This paper describes an estimation scheme of torsional oscillation of turbine-generator shaft system. Large　torsional oscillation of turbine-generator shafts brings about life expenditure of the shafts. In case of using the　torsional oscillation observer in conventional monitor system of shaft life expenditure，it is concerned that the damping coefficients influence on the estimation of shaft life expenditure because the disturbance torque to the　generator is used as the input signal to the observer. Therefore，we proposed an observer where input signal is not the disturbance torque to the generator but the speed deviation at the end of the shaft system. This paper　evaluates the influence of the damping coefficients error in each observer upon the estimation accuracy of shaft life expenditure and shaft torsional torque.

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Earthing is an important technology in the fields of electric power, communication，and lightning protection. The earthing electrode is used as the ground and the electric terminal which comes in various shapes from small scale like rod-shaped and plate-shaped to large scale such as ring-shaped，mesh-shaped etc. When designing earthing，its resistance which is an index of the rise in electric potential must be known. The accurate analytic solution of the earthing resistance excepted for the electrode of the special form such as a rotating ellipsoid electrode cannot be obtained. The earthing resistance of the electrode such as a rod-shaped and a plate-shaped is computed by approximated analysis. There are methods of earthing simulation such as the tank model method or Laplace numerical analysis equation method （for example，the finite element method）used to estimate a shaped earthing resistance without analytic answer. This paper discusses the results of examining；comparing and analyzing the earthing resistance produced using the shape factor method which focuses on the shape of the earthing electrode.

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Distribution of lightning current in a building when it is directly hit by lightning is calculated by directly solving Maxwell’s equations with the help of Numerical Electromagnetic Code （NEC-4）. Lightning current shunts into wiring on each floor of the building unevenly through SPD’s, and current into wiring on the top and the bottom floors is the largest. SPD’s of high energy rating are necessary for apparatuses equipped on the top and bottom floors, irrespective of the height of a building.

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