The Mechanism and Diagnosis of Insulation Deterioration Caused by Moisture Ingress into Oil-Impregnated Paper Bushing

Abstract

Abstract:The healthy state of insulation in oil-impregnated bushings is traditionally evaluated by tanδ and capacitance at power frequency and mostly at 10 kV in the test standard. However, there has frequently been insulation accidents induced by moisture ingress (MI) for bushings that have passed the standard. The mechanism and new diagnostic features for MI into bushings were not distinct enough and an accurate test method is urgently needed research. To address this technical gap, a bushing model with a transparent sheath was designed and an ultrasonic humidifier device was adopted to simulate the environment of MI in bushings and recorded by digital camera. The parameters of dielectric dissipation factor, capacitance, partial discharge (PD), frequency domain response, and moisture content in oil were measured at room temperature with time. The results presented that both the increment dissipation factor at low frequency of 0.001 Hz and the increment dissipation factor of 1.2 U m could be used for detecting the earlier insulation defect of oil-impregnated paper (OIP) bushings. The phase resolved partial discharge (PRPD) can serve as the diagnostic basis of the severe state (S 3 ) of insulation deterioration caused by MI into bushings around the phases of 0-117 • , 151-303 • , and 325-360 • . The research findings would provide a useful reference for the condition diagnosis and maintenance of OIP bushings. Especially, the increment detection of Frequency Domain Spectroscopy (FDS) at the frequency of 1 mHz and 10 kHz was recommended firstly for the operative bushings in real sites.

The Study of VFTO Distribution in the Insulation System of IOCT Used in Traction Network

“…On the other hand, whether it is a lightning shock or a VFTO generated by a switching operation, there are components from DC to tens of MHz, or even higher frequencies, and its energy is mainly concentrated between 1 kHz-10 MHz [4], and the dielectric properties of the insulating material will also change with the change of frequency [5,6]. Such a wide frequency range of voltage excitation intrudes into the transformer insulation, which not only produces uneven voltage distribution, but it also causes the insulation to withstand excessive voltage drops, resulting in aging and damage to the insulation, and may even cause overvoltage breakdown of the insulation.…”

Temperature Distribution in the Insulation System of Condenser-Type HV Bushing—Its Effect on Dielectric Response in the Frequency Domain

“…This article presents laboratory test results of a 110 kV insulator made using the O Both the damage resulting from the degradation of the insulation and the increase in its moisture can be detected with the use of various diagnostic methods, including the so-called dielectric response methods [5]. Measurements of the dielectric response in the time or frequency domain have an advantage over traditional methods (e.g., measurement of tan delta and C at 50 Hz) since they provide more complete information about the tested insulation material [6][7][8][9]. Owing to this more credible type of diagnosis, it is thus possible to observe the symptoms of upcoming failure in advance [10].…”

“…Despite the fact that the dielectric response methods are becoming more and more reliable, the interpretation of the obtained results is still difficult [9,[11][12][13][14]. This is mainly due to the fact that the bushing works as a parallel system of two elements located in different environments, and the measured dielectric response is their resultant.…”

Oil Pressure Monitoring for Sealing Failure Detection and Diagnosis of Power Transformer Bushing

“…At present, many methods are used to monitor bushing status such as measuring insulator capacitance and dissipation factor (tanδ), which are sensitive to dampness throughout the bushing [7,8]. Moreover, the frequency domain spectroscopy method (FDS) is proposed since it is more sensitive to moisture content than conventional parameters such as capacitance and tanδ.…”