Advanced Materials Research Vols. 986-987

Abstract: Non-linear insulating material is widely used in the insulations of XLPE cable terminations and stator windings insulation of electric machines, and has obvious capability to improve the distribution of electric field. Actually, the dielectric loss factor of non-linear insulating materials is not equal to the tan δ describing linear insulating materials, and depends on applied voltage and their structures. This paper firstly discusses the difference between ac loss characteristic of non-linear dielectrics and linear dielectrics and presents a kind model of non-linear composite material. Based on the model, specific characterization and measurement methods and their numeric simulation analysis are given. Finally, a measuring system for non-linear insulating materials based on digital measuring technology is presented.

Abstract: In order to realize real-time detecting for solution conductivity, an on-line detector powered with 9V battery was developed. The detector consists of conductivity electrode, excitation signal generating circuit, RMS detecting circuit, MSP430F2132 microcontroller, DS18B20 temperature sensor, HT1621 displayer and SPI interface. The solution conductivity was measured according to the principle that the electrode’s output resistance varying with conductive ions concentration of the solution, the measured results could be displayed on HT1621 and be sent to other controllers through SPI interface. An optimum excitation signal that a square wave signal (the amplitude was ±3.5V, and the frequency was 1.8 kHz) had been determined by experiments, to minimize polarization effect of the conductivity electrode. Verification test had been performed for the detector, the tested results showed that maximum relative error of the detector was 2.94%, could meet the requirement of practical application.

Abstract: Amplifier is a key component of the Soft X-ray imaging diagnostic system and the system is one of the most important diagnostic systems on J-TEXT tokamak. Signal generated by the photodiode is current and it’s too small. A high-gain amplifier enable us to observe the soft x-ray radiation signal in J-TEXT tokamak accurately. So an amplifier based on transimpedance circuit was proposed. Through theoretical calculations and simulations, the designed amplifier can achieve the set goals that are the V/I gain of 10⁶ and the bandwidth of 20KHz. In order to ensure the quality of the signal, interface and shell of the amplifier are designed specially. Finally designed amplifier works properly in the experiment and it can meet the needs of the experiment.

Abstract: The increase of data access capacity and data types of the power grid leads to a more complex and varied grid running environment. Hence, in order to guarantee the running security of the master station, an online monitoring and evaluation system based on index system for master station is proposed in this paper. It can construct a dynamic evaluation model and complete automated collection, analysis, scoring and evaluation of indexes by using specific index calculation methods. Moreover, this system can provide comprehensive interface display for evaluation results and achieve online alarming for the abnormal situations of the master station. This system offers a new and effective way to guarantee the safe and reliable running of the master station.

Abstract: Selection of secondary variables is an effective way to reduce redundant information and to improve efficiency in nonlinear system modeling. The combination of Kernel Principal Component Analysis (KPCA) and K-Nearest Neighbor (KNN) is applied to fault diagnosis of bearing. In this approach, the integral operator kernel functions is used to realize the nonlinear map from the raw feature space of vibration signals to high dimensional feature space, and structure and statistics in the feature space to extract the feature vector from the fault signal with the principal component analytic method. Assessment method using the feature vector of the Kernel Principal Component Analysis, and then enter the sensitive features to K-Nearest Neighbor classification. The experimental results indicated that this method has good accuracy.

Abstract: According to the communication equipment fault characteristics of complexity, hierarchy, relevance, delay and uncertainty, the method of extracting diagnosis rules based on rough set is presented in order to obtain diagnostic decision rules with good adaptability and maximum matching capabilities. This method can process a large amount of fault data and it can reduce both attribute and attribute value.4 evaluations are selected to evaluate the effectiveness and reasonableness of decision rules, and finally core value table of decision rules which has a certain ability to adapt. Example shows that this method can remove noise in fault diagnosis sample, reduce the computation and improve the efficiency of diagnosis effectively.

Abstract: When a node of power system have a failure, we can deal with it by the multi-time electrical comprehensive phasor data of each node before and after the failure, introduces Bayesian Classifier to handle with the node failure case so as to distinguish and locate fault. Experiments show that Bayesian classifier is an effective method in fault location.

Abstract: The flow measurement of primary air is very important for thermal power plants to maintain the safe state of operation. For direct firing pulverizing system, the measuring is essentially affected by pulverized coal particles. Abrasion and occlusion would bring great trouble to the measurement. Many measuring methods are invalid under that circumstance. Lots of efforts have been made to find appropriate ways to measure the flow of primary air containing pulverized coal. Venturi tube had been successfully used to measure the flow of air. If a venturi tube is used to measure the flow velocity of primary air, the differential pressure goes higher with the increase of the concentration of pulverized coal in the primary air. The neglect of the affection of pulverized coal on the measuring would result in remarkable deviation. With the aids of coal flow rate, a method of using venturi tube to measure the velocity of primary air containing pulverized coal was established. The affection of pulverized coal on flow measuring of primary air cannot be ignored.

Abstract: In this paper, a new approach for harmonic detection in power signals based on fast modified S-transform (FMST) is proposed, which combines the advantages of the incomplete S-transform and the modified S-transform. Initially, the Fast Fourier Transform was performed and dynamic measurement values were obtained from the envelope of power spectrum, then the valid harmonic frequency points were detected by selecting the dynamic measurement values which were larger than the set thresholds. Further, the FMST was specifically performed on these major frequency points and a complex matrix was generated. The row vectors of the matrix reflected the phase and the time location information of harmonic disturbances, while the column vectors reflected the amplitude-frequency characteristics. And the feature vectors extracted from the complex matrix were used to detect the harmonic amplitude, phase and transient information. Simulation results validate the high accuracy, strong noise immunity and rapidity of the proposed approach.

Abstract: The IEC61850-based digital watt-hour meter is different with conventional meters. The testing method and equipment for conventional meter is no longer applicable for digital meters. A newly designed tester for digital watt-hour meter is presented. The hardware structure and working principle are described. The test has traceability to the conventional standard meter. The tracing test result shows that the tester has accuracy grade of 0.05%.