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In the interconnected power systems with VSC-HVDC (Voltage Source Converter-High Voltage Direct Current) transmission links, the failures of VSC-HVDC system can cause large power imbalance for both sending-end and receiving-end power systems. In this paper, the reliability model of the VSC-HVDC system is developed based on series-parallel structure recognition. The frequency dynamics of the power systems are characterized considering the frequency regulation of the power systems in response to the power imbalance arise from the component failures. Moreover, the Monte Carlo simulation method is applied to analyze the frequency dynamics in different contingencies. The indices measuring the frequency stability and the reliability of the interconnected power systems are introduced.

This paper presents the theoretical analysis of capillary absorption dynamics for cemementitious material. Fractal theory is applied to analyse tortuosity of capillary pores in cementitious material and a definition of tortuosity is given. The dynamic equation of capillary absorption considering water evaporation and tortuosity of capillary pores is derived. Based on the dynamic model, the capillary coefficient and sorptivity of concrete are explained theoretically. In absorption test, water evaporation is one of the main reasons caused variations from linearity between water absorption height and the square root of time, or between water amount absorbed and the square root of time. In cementitious material, the evaporation rate is very small compare to capillary flow velocity at the initial time of absorption test. For simplification of testing procedure, there is no meaning to modify absorption test.

Serious damage and collapse of steel towers were easily induced by the ice disaster, the wind disaster and so on. After the disaster, to ensure the overhead transmission line working safely, it is necessary to strengthen the structure of the damaged tower perpetually, but there are few strengthening methods for the tower assembled by angle-shaped members at present. If an identical angle-shaped member is connected on the side of the existing angle-shaped member through bolts, the mechanical performance of the damaged tower can be improved effectively. In this paper several methods for strengthening the angle-shaped tower is proposed, and the mechanical behavior of the strengthened member of the tower is discussed experimentally, and some design suggestions for strengthening the towers are given.