Quantitative evaluation of lightning surge range voltage–time characteristics in high‐pressure SF6 gas

Gas‐insulated switchgear (GIS) is subjected to very fast transient overvoltages such as lightning surges or disconnector switching surges. Therefore, the sparkover voltage and time (V?t) characteristics of SF₆ in a very short time range of less than are of great interest from the viewpoint of insulation design and coordination for a GIS. This paper describes the V?t characteristics of SF₆ at a gas pressure of 0.5 MPa using a steep‐front square impulse voltage under a quasi‐uniform field gap and presents a quantitative evaluation of the V?t characteristics for a nonstandard lightning impulse voltage. In the case of a square impulse, the V?t characteristics of positive polarity were observed to be almost flat over a long time range from 80 ns to , and rose steeply over a short time range from 80 ns down to 20 ns. For negative polarity, the V?t characteristics exhibit a gentle rise from 200 ns down to 40 ns. In the estimation of V?t characteristics, the equal‐area criterion parameters were quantitatively estimated using the square impulse. For a nonstandard lighting impulse, we found that application of the equal‐area criterion with these parameters for the nonoscillating impulse and oscillating impulse of up to 5.3 MHz as a model of lightning surge and disconnector switching surge is possible. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 8– 17, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20309     

Qualification of fiber-reinforced insulating materials based on PDanalysis

For fiber-reinforced insulating materials used e.g. in gas-insulated system (GIS), a test procedure has been created which stresses tube shaped specimens simultaneously dielectrically and mechanically. Mechanical stress is applied by four-point bending at electric ac fields up to 12 kV/mm. To prevent surface discharges the specimens are tested in a 600 kPa SF₆ atmosphere. For diagnosis a partial discharge (PD) system with a sensitivity of 100 fC has been employed. Even for high-quality vacuum-impregnated materials internal PD was detected and a clear influence of mechanical stress was found. The study of PD patterns resulted in the proposal of a prebreakdown model, which reveals the physical failure process taking place in the fiber/matrix-interface of the specimens. The model provides suitable criteria for a clear ranking of the tested materials. Also general suggestions for the improvement of fiber-reinforced insulating materials are given. For a quantitative estimation of life expectancy accelerated multifactor aging-tests are recommended     

Breakdown characteristics of oil and paper insulation for a very fast transient voltage

This paper describes the dielectric breakdown characteristics of oil and oil‐impregnated paper for very fast transient (VFT) voltages. Blumlein circuits generate VFT voltages of 60 and 300 ns in a pulse width that simulates disconnecting switching surges in gas‐insulated switch gears. We measured the breakdown voltages of needle‐to‐plane, plane‐to‐plane oil gaps and several pieces of paper between plane electrodes for VFT and lightning impulse voltages. The measured data were formulated in V‐t characteristics and Weibull probability distributions. The inclination n of V‐t characteristics of insulating paper is 150, which is less than n = 13.7 of the plane‐to‐plane oil gap in the VFT time range. The shape parameters of Weibull distribution obtained in this study show that the scattering of breakdown voltages of paper is much less than that of oil. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 16–24, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10043     

Development of a new detection method of partial discharge for EHV long-distance active cable line

A new method was used to measure the characteristics of partial discharge (PD) for an active 9.5-km long-distance 275-kV XLPE cable line with insulating joints. It was found that the detection of PD and the calibration of detection sensitivity were carried out safely and easily. The proposed method includes:

• 1 detection of PDs and injection of calibration pulses using two pairs of metal electrodes placed on PVC jackets with anti-corrosion layers separated by a joint sleeve sectionalizing insulator;
• 2 measurement of detection sensitivity with distance using calibration pulses injected from an adjacent insulating joint;
• 3 detection of PDs with a high S/N ratio measured at a frequency corresponding to the lowest noise level; and
• 4 usage of rf cores attached at cross-bonding leads and wires for sheath current limiters to reduce the crosstalk of signal and noise through these lines at insulating joints.

Using a combination of these techniques, the highest detection sensitivity was 1 pC in the vicinity of an insulating joint, and 15 pC at 617 m from the adjacent joint. The sensitivity obtained by the conventional PD measurement using a low-frequency method was at most 1000 pC.     

