UHV Systems Research Articles

Study on the Maximum Outgoing Line Count of 750 kV Substations and Exploration of a Bus Short-circuit Current Suppression Method

With the development and construction of new power systems, the power grid structure is becoming increasingly interconnected, and the issue of short-circuiting currents in UHV systems will gradually manifest over the next five years. Existing measures for short-circuit current control typically involve using standby units, lines, and main transformers. However, conventional measures are gradually unable to meet the control requirements, necessitating strict control of the network topology during the planning phase and the exploration of new technologies and methods to keep pace with the evolving era. This paper studies the maximum outgoing line count of 750 kV substations, providing theoretical references applicable to practical operations for planning departments. A conceptual method based on fast-switching technology to suppress the current during a short circuit at the 750 kV voltage level is proposed, establishing the groundwork for the practical implementation of high-speed switching technology in the 750 kV voltage-level power grid.

Two New Evactron® Plasma Cleaners for Small Chambers and UHV Systems

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Switching Surge Design of 1200kV UHVAC Transmission Line

With the increase in operating voltage of transmission system to transport large amounts of power to meet increased demand switching surges became governing factor in the insulation design of EHV and UHV systems. Insulation failure probability under switching surges that is switching surge flashover rate (SSFOR) is the main concern in the switching surge design of transmission lines. In this paper, SSFOR of 1200kV UHVAC transmission line under switching surges which are generated during energization of no-load transmission line is estimated.

Estimation of Switching Surge Flashover Rate of a 1200 kV UHVAC Transmission Line due to Switching Overvoltages

The rapid increase in transmission voltages to fulfil higher demand of the transmitted power yields to put the switching surges as the governing factor in the insulation design process for EHV and UHV systems. Contemporary methods of insulation coordination utilise probabilistic approach and statistical methods particularly in the case of ultra-high voltage systems. This paper determines the statistical distributions of energization, re-energization, fault initiation and fault clearing overvoltages of the 1200 kV system modelled in PSCAD. Decisive figures like mean value, standard deviation and 2% statistical overvoltage values of switching overvoltage are estimated using randomness of the instants of closing with 526 operations for line energization and re-energization, and randomness of faulted phase, fault location and fault times with 3 faulted phases, 8 fault locations and 21 fault timings, 504 simulations for fault initiation and fault clearing. Ascertaining the investigations from the above simulations the stress on the towers is estimated. From the stress and insulation strength of the tower a systematic approach to calculate the switching surge flashover rate (SSFOR) is presented.

Focus on materials, semiconductors, vacuum, and cryogenics

Focus on materials, semiconductors, vacuum, and cryogenics

(Invited) Ethanol Photoreaction over Anatase TiO2(101) and Rutile TiO2(110) Single Crystals. A Combined STM and Online Mass Spectrometry

The reactions of ethanol have been investigated over anatase TiO2(101) and rutile TiO2 (110) single crystals by STM and on-line mass spectrometry to determine the adsorbate species in the dark and post UV illumination, in the presence and absence of O2 or Au nanoclusters, in order to extract initial reaction parameters under photo-excitation. On anatase (101) TiO2 single crystal the reaction rate for the photo-oxidation of ethanol to acetaldehyde is found to be strongly dependent on O2 partial pressures and surface coverage with an order of the reaction for O2 close to 0.15. Carbon-carbon bond dissociation leading to CH3 radicals in the gas phase was found to be a minor pathway, which is contrary to the case of TiO2 rutile (110) single crystal, as previously reported by our group and others. Our STM images distinguished two types of surface adsorbates upon ethanol exposure that can be attributed to its molecular and dissociative modes. Upon UV exposure at (and above) 3×10-8 mbar O2, a third species is identified as a reaction end-product, which can be tentatively attributed to acetate/formate species, in line with XPS C1s measurements. The room temperature photo-oxidation of ethanol has also been investigated over a rutile TiO2(110) single crystal by STM and on-line mass spectrometry, in the presence of O2 to determine adsorbate species remaining post UV exposure and emitted gas phase products. In addition to acetaldehyde, methyl radical was detected in the mass spectrometry resulting from the photo-fragmentation of an acetaldehyde-O complex. Formic acid species bound to Ti5c in a bi-dentate mode were identified by STM on the surface after the reaction. The effect of O2 partial pressure on the reaction selectivity demonstrated a dominance of the photo-fragmentation process with increasing pressure unlike the case of anatase TiO2(101) single crystal. In addition the effect of Au particles on the reaction of the TiO2(110 rutile has been investigated for hydrogen production under photo-irradiation in UHV conditions. It was found that particle size in the range 4 to 8 nm do not change the reaction rate yet particle density does. Detailed reaction mechanism for both reduction and oxidation reactions are addressed based on structural and kinetic information from the UHV systems and compared to those of their corresponding powder forms in liquid-solid photocatalytic reactions conditions.

