1. Field of the Invention
The present invention relates to a method for designing an insulation thickness of a 22.9 kV class high-temperature superconducting cable. More particularly, the present invention relates to a method for designing an insulation thickness of a high-temperature superconducting cable wherein conversion coefficients are applied to conventional cable insulation thickness equations using AC insulation breakdown electric-field, impulse insulation breakdown electric-field, and partial discharge initiation electric-field characteristics of an insulation material, thereby achieving an increase in the accuracy of the insulation thickness of the high-temperature superconducting cable to be manufactured.
2. Description of the Related Art
Nowadays, the demand of electric power throughout the world is on the rise due to a continuous economic growth. More particularly, recent continuing urbanization is causing a concentration of a great amount of electric power supply and demand. For this reason, the world has an urgent need for the development of a high-temperature superconducting cable featuring an extremely low power-transmission energy loss and a remarkably high power-transmission energy density, and therefore, such a high-temperature superconducting cable, which uses liquid nitrogen as a refrigerant, is being developed in various countries. Actually, as a high-temperature superconducting wire rod, having a high critical current and largely improved mechanical properties, has been recently developed, the study of high-temperature superconducting cables using the wire rod is being pursued with much enthusiasm.
Generally, the high-temperature conducting cable is electrically insulated in a composite insulation manner using liquid nitrogen and insulation paper. With the composite insulation manner wherein conductors are laminated by interposing thin polymer insulation tapes for electric insulation thereof, cooling shrinkage and thermal loss can be reduced and conventional oil-field (OF) cable insulation methods are applicable. Therefore, it can be said that, currently, the composite insulation manner has the highest practical application possibility. More particularly, in the case of an AC cable that depends on a dielectric loss, it employs polypropylene laminated paper (PPLP). The PPLP is a semi-synthetic paper of polypropylene and kraft paper, and has a low dielectric constant and dissipation factor.
In view of electric insulation, the high-temperature superconducting cable is designed in consideration of a withstand voltage of a composite insulator which consists of liquid nitrogen and insulation paper, and therefore, has a relatively simplified insulation design. That is, an insulation thickness of the high-temperature superconducting cable is calculated by inserting the withstand voltage to given insulation design equations based on AC insulation breakdown electric-field, impulse insulation breakdown electric-field, and partial discharge initiation electric-field characteristics of the composite insulator. However, to ensure stability of the cable which must be operated for a long time, dozens of experiments must be repeatedly performed to increase the reliability of experimental data In this case, it is difficult for all samples to be made into model cables for use in the experiments, and therefore, generally, a sheet sample having a minimum insulation configuration is used in the experiments. However, general solid insulators have different insulation characteristics in accordance with an insulation thickness of the cable and the area and shape of an electrode. For this reason, it is desirable that conversion coefficients, which are obtained in consideration of the effects of area, thickness, and shape via insulation breakdown experiments using a sheet sample, mini-model cable, and model cable, be applied to given insulation design equations. This ensures an improvement in cable operational reliability.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for designing an insulation thickness of a 22.9 kV class high-temperature superconducting cable wherein AC insulation breakdown electric-field, impulse insulation breakdown electric-field, and partial discharge initiation electric-field characteristics of a sheet sample of polypropylene laminated paper (PPLP), which satisfies standards of a Korean normal purchase specification published by the Korea Electronic Power Corporation and is used as insulation paper of the high-temperature superconducting cable, are set under a cryogenic liquid nitrogen atmosphere, and a mini-model cable and model cable are manufactured to set conversion coefficients between the sheet sample and the mini-model and model cables by use of the AC and impulse insulation breakdown electric-field characteristics.
In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method for designing an insulation thickness of a 22.9 kV class high-temperature superconducting cable having a composite insulation configuration that consists of liquid nitrogen and insulation paper, wherein an AC conversion coefficient and an impulse conversion coefficient between a sheet sample and a model cable are applied to AC insulation breakdown electric-field, impulse insulation breakdown electric-field, and partial discharge initiation electric-field values of the sheet sample of polypropylene laminated paper as the insulation paper to fulfill cable insulation thickness design equations.
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Now, the present invention will be explained in more detail with reference to the accompanying drawings.
To design an electric insulation thickness of a high-temperature superconducting cable, first, AC insulation breakdown electric-field, impulse insulation breakdown electric-field, and partial discharge initiation electric-field characteristics of a sheet sample of polypropylene laminated paper (PPLP), which serves as cable insulation paper, must be set Then, a mini-model cable and model cable are manufactured to set an AC conversion coefficient MAC and an impulse conversion coefficient Mimp, such that an insulation thickness of the high-temperature superconducting cable is determined based on the conversion coefficients. That is, the insulation thickness of the cable is designed by use of the above mentioned three insulation breakdown electric-field characteristics and conversion coefficients. With reference to a Korean normal purchase specification published by the Korea Electronic Power Corporation, an AC withstand voltage of a 22.9 kV class power cable is 80 kV, and an impulse withstand voltage BIL is 150 kV.
Based on the above calculation, an AC insulation thickness tAC of the cable is calculated from the following Equation 1.
where, the above coefficients are as follows:
AC withstand voltage VAC=80 kV
AC maximum breakdown electric-field value Emax(AC)=50 kV/mm
AC conversion coefficient MAC=0.47
inner conductor radius r1=14.5 mm (former radius+wire rod thickness+inner semi-conductive layer thickness).
Based on the above calculation, an impulse insulation thickness timp of the cable is calculated from the following Equation 2.
where, the above coefficients are as follows:
impulse withstand voltage BIL=150 kV
impulse deterioration coefficient L1=1.0
impulse temperature coefficient L2=1.0
impulse design margin L3 =1.32
impulse maximum breakdown electric field value Emax(imp)=82 kV/mm
impulse conversion coefficient Mimp=0.63
inner conductor radius r1=14.5mm (former radius+wire rod thickness+inner semi-conductive layer thickness).
where, the above coefficients are as follows:
system maximum voltage Um=25.8 kV
AC deterioration coefficient K1=1.87
AC temperature coefficient K2=1.0
AC design margin K3=1.32
partial discharge initiation electric-field value Emax(PD)=20 kV/mm
AC conversion coefficient MAC=0.47
inner conductor radius r1=14.5mm (former radius+wire rod thickness+inner semi-conductive layer thickness).
As apparent from the above description, in a method for designing an insulation thickness of a 22.9 kV class high-temperature superconducting cable in accordance with the present invention, conversion coefficients are applied to AC insulation breakdown electric-field, impulse insulation breakdown electric-field, and partial discharge initiation electric-field characteristics of an insulation material, whereby a more stable and quantified insulation thickness design for a high-temperature superconducting cable can be accomplished. As a result, it can be understood that system stability in the application of the high-temperature superconducting cable can be more improved.
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
Number | Date | Country | Kind |
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10-2005-0121707 | Dec 2005 | KR | national |