不同场强下新型绝缘聚合物的变色特性及其介电特性

为了依靠绝缘材料在电场下的颜色变化判断电力设备带电状态,制备了等规/无规聚（3-己基噻吩）（poly(3-hexylthiophene),P3HT）共混薄膜。研究发现,等规P3HT纳米微晶在共混薄膜顶部均匀分布。随无规P3HT含量的上升,共混薄膜沿厚度方向表现出更好的绝缘性能。在无规P3HT含量为95%时,共混薄膜的工频介电常数为5.86,电阻率为3.2 T Ω·cm,直流击穿场强达到113 kV/mm。通过空间电荷积累光谱发现,当电场强度大于40 kV/mm时,电荷主要积累在绝缘的无规P3HT中,且共混薄膜吸收光谱450 nm处峰强度随电场强度的增加而升高,实现了空间电荷驱动的绝缘体系电致变色,为电力设备绝缘带电状态检测提供了新方法。     

Application of a novel polypropylene to the insulation of an electric power cable

Cross‐linked polyethylene (XLPE) has been widely adopted as insulating material for high‐voltage power cables up to 500 kV. Further improvement of electrical and thermal properties on insulating material is required in order to increase cable operation efficiency. Therefore, the development of novel insulating material possessing high thermal properties will be necessary. Recent progress of catalysis technology contributes to obtain new polymeric materials which may be applied to electrical insulation. The authors investigated the basic properties of newly developed stereoregular syndiotactic polypropylene (s‐PP) which is synthesized with homogeneous metallocene catalyst. Though recycling of cross‐linked polymers such as conventionally used XLPE may be difficult because of their poor heat deformation, the s‐PP which is not cross‐linked must be suitable for recycling. A series of experiments on its physical and electrical properties gave the following results.

• (1) s‐PP has sufficient flexibility compared with isotactic polypropylene (i‐PP ).
• (2) Both AC and lightning impulse breakdown strength of s‐PP in spite of no cross‐linking are superior to those of XLPE in the temperature range from 25 to 90 °C.
• (3) Degradation by copper of s‐PP is less than that of i‐PP.
• (4) s‐PP/VLDPE blend shows sufficient brittleness temperature for use.

These results suggested that s‐PP should serve as insulating material for power cables at higher‐temperature operation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 18–26, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002//eej.10210     

Insulation characteristics of GIS under nonstandard lightning impulse oscillations: Insulation characteristics under double‐frequency oscillations with various frequencies and damping ratios

To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatory overvoltage waveforms occurring in the field. This paper describes investigations of insulation characteristics for double‐frequency oscillatory waveforms with various frequencies and damping ratios. It was found that minimum breakdown voltages (V_min) were irrelevant to frequency changes in the range of experimental conditions under the same damping conditions. On the other hand, V_min rose with the damping ratio rising under the same frequency conditions. The insulation characteristics at a valley of oscillation were investigated using actual breakdown voltages. It was found that the insulation characteristics were treated all‐inclusively based on the characteristics of V_min for damping time. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 11–19, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10245     

Insulation characteristics of GIS under nonstandard lightning‐impulse oscillations: Insulation characteristics under single‐frequency oscillations with various frequencies and damping ratios

To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatory overvoltage waveforms occurring in the field. This paper describes investigations of insulation characteristics for single‐frequency oscillatory waveforms with various frequencies and damping ratios. It was found that minimum breakdown voltages (V_min) rose with frequency rising under the same damping condition and V_min rose with damping ratio rising under the same frequency condition. From an analysis of actual breakdown voltage characteristics, the probability of breakdown at a valley of oscillation rose with damping increasing. It was found that the insulation characteristics were treated all‐inclusively based on the characteristics of V_min for rise time or damping time. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(3): 43–49, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10156     

PTFE有机复合材料电气寿命的研究

以聚四氟乙烯有机复合材料为主绝缘的新型干式高压产品,包括电流互感器、穿墙套管、电缆终端等,在电力系统已经应用多年,因为其不充油、不充气、无瓷、维护工作简便、耐污秽能力强、重量轻等鲜明特点,受到用户的热烈欢迎。但对该系列干式产品最主要的特点,以聚四氟乙烯薄膜为主的有机复合主绝缘材料,却缺乏相应的研究。笔者对该有机复合绝缘材料的电气寿命进行了研究,结果显示以聚四氟乙烯为主的有机复合绝缘材料,即使在设计场强3kV/mm下且考虑一倍的安全裕度,其寿命也可以达到45年以上,是值得信任的主绝缘材料。     