Condition assessment strategies of composite insulator based on statistic methods

Composite insulator has significant advantages over porcelain and glass insulator for its light weight and anti-pollution flashover performance and has been widely used in overhead power transmission line systems. These advantages would become more remarkable at higher voltage level. In China, silicone composite insulator has been generally regarded as the first choice in UHV and UHVDC overhead transmission systems. However, as a polymer material, the aging threat of silicone rubber has always been a major concern in the application of composite insulators. It is not just important but also urgent to develop specific strategies to evaluate the operation condition of composite insulators and corresponding maintenance methods. In this paper, 65 composite insulator specimens have been collected and studied. A series of tests and measurements have been conducted and all test results have been gathered and filtered based on statistic methods to form the final condition assessment strategies. In this procedure, Fisher Discriminant analysis, Bayes Discriminant analysis and binary-logistic regression method have been applied to establish the relations between the operation condition of composite insulators and the measured data. A three-group and a two-group classification strategy has been developed in this paper to assess the operation condition of insulators.

Introduction of Insulation Coordination for UHV AC Systems

This paper introduces the insulation coordination study results for UHV AC systems which was performed by CIGRE working group. The study results will be discussed within IEC technical committee in order to amend the IEC Insulation Coordination 60071-1 Ed. 8 2010 and 60071-2 Ed. 3, 1996. This paper includes the insulation coordination of transformer, gas insulated switchgear, metal oxide arresters and clearances of transmission towers. This article also illustrates the overvoltage specific to UHV systems such as TOV(temporary overvoltage), switching overvoltage, lightning overvoltage and VFTO(very fast transient overvoltage).

Understanding the Role of Metal-Modified Mo(110) Bimetallic Surfaces for C–O/C═O and C–C Bond Scission in C3 Oxygenates

Bond scission of C–O/C═O, C–C, and C–H from oxygenates on Mo(110), Ni/Mo(110), and Co/Mo(110) has been investigated via density functional theory (DFT) calculations, temperature-programmed desorption (TPD), and high-resolution electron energy loss spectroscopy (HREELS). Propanal and 1-propanol are used as probe molecules for biomass-derived oxygenates due to their relatively high vapor pressures, allowing their easy introduction into UHV systems. DFT results predict that the binding energy trend of propanal and 1-propanol is Mo(110) > Co/Mo(110) > Ni/Mo(110), which suggests that binding energies are reduced by the modification of Mo(110) with Ni and Co admetals. TPD and HREELS results show that bond scission activity and selectivity can be tuned upon admetal modification of Mo(110). For both molecules, Mo(110) shows a highly selective deoxygenation pathway toward C–O/C═O bond scission to produce propene, while bimetallic surfaces instead exhibit a higher activity for C–C and C–H bond scission. Among the t...

Electric field computation of composite line insulators up to 1200 kV AC

Satisfactory operation of composite insulators is intimately related to the surface electric field (stress) distribution. This paper presents results of calculation of the electric field distribution for composite insulators up to 1200 kV, using a 3D software package based on the Boundary Element Method. The impact of corona and grading rings, single and bundled conductors, insulator orientation (dead-end and suspension), single and double units, and surface condition (dry and wet) on the electric field distribution has been analyzed. For UHV systems (higher than 750 kV ac) the use of dual insulators with individual corona rings at the line and ground end and a common grading ring at the line end is beneficial. The existence of optimal dimensions of corona and grading arrangement has been illustrated on a 1000 kV insulator string. It was found that the dead end insulators experience higher electric stress when compared to their suspension counterparts and this difference gets more prominent as the system voltage increases.

