A design method of adaptive load frequency control with dual-rate sampling

An adaptive control strategy for load frequency control, the purpose of which is to reduce the transient errors in the frequency and scheduled tie-line power deviations and to ensure zero steady state errors of these two quantities, is described. A dual-rate sampling self-tuning regulator whereby data sampling and control output are performed at different rates is designed for interconnected power systems with unknown deterministic load disturbances. the proposed control scheme is applied to a two-area power system provided with reheat thermal turbines and the control effects of the regulator are examined using digital simulation.     

Vertical variations in the concentration of mercury in soils around Sakurajima Volcano,Southern Kyushu,Japan

In an effort to estimate the influence of mercury emitted from Sakurajima Volcano, Southern Kyushu, Japan, on the accumulation of mercury in soil, the vertical distribution of total mercury in soils was investigated together with organic matter content and grain size. The soils were sampled at a thickness of 1 cm from the surface to depth of 1 m at five locations on Sakurajima and two control locations, i.e. Takatoge approximately 11 km southeast and Suzuyama 22 km southwest of the volcano. The concentration in soils increased with the distance from the volcano and was 6.5+/-1.9 ngg(-1) (n=335), 29.0+/-15.6 ngg(-1) (n=100) and 229+/-105 ngg(-1) (n=103) for Sakurajima, Takatoge and Suzuyama, respectively. The concentration of mercury correlated with the amount of organic matter, but not with grain size distribution. The sedimentation rate for Sakurajima, Takatoge and Suzuyama was estimated from geological data to be approximately 1.3, 0.083 and 0.0048 cmyear(-1), respectively. The relatively fast sedimentation of Sakurajima soil was caused by the frequent precipitation of volcanic ash. The annual deposition of mercury estimated for Sakurajima, Takatoge and Suzuyama from the mercury concentration, sedimentation rate and soil density was 9 x 10(4), 3 x 10(4) and 2 x 10(4) ngm(-2)year(-1), respectively. Although the soil of Sakurajima had the lowest concentration among the three sites, it received the largest amount of mercury.     

A method of transient stability estimation for power systems by lyapunov function

The power system stability problem has been one of the major subjects concerning power system engineering, and is becoming much more significant today due to the increasing size and complexity of interconnected power systems. In this problem, it is well known that the direct method of Lyapunov is the most suitable method of on-line transient estimation for power systems, and several different techniques have been proposed for the construction of functions up to this time. However, the effectiveness of these Lyapunov functions for power systems have been demonstrated using only digital computer simulations. The purpose of this paper is to construct a microprocessor-based, on-line, transient-stability estimation system using the Lyapunov function constructed by the Lagrange-Charpit method, and to estimate the transient stability of an alternator connected to a large system. The experimental results show that this system can act satisfactorily for estimating the transient stability of the power systems.     

Bayesian Decomposition Method for Computing the Reliability of an Oriented Network

For a nonoriented network, Bayesian decomposition is straightforward and well known. A keystone element is assumed perfect (shorted), then failed (open) and the reliabilities of the two subnetworks are calculated. But for an oriented network, when the keystone element is assumed perfect, it cannot always be shorted (the 2 nodes brought together), because even a perfect element still retains its orientation. A technique for choosing keystone elements is proposed.     

A Decomposition Method for Computing System Reliability by a Boolean Expression

A substitutionary decomposition method for computing the reliability of a redundant system S given by a Boolean expression is proposed, System S is decomposed into two subsystems S(x) and S(x?) according to up-and down-states of its keystone variable x. This is repeated until all terms become s-independent in each decomposed subsystem. A criterion for choosing the keystone variable and a property which saves computation time are obtained.