Jae-Hyeong Choi

The Electrical Insulation Characteristics for a HTS Cable Termination

A research on several characteristics such as volume breakdown and surface discharge of insulators for a termination of power transmission class high temperature superconducting (HTS) cable was performed. In this paper, we investigated the surface discharge of glass fiber reinforced plastic (GFRP) in the air, nitrogen gas (GN2) and cryogenic nitrogen gas (CGN2) media. The breakdown characteristics of these media were also studied. Experimental results revealed that flashover voltage greatly depends on pressure, temperature, the kinds of insulating media and voltages. However, it is shallowly affected by shape and material of electrode. The breakdown voltage of liquid nitrogen (LN2), GN2 and CGN2 deeply depends on the shape and dimension of electrode, kinds of voltages and pressure. Moreover, the breakdown voltage of CGN 2 and flashover voltage of GFRP in the CGN2 is also influenced by temperature and vapor-mist density of the gas

Research on the Insulation Design of a 154 kV Class HTS Power Cable and Termination

A 154 kV class high-temperature superconducting (HTS) power cable system Is developing in Korea. For insulation design of this cable, the grading method of insulating paper is proposed. The electrical insulation material has been used two kind of laminated polypropylene paper (LPP) that has different thickness. The use of graded insulation gives improved mechanical bending properties of the cable. Also, within a HTS cable technology the terminations are important components. A HTS cable termination is energized with the line-to-ground voltage between the coaxial center and outer surrounding conductors, in the axial direction there is a temperature difference from ambient to about 77 K. For insulation design of this termination, the insulation material of the termination body used glass fiber reinforced plastic (GFRP) and the capacitance-graded method is proposed. Therefore, in order to insulating design of a 154 kV class HTS power cable and termination, this paper will report on the experimental investigations in impulse breakdown and surface flashover characteristics of the insulation materials. Based on these experimental data, the electrical insulation design of a 154 kV class HTS power cable and termination were calculated.

Electrical Insulation Characteristics of PPLP as a HTS DC Cable Dielectric and GFRP as Insulating Material for Terminations

A high-temperature superconducting (HTS) DC cable system has attracted a great deal of interest from the view point of low loss, dense structure and large capacity compared to HTS AC cable system. It has a HTS cable and a termination. A HTS DC cable system consists of a conductor, cooling system and electrical insulation. To realize the HTS DC cable system, it is important to study not only high current capacity and low loss of conductor but also optimum electrical insulation at cryogenic temperature. The electrical insulation technology of HTS DC cable and termination must be solved for the long life, reliability and compact of cable. In this paper, we will discuss mainly on the electrical insulation characteristics and the insulation design of 220 kV class HTS DC cable. Voltage-time (V-t) characteristics of laminated polypropylene paper (PPLP) in LN2 were studied. Furthermore, the surface flashover characteristics of glass fiber reinforced plastic (GFRP) for termination insulators under DC and lightning impulse voltage were studied.

A Study on Insulation Characteristics of Laminated Polypropylene Paper for an HTS Cable

Studies on developing an HTS (High-Temperature Superconducting) power cable with high transmission capacity and less loss are actively being performed worldwide. In Korea, an HTS power cable is being developed which applies cold dielectric type that a cable core wrapped by insulating papers is impregnated in liquid nitrogen. The insulating paper used in cold dielectric type is LPP (Laminated Polypropylene Paper) which has less dielectric loss and a superior dielectric property. In this paper, AC and lightning impulse breakdown strength and V-t characteristics with mini-model cables which were manufactured as the same structure with an HTS power cable were researched. Also, a thickness of insulation layer for a 154 kV class HTS power cable was designed as a result.

The Insulation Design of 154 kV HTS Transformer and on Load Tap Changers

The HTS transformer is one of the promising HTS power applications that are expected to be commercialized in the near future. Among the auxiliary functions of a transformer, the voltage regulation function is known to be the most important one. For the voltage regulation of HTS transformers, they are normally equipped with the on-load tap changers (OLTC). It is also required that, in order to develop a HTS transformer as a complete system, not only the basic technologies for all the components including OLTC and bushing, but also the technologies for the insulation of these components at a cryogenic temperature should be well established as applicable. Taking such facts into account, the breakdown characteristics of the insulation components have been evaluated for such application areas as turn-to-turn insulation, layer-to-layer insulation, c, drive shaft-to-drive shaft insulation, tap connecting terminal insulation and others. In overall, this paper discusses the electric insulation design and experimental results with regard to HTS transformer, OLTC and bushing.

