• Journal of Electrical Engineering and Technology
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• v.9 no.3
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• pp.957-963
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• 2014

Converter transformers play important roles in high-voltage direct current transmission systems. This paper presents experimental and analysis results of the combined electrical and thermal aging of oil-impregnated paper at pulsating DC voltages. Breakdown voltages and time-to-breakdown of oil-paper specimens were measured by using short-time and constant-stress tests. The breakdown characteristics of combined electrical and thermal aging on insulation system were discussed. According to the relationship between failure time and aging temperature, the two-parameter Weibull model was improved. On the basis of the competing risk algorithm and the improved Weibull model, the two factors failure model was calculated. And the influence of temperature in the insulation system has been analyzed. This model performs better than the two-parameter Weibull model when both time and temperature are considered as variables in estimating the lifetime of oil-paper insulation.

• Journal of the Korean Society of Safety
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• v.34 no.5
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• pp.22-30
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• 2019

In 2018, overload, overcurrent, insulation aging, and a contact failure caused 659 electric fires. There is almost no failure of electrical socket outlets during their manufacturing or installation period. After several months or several years, overload or overcurrent of electrical socket outlets leads to a contact failure or short circuit which causes an electric fire. Therefore, this paper analyzed for thermal characteristics based on a current value and the change in insulation resistance along with a temperature rise caused by electrical socket outlets and the state of laboratory use in workplaces. As a results, regarding the thermal characteristics based on the current value of each installation year, a temperature increase was related to a current value, an installation year, and whether the contact unit is corroded. Insulation resistance began to decrease when a temperature increased to a certain level. With a lapse of installation year, the temperature at which insulation resistance began to decrease was lowered. This paper can be applicable for the survey data about electrical socket outlet induced fire accidents and management guidelines.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.3
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• pp.7-10
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• 2013

This study presents an approach to predict insulation resistance failure of multilayer ceramic capacitors (MLCCs) using non-linear modeling. A capacitance aging model created by non-linear modeling allowed for the prediction of insulation resistance failure. The MLCC data tested under temperature-humidity-bias testing conditions showed that a change in capacitance, when measured against a capacitance aging model, was able to provide a prediction of insulation resistance failure.

• Journal of Electrical Engineering and Technology
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• v.3 no.4
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• pp.571-575
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• 2008

Stator insulation quality assessment for high voltage motors is a major issue for the reliable maintenance of industrial and power plants. To assess the condition of stator insulation, nondestructive tests were performed on the sixty coil groups of twelve motors. After completing the nondestructive tests, the AC voltage applied to the stator winding was gradually increased until insulation failure in order to obtain the breakdown voltage. The stator winding of each motor was classified into five coil groups; one group with healthy insulation and four groups with four different types of artificial defects. To analyze the breakdown voltage statistically, Weibull distribution was employed for the tests on the fifty coil groups of ten motors. The 50th percentile values of the measured breakdown voltages based on the statistical data of the five coil groups of ten motors were 26.1kV, 25.0kV, 24.4kV, 26.7kV and 30.5kV, respectively. Almost all of the failures were located in the line-end coil at the exit of the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of dissipation factor and ac current. It is shown that the condition of the motor insulation can be determined from the relationship between the probability of failure and the type of defect.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.7
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• pp.631-635
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• 2007

Diagnostic, surge and ac breakdown tests are widely used to evaluate the insulation condition of stator winding in traction motor. Diagnostic test included ac current, tan delta and maximum partial discharge. The result of diagnostic test indicates that five kinds of stator windings are good condition. Surge test was peformed to confirm the healthy of turn insulation in stator windings. This test is very easy to detect the turn insulation failure between normal and defect stator windings. After completing the diagnostic test, ac breakdown test has conducted gradually increasing ac voltage, until the stator winding punctured. No. 5 stator windings failed near rated voltage of 18.9 kV The breakdown voltage of No. 1 stator windings was 13.0 kV The ac breakdown voltage of normal winding is about 1.45 times higher than that of defect windings. The failure was located in a line-end coil at the exit from the core slot.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.142-145
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• 2008