Long-term characteristics of XLPE cables

To study the long-term characteristics of XLPE cables installed in free air and in water, aging tests were conducted under various testing conditions using XLPE cables with both 3.5 mm and 6 mm insulation. From the Weibull plots of lifetime distribution under the voltage stress E_L as the minimum breakdown strength, the minimum value of time to breakdown t_L under the constant voltage was estimated. The results of accelerated aging tests of XLPE cables installed in free air demonstrated that the V-t characteristics of XLPE cables could not be described by the conventional inverse power law (t ∝ V⁻ⁿ) with a single constant life exponent n. Based on the microscopic observation of a sliced insulation removed from XLPE cables, it was concluded that bow-tie trees with longer tree length observed in cables tested in water were caused by the moisture from outside, whereas the trees in cables tested in free air were caused by the residual moisture originally existing in the insulation. The breakdown strength of the aged cables tested in water increases through cable drying. However, it does not recover to the original values.     

Electrical insulation characteristics of cold dielectric high temperature superconducting cable

For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability.     

Impact of corona on the long-term performance of nonceramic insulators

This work discusses with the impact of corona on the long-term performance of nonceramic insulators. The aging mechanism of insulating materials and the partial discharges measurement (PD) on insulating materials is also discussed. In this measurement the rise of surface temperature of some solid insulating materials during activity of corona in point-dielectric-plain electrode arrangement by means of noncontact infrared (IR) measuring system. As the method measures the mean temperature of the sample surface, it is important to keep the diameter of the measuring target, in a given electrode arrangement, as small as possible. The smallest spot diameter of the sensor was 2.5 mm. The measurements made in the same electrode arrangements but with another IR camera proved that the spot diameter is even smaller than 2.5 mm. It means that the actual surface temperature is higher than indicated one.     

Insulation recovery characteristics of 500 kV class dc insulator assemblies after arc extinction

The insulation recovery characteristics of 500‐kV‐class dc insulator assemblies were measured. Switching impulse voltage was applied to a tension insulator assembly and three kinds of suspension insulator assemblies (V‐, Y‐, and I‐arranged) following arc extinction. Arc current ranged from 400 A to 4000 A and arc duration from 0.1 s to 0.4 s.

• (1) All insulator assemblies show slow insulation recovery after arc extinction up to an impulse withstand voltage of 100 to 200 kV. The insulation recovery rates increase near the impulse withstand voltage of 500 kV.
• (2) At arc current of 400 to 4000 A, for a duration of 0.1 s, the recovery rate for all insulator assemblies decreases with increases in arc current. This is believed to be due to the increases in the postarc gas temperature caused by the increased arc current.
• (3) When the arc duration is increased from 0.1 s to 0.2 s at a current of 4000 A, the insulation recovery of the V‐ and Y‐arranged assemblies is delayed by 0.05 s. This is believed to be due to the increases in the temperature of postarc gas caused by the longer arc duration.
• (4) By measuring the insulation recovery characteristics of the tension insulator assembly and three kinds of suspension insulator assemblies with an arc current of 4000 A and an arc duration of 0.1 s, the minimum value of nonvoltage time for a 500‐kV dc transmission line is calculated to be 0.17 s. © 1999 Scripta Technica, Electr Eng Jpn, 129(3): 29–39, 1999

     

35 kV断路器手车柜绝缘异常技术分析

通过对1999年2月投入运行的一110 kV变电站35 kV断路器手车柜运行中出现的绝缘异常进行初步技术分析,从开关、母线的支持绝缘子3、5 kV开关室内外空气对流、导体间净距、绝缘材料介电性能、安装工艺、污秽凝露、制造厂的生产工艺等方面具体着手,提出了相应的解决方案,如加强清扫、增大爬电距离、降低断路器手车柜内外温差、采用增强型复合绝缘材料、采用防污型绝缘子、涂敷防污闪涂料、采用绝缘螺栓连接绝缘板,在载流导体表面加装绝缘护套等,并通过部分实施,效果较好。     

