AC Test Voltage Research Articles

Dielectric strength of transformer insulation at DC polarity reversal

Among special insulation tests for DC power converter transformers, polarity reversal tests can be substituted by applied AC voltage tests from a stress similarity in oil ducts. In order to investigate equivalent levels of other insulation tests to polarity reversal tests, the dielectric strength of a transformer at polarity reversals was examined by use of a model of typical oil/paper composite insulation. From the comparison of polarity reversal and other insulation tests, it was found that dielectric strength of transformer insulation at polarity reversals is phenomenally similar to that under switching impulse stresses. Equivalent AC test voltage to polarity reversal test was also estimated from the experimental results. The breakdown characteristics of polarity reversal tests showed that partial discharges at polarity reversals impose less harmful stress on insulation barriers than those at usual AC or impulse tests.

AC V‐t and impulse V‐N characteristics of shell‐form transformer insulation model

AbstractTo evaluate an appropriate level of ac test voltage for 1000‐kV transformers, it is necessary to make an accurate estimation of ac V‐t characteristics. For the level of impulse test voltage, V‐N characteristics are important to evaluate effects of impulse stress repetition. Since both of the characteristics are dependent on insulation structures and manufacturing processes of transformers, it is important to make accurate simulations on transformer insulation for reliable insulation data.To obtain some of the basic data for 1000‐kV transformer test levels, long‐time ac V‐t tests and impulse V‐N tests of up to 1000 times voltage application were carried out on an insulation model simulating fundamental structure of shell‐form transformers. The model is composed of a parallel electrodes system with a compound structure of pressboard barrier and oil gap.The tests showed the following characteristics: ac V‐t characteristics of up to several ten days could be described by two lines, each representing short‐time and long‐time characteristics. V‐N characteristics of lightning and switching impulse were expressed by relatively flat lines, which showed a decrease in breakdown voltage by less than 10 percent after 1000 times impulse application.

Commercialization of an extra high‐voltage nonflammable transformer

AbstractA perfluorocarbon (PFC)‐immersed 275‐kV transformer with compressed SF6, gas has been developed. This paper describes the basic cooling and insulation characteristics of PFC, the ac partial discharge voltage, and the aging of PFC‐immersed insulation. The results demonstrate that a prototype 275‐kV 100‐MVA three‐phase transformer can be operated without any difficulties for an extended period of overvoltage. This prototype has an ac partial discharge initiation strength which is 1.5 times that of the ac test voltage and a lightning impulse breakdown strength which is 1.5 times that of the test voltage. A 275‐kV 250‐MVA three‐phase transformer was built and is being operated at the Abe substation of Chubu Electric Power Co., Inc. The transformer has been operating satisfactorily.

Development and practical operation of perfluorocarbon immersed 275 kV transformers with compressed SF/sub 6/ gas insulation

A perfluorocarbon (PFC) immersed 275 kV power transformer with compressed SF/sub 6/ gas insulation has been under development. This paper clarifies the AC partial discharge inception voltage and time characteristics of PFC immersed insulation and also clarifies that a prototype 275 kV 100 MVA three-phase transformer could be operated without any trouble during long-term overvoltage tests. This prototype proved that it had AC partial discharge inception strength of higher than 1.5 times the AC test voltage and lightning impulse breakdown strength of 1.5 times the test voltage. A 275 kV, 250 MVA three-phase power transformer was developed and operated at the outdoor substation of the Chubu Electric Power Co., Japan. This transformer has been successfully operated to date and a detailed internal inspection of the transformer was carried out after one year and 9 months of successful practical operation. No significant abnormal condition was recognized. >

外鉄形変圧器絶縁モデルの交流V-t特性とインパルスV-N特性

To evaluate an appropriate level of ac test voltage for 1000-kV transformers, it is necessary to make an accurate estimation of ac V-t characteristics. For the level of impulse test voltage, V-N characteristics are important to evaluate effects of impulse stress repetition. Since both of the characteristics are dependent on insulation structures and manufacturing processes of transformers, it is important to make accurate simulations on transformer insulation for reliable insulation data. To obtain some of the basic data for 1000-kV transformer test levels, long-time ac V-t tests and impulse V-N tests of up to 1000 times voltage application were carried out on an insulation model simulating fundamental structure of shell-form transformers. The model is composed of a parallel electrodes system with a compound structure of pressboard barrier and oil gap. The tests showed the following characteristics: ac V-t characteristics of up to several ten days could be described by two lines, each representing short-time and long-time characteristics. V-N characteristics of lightning and switching impulse were expressed by relatively flat lines, which showed a decrease in breakdown voltage by less than 10 percent after 1000 times impulse application.

Development of prefabricated type straight through joint for 275 kV XLPE cable

The research involved in developing a prefabricated type straight through joint for 275 kV XLPE cable is described. Based on a review of the results of electric field analyses, a compact insulation structure using a molded epoxy insulation unit and a molded EPR stress-relieving cone were designed. The AC and lightning impulse voltage test as well as the short-circuit test and the offset test were conducted on the joint. The results show that the joint possesses excellent assembly properties and superb insulation performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modulation of a gated ion channel admittance in lipid bilayer membranes

A future class of amperometric biosensors may utilize gated ion channels such as acetylcholine and glutamate receptors as chemical detection components. In this study, bilayer lipid membranes containing voltage-dependent anion channels (VDAC) were used to model an ion-channel-based biosensor which could continuously monitor AC amperometric changes resulting from induced changes in channel conductance. The in-phase and quadrature components of the induced alternating membrane current were monitored as a function of the applied DC offset voltage which was superimposed on the sinusoidal test voltage. The accuracy and sensitivity of the AC-measured VDAC response was dependent on the magnitude of the AC test voltage relative to the DC offset necessary for channel closure. The VDAC channel appears to be a suitable model protein for AC impedance-based biosensor fabrication.