Electrical Insulation Characteristics Research Articles

Electrical insulation characteristics of alumina, titania, and organoclay nanoparticles filled PP/EPDM nanocomposites

ABSTRACTIn this study, nanofillers composed of alumina, titania, and organoclay were separately embedded in 50% polypropylene (PP) and 50% ethylene propylene diene monomer (EPDM) blends. Several formulations of PP/EPDM nanocomposites were prepared using an internal mixer and were molded using a compression mold to produce test samples. The effects of filler loading (2, 4, 6, and 8 vol %) on the dielectric breakdown strength, dielectric properties, hydrophobicity, and flammability were determined. The addition of nanofillers improved the breakdown strength (up to 2 vol %) and increased the dielectric constant and dielectric loss of the PP/EPDM nanocomposites. The hydrophobicity of PP/EPDM/Al2O3 increased, whereas the hydrophilicity of PP/EPDM/TiO2 and PP/EPDM/organoclay increased. Flammability test results showed that PP/EPDM/TiO2 had a lower burning rate than PP/EPDM/Al2O3 and PP/EPDM/organoclay. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41184.

Study on the insulation of HTS bushing at cryogenic temperature

In the development of high temperature superconducting (HTS) power machines, HTS bushing is one of core technologies. In particular, the insulation body with sheds and electrical insulation at cryogenic temperature have attracted a great deal of interest from the view point of the size, weight and efficiency of bushing. In this study, the electrical and mechanical characteristics of various insulators for body in liquid nitrogen (<TEX>$LN_2$</TEX>) were investigated. And the surface discharge distance, collar length of GFRP sheds were studied. To emit bubbles between sheds, the shape and arrangement of shed were studied. The shed structure for 60 kV class HTS bushing were designed with regular arrangement.

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.

The electrical characteristics of solid insulators for 154 kV class HTS transformer

HTS transformer, without any loss of insulation lifetime due to the reduction in terms of size and weight, can increase the overload capacity, and have some benefits such as the improvement in efficiency, minimization of environmental pollution, and convenient spatial arrangement, which contribute a lot to electric power system operation. However, for practical insulation design of the HTS transformer, it is necessary to establish the research on electrical properties LN2 as well as solid insulators. These solid insulators have been used as main insulations for HTS transformer.In this paper, we discussed breakdown and V–t characteristics of glass fiber reinforced plastics (GFRP) and pressboard in LN2.

Surface treatment of stainless steel to improve coating strength of ZrO2 coated stainless steel needle

In the present study, stainless steel 316L was coated with ZrO2, a bioceramic, to insulate the needles and improve their biocompatibility. Three types of stainless steel 316L specimens were used in the experiment: an untreated specimen (case 1), an electropolished specimen (case 2) and an electropolished and plasma treated specimen (case 3). The effects of electropolishing and plasma treatment on coating strength and the relationship between coating thickness and electrical conductivity were investigated. The result showed that the coating strength of case 3 was 130% greater than that of case 1 and 40% greater than that of case 2. The electrical insulation characteristic of ZrO2 coating on stainless steel 316L was superior to that of uncoated stainless steel 316L. It was also found that appropriate thickness of ZrO2 coating was 500 nm for the electrical insulation.

Partial discharge activities under AC/impulse superimposed voltage in LN2/polypropylene laminated paper insulation system for HTS cables

This paper discusses electrical insulation characteristics of high temperature superconducting (HTS) cables for their reliable and rational insulation design. We focused on a severe and practical operational condition of HTS cables, i.e. under commercial ac / lightning impulse superimposed voltage. Experimental results for a HTS cable insulation model composed of liquid nitrogen (LN2) and polypropylene (PP) laminated paper revealed that ac / impulse superimposed voltage could trigger partial discharge (PD) by the impulse voltage invasion and cause consecutive PD under the subsequent ac voltage. The PD generation characteristics were summarized for different ac / impulse superimposed voltages, and a criterion for consecutive PD generation was identified.

Electrical and material characterization of field-aged 400 kV silicone rubber composite insulators

This paper presents the electrical and material characteristics of field-aged silicone rubber composite insulators, which have been deployed for 15 years on a 400 kV transmission line in a coastal region of the UK. There were no indications of reduced performance in service. Observations indicate non-uniform aging of the insulators on the different surfaces of the insulator sheds and core, along the insulator string length and in the different compass orientations. A uniquely large number of contact angle measurements, made on each of the insulators' different surfaces, confirm the visual aspect of nonuniform aging. Electrical investigations of the insulators have been performed in terms of leakage current analysis, ac flashover / withstand and switching-surge impulse flashover. A correlation is seen between the ac leakage current and the hydrophobicity measurements. Energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR) analysis of the changes of the materials' surface chemistry is presented. The role of solar radiation and organic growth appears critical to the observed non-uniform aging and must be considered if the longer term operation of the insulator is to be forecast. It is proposed that a reduction of the difference between positive and negative wet-flashover voltages may be a good indicator of early insulator aging.

