Tokihiro Umemura

Life expectancy and degradation behavior of electric double layer capacitor part I

General properties of various electric double layer capacitors (EDLC) have been introduced for power and industrial application. In this report, degradation behavior of the EDLCs was clarified. The capacitance decrease might be caused by the degradation of the electrolysis, propylene carbonate, and also the degradation by-products which piled on the nano-scale micro-cavity surface of the activated-carbon particles of the electrodes. The degradation mechanism was found to be governed by the Arrhenius chemical kinetics theory and consisted of two stages with different activation energy.

Long-Term Sequential Characteristics of Negative Partial Discharge in Pressurized SF6 Gas

SF6 gas insulated electric power apparatus such as GIS and GIL have been operated under high gas pressure condition at around 0.5 MPa-abs[1,2]. Here, metallic particle contaminants in GIS would generate negative partial discharges (PD) firstly, because negative PD inception voltage is lower than positive one. In such high gas pressure condition, there is a possibility that breakdown occurs without replete positive PD precursor to it. In this case, only negative PD measurement could be a method for the insulation diagnosis. Therefore, in the commissioning process and under operation, it is important for the insulation diagnosis at the early stage to clarify the negative PD mechanism under high gas pressure condition.

Corona Discharge Phenomenology at Onset in Weakly Electronegative Gas Mixtures

Loss of insulation integrity from a gas-insulated system is at first a subtle phenomenon. It is contended that this early stage of degradation contains privileged information, to be gleaned in order to unravel precursor signs preceding the eventual outbreak of minor faults, viz. partial discharges and associated patterns.

Thermal aging of silicone oil aromatic polyamide insulation systems

The thermal degradation behavior of silicone oil/aromatic polyamide insulation system was studied. It was found that the flash and fire points decreased due to the formation of low molecular weight by-products of such cyclic siloxane oligomers as D/sub 3/, D/sub 4/ and D/sub 5/. The gel permeation chromatography (GPC) and high performance liquid chromatography (HPLC) analysis clarified that the depolymerization of siloxane molecules happened during the thermal aging, resulting in the high- and low- molecular by-products formation. The thermal stability index (TGI) index obtained by the thermogravity (TG) measurements and cyclic oligomer detection could be used for the insulation diagnosis.

On the stochastic nature of SF/sub 6/ partial discharges close to onset conditions

Discharges in compressed pure SF/sub 6/ were produced in a plane-point-plane electrode configuration. The present report focuses on the pulse characteristics, as observed by recording real-time discharge frames via a fast digitizer. Sampling by frame of a duration of typically 1 ms with time resolution of 1 ns, has given access to the relation between consecutive pulses. Results obtained for the negative DC corona at 500 kPa are presented. Discharge characteristics closeby corona threshold were overexamined in detail. The experimental approach, in conjunction with the rendered-possible analyses, allowed to unravel very distinctive features associated with the discharge events.

Partial-discharge phenomenology in compressed SF/sub 6/ under stochastic conditions

Erratic discharges of low intensity in compressed SF/sub 6/ were produced in a plane-point-plane electrode configuration. Both DC (negative-corona conditions) and AC voltages were used, the applied voltage-values being chosen close to corona threshold. The test cell was filled at 500 kPa and the gap length, fixed at 5 mm. The present paper focuses on the pulse characteristics, as observed by recording real-time sequences via a fast digitizer. The high-resolution sampling has given a detailed access to the time relation between consecutive pulses. Emphasis of measurements was put on the DC conditions, while comparison of some AC results is offered. The large data set obtained under DC conditions allowed to establish the existence of a discharge regime and to characterize it quantitatively. In the AC-situation, the discharge events showed similar traits, but pulse parameters differed in magnitude, and stochasticity was different.

Partial discharge detection using ferrite antenna

Some examples of partial discharge detection by using a loop antenna wound on a ferrite core were demonstrated. The prototype of a partial discharge detector system using a ferrite antenna was demonstrated. It was found that the partial discharge can be detected by measuring the electromagnetic waves irradiated from the discharge event, using the loop antenna and a wideband amplifier. The frequency range of the detected electromagnetic waves was up to 50 MHz. The maximum sensitivity of the prototype detector was found to be about 500 pC in practical use.<<ETX>>

Evaluation of distinctive PD parameters in SF/sub 6/ under ac voltage

Discharge measurements have been carried out in SF/sub 6/ at pressures of 1 and 5 bars in a laboratory test cell with a needle plane electrode configuration. The plane electrode was subjected to an ac high voltage. The discharge sequences were recorded by a combination of phase resolved partial discharge analysis (PRPD) and fast digitizing oscilloscope. It was found that each of those techniques brought distinctive information, while none of them would give all the information about a discharge sequence. Cross correlation between the different results was used to validate the information. The PRPD analysis was found to give a more global information that allowed recognition of characteristic patterns with regard to the ac voltage. This information was lost during the recording of a 1-millisecond digitized frame. The use of the fast digitizer made it possible to evaluate the dependency of successive pulses within a discharge sequence. The measurements performed at low and high pressure presented sequences completely different in nature. This paper shows that some parameters, such as the time between pulses within a discharge sequence need to be used in addition to the PRPD patterns to fully characterize a discharge source or to monitor it over time.

Partial discharge resistant mechanism of newly developed enameled wire

A new enameled wire with inorganic additives has been developed. The wire is a double layered structure whose outer layer contains inorganic additives. It was shown that the new wire has good partial discharge endurance at power-frequency, leading to a lifetime improvement of about an order of magnitude. It was also found that the higher conductivity of the outer layer improved the partial discharge resistant nature owing to the decrease in partial discharge energies.

A sensing system for degradation diagnosis of oil-filled transformers

Under normal operating conditions the insulation of power transformers undergoes gradual deterioration that produces various degradation by-products. Properties of the insulation, such as degree of paper polymerization, also change. To evaluate the degradation state of the insulation the detection and analysis of the degradation by-products have been widely performed. However, the diagnostic techniques presently used are rather complicated and time consuming. This paper describes a new diagnostic technique for oil-filled transformers based on a semiconductor-type sensor. The technique can be used for in-situ measurements in the field, requires very small amounts of oil for analysis and allows for rapid test data analysis. The detection of ketonic by-products with the newly developed sensor was found to be very useful as a diagnostic tool.<<ETX>>