Muqin Tian

Breakdown performance and electrical aging life model of EPR used in coal mining cables

Ethylene Propylene Rubber (EPR) with excellent dielectric properties has been widely used as cable insulation specially to be used where cables need to be moved frequently, such as in coal mine. Usually, theses cables will be bending excessively, coupled with the electric stress and thermal stress, the aging of the insulation tend to accelerate and the strength of insulation could decrease, with the time prolonging, breakdown may be happened. So, it is necessary to make research on the breakdown characteristics of EPR. To understand the breakdown performance, a step-stress test method is used in the accelerated life tests of EPR and WEIBULL distribution is used to analyze the test dates. Finally, based on inverse power life model, the voltage life index of EPR have been obtained. Finally, the electrical aging life model of EPR have be obtained. Research on the breakdown characteristics and the voltage life index of EPR is significance for insulation structure design and residual life assessment.

Characteristic analysis of asynchronous motor fault signal based on wavelet packet decomposition

This paper presents characteristic frequency analysis of asynchronous motor fault signal based on wavelet packet decomposition. Asynchronous motors current and vibration signals are acquisition objects, Fault diagnosis is based on frequency information contained in motors signals. The wavelet packet decomposition (WPD) method is applied to extract their characteristic frequency, and then its necessary to ascertain WPD layers according to signal sampling frequency and the requirement of frequency resolution. A method is put forward, which characteristic frequency is located quickly to node in the WPD layer. It may promote the application of wavelet packet analysis method in motor fault diagnosis system.

Influence of thermal aging on AC leakage current in XLPE insulation

Cross-linked polyethylene (XLPE) has been widely used as cable insulation material because of its excellent dielectric properties, thermal stability and solvent resistance. To understand the influence of thermal aging on AC leakage current in XLPE insulation, all XLPE specimens were aged in oven in temperature range from 120 °C to 150 °C, and a series of tests were conducted on these XLPE specimens in different aging stages to measure the characteristic parameters, such as complex permittivity, leakage current and complex dielectric modulus. In the experiments, the effects of thermal aging, temperature and frequency on the AC leakage current in XLPE insulation were studied by analyzing complex dielectric constant and dielectric relaxation modulus spectrum, the change of relaxation peak and activation energy. It has been found that the active part of leakage current increases sharply with the increase of aging degree, and the test temperature and frequency have an influence on AC leakage current but the in...

Development of Intelligent Information Monitoring System in Greenhouse Based on Wireless Sensor Network

In order to solve the problems of complicated wiring, difficult maintenance and easy line corrosion in traditional greenhouse monitoring system, a greenhouse intelligent information monitoring system based on wireless sensor network was developed. In which ZigBee wireless sensors were used to collect field environmental parameters, such as indoor temperature, indoor humidity, light intensity, carbon dioxide concentration, soil humidity and etc. The information center interface was designed by Kingview, which can realize centralized monitoring, data display, data storage and data mining. The system can monitor and control greenhouse environment parameters, with four control modes, i.e. manual control, automatic control, intelligent control and remote control. The system has been applied in demonstration base for three years, and it has been shown that it is accurate, reliable, stable and friendly UI, which could meet the requirements in the modern management of solar greenhouse.

AC flashover performance and polarization current of ethylene propylene rubber under different temperature

In order to evaluate the influence of AC flashover on the insulation performance of Ethylene Propylene Rubber (EPR) at different temperature, the characteristic indicators were studied, based on the polarization and depolarization current (PDC). In the paper, the partial discharge inception and extinction voltage and the flashover voltage were firstly measured under AC voltage at the ambient temperature and 90 °C, respectively. Before the occurrence of flashover, the partial discharge distribution was discussed under different voltage amplitude. Then, PDC was measured after the flashover test. The fit lines of PDC were drawn through the empirical formula for explaining the mechanism of AC flashover over the surface of EPR.

Partial discharge properties of electrical trees in XLPE

Cross-linked polyethylene is widely used as the insulation of power cables due to its superior insulation and mechanical properties. Electrical trees is one of the main reasons for the breakdown of cable insulation. In order to explore the growth process and partial discharge characteristics of electrical trees in cross-linked polyethylene, cuboid samples taken from a commercial cable and a needle-plane electrodes were used to develop electrical trees. In this paper, a real-time observation system was designed to record the growth picture of electrical trees and a partial discharge measurement system was used to obtain the partial discharge patterns during treeing. The experimental results show that the structure of electrical tree varied in stages. There are four stages during the growth of electrical trees, namely, initiation stage, slow growth stage, rapid growth stage and sustained growth stage. The outline of PD distribution patterns is bimodal shape. During treeing, the numbers of PDs in the two cycle are almost equal.

