• Journal of Electrical Engineering and Technology
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• v.1 no.4
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• pp.528-533
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• 2006

Electrical discharges may occur in gas, liquid as well as solid insulating materials. This paper describes the investigation results on the discharges in air, silicone oil and low density polyethylene (LDPE) using needle plane electrode system under AC voltage of 50 Hz. The experimental results showed that for discharge in air (corona), discharge pulses were concentrated around the peak of applied voltage at negative half cycle. For silicone oil positive as well as negative discharges were observed which concentrated around the peak of applied voltage. The positive pulse number was smaller but the magnitude was higher than that of negative discharge. Discharges in void took place at wider range of phase of applied voltage. The unbalance in pulse number and magnitude similar to that of oil discharges were observed. For electrical treeing in LDPE, the discharges were spread before the zero cross of the applied voltage up to the peak at both positive and negative half cycles. The discharge pulse sequence analysis indicated that the PD occurrence in air, oil and void were strongly affected by the magnitude of applied voltage. However, for electrical treeing it was observed that the discharge occurrence was strongly affected by the time derivative of the applied voltage (dv/dt).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.11a
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• pp.202-205
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• 1994

There is a close relation between electrical treeing and internal partial discharges in solid dielectrics. In this paper, the characteristics of electrical treeing and partial discharge in solid dielectrics are investigated. We carried out the measurements of electrical treeing and PD(partial discharge) characteristics. From the experimental results, we found out that maximum PD magnitude increased linearly with time at first stage, thereafter increased remarkably. These tendencies are very similar to the characteristics of tree growth with time.

• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1725-1727
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• 1998

In this paper the patterns of partial discharges(PD) occurred from some defects at the interface of cable joints as the function of the phase of the applied voltage were investigated in order to discern the kind of a defect. The results obtained in this study show that it is possible to distinguish the PD patterns between the void discharges and the treeing or tracking discharges which were occured at the cable joint interface. While the state of defect transfers from a void discharge into a tree or tracking discharge with a aging time, the skewness for both half of the applied voltage cycle is observed to go to the negative value.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.898-903
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• 2004

In this paper, neural networks is studied to apply as a PD source classification in XLPE power cable specimen. For treeing discharge sources in the specimen, three defected models are made. And these data making use of a computer-aided discharge analyser, statistical and other discharge parameters is calculated to discrimination between different models of discharge sources. And also these parameter is applied to classify PD sources by neural networks. Neural Networks has good recognition rate for three PD sources.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.558-562
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• 2003

In this paper, neural networks is studied to apply as a PD source classification in XLPE power cable specimen. For treeing discharge sources in the specimen, three defected models are made. And these data making use of a computer-aided discharge analyser, statistical and other discharge parameters is calculated to discrimination between different models of discharge sources. And also these parameter is applied to classify PD sources by neural networks. Neural Networks has good recognition rate for three PD sources.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1999.11a
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• pp.136-140
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• 1999

Measurements of AE signals caused by partial discharges were performed by using an ultrasonic measurement technique to diagonise the electrical treeing deterioration in XLPE cable. We also examined the partial discharge magnitude and AE signals(peak-to-peak) with the increase of the deterioration time. From these results, it was found that AE signal due to partial discharge can be greatly detected at the peak value of positive polarities prior to the breakdown voltages, and the magnitude of AE signals was closely related to the current pulses by the increase of deterioration, and it appeared that AE signals(peak-to-peak) was proportional to partial discharge magnitude. Attenuation and time-delaying characteristics of ultrasonic signals propagated in various polymers sample by using ultrasonic oscillation and receiving systems are also reported as a basic data of ultrasonic measurements in XLPE cable.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2093-2096
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• 1999

This paper describes to access the insulation deterioration condition of the stator windings in three large turbine generators. Nondestructive tests have been carried out on stand-still generators which have been in service for 2 to 30 years. In most cases these tests include ac current increase rate($\Delta$I), delta tan delta( ${\Delta}tan{\delta}$), and maximum partial discharge(Qm). Gen. 2 show that the $tan{\delta}$ is higher than other two generators in the $tan{\delta}$-voltage curve. Partial discharge(PD) patterns were observed internal, corona and treeing discharges in large turbine generators. The PD tests were confirmed the correlation between discharge patterns and the kinds of defects.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2392-2395
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• 1999

This paper describes to access the insulation deterioration condition of the stator windings in six high voltage motors. Nondestructive tests have been carried out on stand-still motors. These tests include ac current increase rate($\Delta$I), delta tan delta(${\Delta}tan{\delta}$), and maximum partial discharge(PD). AC current and $tan{\delta}$ were measured by Schering bridge. The measurement of PD patterns were conducted using digital partial discharge detector. PD patterns were observed treeing and internal discharges in Motor 1 and 2. The stator windings of two motors were found to be in a poor condition and their were recommended to rewind. The stator. windings of four motors were judged to be in serviceable condition.

• 전기의세계
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• v.19 no.6
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• pp.18-25
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• 1970

The object of this project is to manifest the mechanism of deterioration phenomena for dielectrics causing corona discharge and applies it for determine the standard corona detection technique. As the results, we observed that corona discharges may occur more strongly around cylindrical shape electrode in air than hemisphere shape electrode in vacuum, so that it depends on effects such as shape of the electrode, moisture, surface coditions, etc. According to observed the deterioration of dielectrics takes place in following stages. At first the attacked surface by an electron avalanche is uniformly eroded; then pits are formed; after that sharp channels are formed which lead to break-down as a treeing. The test are accelerated with higher frequencies by the cylindrical bar shape electrode in the pulse stright detection method more sensitive than Lissajous patterns. Lissajous patterns detection method is simple but usually insensitive and has disadvantage that the magnitude of the individual discharge is not measured.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.3
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• pp.73-81
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• 1999

Measurements of ultrasonic signals caused by partial discharges were perlonnrl by using an ultrasonic measurement technique to diagnose the electrical treeing deterioration in an epoxy mold-type power transformer. We also examined the characteristics of tree growth, partial discharge magnitude and ultrasonic pulse number with the increase of the deterioration time. From these results, it was found that the shape of the tree was a branch-type, and the rates of the tree growth were examined when ac voltages of 16[kV] and 20[kV] were applied Ultrasonic pulse number and discharge magnitude were rapidly increased as the length of the tree grows after the middle stage of the deterioration time, and it appeared that ultrasonic pulse number was proportional to discharge magnitude. Attenuation, time-delaying and directivity characteristics of ultrasonic signals propagated into epoxy resin by using ultrasonic oscillation and receiving systems are also re[prted as a basic data of ultrasonic mesasurements in mold-type power transformer.former.