Ultraviolet curing adhesive-based optical fiber feedthrough for ultrahigh vacuum systems

We present an inexpensive, simple, and robust method of making an optical fiber feedthrough for ultrahigh vacuum UHV systems. This system is particularly devoted for cold atom experiments. A drilled standard UHV DN16CF flange allows us to pass a fiber inside an UHV chamber. An optical ultraviolet UV curing adhesive is simultaneously used for holding the fiber through the flange and as a vacuum sealant. A vacuum down to 10−9 mbar is currently observed, while the optical insertion loss of the feedthrough is monitored and does not exceed 0.01 dB. In most of light-matter interaction experiments, laser light must pass through ultrahigh vacuum chambers. Although light beams can be propagated in free space through glass view-ports, more and more recent cold atom experiments use optical fibers to carry or collect light to or from a well defined area. This covers a wide variety of experiments such as atom-surface interactions or atomic samples guided inside hollow-core fibers. This kind of experiments requires continuous fibers through the vacuumatmosphere interface. A feedthrough for optical fiber based on a Teflon ferrule has been successfully demonstrated. However, this technique has several drawbacks. It requires a very high drilling precision, and as a consequence, must be accurately designed for a specific fiber diameter. As the ferrule must avoid any leaks, a constraint is applied to the fiber, which can induce birefringence and excess losses. Furthermore, as the polymer coating of the fiber ages under mechanical constraints, leaks might appear with time. We have developed a simple method to realize an optical fiber feedthrough completely free of those problems. It is based on a commercially available UV curing adhesive. The realization is easy and does not require accurate mechanical pieces. A multiple-fiber configuration is also achievable.

Micro-damage propagation in ultra-high vacuum seals

The paper addresses a fundamental problem of tightness of ultra-high vacuum systems (UHV) at cryogenic temperatures in the light of continuum damage mechanics (CDM). The problem of indentation of a rigid punch into an elastic–plastic half-space is investigated based on rate independent plasticity with mixed kinematic and isotropic hardening. The micro-damage fields are modeled by using an anisotropic approach with a kinetic law of damage evolution suitable for ductile materials and cryogenic temperatures. The model has been experimentally validated and the results are used to predict the onset of macro-cracking (loss of tightness) and the corresponding load (contact pressure). The algorithm is applied in the design of UHV systems for particle accelerators.

ガス絶縁開閉装置の非標準雷インパルス波形に対する不平等電界下での絶縁破壊特性

To improve insulation specification of a gas insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF6 gas under actual surge (called non-standard lightning impulse waveform) occurring in the field substation. The authors had observed the insulation characteristics of SF6 gas gap under various types of non-standard lightning impulse waveforms and compared them with under standard lightning impulse waveform quantitatively. From the investigation of the experimental results, the evaluation method for real surges is shown and the method is applied to typical surges for various UHV and 500kV systems. In the proceeding study, therefore, only for the quasi-uniform electric field (with a typical range of the field utilization factors in the bus of a GIS) was investigated. In this paper, the insulation characteristics of SF6 gas gap for non-uniform electric field were observed experimentally and investigated about the evaluation method of converting non-standard lightning impulse waveforms equivalently to the standard lightning impulse waveform.