Effect of hydrophobicity coating on insulator icing and DC flashover performance of iced insulators

How to decrease the ice on insulators and increase the flashover voltage of iced insulator are hot topics of power system in the world. Many tests have been carried out to investigate whether the permanent room temperature vulcanized (PRTV) coating can change the electrical characteristics of iced insulators both in laboratory and field. Firstly, the test to investigate the icing and electrical characteristic of dc insulator with PRTV coating was carried out. Moreover, comparison has been made between artificial polluted insulator and field polluted insulators. Results indicate that the PRTV coating can not decrease the ice accretion on insulators. Instead, it results in accumulating more ice at the beginning of icing regime, but the influence of PRTV coating will not be remarkable to accumulate ice when there is heavy ice on insulators. . In addition, the PRTV coating can decrease the flashover voltage by 10%. It is also revealed that the flashover voltage for the artificial polluted insulators is lower than that of the field polluted insulators due to the non-uniform of the natural pollution.

Nanodielectrics for Cryogenic Applications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper we report the recent advances in nanodielectrics that were developed and tested for cryogenic dielectric applications. The systems studied are composed of nanometer size particles. Particles were produced using either an <emphasis emphasistype="boldital">ex-situ</emphasis> or <emphasis emphasistype="boldital">in-situ</emphasis> technique. It is observed that there are clear differences in the structural properties of materials produced using these two approaches. Either no significant degradation or improvement in the electrical insulation properties were observed for <emphasis emphasistype="boldital">ex-situ</emphasis> nano-particle samples processed with an ultrasonic processor and <emphasis emphasistype="boldital">in-situ</emphasis> nano-particle samples. Nanodielectrics have the potential to be tailored with better thermal and mechanical properties without losing their electrical insulation characteristics. </para>

Electrical Insulation Characteristics of Glass Fiber Reinforced Resins

Non-metallic structural materials that act as an electrical insulation are needed for cryogenic power applications. One of the extensively utilized materials is glass fiber reinforced resins (GFRR) and may also be known as GFRP and FRP. They are created from glass fiber cloth that are impregnated with an epoxy resin under pressure and heat. Although the materials based on GFRR have been employed extensively, reports about their dielectric properties at cryogenic temperatures and larger thicknesses are generally lacking in the literature. Therefore to guide electrical apparatus designers for cryogenic applications, GFRR samples with different thicknesses are tested in a liquid nitrogen bath. Scaling relation between the dielectric breakdown strength and the GFFR thickness is established. Their loss tangents are also reported at various frequencies.

154 kV급 HTS 케이블의 절연설계 및 굴곡시험

It is important that study on cryogenic electrical insulation design to develop the cold dielectric(CD) type HTS cable because the cable is operated under the high voltage environment in cryogenic temperature. This paper proposes two types of insulation design to carry out the maximum insulation design for 154 kV-class HT cable. The proposed insulation design method takes into consideration AC and lightning impulse withstand voltage so as to prevent AC breakdown for power frequency operating voltage during operating the cable and breakdown for lightning impulse voltage. The final insulation thickness is determined by selecting high value out of two insulation thickness calculated through the two insulation design methods. And we researched electrical insulation characteristics of HTS cable according to bending ratio and the number of bending.

DC critical current and AC loss measurement of the 100 m 22.9 kV/50 MVA HTS cable

We had designed and manufactured a 22.9 kV/50 MVA class HTS (high temperature superconducting) power cable in cooperation with LS Cable Ltd. The HTS cable system was installed on the testing site of KEPCO (Korea Electric Power Corporation) in Kochang, Korea on March 2007. Some measurements which are related with electrical insulation characteristics such as partial discharge (PD) and tan δ were performed in accordance with the general guidance prescribed in IEC cable qualification standards. And also we measured the DC critical current of the HTS cable core and the AC loss for various transport currents and some temperature levels. These two testing results will be used just as a reference added on the IEC cable qualification standards for the 3rd party inspection test. In this paper, we describe the methods and results of the DC critical current and AC loss measurements of the superconducting cable core.

여러종류의 Organoclay에 대한 에폭시-나노콤포지트의 열적, 유전특성에 관한 연구

Nanostructured materials are attracting increased interest and application. Exciting perspectives may be offered by electrical insulation. Epoxy/Organoclay nanocomposites may find new and upgraded applications in the electrical industry, replacing conventional insulation to provide improved performances in electric power apparatus, e.g, high voltage motor/generator stator winding insulation, dry mold transformer, etc. In the paper work, the electrical and thermal properties of epoxy/organoclay nanocomposites materials were studied. The electrical insulation characteristics were analyzed through the permittivity characteristics. by analyzing the permittivity spectra, it was found that dielectric constant becomes smaller with increase frequency and becomes larger with increase temperature. This indicates restriction of molecular motion and strong bonds at the epoxy/organoclay nanocomposites. The morphology of nanocomposites obtained was examined using TEM and X-ray diffraction. It has been shown that the presence of polar groups leads to an increased gallery distance and partial exfoliation. Nevertheless, full exfoliation of clay platelets has not been achieved.

