1 Abstract—Transient single-phase short circuits are the most common transmission line faults. The short circuit arc of a transient fault is usually self-extinguishing after opening the line circuit breakers. High-speed single-phase reclosing of transmission line can help to improve system stability. Employing a pre-set reclosing interval may pose problem if the time interval is not sufficient to fully deionize the fault arc. It is desirable to have adaptive reclosing interval and fast detection of arc extinction, which could facilitate successful high-speed reclosing of transmission line and bring benefit to the system stability. A new adaptive reclosing algorithm is proposed in this paper. It uses the pattern of the faulted phase voltage in the complex plane to distinguish between transient and permanent faults and is also able to detect the time when the arc is extinguished. Theoretical analysis is provided to support the technique. In addition, the performance of the proposed technique is verified using a recorded field data from 765 kV transmission line and several cases simulated in EMTP including detailed arc and CVT modeling. Index Terms— Adaptive Single-Phase Reclosing, Secondary Arc Extinction, Four-legged Shunt Reactor Compensation, EMTP Simulation. I. INTRODUCTION or Extra and Ultra High Voltage (EHV, UHV) transmission lines, the setting of reclosing time interval is based on the maximum deionization duration of fault arc [1] and other system requirements. . For high voltage transmission systems, short circuit capacity of the system usually increases with the higher system voltage level. The higher short circuit power results in higher fault current and longer arc extinction time that requires the reclosing time interval to be extended to allow deionization of the air gap at the fault point [2]. Application of single-phase reclosing helps to increase the system stability limit as system voltage and short circuit level increase. According to statistics, more than eighty percent of transmission line faults are single-phase to ground faults and a high percentage of these faults are of transient type. Therefore, most of the line faults could be cleared by using high speed automatic single-phase reclosing. If arc is extinguished completely before the first shot of reclosing, the chance of successful reclosing would be maximized. In order to have successful high speed reclosing, different methods have been applied to extinguish the arc faster. One of the common methods is to use a four-legged shunt reactor at each end of the line. By appropriate selection of neutral reactor, the arc current can be limited and extinguished fast [3], [4]. This method is more effective for transposed lines than untransposed lines. Whereas, use of a four-legged reactor at one end and another four-legged reactor with switching scheme has been applied for untransposed lines at very high voltage levels [4][5]. Fixed reclosing interval setting is applied to majority of transmission lines. It may cause problem if the time interval is not sufficient to fully deionize the fault arc. The reclosing before arc extinction results in arc restrike and could cause the line protection to trip again, which may incur more stress to the power system. Under certain conditions, the reclose-onto- fault may put system stability at risk or damage the equipment. Hence it is desirable to have adaptive high-speed reclosing that uses variable open time interval to allow the breaker to close only after the fault arc has extinguished. Most of the techniques available or presented in the literature for adaptive reclosing are based on harmonic components of faulted phase voltage taken after breaker tripping [6][7][8]. These techniques were tested on transmission lines under certain system configurations. However, the pattern of the faulted phase voltage and its harmonic components varies drastically when transmission line is transposed, partially transposed or untransposed, shunt compensated with four-legged reactor that may or may not have switching capability. Practical adaptive single-phase reclosing algorithm has to consider all these conditions and perform proper operations under any system configurations or arcing conditions. Few papers also propose a hybrid reclosing scheme suitable for UHV transmission lines in which first the faulted phase is tripped; then, the remaining two phases are tripped with a brief delay. After three phase opening, the remaining charged energy in line capacitances and inductances will feed the arc till it is consumed and arc is quenched. In this case, if the fault is transient and arc is extinguished, a sinusoidal signal with a non-zero DC offset in faulted phase voltage appears that can be simply detected as a sign of arc extinction [9][10]. Whereas, if the fault is permanent, the faulted phase voltage becomes zeros and a permanent fault can be simply detected. The proposed algorithm in this paper uses the pattern of the faulted phase voltage in the complex plane, which is compared with the other two healthy phase voltages to distinguish between transient and permanent faults and also to detect when the arc is extinguished. Theoretical analysis is provided An Adaptive HV Transmission Lines Reclosing based on Voltage Pattern in the Complex Plane M.R. D. Zadeh, I. Voloh, Mital Kanabar, GE Digital Energy Y. Xue, American Electric Power F