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This paper presents the result of the estimation of the power interruption costs of Korean commercial customers. Commercial customers are usually located in urban areas and considered very important because a power interruption on them can expand to additional damage to related users. Their power interruption costs were calculated through a survey with the process of data selection. Also, the power interruption cost for each customer's business type was calculated and compared with that of foreign cases.

As the increasing HIF(High Impedance Fault) with the arc cannot be easily detected for the low fault current magnitude compared to actual load in distribution line. However, the arcing current shows that the magnitude varies with time and the signal is asymmetric. In addition, discontinuous changes occur at starting point of arc. Considering these characteristics, wavelet transformation of actual current data shows difference between before and after the fault. Althogh raw data(detail coefficient) of wavelet transform may not be directly applied to HIF detection logic in a device, there are several developing methods of HIF monitoring data using the original wavelet coefficients. In this paper, a simple and effective developing methods of HIF monitoring data were analized by using the signal data through an actual HIF experiment to apply them to economic devices. The methods using the sumation of the wavelet coefficient squares in one cycle of the fundamental frequency as the energies of the wavelet coefficeits and the sumation of the absolute values were compared. Besides, the improved method which less occupies H/W resouces and can be applied to field detection devices was proposed. and also Verification of this HIF detection method through field test on distribution system in KEPCO power testing center was performed.

– Korea has introduced power trading system since 2001 but long-term Generation system planning has been executed by government for cost minimization every 2 years. Until currently the model which is used for generation system planning and best-mix only considers cost minimization and total yearly or quarterly electricity demand every year. In a view point of one day power supply operation, the ramp up/down rate of total generation system, minimum up/down time and GFRQ(Governor Free Response Quantity) are very important. This paper analyzes optimal fuel-mix for 2022 Korea generation system satisfying these constraints of each fuel type and considering pump storage plants, construction cost and CO 2 Charge Using MILP(Mixed Integer Linear Programming) method. Also the sensitivity analysis which follows in future power industry environmental change accomplished. Keywords : Optimization model, LDC, Fuel-Mix, Daily operation, Load-Follow, Fuel cost change 1. Introduction In 2008, The ratio of LNG in total cost is about 50% while the ratio of LNG in total generation energy is 19%. And 80% and more of production cost are generation cost when total cost consists of generation, transmission, distribution and sales cost. For this reason, a sales company, as well as generation companies became interested in the optimal fuel-mix. Best mix can be defined as a power generation con-figuration that satisfies a specific purpose in maximum. Such purposes can be cost minimization, profit maximization or guaranteed return of investment for the market participants. Cost minimization is used as an objective function when preparing best mix in a national scale. In Korea, ‘Basic Plan of Long-Term Electricity Supply and Demand[1]’ is established every 2 years by government. The generation expansion plan announced as a result of the plan is the optimized result for cost minimization that satisfies such constraints conditions of supply safety or environmental burden. Generation fuel-mix, as well as the cost is very important for the stable system operation. Power system in real-time power supply and demand should be balanced. It is difficult to predict demand changes which consist of long-period variation more than ten minutes, short-period variation and small incremental changes within a minute(due to sudden load changes and faults). So, the grid system operator must keep the reserve margin. Fig. 1 shows the characteristics of frequency regulation and represents the controlling subjects which are related to the amount of changes over time.