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Reference: ISH2015_538

Type:
ISH Collection
Title:

MOISTURE ANALYSIS OF HIGH VOLTAGE BUSHING OIL-PAPER INSULATION BASED ON FREQUENCY DOMAIN SPECTROSCOPY CONSIDERING TEMPERATURE DEPENDENCY

 

Abstracts

Oil-paper insulated high voltage bushing is widely used in high voltage power system, especially for the high voltage bushing. The estimation of moisture content is crucial to the bushing's oil-paper insulation due to its significant acceleration on the long-term aging process. However, conventional estimation techniques lack adequate accuracy and information for moisture estimation. Recently, polarization-based dielectric response methods such as return voltage (RV), polarization and de-polarization current (PDC), and Frequency Domain Spectroscopy (FDS) used in power transformer oil-paper insulation analysis would be appropriate to solve this problem for high voltage bushing. This paper mainly discusses the moisture estimation of oil-paper insulated bushings based on FDS measurement considering temperature dependency. For this purpose, firstly some laboratory experiments are designed. The oil-immersed Kraft paper samples are prepared with 8 different moisture content (dry~7%) using natural moisture absorption in air. The actual moisture content of the test sample is measured by Karl-Fischer Titration (KFT). FDS test on the dry and 7% samples is performed under different temperature (30~80°C) and on other samples under 40°C. All the dielectric loss (tan d) and complex capacitance (C*) under variable frequency (1mHz~5kHz) are obtained. In addition, some real bushings with different manufacture process and damp type are tested. In the results, FDS curves tend to shift both upwards and rightwards with the rising of moisture and correlation between some curve geometry characteristics and the moisture content value is discovered. Furthermore, it is observed that the temperature variation will results in frequency-shifting of the results. Temperature correction method using Arrhenius equation is discussed and the activation energy of the bushing insulation for correction is calculated based on the frequency shifting factor. Tests on real bushings prove the sensitivity and applicability of FDS method for bushing moisture estimation.
 

File Size: 324,4 KB

Year: 2015

 
 
 
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