회전기 고정자권선의 절연열화위험도 평가를 위한 파라미터 도출 = Parameter Deduction for Insulation Deterioration Risk Assessment of Rotating Machine Stator Winding

다국어 초록 (Multilingual Abstract)

Electrical insulation of hydro generator stator winding is one of the most important parts in generator facilities. Reliable operation of a hydro generator depends critically on the integrity of its stator winding insulation. The stator winding insulation is deteriorated by exposure to a combination of thermal, electrical, mechanical, and environmental stresses. Diagnosis of stator winding insulation is an important measure of ensuring the safe operation and extending the remaining life of hydro generator.
This paper presents reliable insulation deterioration diagnosis parameters that show insulation deterioration condition checked out by applied the voltage dependence and the time dependence of partial discharge(PD) magnitude. The specimens used in the tests of this study were the stator winding of an actual hydro generator having operated for more than 30 * A thesis for the degree of Master in February 2008.years, so it should be pointed out that the specimen had been aged to some extent. For aging tests, the stator winding was divided into 3 parts (the center part, the slot exit part and the end arm part) to examine insulation condition and insulation strengths according to the location at the core. The results drawn from the tests can be summarized as follows.
As a results on the insulation strength according to the location at the core, the insulation strength was found out to be greatest at the center part specimen followed by the end arm part specimen and slot exit part specimen. More than 90 % of all the specimens had the breakdown of insulation, particularly in the edge of the winding, and the edge of the slot exit part of the stator winding was found out to be most vulnerable to insulation degradation.
As a result of diagnosis using parameters which were considered to get the deterioration diagnosis parameters, the PD inception angle and the PD changeover voltage were derived from the voltage dependence of PD, and, from the time dependence of PD, the slope of decrease in PD which was measured during a specific time and the characteristic ratio of the time dependence compared to a previous cycle were deduced.
Data measured from breakdown specimens and non-breakdown specimens in the aging cycle were quantified according to the normalized aging rate, and the features of aging progress were analyzed with the deterioration diagnosis parameters. The PD inception angle increased, the PD changeover voltage decreased while the test voltage was increasing, and the slope of decrease in PD increased. In the case of the characteristic ratio of the time dependence compared to the previous cycle, it was found out that the insulation risk was remarkably high if it vibrates or has an increasing decrease rate, or increases without decreasing.
Among these diagnosis parameters, PD changeover voltage, the slope of decrease in PD and the characteristic ratio of the time dependence of PD were described as an effective parameter to evaluate the insulation deterioration risk degree.
Especially, the study shows that the new insulation diagnosis parameters help analyze the risk of deterioration even without accumulated data analyses, compared to the existing traditional parameters.
The application of the insulation deterioration diagnosis parameters drawn from the voltage dependence and the time dependence of PD will allow the accurate prediction on states of aging progress and on insulation risk, so it is expected that further studies on life prediction by applying those parameters will be very useful and helpful.

목차 (Table of Contents)

• Ⅰ. 서 론 1
• 1.1 연구배경 1
• 1.2 연구개요 4
• Ⅱ. 수력발전기 고정자권선의 절연열화 및 진단법 6
• 2.1 수력발전기 고정자권선의 절연구조 6
• 2.2 고정자권선의 절연열화요인 8
• 2.3 고정자권선의 절연열화 진단법 11
• 2.3.1 직류전압을 이용한 진단법 13
• 2.3.2 교류전압을 이용한 진단법 14
• 2.4 부분방전법에 의한 열화진단 17
• 2.4.1 부분방전 특성 17
• 2.4.2 회전기에서의 부분방전 21
• 2.4.3 부분방전 열화진단인자 24
• Ⅲ. 시편권선 제작 및 절연특성 측정 31
• 3.1 시편제작 및 방법 31
• 3.2 복합열화실험 34
• 3.2.1 실험장치 34
• 3.2.2 시편의 절연특성시험 39
• Ⅳ. 절연열화 실험결과 및 열화진단파라미터 고찰 43
• 4.1 30년간 사용된 고정자권선시편의 가속열화 전 절연특성 43
• 4.2 가속열화시험 조건 및 절연진단인자 도출을 위한 절연특성 분석 51
• 4.2.1 부분방전의 전압 및 시간의존성의 절연열화진단인자 59
• 4.2.2 절연진단인자의 정량화 및 상관성 검정 64
• 4.3 복합스트레스에 의한 고정자권선 절연물의 열화특성 66
• 4.3.1 광학현미경 분석결과 67
• 4.3.2 위상기준 부분방전분포 특성 72
• 4.3.3 부분방전개시전압 변화특성 89
• 4.3.4 최대부분방전량 변화특성 96
• 4.3.5 유전손실계수 변화특성 103
• 4.3.6 부분방전량의 전압의존성 110
• 4.3.7 부분방전량의 시간의존성 125
• 4.3.8 권선위치에 따른 고정자권선의 절연파괴전압 분석 139
• 4.4 절연열화 진단파라미터에 대한 검토 143
• 4.4.1 열화진단파라미터와 절연열화의 상관성 143
• 4.4.2 부분방전의 전압 및 시간의존성을 이용한 현장설비 열화진단 시험결과 144
• 4.4.3 절연열화위험도 평가를 위한 열화진단인자의 효용성 고찰 152
• Ⅴ. 결 론 153
• 참고문헌 155