Design of Hybrid Compensators for Power Quality Improvement of Oilfield Drilling Electrical System

With large-scale use of kinds of motors, oilfield drilling electrical system always accompanied by serious power quality problem, including reactive current, harmonics current and grid voltage distortion, which would greatly threaten the safety and proper working of the whole system. This paper focuses on a power quality improvement project to solve these problems. A hybrid compensating scheme, including an active compensator and a passive compensator, is carried out. Because of the specificity of oilfield drilling electrical system, compensators are redesigned against features of this application background. And then the current detection point arrangement of this hybrid system is also taken into consideration to build the whole system much more effective and reliable. Now the improvement project is already implemented in application field, and the power quality of the system is greatly improved.

Apatite formation and weight loss study in EDMed perforated AZ31 Mg-alloy

Porous structures are highly preferred for bone regeneration and high tissue in-growth.In present work,electrical discharge drilling(EDD),a thermal erosion process was used to produce through holes in Mg-alloys to fabricate perforated structure similar to open cell porous structure in extruded AZ31.Apatite formation and weight loss study was conducted for 7 days,14 days and 21 days after immersion tests in SBF solution.The perforated structure in AZ31 with 26 through micro-holes provides 72%increase in surface area but with marginally 4%higher weight loss as compare to non-perforated structure.Comparing perforated and non-perforated samples of Mg-alloy,it was well observed that perforated structure forms high volume of apatite as compared to non-perforated structure.Scanning electron microscopic(SEM)study revealed that in perforated structure,drilled holes retain their circularity after 21 days of immersion test and distinct corrosion phenomenon occur at localized sites.

Stage identification and process optimization for fast drilling EDM of film cooling holes using KBSI method

Fast drilling electrical discharge machining(EDM)is widely used in the manufacture of film cooling holes of turbine blades.However,due to the various hole orientations and severe electrode wear,it is relatively intricate to accurately and timely identify the critical moments such as breakout,hole completion in the drilling process,and adjust the machining strategy properly.Existing breakout detection and hole completion determination methods are not suitable for the high-efficiency and fully automatic production of film cooling holes,for they almost all depend on preset thresholds or training data and become less appropriate when machining condition changes.As the breakout and hole completion detection problems can be abstracted to an online stage identification problem,in this paper,a kurtosis-based stage identification(KBSI)method,which uses a novel normalized kurtosis to denote the recent changing trends of gap voltage signals,is developed for online stage identification.The identification accuracy and generalization ability of the KBSI method have been verified in various machining conditions.To improve the overall machining efficiency,the influence of servo control parameters on machining efficiency of each machining stage was analyzed experimentally,and a new stage-wise adaptive control strategy was then proposed to dynamically adjust the servo control parameters according to the online identification results.The performance of the new strategy is evaluated by drilling film cooling holes at different hole orientations.Experimental results show that with the new control strategy,machining efficiency and the machining quality can be significantly improved.