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Shigeki Minami,1 Chika Sakimura,1 Junji Irie,2 Yukiko Tokai,3 Hitoshi Okubo,4 Tsuyoshi Ohno5 1Department of Breast and Endocrine Surgery, Nagasaki Harbor Medical Center, Nagasaki 850-8555, Japan; 2Department of Pathology, Nagasaki Harbor Medical Center, Nagasaki, Japan; 3Department of Breast Surgery, Imamura Women’s Clinic, Nagasaki, Japan; 4Okubo Breast Clinic, Nagasaki, Japan; 5Ohno Breast and Thyroid Clinic, Nagasaki, JapanCorrespondence: Shigeki MinamiDepartment of Breast and Endocrine Surgery, Nagasaki Harbor Medical Center, 6-39 Shinchi-machi, Nagasaki 850-8555, JapanTel +81-95-822-3251Fax +81-95-826-8798Email br9-origam@umin.netBackground: The axillary lymph node status is an important prognostic factor of breast cancer. This study explores the predictive factors for sentinel lymph node (SLN) metastasis among the preoperative clinicopathological features, including impaired glucose tolerance (IGT).Methods: This study comprised patients diagnosed with breast cancer who underwent surgery at Nagasaki Harbor Medical Center between April 2014 and December 2019. The factors assessed using univariate and multivariate analyses were the clinicopathological data of these cancers, including the patient age, gender, menstrual status, breast or ovarian cancer family history, body mass index, glycosylated hemoglobin, clinical tumor size, nipple-tumor distance (NTD), tumor histology, histological grade, node status, estrogen receptor, progesterone receptor, human epidermal growth factor receptor type 2 status, and Ki67 labeling index.Results: In the cohort of 313 cases, the ratio of SLN metastasis was 17.3%. A univariate analysis found that the tumor size, NTD, IGT, and clinical tumor stage were associated with SLN metastasis. In a multivariable analysis, the tumor size, NTD, and IGT were associated with SLN metastasis. The receiver operating characteristic curve showed a sensitivity and specificity of 61.1% and 65.6%, respectively, at a cut-off of 1.7 cm for the tumor size (area under the curve [AUC]: 0.664; 95% confidence interval: 0.592– 0.736), and a sensitivity and specificity of 60.4% and 62.9%, respectively, at a cut-off of 2.0 cm for NTD (AUC: 0.651; 95% confidence interval: 0.571– 0.731) to predict the risk of SLN metastasis.Conclusion: T1 and T2 breast cancer patients with a larger tumor size, tumor located closer to the nipple, and IGT have a higher risk of SLN metastases than others.Keywords: breast cancer, sentinel lymph node metastasis, predictive factor, nipple-tumor distance, impaired glucose tolerance

This paper discusses electrical insulation characteristics of liquid nitrogen ([LN.sub.2]) / 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. Index Terms--Superconducting cables, dielectric liquids, paper insulation, partial discharges, electrical breakdown, laminated paper.

The development of the second generation (2G) high-temperature superconducting fault current limiting transformer (HTc-SFCLT) with coated conductors is discussed. Results suggest the exhibition of excellent current limiting function by 2G HTc-SFCLT as a superconducting fault current limiter.

An improvement in dielectric strength is required in vacuum circuit breakers (VCBs) intended for use in higher voltage systems. In order to develop higher voltage VCBs, it is important to improve the dielectric strength in a vacuum based on consideration of the vacuum breakdown mechanism. Particularly for gaps longer than 10 mm, little is known about the breakdown mechanisms and their quantitative analyses in a vacuum. This paper discusses the breakdown conditioning characteristics of long gap electrodes, under a non-uniform electric field in a vacuum. We treat gap lengths of up to 50 mm in this paper. The conditioning characteristics are investigated under impulse voltage applications. A negative standard lightning impulse voltage was applied to rod-plane electrodes made of Cu-Cr and SUS304 for different tip radii and gap distances until the conditioning effect was completed. We observed illumination spots on electrodes at each breakdown during the conditioning process and calculated the corresponding breakdown field strengths. Experimental results revealed that the tendency of breakdowns associated with long gaps is different from that for the short gaps. As a result, we clarified that the breakdown field strengths are nearly constant at 110-120 kV/mm at the distances longer than 10 mm, and the breakdown field strength is at its maximum when the gap distance is about 5 mm. Index Terms--Breakdown conditioning, non-uniform electric field, long gap, lightning impulse voltage.

