Advanced Materials Research Vol. 676

Abstract: The design of impedance measurement instrument in electrical engineering based on phase-sensitive detector is introduced. The orthogonal vector measuring circuit based on phase-sensitive detector is employed in this design. The microprocessor C8051F410 is used to output the detecting signal and execute the control, calculation and display during the measurment process. The impedance measurement instrument has been applied in the Comprehensive Experimental System for Electronic Measurement Principle.

Abstract: In this paper, we consider an electrical sensor dispatching problem for automatic control systems(ACS). We propose an algorithm which selects one (or a group of) electrical sensor at each time from a set of electrical sensors. Then, the automatic control prediction algorithm computes the estimates of the continuous state and the discrete state of the ACS based on the observation from the selected electrical sensors. As the electrical sensor dispatching algorithm is designed such that the Bayesian decision risk is minimized, the true discrete state can be better identified. At the same time, the continuous state prediction performance of the proposed algorithm is better than that of automatic control prediction algorithms using only predetermined electrical sensors. Finally, our algorithm is validated though an illustrative target tracking example.

Abstract: This article analysis the relationship between geomagentically induced currents(GIC) in electrical power system flowing through 500kV transformer neutral point in Ling’Ao power grid and the geomagnetic data observed at Guangzhou geomagnetic observatory during 2004/11 -2006/12. It is found that correlation coefficient between GIC and magnetic field component variation may be greater than that of time derivative of the geomagnetic field, which are all less than -0.5. According to the relation, The minimum amplitude of geomagnetic component variation is 7.08(nT/min) in term of transformer of single or three phase five columns while is about27.47(nT/min) when the type is three phase three columns.

Abstract: the loss-of-field failure of synchronous generator is having an increasingly impact on the generator itself and the external power grid security. EHV (Extra High Voltage) generator is a new type of generator that can be directly connected to grid. Therefore, research on EHV generator’s loss-of-field failure is of realistic significance. This paper first draws from simulation analysis the changes of electrical parameters during the loss-of-field process of the EHV generator, and then analyzes the load-angle characteristics and generator terminal impedance characteristics during the loss-of-field process, and finally using the analytical results determines the EHV generator loss-of-field protection program to provide reference data to the protection of EHV generator running.

Abstract: Short circuit impedance test is one of the important methods for the transformer winding distortion diagnose. At present the test current is too low when we using short circuit impedance method. Upon the understanding for electrical properties of the transformer we developed a device with test current up to 10 Ampere, and combined longitudinal comparison method and lateral comparison method as our criterion algorithm. The device we developed matches the requirements of related standards. It comes in a complete set and fits on-site application. Through three practical examples we can see the improvement of the current is effective for the test accuracy in the transformer winding distortion diagnose.

Abstract: An improved instantaneous symmetrical component method is adopted to improve the performance of inverter with LCL filter under asymmetric voltage conditions in electrical power system. Positive and negative sequence components in voltage and current in electrical power system are calculated with fewer calculation time,which is suitable for pratical application.In addition,this paper analyses active and reactive power in the system.A double-loop control strategy is proposed to eliminate the influence of double frequency components in power and negative sequence current.The simulation results verify its feasibility and effectiveness.

Abstract: High-voltage circuit breakers (HVCBs) play an essential role in electrical power systems, which can ensure and control the smooth operation of power grids. Therefore, a fault diagnosis method of HVCBs based on Kernel Principal Component Analysis (KPCA) is proposed in this paper. As the fault data of HVCBs have the characteristic of multi-dimensional nonlinearity, the proposed method calculates inner kernel function of HVCBs' closing current in the original data space so as to achieve nonlinear mapping to the feature space of the original data. Afterwards, feature extraction and pattern classification of fault data can be accomplished in the feature space by means of monitoring SPE statistics. Experiment results have proved that the KPCA method can effectively improve the precision of fault diagnosis of HVCBs.

Abstract: Shunt active power filter (APF) is an electric equipment which effectively optimizes harmonic waves. By measuring the load current, it produces compensated current with opposite amplitude to the load current in order to improve the power quality of the power grid. Little has been reported on how to effectively design the LPF employed in the link of shunt APF and power system. The paper theoretically analyzes constrains for parameters of the LCR output filter, and then determines the optimal LRC filter parameters by comparing different output filter (OF) functions. At last, the experiment results further verify the correctness of the design method.

Abstract: A novel grid-connected photovoltaic system in electrical engineering with energy storage based on DC bus is proposed, which can integrate a microgrid system into a single device and make the development of distributed generation more flexible and accessible. The system is controlled to keep the voltage of DC bus constant, to utilize solar energy effectively and to prolong battery’s life. The control strategies of each of the subsystems are designed based on their characteristics and system requirements. The energy flow states containing all the possible operation states of the DC bus based system are presented in this paper, followed by the process control state machine to illustrate the energy management strategies is achieved. Finally, a simulation platform is established in MATLAB/Simulink to verify the presented control method.

Abstract: Neutral point grounding method with an arc suppression coil and a parallel resistance is a method that can inhibit arc overvoltage effectively. Through the simulation of arc suppression coil with parallel resistance in the situation of different resistance value, we can obtain if the parallel resistance is too big, it will produce overvoltage in the later of voltage recovery; if the parallel resistance is too small, it is easy to produce larger grounding residual flow, going against quenching of arc; Whether over compensation or owe compensation, oversized out-of-resonance degree will cause the fault phase voltage recovery oscillation overvoltage, small out-of-resonance degree is beneficial to the fault phase voltage rise slowly.