Studies On Adaptive Single-phase Auto-reclosure Of Transmission Lines Based On Mathematic Morphological Transform

The auto-reclosure technique has been widely applied in real power systems now. It is an effective method to improve the stability and synchronism of power systems. However, the present auto-reclosure technique normally employs a prescribed reclosure time, that is, the breaker is re-closed after a fixed period following a tripping operation. Main problem with the conventional reclosure scheme is a risk of a second shock to the system in the case of a permanent fault, when may lead to system oscillation. In order to overcome this disadvantage, the concept of distinguishing between transient and permanent faults was raised by some researchers.In this paper, the above problems are studied and criteria of dual-window transient energy ratio based on mode current and residual voltage to implement the adaptive auto-reclosure of transmission lines are proposed respectively. To effectively extract the high frequency (HF) energy of the mode current or the residual voltage, a novel signal processing tool named as Mathematical Morphological is proposed.Mathematical morphology (MM) is developed from set theory and integral geometry, which is concerned with the shape of a signal waveform completely in the time domain rather than the domain frequency. MM has been widely used in the areas of image processing, machine vision and pattern recognition. The mathematical calculation involved in MM includes only addition, subtraction, maximum, and minimum operations. When acting upon complex shapes of signal, MM operations are capable of decomposing a signal into meaningful parts and separating them from the background, as well as preserving the main shape characteristics.To effectively extract the high frequency (HF) energy of the mode current and residual voltage, two novel mathematic morphological filter operators named as generalized multi-resolution morphological gradient (GMMG) and Close-opening-Open-closing morphological gradient (COOCG) are put forward on the basis of multi-resolution morphological gradient (MMG). Compared with multi-resolution morphology gradient (MMG) transform, the design of the relative factors of the structure element is more flexible and COOCG has lower unbalanced output when processing the steady-state signal. The criterions are described detailed latterly. Finally, the disadvantages of existent schemes and proposals to improve the criteria are pointed out.