Chen Weigen

The Measuring Method for Internal Temperature of Power Transformer Based on FBG Sensors

Thermal modeling of the power transformer to estimate the internal temperature only reflects the winding hot spot to a certain extent. The application of optical fiber sensors to measure transformer internal temperature directly can obtain the true temperature with high accuracy and stability and overcome the shortcomings of traditional electric sensors. This paper analyses the measuring principle of FBG (Fiber Bragg Grating) sensor, and constructs transformer internal temperature measurement platform with FBG temperature sensors, then adopt short-circuit method to simulate the process of winding heat under different load conditions. Finally the measurement of transformer internal temperature is conducted respectively with FBG temperature sensors and thermocouples. Comparison and analysis of the results shows that FBG sensors can effectively measure the internal temperature of the transformer.

A practical PD online monitoring system used for transformers

In this paper, we develop a partial discharge (PD) online monitoring system with frequency band from 50 kHz to 1 megahertz used for transformers. The monitoring system mainly consists of wide-band signal detectors for multi-terminal measurements, signal pre-processing circuit, high speed A/D converter and cascaded 2nd order IIR lattice digital notch filter. The major measures to suppress narrowband interference are the signal pre-processing device and the digital notch filter. With analysis to field monitored signal from a transformer at a 220 kV substation, it is shown that the monitoring system can detect and extract the discharge pulse signal effectively. With PD pattern recognition method, the monitoring system can get more stable and reliable detection results.

On-line detection of gases dissolved in transformer oil and the faults diagnosis

This paper describes the theory of on-line detection of six kinds of gases-H/sub 2/,CO,CH/sub 4/,C/sub 2/H/sub 4/,C/sub 2/H/sub 2/,C/sub 2/H/sub 6/-which are dissolved in transformer oil, and analyzes the characteristics of the microcomputer detection system. The back propagation neural network (BPNN) is applied to diagnosing the transformer faults, and the results of verification show that the BPNN diagnosis method is effective.

A Fault Diagnosis Method for Power Transformers Based on Wavelet Neural Network and D-S Evidence Theory

Transformer faults are quite complicated phenomena and can occur due to a variety of reasons. There have been several methods for transformer fault synthetic diagnosis, but each of them has its own limitations in real fault diagnosis applications. In order to overcome those shortcomings in the existing methods, a new transformer fault diagnosis method based on a wavelet neural network optimized by adaptive genetic algorithm (AGA) and an improved D-S evidence theory fusion technique is proposed in this paper. The proposed method combines the oil chromatogram data and the off-line electrical test data of transformers to carry out fault diagnosis. Based on the fusion mechanism of D-S evidence theory, the comprehensive reliability of evidence is constructed by considering the evidence importance, the outputs of the neural network and the expert experience. The new method increases the objectivity of the basic probability assignment (BPA) and reduces the basic probability assigned for uncertain and unimportant information. The case study results of using the proposed method show that it has a good performance of fault diagnosis for transformers.

Identifying the Overvoltage in Distribution Networks Based on Support Vector Machine

The internal and external overvoltage in distribution networks are the main reasons of accidents. Based on overvoltage data in distribution network recorded by overvoltage on-line monitoring system, this paper analyzes the characteristics of zero sequence voltage waveform. The maximum amplitude and RMS value of zero sequence voltage, the minimum RMS of low frequency component of three phase voltage in stable range and other five parameters are selected as characteristic parameters to identify internal and external overvoltage. According to the operation data and record, all overvoltage data record by on-line monitoring system were labeled as internal or external overvoltage and the discrimination function is constructed by support vector machine method. The test results of field acquired overvoltage data indicate that the identification parameters and method base on the zero sequence voltage and SVM are correct and effective.

Study of an Assessment Method for the Reliability of Tap-changers in Power Transformer Based on Fault-Tree Analysis

Based on the further analysis of typical failure modes and influences of tap-changers in power transformer, the fault-tree of tap-changers is set up by using fault-tree analysis(FTA) techniques and the assessment method for the reliability of tap-changers, combined with the index of the importance and the method of Improved Analytic Hierarchy Process(IAHP), is put forward. The assessment examples show the method can deduct the failure modes of tap-changers clearly, meanwhile, find out the weaknesses in time during the operation and get better assessment results.

Research on the measurement error of capacitor voltage transformer under various insulation characteristics

Capacitor voltage transformer (CVT) is one of the most important measuring and protecting devices in power system, whose measurement error is relevant with insulation characteristics of voltage divider. In daily operation, dielectric aging, moisture, dielectric breakdown etc. will exert a mixing effect on its insulation characteristics, changing voltage dividers equivalent parameters, further resulting in the measurement error. This paper proposes a more accurate model to represent CVT, which takes insulation characteristics of voltage divider into consideration. After theoretical analysis and software simulation, the relationship between measurement error and insulation characteristics is obtained. It indicates that varying of insulation characteristics in CVT will cause a reasonable measurement error.

Research Situation and Development Trend of Cable Distributed Temperature On-line Monitoring Technologies

According to the analysis of existing technologies of on-line monitoring power cable insulation fault, aiming at that the temperature can better reflect the power cable insulation and the diversity of its monitoring methods, this paper mainly introduces the research situation and development trend of cable distributed temperature on-line monitoring technologies. Combined with application examples, it makes a brief analysis for the technologies, and describes basic principles of distributed temperature monitoring technologies which based on the master-slave structure, temperature sensing cables and optical fiber sensors, in accordance with the application of these technologies, the paper focuses on analyzing advantages and deficiencies of these technologies. Based on the various programs in engineering application, the paper points out the developing direction of these technologies, which provides an important reference for future research.

Research of on-line monitoring of moisture content in transformer oil

The moisture distribution in the transformer and variation mechanism of moisture in oil is analyzed in this paper, and using relative saturation and temperature as characteristic parameters, a detail scheme of online moisture content monitoring in transformer oil is put forward. The polyimide-based capacitive humidity sensor and temperature sensor are employed in online monitoring moisture content in oil. Computer is utilized to sample and analyze the data from sensors. The experiment on test transformer confirms that the sensors can work reliably, and accurately reflect the moisture content in transformer oil. The proposed method can realize the purpose of on-line monitoring.

Transducers for electrical apparatus insulation online monitoring

This paper presents detail analysis on transducers used for online monitoring system for electrical apparatus. Transducers are the key components of the online monitoring system; they play important roles on the stability and accuracy of monitoring results. Two types of transducers are discussed in this paper - the transducers used for dielectric loss angle measurement and the ones for partial discharge measurement. Basically their characteristics can be derivative from a uniform equation according to the materials used and structure, but the aspect differs from the frequency domain and time domain analysis. The transfer function of the transducers is put forward, the phase-frequency, amplitude-frequency characteristics are discussed and the time-domain response is concluded from unit pulse response convolution. The structure, shielding are also mentioned. For the characteristics may be changed with the temperature shift, the error analysis is implemented to compensate the result. The results of the field test have proven the stability and feasibility, and these transducers can be used for electrical apparatus insulation online monitoring.