Electrical insulation of small hydro generator stator winding is one of the most important parts in generator facilities. Some stator winding insulation problems can be identified through analysis of insulation diagnostic test. So, Diagnosis of stator winding insulation is an important measure of ensuring the safe operation and extending the remaining life of small hydro generator. This paper presents case studies of insulation failure in generator stator windings and the results of insulation diagnostic test for small hydro generator stator windings. Especially, Conducting the insulation diagnostic test before the generator installed in site is very important process to keep the good insulation condition in service.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.16-19
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• 2012

In power cables as one of the important power applications adopting HTS tapes, a good insulation should be kept at its optimum performance. As an insulation material for superconducting device applications, polypropylene laminated paper (PPLP) is now widely used instead of the conventional Kraft paper. In addition to its dielectric property, the insulation material should also possess superior mechanical property at cryogenic temperatures and operability that is necessary for the insulation winding process. This study aims to evaluate the mechanical property of the PPLP material at ambient and cryogenic temperatures. At cryogenic temperature, the failure stress of PPLP increased significantly as compared with that at ambient temperature. The failure stress at both temperatures depended upon the sample orientation to the load application.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.280-285
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• 2014

In order to evaluate the insulation deterioration in the stator windings of five gas turbine generators(137 MVA, 13.8 kV) which has been operated for more than 13 years, diagnostic test and AC dielectric breakdown test were performed at phases A, B and C. These tests included measurements of AC current, dissipation factor, partial discharge (PD) magnitude and capacitance. ${\Delta}I$ and ${\Delta}tan{\delta}$ in all three phases (A, B and C) of No. 1 generator stator windings showed that they were in good condition but PD magnitude indicated marginally serviceable and bad level to the insulation condition. Overall analysis of the results suggested that the generator stator windings were indicated serious insulation deterioration and patterns of the PD in all three phases were analyzed to be internal, slot and spark discharges. After the diagnostic test, an AC overvoltage test was performed by gradually increasing the voltage applied to the generator stator windings until electrical insulation failure occurred, in order to determine the breakdown voltage. The breakdown voltage at phases A, B and C of No. 1 generator stator windings failed at 28.0 kV, 17.9 kV, and 21.3 kV, respectively. The breakdown voltage was lower than that expected for good-quality windings (28.6 kV) in a 13.8kV class generator. In the AC dielectric breakdown and diagnostic tests, there was a strong correlation between the breakdown voltage and the voltage at which charging current increases abruptly ($P_{i1}$, $P_{i2}$).

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.151-159
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• 2003

According to the records, approximately 50 percent of power failure were caused by lightning. Conventional fault preventive measures against lightning include reduction of the footing resistance of the tower, multiplication of overhead ground wires and unbalanced insulation of the double circuit transmission tower. In addition to these, transmission line arresters have been recently appeared as an alternatives. In this paper an unbalanced insulation method with transmission line arrester was assumed as another countermeasure against simultaneous double circuit trip of 154 kV transmission line by lightning strike. The lightning performance of line arrester was compared with conventional insulation concept using different numbers of porcelain and glass insulator. Larger numbers of insulator simply increase flashover current level by lightning but the lightning performance doesn't proportional to it. EMTP simulation and predictive calculation of lightning failure rate were carried out to evaluate the performance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.474-480
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• 2012

Diagnostic tests were performed on two high voltage(HV) motor stator windings. These tests included the measurement of insulation resistance, polarization index, AC current, dissipation factor($tan{\delta}$) and partial discharge(PD) magnitude. Surface contamination of HV motor stator windings has an effect on the AC current and $tan{\delta}$. When the stator windings were finished cleaning and insulation reinforcement, the increase rate of AC current(${\Delta}I$) and dissipation factor(${\Delta}tan{\delta}$) were very small compared to those before cleaning. However, the PD magnitude remained the same. These tests show that cleaning and insulation reinforcement of HV motor stator windings can reduce the insulation failure.