Insulation Design and Experimental Results for Transmission Class HTS Transformer With Composite Winding

In the response to the demand for electrical energy, much effort aimed to develop and commercialize high temperature superconducting (HTS) power equipments has been made around the world. In Korea, companies and universities are developing a power distribution and transmission class HTS transformer that is one of the 21st century superconducting frontier projects. The composite winding of transmission class HTS transformer is concentrically arranged primary winding (High)-Secondary winding (Low)-tertiary winding (High) from center. Primary winding is continuous disk type, Secondary winding is layer type and tertiary winding is Double pancake type. For the development of transmission HTS transformer with composite winding, the cryogenic insulation technology should be established. We have been analyzed insulation composition and investigated electrical characteristics such as breakdown of , barrier, kapton films and surface flashover on Fiber Reinforced Plastic (FRP) in Liquid nitrogen . We are going to compare with measured each value and apply the value to most suitable insulating design of the HTS transformer.

The Insulation Characteristics of Coil—Cryocooler for Conduction Cooled HTS SMES

The conduction cooled high-temperature superconductor (HTS) SMES (superconducting magnetic energy storage) was operated in cryogenic temperature and high vacuum conditions. Thus, the insulation design at the conditions is an important element that should be established to accomplish compact design is a big advantage of HTS SMES. However, the behaviors of insulators for the conditions are virtually unknown. Therefore, we need to researches and development of insulation concerning application of the conduction cooled HTS SMES. In this study, we experimented on insulation characteristics of SMES system. Also, we investigated about insulation characteristics of suitable materials to insulator for conduction cooled HTS SMES. As these results, we had basic data for insulation materials selection and insulation design of cryocooler-to-magnet coil for the development of 600 kJ class conduction cooled HTS SMES.

A study on thickness effect of HTS cable for insulation design

The electrical insulating design is important to realize the HTS (high temperature superconducting) cable because this cable is operated under the high voltage environment. For the insulation design of HTS cable, it is necessary to investigate the PD (partial discharge) inception, ac and impulse breakdown strength of LN2 (liquid nitrogen)/LPP (laminated polypropylene) composite insulation system. However, the designed insulation thickness by ac and impulse could not be applied to cable fabrication process due to much low electrical breakdown strength. The effect of the multi-layered insulation paper was not considered on the previous insulation design and the insulation thickness by PD inception strength could be applied only. In this paper, the electrical breakdown characteristic, which considered the effect of multi-layered of LPP, was investigated to design the insulation thickness.

Insulation Design of 60 kV Class Bushing at the Cryogenic Temperature

The technologies to be required to commercialization a HTS transformer are of a reduction in AC loss, an improvement of conductor characteristics, cooling technology, high voltage technology, bushing technology and so on. Amongst the technologies, the development of bushing is the important technology which should be accomplished to apply high voltages into the winding of the HTS transformer. However, the studies and developments have done on bushing for HTS transformer are not enough. The bushing is energized with the line-to-ground voltage between the coaxial center and outer surrounding conductors, in the axial direction there is a temperature difference between room temperature and 77 K. So it has to endure for electrical insulation as well as the thermal contraction as well. Therefore, in order to insulating design of a 60 kV class bushing for HTS transformer this paper will report on the experimental investigations in impulse breakdown and surface flashover characteristics of the insulation materials. Insulation design was realized in a way of calculating breakdown voltage of 0.1% through Weibull statistical treatment of the obtained experimental results and calculating insulation thickness and separation distance meeting BIL 325 kV, a target voltage.

Manufacture and Insulating Test of a Mini-Model for 154 kV-Class HTS Cables

High-temperature superconductor (HTS) power cables enable larger transmission of electrical power than that of the conventional counterparts. As electrical power consumption is increased, HTS power cables are expected to play an important role in a next generation electrical power transmission grid because of their smaller transmission loss and, in consequence, better efficiency of operational cost. Currently, a world-wide research has been undertaken, particularly focused on the development and practical applications of HTS cables. With the importance of an insulation design of a 154 kV-class HTS power cable taken into consideration, this paper presents research on AC breakdown characteristics of various thickness insulators. Based on the present research results, the layer thickness of an insulator that will be used for a 154 kV-class HTS cable was optimized. Also, an effect of bending in an HTS cable on the ac breakdown characteristics was also investigated with various testing conditions, such as different radii of bending curvature.