Breakdown (BD) characteristics in vacuum are strongly dependent on the electrode surface conditions, such as surface roughness. However, there is little known concerning the details of the relationship between the surface roughness and BD conditioning effect. In practical application, it is important to clarify how the surface roughness affects the breakdown conditioning characteristics, especially for the non-uniform field configuration. This paper discusses the effect of surface roughness on breakdown conditioning characteristics under non-uniform electric field in vacuum under applications of negative standard lightning impulse voltage. For this purpose, we examined the BD conditioning of a rod-to-plane electrode made of SUS304 and Cu-Cr. The surface roughness of [R.sub.a] is controlled from 0.3 to 2.5 [micro]m. Experimental results revealed that the enhancement of surface roughness of electrodes increases the number of BD to complete the conditioning effect. We explained the results from the observed results of the electrode surface. Consequently, we could clarify the effect of surface roughness on the conditioning effect under non-uniform electric field in vacuum quantitatively. Index Terms--Vacuum, conditioning effect, non-uniform electric field, lightning impulse voltage, vacuum circuit breaker, electrode surface roughness.

This paper reports on a new cross-equipment study on the charging phenomena of solid insulators, evaluating the influence of charging on high-voltage equipment such as gas insulated switchgear (GIS), oil-immersed transformers, gas-insulated transformers and high-voltage vacuum-insulated equipment. New parameters of normalized charge density and surface resistance are introduced to consistently explain all the characteristics of the surface charge density on solid insulators and the decay time constant of the accumulated charges between the equipment. The results show that the surface charge density and the decay constant decrease as the surface resistance of the insulators is lowered. Combinations of insulating media of solid insulators and fluids (gas or liquids) are discussed for GIS and oil-immersed transformers in terms of the relation between the relative permittivity and the volume resistivity. The decay time constant of the accumulated charges is generally dominated by the insulating media of a fluid like oil which has lower volume resistivity than solid insulators in cases like transformers. However, the time constant is determined by the resistivity of the solid insulator rather than the fluid (gas) for GIS. Furthermore, it is suggested that low resistivity coatings on solid insulators are effective in suppressing the charge accumulation on the insulators. These new cross-equipment studies on the charging phenomena are an effective approach to reliable insulation design especially when downsizing high-voltage equipment. Index Terms--Cross-equipment study, charge accumulation, solid insulators, GIS, oil-immersed transformers, gas-insulated transformers, high-voltage vacuum-insulated equipment, charge density, surface resistance, decay time constant.

Partial discharge (PD) inception and breakdown (BD) characteristics of liquid nitrogen (L[N.sub.2]) / polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables are presented. In this paper, we measured PD inception characteristics under lightning impulse and ac voltage applications by electrical, optical and acoustic methods. The impulse PD inception characteristics were compared with those under ac voltage application, and the PD generation mechanisms are discussed. Experimental results reveal that PD detection sensitivity under lightning impulse voltage application is as small as 6 pC. PD inception at the lower stress was verified to be generated not only in the butt gaps but also in micro gaps between PP laminated paper layers under both lightning impulse and ac voltage applications. Alter PD inception, PD activity could be developed in the butt gaps at the higher stress, finally leading to BD. Index Terms--High temperature superconducting cable, liquid nitrogen, polypropylene laminated paper, partial discharge, breakdown.

In the future, environmentally friendly insulating oil such as rapeseed ester oil is expected to be utilized as a substitute for mineral oil for power transformers. In addition, electrical insulation design for transformers becomes more important regarding size reduction and enhancement of electric field stress. The fundamental property of the electric field distribution in the rapeseed ester oil and in the oil / solid dielectrics composite insulation system should be clarified. In this paper, we have directly measured the electric field in the rapeseed ester oil with parallel-plane electrode and the rapeseed ester oil / pressboard (PB) composite insulation systems under dc voltage application using the Kerr electro-optic technique. From the results, we compared measurements of electric field and charge behavior for the rapeseed ester oil and the mineral oil and confirmed the applicability of the rapeseed ester oil for use in transformers. Index Terms--Rapeseed ester oil, Kerr effect, Kerr constant, electric field measurement, charge behavior, composite insulation system.

Partial discharge (PD) inception characteristics of liquid nitrogen (L[N.sub.2])/polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables were investigated in terms of the volume effect and the V-t characteristics. The electrical and optical measurements of PD inception characteristics showed that initial PD could be generated between PP laminated paper layers, as well as in a butt gap. Using a parameter called statistically stressed liquid volume (SSLV) based on the discharge probability in both butt gaps and L[N.sub.2]-filled thin layers between PP laminated papers, we could systematically analyze and evaluate the volume effect on PD inception stress (PDIE). Furthermore, experimental results revealed that n values of V-t characteristics at PD inception were as high as 80-110. On the other hand, the lower n values obtained at breakdown were interpreted by the intensified PD development in thermal bubbles generated after the PD inception. Index Terms--High temperature superconducting cable, partial discharge, butt gap, volume effect, V-t characteristics.