Partial discharge activity in electrical insulation for high temperature superconducting (HTS) cables

This paper discusses electrical insulation characteristics of liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) / polypropylene (PP) laminated paper composite insulation system for the practical electrical insulation design of high temperature superconducting (HTS) cables. Partial discharge (PD) inception, propagation and breakdown (BD) characteristics under ac voltage application were obtained and discussed at atmospheric and pressurized conditions. Experimental results were analyzed quantitatively and revealed that void- type discharge was categorized as an important form of discharge to characterize the transition of PD activity leading to BD.

Quench-induced partial discharge characteristics of HTS cables

This paper discusses the partial discharge (PD) characteristics of HTS cables under quench condition, where the thermal stress due to quench would be transiently superposed on the electric field stress under the operating voltage of HTS cables. Such electrical insulation characteristics under thermal/electrical combined stress can be referred to as the "quench-induced PD characteristics" of HTS cables, which should be taken into account for the reliable insulation design of HTS cables. Experimental results using coaxial HTS cable samples revealed that the quench-induced PD could be generated, even under the intrinsic or static PD inception voltage (PDIVsta) without the quench. The criteria of the thermal/electrical combined stress level for quench-induced PD inception were quantified for different LN2 pressures and fault durations under sub-cooled condition.

Electrical Insulation Characteristics of Silicone and EPDM Polymeric Blends. I

The typical parts of a polymeric insulator are core, metal end fittings and polymeric housing material. The housing is intended to protect the fibre glass rod from the environment and electrical surface discharges. Since the housing materials are made of organic polymeric material, its insulation characteristics need to be studied. Amongst the many different polymers available, this work focuses on silicone rubber and ethylene propylene diene monomer (EPDM). Blends of EPDM and silicone rubber are prepared in a two roll mixing mill. Dicumyl peroxide is used as vulcanizing agent. The blends consisting of various proportions of component polymers are prepared, compression moulded into sheets, and post cured. The blends are tested for their insulation characteristics as per IEC and ASTM standards. Volume and surface resistivity, dielectric strength, dielectric constant, tan delta, tracking resistance, arc resistance, comparative tracking index, tensile strength, and percentage elongation at break of the blends are studied and discussed. The test results show that the increasing proportion of silicone enhances the electrical insulation properties whereas increasing weight percentage of EPDM improves the mechanical strength of the blends.

Research on the electrical insulation design of a bushing for a 154 kV class HTS transformer

The cryogenic high voltage bushing for a 154kV/100MVA high temperatures superconducting (HTS) transformer is described. 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 ambient and 77K. Therefore, it has to endure for electrical insulation as well as the thermal contraction as well.In this research, the electrical insulation characteristics of GFRP to achieve high durability in the cryogenic environment were surveyed in the air and LN2. Moreover, the insulation constructions of the commercial condenser type bushing were studied. Based on these data, the electrical insulation design of the cryogenic condenser type bushing for a 154kV class HTS transformer was performed.

Quench Properties of 500-m HTS Power Cable

To cope with the increase in electric power demand and provide an alternative technology to conventional electric power transmission cables, it is hoped that high-temperature superconducting (HTS) cables would be developed. A protective layer has been adopted in HTS cables as a countermeasure against short-circuit current. This protective layer is established in parallel, and is connected to the HTS cable at both ends of the cable. However, this protective layer is not effective for quenching the local degradation of HTS wire in the overload-current domain, which slightly exceeds the rated current in real cables with lengths of several km. Therefore, of concern is the possibility in which the generation of bubbles via an exothermic reaction affecting the electrical insulation, when local quenching occurs. In a 500-m HTS power cable, we applied an external magnetic field to a part of the HTS cable, and the superconducting cable was locally quenched. Quench propagation features and electrical insulation characteristics based on this enforced quenching were determined experimentally.

Electrical Insulation Characteristics of HTS Cables Under Quench-Induced Thermal Stress Condition

This paper discusses the electrical insulation characteristics of high temperature superconducting (HTS) cable under quench condition exposed to thermal and electrical combined stress. We applied a high voltage of 60 Hz ac to the sample electrode, and injected a large current of 60 Hz ac into Bi2223/Ag tapes to induce quench. Experimental results revealed that partial discharges (PD) were induced by the transient thermal stress due to quench under the high voltage condition. A criterion of the combined stress for PD inception was experimentally obtained.

Temperature of Insulators as Heated by Conductor

In order to investigate temperature rise of transmission line insulators when the current carried by the line conductor is high, a series of laboratory experiments were carried out by flowing current in aluminum conductor steel reinforced by using current transformers. Remarkable temperature rise was not observed at porcelain and cement of insulators in spite of the high conductor temperature, suggesting almost no reduction in electrical and mechanical characteristics of insulators