Zhang Bi-de

A Method of Diagnosing Power Transformer's Fault Based on Fuzzy c and Immune Genetic Algorithm

The local best solution is often gotten by fuzzy c. But the whole best solution can be gotten by immune genetic algorithm (IGA) effectively. In this paper, a new method that integrates fuzzy c with IGA is put forward for fault diagnosis of power transformer. The method converts the problem about minimum for fuzzy c to the problem about maximum for IGA. From the practice, the new method can diagnose the power transformerpsilas faults effectively. It has higher reliability and practicability.

Design and experimental investigation on the electromagnetic repulsion mechanism of high speed vacuum disconnect switch

The development of a large-scale HVDC power grid requires a reliable, fast and low-loss hybrid HVD circuit breaker. The high speed disconnect switch is an essential part of hybrid HVDC circuit breaker concept. The objective of this paper is to design an electromagnetic repulsion mechanism for high speed vacuum disconnect switch of a hybrid HVDC circuit breaker and meet the premise that the motion distance of the moving contact is larger than 10mm in the first 2ms. A multi-physics FEM simulation model that can predict the dynamic characteristics of high speed vacuum disconnect switch with a high degree of accuracy is developed. The parameters of the electromagnetic repulsion mechanism are analyzed and a brute force optimization algorithm is implemented to obtain the optimal model of the electromagnetic repulsion force mechanism. The developed model was validated experimentally with a built a high speed vacuum disconnect switch prototype and the results show that the proposed model can be used to accurately predict the performances of high speed vacuum disconnect switch.

Modeling of high frequency transients of vacuum circuit breaker switching transformers in offshore wind parks

Switching transient as one of the main transient phenomena in power systems has been simulated and measured in many studies. Since offshore wind farms have been integrated to power system only in recent years, the consequences of switching phenomena in offshore wind farms have not yet been thoroughly analyzed. In this paper, the high frequency transient over-voltages of vacuum circuit breaker switching transformers in collection grid of offshore wind parks are studied. Based on the reflection and refraction of traveling waves and vacuum circuit breaker characteristics, the Vacuum circuit breaker has been modeled in PSCAD/EMTDC, which simulates the occurrence of current chopping, re-ignition and pre-strike that will cause high frequency, steep fronted transient voltages and currents. The main reasons for the occurrence of over-voltages in collection grids for offshore wind parks have been analyzed. Finally, the offshore wind farm internal electrical system model has been developed and the case of breaking transformer with VCB in three-phase system has been simulated.

Research on controlled switching in reducing unloaded power transformer inrush current considering circuit breaker's prestrike characteristics

A random energization unload power transformers may cause large inrush currents and overvoltages, which have high magnitudes and rich harmonic components. These transients have undesirable effects, including potential damage or loss-of-life to the power transformer, protective relay misoperation, and reduced power quality on the system. Controlled switching is one of the most effective methods to eliminate inrush currents when energizing an unload transformer, and the performances of controlled energizing unload power transformers mainly depend on the optimum closing instants of circuit breakers. The influences of the prestrike characteristics of circuit breaker on controlled energizing unloaded power transformers are analyzed. And a math model of is given to determine the optimum closing instant in terms of the prestrike characteristics of circuit breakers. Experimental investigations are carried out in order to demonstrate the proposed method. The results show the validation to reduce the unloaded power transformer inrush currents.

Notice of Retraction Research on high accurate position control of synchronous vacuum circuit breaker

In order to compensate for the influence of temperature, control voltage, ageing and other disturbances, guarantee that the operating times will remain stable in the long term, a high accurate position control of synchronous VCB is presented. An adaptive fuzzy controller of controlled motion was developed to ensure the movable contact of the circuit breaker always follows the pre-defined optimal travel curves. Test the vacuum circuit breakers operating characteristics, the test results show that the position control can meet with the consistency of operating times requirements of IEC62271-302 for synchronous switching and the drifts of operating times are less than ± 0.5ms.