In this paper, we quantitatively investigated the impulse conditioning mechanism under non-uniform electric field electrodes in a vacuum. A negative standard lightning impulse voltage was applied between rod and plane electrodes whose materials were Cu-Cr, stainless steel and Cu and the gap lengths were d = 5 and 10 mm, respectively. Experimental results revealed the transition of the breakdown (BD) spot region on the rod electrode and the corresponding BD field strength in the conditioning process. As a result, we found that the BD spot region started at the tip of the rod electrode and moved to the wider region of the rod electrode with lower electric field as the shots of the voltage application increased before the saturation of the BD voltage. Finally, by analyzing the results with an electric field strength, we propose that 'the conditioning degree' along the electrode surface distributed directly proportional to the electric field distribution under a non-uniform electric field in a vacuum, irrespective of the electrode materials. Index Terms--Vacuum, conditioning effect, non-uniform electric field, impulse voltage, Cu-Cr, up-and-down method, vacuum circuit breaker, conditioning degree.

A High Temperature Superconducting Fault Current Limiting Transformer (HT(sub c)-SFCLT) with functions of both superconducting transformer in normal operating condition and superconducting fault current limiter in fault condition is developed. The findings indicate the operational feasibility of HT(sub c)-SFCLT through no-load and short-circuit tests, current limiting test and recovery test.

The electrical insulation structure of most power transformers is a combination of insulating oil and solid materials. One of the crucial problems we face in transformer operation is flow electrification, which occurs at a flowing oil/solid material interface. Thus, for the transformer insulation design, we need to clarify the flow electrification phenomena. In this paper, we measured the electric field strength in an oil/pressboard composite insulation system using an electro-optic method of the Kerr effect. We obtained the time variation of electric field distribution in both flowing uncharged and charged oil. It is notable that we could quantitatively clarify the electric field distortion in flowing charged oil by flow electrification. Furthermore, we measured the leakage current from divided electrodes and derived a charge density distribution along the flow direction. Finally, we quantitatively discussed the electric field distribution and the charge behavior from the measurement results. Index Terms--Charge behavior, flowing charged oil, oil/pressboard transformer model, Kerr effect, electric field measurement.

An insulating oil/pressboard (PB) composite insulation is generally utilized in oil-immersed power transformers. In such a transformer, charges accumulate at oil/PB interface which changes the electric field distribution depending on time and oil condition. In this paper, we report on directly measured dc electric field in oil/PB composite insulation system using the Kerr electro-optic field measurement technique. From measurement results, we propose a physical model for the charge behavior. We have calculated an electric field distribution using finite element method (FEM) based on the charge movement. We compared the results of measurements and calculations and confirmed that the proposed charge behavior model explains well the experimental results in the case of the polarity reversals as well. As a result, a significant validity of the charge behavior model was confirmed. Index Terms--Charge accumulation, polarity reversal, oil/pressboard, transformer model, Kerr effect, electric field measurement, FEM calculation.

The electrical insulation performance of resistive superconducting fault current limiters (SFCL) under quench condition, exposed to thermal and electrical stress, is examined and reported.

It is important to investigate electrostatic charging phenomena in insulating oil / pressboard (PB) composite system in electrical insulation design of oil-immersed power transformers. Our research aim was to clarify the charge accumulation mechanism at the oil / PB interface under static and flowing oil. In this paper, we directly measured the time variation of the electric field in the insulation system using a Kerr electro-optic technique. Results show the time decaying characteristics of an electric field in oil by charge accumulation. The results are influenced by oil flow conditions. Based on the measurement results, we propose a theoretical model for charge accumulation to clarify the process quantitatively. In the model we took the oil volume contributing to the charge accumulation into account, and analyzed the charge behavior. Finally, we clarified the charge accumulation mechanism at the oil / PB interface under oil flow conditions both with and without charging. Index Terms--Charge accumulation mechanism, oil flow, charged oil, electric field measurement, Kerr effect, oil/pressboard composite system, streaming electrification.

