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.
A combined permanent magnet actuator with auxiliary flux weakening for 126kV vacuum circuit breakers
Compared with the actuator applied in vacuum circuit breakers of middle-voltage power system, the actuator used in high-voltage power system has much longer stroke. This difference limits the traditional actuator of middle-voltage vacuum circuit breakers to be used in high-voltage power system because the dynamic performance cannot be well satisfied. This paper proposes a novel permanent magnet actuator (PMA) for 126kV vacuum circuit breakers with auxiliary flux weakening coils. The proposed PMA can decrease the holding force in the open and closed positions, shorten the time of operation and decrease operating power. The electromagnetic performance is calculated using finite element method. The simulated results show that the proposed PMA has excellent work performance, meeting the requirements of high-voltage vacuum circuit breakers.
ARRESTS AMONG HOMELESS AND RUNAWAY YOUTHS: THE EFFECTS OF RACE AND GENDER
ABSTRACT This study examined the contributions of race and gender to the likelihood of a first post-run arrest for a more serious and less serious offense in a sample of homeless and runaway youths from four Midwestern states. Event history analysis was used to test the hypothesis that race and gender would interact so that the likelihood of a first post-run arrest for a more serious and less serious offense would be highest for non-white males and non-white females, respectively. Potentially confounding factors—deviant subsistence strategies, substance use, gang involvement and membership, prior arrests, age, prior physical abuse, age on own, and spending time on the street—were controlled in the analyses. The hypotheses regarding the interaction of race and gender were not supported by the data. Non-whites were more likely than whites, and males were more likely than females, to be arrested for a more serious offense, and white females were more likely than non-white females to be arrested for a less serious offense.