Zhengxiang Song

Simulation of Pressure Rise in Arc Chamber of MCCB During its Interruption Process

Pressure rise of the gas due to high current arc in the arc chamber of molded case circuit breaker (MCCB) may accelerate the arc movement and improve the corresponding interruption performance. However, this pressure rise may result in a heavy stress on the enclosure of the arc chamber. The paper is devoted to calculate the pressure rise and analyze its characteristics. Based on thermodynamics and ideal gas law, the pressure rise variation with time could be calculated taking into account the influence of arc current, venting size, splitter plates and gassing material. Relevant experiments also were carried out to verify the proposed calculation method. It demonstrates that the pressure rise in the arc chamber will be increased with the higher arc current, less venting and the existence of gassing material.

An Ultrasound-Based Liquid Pressure Measurement Method in Small Diameter Pipelines Considering the Installation and Temperature

Liquid pressure is a key parameter for detecting and judging faults in hydraulic mechanisms, but traditional measurement methods have many deficiencies. An effective non-intrusive method using an ultrasound-based technique to measure liquid pressure in small diameter (less than 15 mm) pipelines is presented in this paper. The proposed method is based on the principle that the transmission speed of an ultrasonic wave in a Kneser liquid correlates with liquid pressure. Liquid pressure was calculated using the variation of ultrasonic propagation time in a liquid under different pressures: 0 Pa and X Pa. In this research the time difference was obtained by an electrical processing approach and was accurately measured to the nanosecond level through a high-resolution time measurement module. Because installation differences and liquid temperatures could influence the measurement accuracy, a special type of circuit called automatic gain control (AGC) circuit and a new back propagation network (BPN) model accounting for liquid temperature were employed to improve the measurement results. The corresponding pressure values were finally obtained by utilizing the relationship between time difference, transient temperature and liquid pressure. An experimental pressure measurement platform was built and the experimental results confirm that the proposed method has good measurement accuracy.

A method for arc fault detection based on the analysis of signal's characteristic frequency band with wavelet transform

Arc fault is one of main causes of fires which bring great loss and damage every year. It is identified that the traditional current breakers will not successfully interrupt the circuit all time, when an arc fault occurs. It is very important and necessary to find a new method to identify and interrupt the arc fault, although it is hard to be detected. This paper presents a method using wavelet transform to analyze current signals characteristic frequency bands to detect arc faults. An experiment setup is designed to obtain both of the current in normal operation and the current with arc faults. Both of them are decomposed by wavelet function to obtain the characteristic frequency bands. The frequency bands of arc fault current represent a special character. By using this special character, the arc fault can be detected accurately and rapidly.

A new method to detect the short circuit current in DC supply system based on the flexible Rogowski coil

The short circuit current in DC (Direct Current) supply system will rise to a risk value within a few milliseconds. The current limiter must detect this fault on microsecond level to restrict the amplitude of short circuit current more effectively. For the existing method, the shunt is always employed for such fault detection, where the time to detect the fault current is relative long and hard for the rapid detection. In this paper, a novel method based on the flexible Rogowski coil is proposed, where the differential signal and the integral signal of the Rogowski coil are combined to perform the relay protection function. The design method of the coil, the relative experiments and the simulation result of the relay protection system are all discussed in sequence. Firstly, the equivalent circuit of the Rogowski coil is established, in which the distributed parameters of the coil are calculated with the Finite Element Method. Secondly, the frequency response of the coil is calculated and validated experimentally. The parameters of the Rogowski coil can be adjusted and designed according to the simulation result. Finally, the simulation of the relay protection system is performed, which shows that the demand of short current protection in ship DC distribution system can be satisfied and the method proposed in this paper is verified.

