This study concerns the analysis and minimisation of the force ripples existing in ironless permanent magnet planar motors. The force ripples is one of the key factors for moving accuracy of the planar motors. One of the main sources of the force ripples, the neglected higher harmonics of the magnetic flux density distribution, is analysed for synthesis of real-time control model in this study. An analytical model of the planar motor is firstly developed, which illustrates that the force ripples part caused by some higher harmonics can cancel each other when the length of the coil is an even multiple of the pole pitch of the magnet array. As a result, the force ripples caused by the higher harmonics can be basically eliminated with a selected coil. Finally, the analysis results are both validated by comparative simulation and experiment of two partial motors.

With a grid fault in mountainous area as an example, the defect of the small power source side recloser is presented, which takes no-bus-voltage as its criterion. It has longer latency time, risks the disconnection of all small power sources, and needs long time to restore normal operation. Based on the principles of automatic quasi-synchronization capture and low frequency unloading, a self-adaptive recloser scheme suitable for the tie-line in small power source area is proposed, which automatically selects the quasi-synchronization capture mode during high water period and the no-bus-voltage detection mode during low water period, and combines with the low frequency unloading to quickly restore region power supply. It is realized in the prototype equipment and the simulation with the fault record data and power grid parameters of recent years proves that it improves the safe and stable operation of power grid and the reliability of power supply.

In this paper, the burning reason of 220 kV breaker trip coil is analyzed in detail and suggestion of improving traditional trip circuit and closing circuit is made. The improving circuit can not only avoid burning of breaker trip coil or closing coil, but also monitor readiness of trip or closing mechanical structure and auxiliary contact.

This article discusses the fiber optic temperature sensors for temperature measurement methods used in power system. Such network distributed real-time detection system integrated fiber technology,modern sensor technology,network and computer monitoring and control technologies.Finally,actual temperature monitoring application in Taoshan-Chuanshan 110 kV high voltage power lines in a city power grids is showed.Test results show the high positioning accuracy and short response time.The system is reliable and can achieve large-scale temperature measurement.It can be effectively applied to on-line monitoring of temperature.