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Recently, the application of the magnetic field during the solidification process of alloys has become of great interest, owing to its ability to enhance microstructures. Hence, the present work aims to study the impact of a rotating magnetic field on the microstructure, thermal, and creep properties of the Sn–2.0Ag–0.5Cu (SAC205) alloy during solidification. Results demonstrated that applying a rotary magnetic field homogenized the distribution of intermetallic compounds and improved the microstructure. Additionally, the magnetic field diminished undercooling from 22.5 oC to 11.4 oC, indicating that the magnetic field is very useful in enhancing the microstructure and the alloy's reliability. The pasty range values for SAC205 and SAC205-B were 7.2 oC and 8.6 oC lower than 11.0 oC for lead-tin, leading to a reduction of the alloy porosity. The SAC205-B alloy exhibited the longest creep rupture time of 158.5% compared to the SAC205. The n values of SAC205-B were higher than those of SAC205. Consequently, the SAC205-B alloy displayed the highest creep resistance and lowest creep rate (28.53%) compared to the SAC205. The Q values were 51.2 and 67.5 kJ/mol for SAC205 and SAC205-B, respectively, controlled by pipe diffusion. This research will provide practical advice for the manufacture of the solder alloy. [ABSTRACT FROM AUTHOR]

A generic concept combining transient angle and voltage stabilities of parallel ac/dc transmission is introduced. It proves that HVDC schemes in parallel operation with ac transmission are prone to both transient swing angle and voltage instabiliities. This tendency is intensified as the parallel ac interconnection becomes more stronger. The concept also explains why an HVDC scheme fitted with classical dc power controls does not contribute to system synchronizing torque and may increase the risks for instability. The concept offers a solid means to develop robust strategies to control the dynamic operation of dc and ac transmissions in parallel. With such strategies, the HVDC scheme can positively participate in the instantaneous rescheduling of power according to arising network conditions, particularly during disturbance conditions. Keywords: transient stability, voltage stability, dc transmission, controls

The phenomenon of transient voltage stability in power transmission systems is explained. A generic method is used to examine the dynamics of stabilization as influenced by mechanically switched shunt capacitors and by static compensators. A comparison is made for the voltage stabilizing performance of different configurations of static VAr compensators. Technical merits of newly developed devices, such as voltage-source GTO converter based VAr compensators and thyristor-controlled series capacitors, in terms of counteracting voltage instability are also examined. A newly developed special controller for SVC schemes with TCR in transmission systems is presented. The controller ensures a stable operation of the load interconnecting network at the usually unstable region where conventional SVC controls are void. Keywords: voltage stability, Static VAr Compensators, shunt capacitors, voltage-source converters, thyristor controlled series capacitors, FACTS.

This paper introduces a practical control philosophy for HVDC transmission in parallel operation to an AC system with particular emphasis on co-ordination of both transient and dynamic stability. Systematic development of the control scheme on the basis of on-line identification, optimal control and rule-based bang-optimal co-ordination principles is presented. Verification tests of the scheme on a physical HVDC/AC system simulator show that the simple control computer algorithm is practical and robust. The controller can successfully distinguish between different system fault severities and adapts its output signals to provide maximum synchronising torque and ensure optimal damping of power oscillations.

A didactic explanation of voltage stability associated phenomena at HVDC terminals is presented. Conditions leading to ac voltage collapse problems are identified. A mechanism that excites control-induced voltage oscillations is shown. The voltage stability factor is used for obtaining the maximum power limits of ac/dc systems operating with different control strategies. Correlation to Pd x Id curves is given. Solutions for eliminating the risks of voltage collapse and for avoiding control-induced oscillations are discussed. The results are supported by detailed digital simulations of a weak ac/dc system using EMTP.