In this paper, we studied partial discharge (PD) inception characteristics and V-t characteristics of PD inception in liquid nitrogen (L[N.sub.2])/polypropylene laminated paper (PPLP[R]) composite insulation system for high temperature superconducting (HTS) cable. Experimental results revealed that the magnitude of initial PD was in the range of 2.0-30 pC irrespective of butt gap condition and the initial PD was generated at the first and third quadrant of voltage phase. PD inception electric field strength (PDIE) without butt gap was 5-10% higher than that with butt gap and thicker butt gap gave larger PDIE drop. Moreover, PDIE with butt gap depended on the butt gap thickness and the number of PPLP[R] layers. The reason is explained by the existing probability of weak points of electrical insulation at butt gap. Finally, lifetime indices n of V-t characteristics at PD inception were obtained as 80-100 irrespective of butt gap condition. These values showed enough flat characteristics of V-t phenomena of electrical insulation.

The partial discharge (PD) inception characteristics are studied in liquid nitrogen (L[N.sub.2])/polypropylene laminated paper (PPLP[R]) composite insulation system for high temperature superconducting (HTS) cable. Experimental results revealed that the magnitude of the initial PD increased as the PD inception electric field strength was increased, because the injected energy increased. Initial PD was generated at the first and third quadrant of applied ac voltage phase. The probability of initial PD at the positive and negative voltage phase was almost the same. The reason is because liquid nitrogen is nonpolar molecule and we used symmetric electrode configuration with uniform electric field distribution. Finally, it was pointed out that PD inception electric field strength (PDIE) depended on the volume of the butt gap because of the increasing probability of weak points of electrical insulation, and PDIE linearly decreased with increasing stressed volume of the butt gap in the log-log scale.

Impulse partial discharge (PD) and breakdown (BD) characteristics of rod-plane gaps in [N.sub.2]/S[F.sub.6] gas mixtures were investigated for different gap geometry, gas pressure and S[F.sub.6] gas content. Experimental results revealed that the 50% probability breakdown voltage increased with gas pressure, which agreed with the theoretical values with consideration of discharge time lag for impulse voltage application. For the calculation of discharge inception voltage, the volume-time theory was successfully applied to the [N.sub.2]/S[F.sub.6] gas mixture. Furthermore, impulse PD light emission image was observed together with PD current pulse and light intensity waveforms. The long discharge with stepwise propagation and double-peak PD pulses could be observed, which corresponded to the streamer/leader transition leading to breakdown.

This paper describes the dependence of the charging characteristics on the electric field distribution on the alumina ([Al.sub.2] [O.sub.3]) surface as affected by the triple junction in vacuum. For HV electrical insulation design of vacuum interrupter, surface flashover in vacuum is very important problem to be solved. Attention should be paid to the fact that the insulation characteristics on the dielectric surface are strongly influenced by field emission of electrons from the triple junction and the accumulated charges on the dielectric surface. In order to clarify the charging mechanism, we measured the charging characteristics for various types of triple junctions. In particular, we focused on the influence of the electric field distribution along the solid dielectrics and near the cathode triple junction (CTJ) on the charging characteristics. The results confirmed that the electric field distribution strongly affected the 2-dimensional (2D) distribution of the surface charge on the dielectric sample. Consequently, it was found that positive charging was generated on alumina, when the incident angle of the electric line of force on the alumina surface became > 60 [degrees].

A superconducting fault current limiting transformer is proposed and the operating characteristics are reported.

Quench-induced dynamic breakdown strength of liquid helium was measured within the quench environment of superconducting coils.

Ac superconducting wires were studied to determine propagation characteristics at quench inception, and transient propagation velocity was found to reach 90km/sec.

This paper describes charging characteristics on a dielectric surface in vacuum by electron irradiation, and field emission by a triple junction under negative and positive dc HV applications. We measured the 2-dimensional distribution of electrostatic charging on a dielectric surface in situ. Experimental results revealed that the negative charge distribution caused by the electron beam had a conical shape over the whole surface. On the other hand, for a triple junction, it was an acute distribution around the triple junction. Moreover, we quantitatively investigated the difference of the 2-dimensional charging distribution, using certain shape parameters, between the two charging processes mentioned above. In addition, we examined the time decay characteristics of the surface potential on the dielectric in vacuum.

We have been studying quench-induced 'dynamic' breakdown characteristics of [LHe.sup.*] and have already found that the electrical insulation performance of LHe was degraded drastically by the thermal bubble disturbance due to quench of superconductors. In this paper, in order to improve the insulation performance of LHe under quench conditions, we measured dynamic breakdown and prebreakdown characteristics of pressurized LHe. Experimental results revealed that breakdown voltage of LHe under quench conditions at 0.2 MPa was greatly improved, reaching 2 to 4x compared with that at atmospheric pressure under both uniform and non-uniform electric fields. Moreover, for practical and efficient insulation design of superconducting power apparatus, we investigated the dynamic breakdown voltage of LHe as functions of pressure and gap length.