopted as orthogonal filter functions, and the real and imaginary parts of phasors in their different data window lengths are obtained. The calculational formula of narrow-band filter initial value in each data window length is derived, thereby seeking the initial value of narrow-band filter to shorten the response time delay. The filtering algorithm has good filtering effect and fast response time, and can greatly improve the rapidity of electrical protection and control systems.Due to the high voltage level, long transmission distance, the function of the mutual inductance between the double lines, cross line fault and other factors, some changes have taken place in the electrical characteristics of double circuit UHV transmission lines on the same tower after the line fault.The traditional double circuit lines fault location methods are not suitable for double circuit UHV transmission lines on the same tower. Therefore, a new fault locating method based on the amplitude characteristics of hyperbolic cosine function is presented for double circuit UHV transmission lines on the same tower. Electrical fundamental component on both ends of double circuit UHV transmission lines on the same tower is extracted. Then six sequence component method is used to decouple it. This paper builds up a hyperbolic cosine fault locating function on the basis of the synthetic positive sequence fundamental component. When the reference point matches the fault position, the amplitude of fault locating function equals to maximum. By the amplitude characteristics of the function, a new fault location algorithm is proposed. Inspired by the structure process of the hyperbolic cosine fault locating function, based on double circuit UHV transmission lines on the same tower reverse(common) positive sequence fault component sequence network diagram, two methods of ohm's law and the long telegraph equation are respectively used to deduce the ratio of the currents on both sides of fault point. Calculate the absolute value of the difference between the ratio of the the currents on both sides as a function of fault location. If and only if the reference point matches the fault position, the value of fault locating function equals to minimum.Theoretical analysis and simulation tests prove that the proposed two methods are not affected by system impedance, the fault point transition resistance, line distributed capacitive current and other factors, can guarantee high fault location accuracy and quick calculating speed, and can fulfill the requirements in the field.