750 kV变压器现场工频感应耐压和局部放电试验

介绍了我国750 kV输变电示范工程中变压器现场局放交接试验的标准、程序和过程,分析了局放起始电压和熄灭电压定义中的含混之处,比较了750 kV变压器的工频耐压值和局放试验电压值、分析了局放试验中经常出现的问题。提出如下建议：①提高750 kV变压器的工频绝缘水平;②放宽变压器局放现场交接试验标准至1 000 pC;③重新定义局部放电起始电压和熄灭电压;④加强现场实用技术的研究;⑤试验人员持证上岗;⑥试验仪器定期校验;⑦必要时采用在线监测。这些建议不限于750 kV变压器,也可为 1 000 kV变压器的现场局放交接试验参考。     

Steep Impulse Voltage Characteristics of Suspension Insulators

Transmission and distribution lines are sometimes struck by lightning and there is some risk of electrical puncture of suspension insulators due to high and steep lightning surge voltage. When the insulators suffer from steep lightning surge voltages, the solid insulating body of the insulators sometimes is punctured before external flashover in the air occurs. These characteristics were investigated on the insulators in the laboratory by using different steep impulse voltages. From the investigation results, both V-t characteristics of external flashover and internal puncture were obtained on the insulators. It was found that the puncture of the insulators is a matter of probability, depending on the dimensions of the insulators, steep impulse voltages and number of impulse voltage applications. Especially, the effect of number of voltage applications on puncture probability was clarified and partial damage by a small number of voltage applications was verified before complete puncture occurred. Based on the study results, an empirical equation relating to probability of puncture (P), impulse voltage (V) and number of voltage applications (N) was established.     

Basic characteristics of high-Tc superconductor as a current-limiting element

This paper shows the basic characteristics of a current-limiting element for the power system using y-type high-T_c superconductor. (1) A YBa₂Cu₃O_x-type superconductor was produced. Its size was 4.7 × 1.5 × 47 mm. (2) Current I and voltage V were measured under the low temperature of 50 to 100 K. (3) The flow resistance and the resistance of the element were defined and evaluated from the I - V characteristics obtained under the conditions of lower temperature than the critical value T_c, and larger current density than the critical value J_c. (4) The resistance value change due to temperature rise also was evaluated under the larger current than the critical current. (5) A schematic calculation was tried for practical use in some system condition.     

Characteristics of laminated tape insulation in high vacuum at cryogenic temperature

A composite insulation system of laminated tape and high vacuum is newly proposed for a superconducting bus-line cable operated at relatively low voltage. Its breakdown characteristics were investigated using model cable specimens with different kinds of laminated tapes such as semisynthetic paper, polypropylene film, and kraft paper of insulation thickness less than 1 mm. First, ±dc, ac, and —Imp breakdown stresses of the semisynthetic papers were investigated. +dc breakdown stress was 21.7 kV/mm for a specimen of insulation thickness 1 mm and −dc breakdown stress was 41.5 kB/mm, so that the remarkable polar effect was observed. ac breakdown stress was 18 kV/mm. Also, the ratio of −Imp breakdown stress was about 3. Furthermore, ac breakdown stresses of other tapes were investigated, but remarkable differences among their stresses were not observed. Most of the specimens were broken from the “butt gap” between tapes. To understand this cause, measurements of the partial discharge were carried out. It was found that the inception stress of partial discharge of butt gap located just on the conductor was about 20 kV/mm, not dependent on the kind of tape. This value is much lower than the breakdown stress of the same length of vacuum gap. Therefore, it is considered that the trigger of the breakdown of this insulation system is the surface discharge along the edge of the butt gap. © 1998 Scripta Technica, Inc. Electr Eng Jpn, 121(3): 20–26, 1997     

500kV XLPE电缆局放屏蔽试验室

本文介绍了浙江晨光电缆集团公司成功建立的500 kV交联聚乙烯(XLPE)电缆局放屏蔽试验大厅,并阐明了设计理念。屏蔽室尺寸:长28.0 m×宽21.0 m×高15.0 m;大门:宽5.5 m×高6.0 m,供有电缆盘进出的25 t轨道车。试验电源:10 kV,500 kVA经专用电缆供电。接地电阻0.14Ω;地下绝缘槽电阻>103MΩ;屏蔽系数(衰减值):80~100 dB(局放频带)。高压测试设备由德国High Volt公司提供,整体试验表明:系统空载输出电压700 kV时,局放水平≤0.8 pC。     

Effect of Buffer Layer on the Properties of Laser Ablated PZT Thin Films

Lead zirconate titanate (PbZr _x Ti_1?x O₃) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.