A permanent magnetic actuator with scheduled stroke curve for vacuum circuit breakers
The load characteristics of vacuum circuit breakers (VCB) are very close to the output characteristics of permanent magnetic actuator (PMA). The combination of PMA and VCB facilitates the development of phase-controlled switching technology because of its controllability. The operation time dispersion of PMA is very small, but when the actuator is impacted by the change of environment or its components, its dispersion will be unfit for phase-controlled switching. A new type of actuator driving system for PMA was proposed, which was combined with sensors, embedded system and capacitor controlled by high-current power electronic devices. The iron core trajectory of PMA was measured by a displacement sensor and compared to a scheduled action curve, the environment temperature is from a temperature sensor and the current from a Hall current sensor, then compensation to displacement was made based on the adaptive control algorithm and history data in order to match the optimal stroke curve of vacuum circuit breakers. In different conditions, the test results show that the stroke curve was in keeping with the scheduled curve and the operating time dispersion of VCB meets the requirement. The new type actuator driving system can supply an easy-controlled, constant-operating- time execution unit to controlled switching.
MV vacuum switchgear based on magnetic actuators
Vacuum switchgear puts special demands on the operating mechanism, such as a large holding force and impact breaking capability. Characteristics of a permanent magnetic actuator are closer to what is required for vacuum switchgear then those of the usual spring operated mechanism. Application has advantages for simplicity, reliability and controlled switching. Tests prove these statements, for instance by switching 50000 times. Two new ideas are presented in the paper: (1) separating of the magnetic circuits for closing and opening leads to optimisation, larger forces and a more compact actuator; amd (2) application of a new designed permanent magnetic lock makes the closing characteristic to be reproduced very accurately, which can ideally be applied in the case of controlled switching. Tests confirm this feasibility.
Concentration of amino acids in wine after the end of fermentation by Saccharomyces cerevisiae strains
Both quantitative and qualitative differences in the utilization and release of assimilable nitrogen by two wine strains of Saccharomyces cerevisiae (cerevisiae and capensis) under different conditions of oxygen were observed. These differences were influenced by the presence of oxygen at the beginning of the fermentation, and by the strain of S cerevisiae. The release of some amino acids post-fermentation may be the result of reoxidation of NAD(P)H in order to maintain a normal redox balance. Copyright © 2003 Society of Chemical Industry