Shuangzan Ren

Dynamic and flexible effectivity evaluation system of live test approaches for power equipment

Ever since Chinese electric power reform in 2002, different live test approaches were introduced and applied in relative industries. There were at least 26 live test approaches applied in the field of power transformation, power transmission and power distribution. The essay introduced a comprehensive dynamic and flexible effectivity evaluation system, which helped to evaluate the strengths and weaknesses of different live test approaches.

Novel and necessary approaches ensuring statistically effective partial discharge testing for equipment in service

Serving for condition-based maintenance, researchers and engineers, who conducting, designing and researching partial discharge testing for equipment in service, used to focus on PD (partial discharge) locating. The novel idea of test sensor (instrument) locating was introduced. Locating the sensor instead of PD source would ensure PD testing results statistically effective. The concept of PD mapping and PD transmission zone were also introduced. The former takes effective sensor locating as prerequisite and the latter functions during PD locating. Available approaches and applications of sensor locating and PD mapping were demonstrated. The succession relationship of sensor locating and PD source locating were analyzed and the vistas of both were discussed.

Partial discharge characteristics and development of typical XLPE power cable insulation defects

It is well known that preventive tests have been widely used as an important means to ensure reliable operation of the power cable. Nevertheless, in the early stages of insulation deterioration, the traditional preventive tests cannot effectively detect the faint abnormal signals caused by defects. As insulation failure usually starts with PD activities, which is not only one of the primary reasons to cause the insulation deterioration of the cable, but also the characteristic scalar to describe the insulation state of cable. Therefore, PD diagnosis is recommended by IEC, IEEE and CIGRE as an effective method to evaluate the properties of cable insulation condition. In order to study the PD characteristics of the typical defects in XLPE(Cross-Linked Polyethylene)power cable, two PD models as protrusion defect of cable joint and void defect in main insulation were designed, and then the PD measurement and analysis system based on the PDBase was established. The PD characteristics of typical defects were detected and compared, also the effects of the applied voltage on the phase-resolved PD (PRPD) pattern, waveform characteristic, discharge frequency, center-phase distribution and statistical features were investigated. The experimental results indicated that it has the high stability and repeatability of the discharge on the identical defect model under the same condition. The discharge development process, PRPD patterns, time domain waveforms, central phase changing of PD signals and statistical features had very similar distribution characteristics and those of different defect had different ones. So it provides a test basis for the pattern recognition of PD types and a deeper study on the PD mechanism of XPLE cable.

Research on some related mechanisms of corrosive sulfur problems in mineral oils

Since a number of failures have happened on transformers and reactors due to the corrosive sulfur problem, especially for Dibenzyle-disulfide (DBDS) in mineral insulation oils, many researchers have carried out a series of studies on such issue. In this paper, some related mechanisms of corrosive sulfur problems in mineral insulation oils are introduced in detail. Such as the mechanism of DBDS how to change into copper sulfide (Cu2S), and which results are proved and checked by gas chromatography equipped with mass spectrometry (GC-MS), when there is copper sulfide deposited, what the surface color and microstructure of copper and insulation paper would be change are shown via scanning electron microscope (SEM), and the mechanism of Cu2S how to influence the dielectric properties of oil immersed insulation pressboard, together with the changing tendency of dissipation factor, permittivity and breakdown strength etc are introduced. Besides, the mechanism that how oxygen in oil to influence the Cu2S migrating from the copper surface into oil or insulation paper is given, and the activation energy of DBDS reacting with copper is obtained by Arrhenius equation, which is about 43.73 kJ/mol in air condition and 98.61 kJ/mol in nitrogen condition, at last, the mechanisms that how to inhibit such corrosive phenomena in mineral insulation oil via adding some passivators are introduced as well.