Ant Colony Optimizations for Initialization of Synchronous Sequential Circuits

In this paper, the problem of initializing sequential circuits is present. Achieving generation the shortest sequence able to drive the circuit to a known state, regardless of the initial state, ant colony optimization (ACO) is proposed, which has been effective in combination optimization problems. In this work, sequence generation problem is described in searching over a large vector graph, it is appropriate to ACO. We describe one form of applying a modified Max Min Ant System (MMAS) to the initialization that includes a dynamical local heuristics and a recent proposal for the pheromone updating rule to improve performance of algorithm. The experimental results for ISCAS89 benchmark sequential circuits illustrate that the algorithm can achieve better results in terms of the number of initialized flip- flops and sequence length.

A Fast and Practical Algorithm for Absolute Dominators Searching

Absolute dominator search is an effective topological analysis method to improve performance of computer-aided design (CAD) and automatic test pattern generation (ATPG). In this paper, we present a new algorithm for searching absolute dominators of multiple- output circuits to solve inefficient and complex computing in tradition algorithm. Compare with the tradition algorithm, the new algorithm analyzes the relations between different fanout nodes, and identifies absolute dominator for every fanout node in circuit, thus, the overall dominator graph is constructed without any changes for original circuit directly. The experimental results based on ISCAS85 and ITC99 benchmarks show a signification improvement in runtime, and it can meet the requirement of modern design and test for VLSI.

A modeling method on electromagnetic interference coupling path of digital relay in power system

To realize systematic analysis for electromagnetic susceptibility (EMS), forecast for electromagnetic compatibility (EMC), a modeling method on electromagnetic interference coupling path of digital relay in power system was presented. The simulated model of electromagnetic interference coupling path can be gotten by this method through the system identifying according to the experiment data. A mathematical modeling of the input port of alternate current (AC) signal in digital relay under electrical fast transients (EFT) interference was also been constructed according to the input and output response of this module measured by oscillograph. Good agreements between the simulated result and the measurements demonstrate the validity of this modeling method.

Electromagnetic topology analysis on relation between electromagnetic interference inside equipment and external electrostatic discharge

Simulation based on electromagnetic topology theory was applied to analyze the relationship between internal electromagnetic interference (EMI) and external electrostatic discharge (ESD) of semi-shielded electrical equipment. The topological structure model of the equipment was built to analyze the coupling paths of external disturbance. To the aperture coupling path, a new method was adopted to determine the transfer function between external disturbance and internal sensitive component, which was modeled as a wire conductor in this paper. The simulation result shows that the EMI induced by external ESD on the wire conductor depends on its length and location. The results compare well with previous reports.

Hybridized 3D-FDTD and circuit simulator for analysis of PCB via's signal integrity

In this paper, the equivalent circuit model containing two pairs of vias is established, and a hybrid method is applied, which combines the full-wave finite difference time domain (FDTD) with an S-parameter based macromodel by using the rational function approximation and circuit simulation. The electromagnetic feature of the model is described by S-parameters, result of the simulation of FDTD. The vector fitting method is adopted to perform the rational function approximation of complex pole pairs. This method is robust and can supply results precise enough for the procedure of macromodeling while the resonances on PCB under very high frequency are being considered. Based on above steps, the SPICE compatible equivalent circuit can be established and be connected with other circuit model in the same pattern. In this way, the analysis of signal integrity for a complicated interconnecting system can be performed more efficiently

Noise reduction method for the multisensor system measuring DC current

Multi-Sensor system has been proposed to measure electric current in a non-contact way. According to the Amperes Law, the value of the current flowing in a conductor can be obtained through processing the outputs of the magnetic sensors around the conductor. As the discrete form of the Amperes Law is applied, measurement noises are introduced when there exists the interference magnetic field induced by nearby current flowing conductors. In this paper, the measurement noises of the multi-sensor system measuring DC current are examined to reveal the impact of the interference magnetic field and the number of the magnetic sensors on the measurement accuracy. A noise reduction method based on Kalman filtering is presented. Computer simulation and experiment results show that the method greatly improves the accuracy without seriously increasing the computation load in comparison with other approaches.