Development of 1100 kV gas circuit breakers —Background, specifications, and duties—

AbstractIn Japan, for the UHV AC transmission system, 1100 kV, 50 kA two‐breaks gas circuit breakers (GCBs) were developed. They apply a resistance closing and opening scheme to suppress switching overvoltages that dominate the tower size of transmission lines. To secure high reliability and economy, specifications for the interruption duties were determined by detailed system analyses considering the phenomena arising from the inherent characteristics of UHV systems. The transient recovery voltage (TRV) duties were specified based on the resistance interruption and high‐performance metal oxide surge arresters (MOSAs) arrangement, both of which effectively relax the TRV. Developed GCBs were subjected to various verification tests, and their long‐term reliability and performance have been confirmed by the field testing since 1996 at the UHV Test Station of Tokyo Electric Power Company (TEPCO). Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Evaluating station post insulator performance from electric field calculations

This paper illustrates the use of electric field calculations for evaluating the performance of porcelain post insulators in stations for AC system voltages up to 1200 kV. The electric field was calculated using a 3-dimensional commercially available computer package that is based on the Boundary Element Analysis method. A comparison has been made of the effectiveness of several commonly used methods for improving contamination performance, namely, adding leakage distance (taller posts, ribbed sheds and creepage extenders) and coating the insulator with hydrophobic materials. It is shown that for station post insulators used in EHV and UHV systems (greater than 240 kV), coating the insulators with hydrophobic materials or replacing them with composite insulators offers superior protection to flashovers initiated under wet and contaminated conditions than provided by methods that simply increase the leakage distance. For lower voltages (less than 240 kV), all methods considered are effective.

Electron deflector in UHV system: Scattered electrons in ebeam evaporation

The evaporating electron gun in UHV systems has a side-effect that it gives rise to large quantities of scattered and secondary electrons. These electrons may cause damage to sensitive samples and may yield lift-off problems of resist defined patterns. We designed an electron deflector to deflect the electrons and measured the current caused by the electrons during the evaporation of iron.

Portable chamber for the study of UHV prepared electrochemical interfaces by hard x-ray diffraction

We report on a new electrochemical cell setup, combined with a portable UHV chamber, for in situ x-ray diffraction using synchrotron radiation. In contrast to more traditional electrochemical sample preparation schemes, atomically clean and well-ordered surfaces are routinely prepared by UHV methods, even in the case of reactive elements or alloys. Samples can be transferred from larger UHV systems into the portable chamber without exposure to ambient air. They can then be studied successively in UHV, in controlled gas atmospheres, and in contact with electrolyte solutions under applied electrochemical potential. The electrochemical setup employs a droplet geometry, which guarantees good electrochemical conditions during in situ x-ray measurements combined with voltammetry. We present first experimental results of Cu deposition on GaAs(001) and on freshly produced nanometric Pd(001) islands on Cu(0.83)Pd(0.17)(001), respectively.

Vacuum Characteristics of Titanium Materials and Applications to UHV Systems

This paper reviewed the vacuum characteristic of titanium materials and applications to an UHV system of the current research and development. It has been found that the outgassing rate of the titanium material is very low compared with an existing material such as a stainless steel or an aluminum alloy, and the UHV system made of the titanium material has very high vacuum performance, e.g., very quick pumping and the achievement of UHV/XHV pressure under the simple pre-baking condition.

Chemical Polishing on Titanium Materials for UHV Systems

The surface treatment, which improves outgassing property for the titanium materials, was examined in this paper. A chemical polishing using a nitric acid solution was found to be the most suitable for the titanium materials, because the polished titanium has a surface roughness of 1.80 nm in a microscopic range of 1 micro m and thin oxide surface layer thickness of 7 nm, and the polishing solution has stability and workability. And the surface processing for the titanium was developed by the combination of the chemical polishing and the precision cleaning. The chemically polished pure titanium of JIS grade 2 showed excellent outgassing rate below 10^-12 Pa m s·1 after baking process, which is two orders of magnitude smaller than that for standard vacuum materials under the same baking condition. Outgassing rates of the titanium is about 1/6 of that for a stainless steel without baking process.

SSIOD: The next generation

Surface stress induced optical deflection (SSIOD) is a bending sample method for the in situ determination of the surface stress with a typical resolution of about 0.15N∕m. Here we present the latest version of SSIOD with major improvements concerning the sample shape and clamping, the laser system and the position detectors. With these modifications SSIOD becomes an easily applicable method to most UHV systems and can be combined with other surface analytical methods like SPA-LEED, Auger-CMA, XPS, UPS or maybe even with microscopy such as the flange-on LEEM. The presented modifications also improve the resolution of the method to below 0.01N∕m.