Research on anti-interferences methods in the PD detection on power transformer

The paper concerns improvement of the acoustic emission (AE) methods applied in diagnosing of insulations systems of electric power transformer. During detection of AE signals emitted by partial discharges (PD) occurring in insulation systems of power transformer, there exist different forms of interference sources, which may have a direct impact on the correct evaluation of the measured signals obtained using the AE method. Thus, analysis of the impact of interfering signals on the PD detection and classification is performed. In this study, a correlation-based wavelet base selection method is introduced. The proposed wavelet analysis approach capable of conserving a significant portion of the original signal, while the threshold value determined based on the relative difference between the original and noisy signal. The proposed method is applied to PD signals that obtained in the field. With the comparison of other de-noising methods, the de-noised PD signals indicate that the proposed method yields higher reduction in noise levels.

Field application of partial discharge detection and location on 750kV reactor

In this paper, a series of problems of detecting partial discharge (PD) and locating PD sources using acoustic signal on high voltage reactor are systematically discussed. The complex circumstance of acoustic propagation in reactor and the diffraction influence on the acoustic velocity are fully considered. Based on abnormal signals detected on 750kV reactor in one substation of Shaanxi power grid and time-based distance calculation method, the PD source location was presented according to the acoustic emission (AE) associate with high frequency (HF) earthing current detection. Finally, the effectiveness of previous analysis was proved by the internal inspection.

Partial discharge characteristics and mechanism in SF 6 Gas under oscillating impulse voltages

Impulse voltages strongly affect the reliability of gas insulated switchgear (GIS) under actual operational conditions. The alternating-current (AC) withstand voltage test and its corresponding partial discharge (PD) measurement are inadequate for the detection of all the hidden flaws in GIS. Such inadequacy can be compensated by additional impulse withstand voltage test and its PD detection measurement. However, the bulkiness and inefficiency of aperiodic impulse voltage generator makes it unsuitable for on-site application. Therefore, in practical tests, oscillating impulse voltage is generally adopted instead of aperiodic impulse voltage. This paper reports on experiments to study corona discharge in SF6 gas under two types of oscillating impulse voltages. The needle-plate gap model was used to study the characteristic of PD. The PD signals were detected by electrical and optical methods. Oscillatory phase-resolved partial discharge (OPRPD) spectrum under oscillating impulse voltage was introduced to describe the PD characteristics. The physical mechanisms of the PD under the two oscillating impulse voltages were discussed. The PD characteristics under AC voltage were investigated for comparison. The experimental results revealed that the PD development process under the oscillating impulse voltage was mainly dominated by a combination of high-frequency and precursor mechanisms. The difference of the PD characteristics under the oscillating impulse voltages and AC voltage were also presented.

Anti-interference measures for GIS partial discharge detection on field

It is well known that there is much electromagnetic interference on the gases insulated switchgear (GIS) operation environment, and which would bring some difficulties to distinguish the actual partial discharge signals with those interference. In this paper, three kinds of measures are introduced in detail, which have been proved to be effective to realize anti-interference for GIS partial discharge detection on field. The first one is aluminum foil coated shielding, the second one is acoustic-electric joint measuring, for which could verify each other, i.e. once there is a partial discharge defect in GIS, the ultrasonic and UHF signals should be appeared simultaneously, the third one is time difference method, which could judge the measuring signals are from GIS internal or outside. The three above mentioned measures could do some favor for the electric engineers who will carry out any similar partial discharge detection on field.

Experimental study of the influence of BTA and Irgamet39 ® TM on the mineral insulation oil under thermal aging

As we all know, BTA and Irgamet 39^®TM are widely used as metal passivators in electrical industry, while BTA is mainly used to inhibit the electrostatic charging tendency (ECT) of transformer oil, and Irgamet 39^®TM is applied to the corrosive sulfur problems in mineral insulation oils. In this paper, some oil samples that with different concentration BTA and Irgamet 39^®TM added were aged at 120°C, and which for 0h, 250h, 450h and 675h respectively. Subsequently, the ECT values, dissipation factor (tanδ) as well as the acid number of those aged oil samples were measured. The results show that Irgamet 39^®TM also has an inhibitory effect on ECT of oil, however, while compared with BTA, the dissipation factor and acid number of the aged oil samples that with Irgamet 39^®TM added are much larger than those with BTA or without any passivator added ones, which means that the side effect of Irgamet 39^®TM is larger than BTA to a certain extent.