• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1025-1027
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• 1999

Recently, many researches on a diagnosis of stator winding insulation of large generators are reported. They mostly utilize a trend analysis of Partial Discharge (PD). In this paper, a novel on-line monitoring system for an insulation diagnosis is proposed. This system obtains the parameters such as Maximum Partial Discharge Magnitude (QM), Normalized Quantity Number (NQN) and Dynamic Stagnation Voltage (DSV) by continuous on-line monitoring of winding insulation. It is capable of diagnosing the insulation condition by analyzing the trend of PD and utilizing the database built by the system.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1892-1896
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• 2008

Inverter-fed induction motors (IFM) are prevalent in traction vehicles. However, the winding insulation of IFM is substantially more stressed than of line-powered motors by surge voltages. Consequently, the winding insulation of IFM should be estimated by surge voltages. Also, the weakness of coil insulation can be detected by the surge voltage test. This paper described the insulation evaluation of induction motors by application of surge voltages. A surge voltage generator with the maximum voltage of 5 kV and the selectable rise-time in ranges of $50\;ns\;{\sim}\;500\;ns$ was fabricated. In the experiment, we applied surge voltages into induction motors with the magnitude and the risetime according to IEEE 522. By the analysis of applied surge voltage and current waveforms, we could find difference between normal and defection windings.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.9
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• pp.783-789
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• 2003

The winding problems of traction motor are the major determinant of motor's life. The root cause of winding failure is gradual deterioration of the insulation due to thermal, electrical, mechanical and environmental stresses. The aging of the insulation reduces the electrical and mechanical strength of the insulation. At same point, a voltage surge or mechanical shock from a traction motor start will fracture or break down the insulation. To achieve the expected life usually requires extensive laboratory evaluation of the insulation systems and the use of accelerated aging tests. There are several nondestructive test available for checking, the condition of motor insulation, the probable extent of aging, and the rate of which aging is taking place. So the insulation characteristics of stator coil were each analyzed by measurement of dielectric loss(tan$\sigma$), capacitance and partial discharge. The method of diagnosis is able to analyze the insulation condition and evaluate the life of the traction motor.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.11
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• pp.735-741
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• 1999

The monitoring and assessment on the insulation condition of generator stator windings have been an important task of utility companies. The interest for the assessment of insulation condition has been increasing due to the need to keep old generating equipment reliable in order to extend the equipment life and to increase the generating capacity. Even though many developments and research activities for the condition assessment of generator insulation have been performed for decades, the assessment criterion in order to consistently predict the actual insulation condition is still in question. In this paper, the correlation between the parameters and the insulation condition is analyzed through the various non-destructive diagnostic tests in order to establish the assessment criterion on insulation deterioration of generator stator windings. By analyzing the correlation, PDI(Partial Discharge Index) as a novel parameter for the assessment criterion on insulation diagnosis of stator winding is proposed and verified.

• Journal of the Korean Society of Safety
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• v.38 no.3
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• pp.35-42
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• 2023

This study analyzed the current and temperature characteristics of major components of an induction motor during normal and abnormal operations as functions of the difference in the rated capacities of medium and large-sized motors widely used in industrial settings. The temperature rise equation of the induction motor winding was derived through locked-rotor operation experiments and linear regression analysis. When the ambient temperature is 40 ℃, the time to reach 155 ℃, the temperature limit of the insulation class (F class) of the winding of the induction motor, was confirmed to be 48 seconds for the 2.2 kW induction motor and 39 seconds for the 3.7 kW induction motor. This means that when the rated capacity is large or the installation environment is high temperature, the time to reach the temperature limit of the insulation class during locked-rotor operation is short, and the risk of insulation deterioration and fire is high. In addition, even if the EOCR (Electronic Over Current Relay) is installed, if the setting time is excessively set, the EOCR does not operate even if the normal and locked-rotor operation of the induction motor is repeated, and the temperature limit of the insulation grade of the winding of the induction motor is exceeded. The results of this study can be used for preventive measures such as the promotion of electrical and mechanical measures for the failure of induction motors and fire prevention in industrial sites, or the installation of fire alarm systems.

• 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.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.723-724
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• 2006

In this study, superconducting coil arrangements and cryostat concept design were conducted for the development of 13.2kV/630A bifilar winding type high temperature superconducting(HTS) fault current limiter(FCL) with YBCO coated conductor(CC) wire. The coil consists of several layers with unique non-inductive solenoid winding method. Six types of HTS coil arrangements were investigated for the optimal insulation design of HTS FCL. And, conceptual design of cryostat was conducted for the decrement of thermal invasion and the prevention of low voltage insulation breakdown in the LHe which is used as pressurization gas in sub-cooling condition of liquid nitrogen(LN2). As the results, it was found that the modified suspended type cryostat with horizontal coil arrangement is beneficial to the insulation design of 13.2kV level bifilar winding type HTS FCL.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1526-1529
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• 1994

In hydro-generator, a groundwall insulation of stator windings gradually deteriorates due to mechanical, thermal, electrical and environmental stresses. These stresses combine to result in loose windings, delamination of the stator insulation and/or electrical tracking of the end winding, all of which can lead to stator insulation failures. Conventionally, off-line tests such as partial discharge measurement, DC/AC current test and ${\Delta}tan{\delta}$ test has been used for estimation of winding condition. However, off-line test requires large power supply and generator outage. In addition, major cause of insulation problems such as loose wedges and slot discharges may not be found with off-line diagnoses. This paper describes the on-line partial discharge measurement techniques in the generator stator windings. The experimental results from the UIAM #1 hydro-generator confirms a optimistic application of on-line generator diagnosis method as a reliable tool for evaluation of winding condition.

• Korean Journal of Materials Research
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• v.7 no.8
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• pp.650-653
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• 1997

In large generators in power plants, stator winding insulations is exposed to a combination of thermal, electrical, mechanical, environmental stresses in service. These combined stresses cause insulation aging which leads to final insulation breakdown. In order to identify the breakdown mechanism, the stator winding insulation materials which are composed of mica-epoxy is analyzed by the component of materials with EDS, SEM techniques. We concluded that the potassium ions of mica are replaced by hydrogen ions at boundary area of mica-epoxy and/or mica-mica. It is proposed that through these phenomena, the conductive layers of potassium ions enable high voltage fields of multiple stresses to create voids and microcracks.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1692-1695
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• 1997

This paper describes the relationship between the various non-destructive parameters and the breakdown voltage for the 17 kV, 300 MVA and the 22 kV, 500 MVA generators stator bars with polyester and epoxy/mica insulation respectively. Also, this study reports the results of an investigation into the factors which can assess the insulation condition of generator stator winding. Furthermore, a new parameter, Partial Discharge Index(PDI), is introduced as the valuable parameter for the assessment of insulation condition. The ratio between partial discharge increment and the stepwise voltage increment from the Discharge Inception Voltage (DIV) at the characteristic or resonant frequency band shows the close relationship between the breakdown voltage and PDI.