Influence of temperature and frequency on leakage current of XLPE cable insulation

Crosslinked polyethylene (XLPE) with outstanding high temperature performance and electrical properties has been widely used as cable insulation. Leakage current of cable is the inevitable product in the process of electric energy transmission, and the gathering of leakage current is easy to cause gas combustion, explosion of the cap and other accidents. To understand the influence of temperature and frequency on the leakage current of cable, Novcontrol Broadband Dielectric Spectroscopy measurement system has been used to measure the dielectric spectroscope of XLPE samples in the temperature range from 20 °C to 200 °C and frequency range from 10−2 Hz to 105 Hz. In the experiments, the dependency of permittivity, conductivity and electric modulus on frequency and temperature has been conducted. By observing the dielectric spectrum, some variation rules of parameters could be found, for example, the real part of complex permittivity decrease repidly and dissipation factor decrease slowly with increasing frequency at higher temperature. The AC conductivity follows the Jonscher power law, which DC conductance region follows the Arrhenius rule. The dielectric dispersion phenomena can be also observed on the spectroscope of the electric modulus as well, the dielectric loss peak move to the higher frequency area with the increase of temperature. Finally, the mechanism and process of XLPE relaxation polarization were discussed, the contribution of relaxation polarization to leakage current and the generation of leakage current was explained. The results show that the leakage current of XLPE cable has a strong dependence on the temperature and frequency.

The effects of cavity on the growth of electrical trees in XLPE

Cross-linked polyethylene(XLPE) is widely used as the insulation of power cables due to its good properties. Nevertheless, some inevitable defects like cracks and cavities existing in cables will initiate electrical trees which is one of the main reason leading to the breakdown of cable insulation. Thus, it is necessary to conduct the study on the effects of cavity on the growth of electrical trees in XLPE. A needle electrode was inserted in XLPE to simulate the concentration of electrical field in this paper. Two kinds of samples were designed to explore the effects of cavities on the growth of electrical trees in XLPE. Samples with a cone-shape cavity underneath the point of the needle were named sample B, and other samples without cavity were sample A. The initiation and development of electrical trees under 50Hz ac voltage were investigated in this paper. The measurement system of electrical trees was designed to measure the partial discharge and to record the growth of electrical trees. The experimental results shows that tree initial voltage of XLPE decreases due to the existence of a cavity. A long time stagnation appears in the process of tree growth in samples with a cavity, which prolongs the tree growth cycle. The partial discharge phase width in the initiation period of sample B is wider than that of sample A.

Analysis of partial discharge of spherical cavities in EPR at different frequency

Cavities are one of the typical defects resulting in partial discharges (PDs) in extruded power cables. This paper focuses on studying the PD characteristics of arbitrary dielectric bounded cavities and electrode bounded cavities embedded in EPR insulation, such as PD distribution, PD inception and extinction voltage, under different type of testing voltage. During the experiment, the applied voltage is sinusoidal waveform at frequencies of 20, 50 and 200 Hz and damped AC waveform at frequencies of 20, 50, 200 and 500 Hz. The amplitude of applied voltage, the peak value, is 1.25, 1.5 and 2 times of the amplitude of PD inception voltage (PDIV). The diameter of cavities is 1.2, 1.5 and 2.0 mm. A batch of five simples has been tested during PDIV test. Each sample has been tested five times so as to obtain accurate data. It has been found by the experiments that the PD inception voltage increases with increasing frequency of applied voltage. The symmetrical PDs distribution can be observed in the time lag. It seems that the PD distribution depends on the frequency. The maximum PD amplitude at higher frequency is slightly larger than at lower frequency. PD distribution spreads more widely at higher frequency. It is also found that the cavity diameter and the amplitude of applied voltage influence the frequency dependence of PD distribution. The speed of degradation of EPR insulation is related with the frequency of applied voltage. PDs can also corrode the surface of dielectric bounded cavities embedded in EPR insulation, whereas there is not obvious change on the surface of electrode bounded cavities.