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The purpose of this study is to evaluate the effects of glass fiber (GF) of PA66-GF30 orientation on very high cycle fatigue (HVCF) life and also to develop an optimized test apparatus such as measurement of dynamic elastic modulus and design of test specimens. Dynamic elastic modulus, tensile strength and fatigue strength tests were conducted at room temperature based on GF orientation (0°, 45°, 90°). Conventional fatigue (3 Hz) and ultrasonic fatigue (20 kHz) tests were performed at the same stress ratio (R = −1). Fracture surface observation showed that GF 0° exhibited a higher fatigue strength in comparison with GF 45 and 90°. Various defects such as voids and microcracks to the load direction around the GF end or debonding in glass fiber reinforced plastic (GFRP) and the slope change in very long life regime of S–N diagram.

It is anticipated that AC distribution system can be replaced by DC distribution system in the near future because of the operation of various distributed source or microgrid system. However DC distribution system replacing 22.9kV AC distribution line is not sufficiently studied still. This paper describes lightning overvoltage analysis among many research fields should be studied to realize DC overhead distribution systems. DC distribution system is modeled using EMTP and overvoltage is analyzed according to interval of arrestor location, earth interval of overhead grounding wire and grounding resistance. It is evaluated that analysis results can be effectively used to design of future DC distribution system.

This paper describes switching surge analysis for reclosing decision in 345kV combined transmission line with GIL. Reclosing operation should be decided based on the detailed technical analysis in combined transmission line because this line includes power cable section which is week on insulation. Insulation of power cable can be breakdown at the week point in case of reclosing moment. Therefore the detailed analysis has to be carried out by considering several conditions such as charging rate, inserting resistance, arrester, length ratio of power cable section, grounding resistance, etc. Analysis is performed by EMTP/ATP.

In 22.9kV underground distribution system, power cables are provided with multiple-point ground in which each neutral line of the distribution cable(A, B, C phases) and three-wire common grounded at every connecting section. But in such grounding methods, circulating current flows between the neutral wire and grounding wire. And power loss due to circulating current also occurs in all conductors. Therefore it is getting necessary reducing circulating current in underground distribution system. This paper presents improved grounding method to overcome such problems. The proposed grounding method eliminates circulating current in the neutral line effectively and is verified that there is no electrical problem or any ineffectiveness of operating protection systems. These analyses are carried out by EMTP/ATPDraw to compare each grounding methods in steady and transient state. This grounding method suggested in this paper can be applied on real distribution system after field tests considering elimination of circulating current was implemented.

This paper describes that the evaluation on operation practicality of Al conductor cable will be used instead of Cu conductor cable. Analysis is divided into two kinds of cases as transmission and distribution. To evaluate that Al conductor line has the insulation strength indeed safely, various analysis and calculation such as single line-to-ground fault current, lightning surge and allowance current were carried. Model was established based on real combined transmission and distribution is being used in utility with EMTP. The analysis results on Al and Cu conductor line were compared each other. It was proved that Al conductor line can be operated instead of Cu conductor line without special insulation problem in transmission and distribution, in electrical view point such as overvoltage and allowance current.