Gas Insulated Research Articles

Assessment of SF6 and N2 Gas Mixtures as a Dielectric Medium in a Gas Insulated Busduct

SF6 gas is used as a dielectric medium in Gas Insulated Systems; it has an excellent dielectric strength and high arc quenching property. Despite of having these properties SF6 gas has high GWP, thus it is required to reduce the usage of the gas. In this paper SF6 and N2 gas mixtures were used as an alternate to the SF6 gas. The movement of free moving metallic particles present in a GIB has been analyzed for both the pure SF6 gas and by using various percentages of N2 gas and SF6 gas as an insulating medium

Effect of Coating of Dielectric in a 3-Phase GIB with Particle Movement

The dielectric coating effect on the motion of the Particle inside a Gas Insulated Bus duct (GIB) of three phase using epoxy resin coating of dielectric inside f GIB outer enclosure of inner surface without image charge is presented in this paper. Simulation is performed by considering various parameters like drag, gravitational and the electrostatic forces acting on the particle and a mathematical model was derived. A 2nd order differential equation for the particle motion is solved and restitution coefficient was considered at each impact of particle with the GIB enclosure. At the particle locations, estimation of electric fields instantaneously was made by CSM. The particle motion in the absence of effect of image charge is considered in a 3-phase GIB with dielectric coating. For voltage levels like 220kV, 400kV, 600kV and 800kV class, the movement of radial in nature is found for particles like aluminum and copper inside GIB. Analysis of all the results were done and presented in this paper.

Impact of Lightning Impulse on Electric Field Stress of Spacer in Single Phase Gas Insulated Busduct

During the last two decades, for reliable power supply, GIS have found a broad range of application in power systems because of their high reliability, easy maintenance, small space requirement, etc. Gas insulated sub-stations employs a superior dielectric gas, SF6 at moderate pressure for phase to phase and phase to ground insulation. Several troubles and system outages in GIS have been reported world-wide due to insulation failures which resulted in the intensification of electric field along the spacer surface and especially at the triple point electrode – spacer – gas. Hence, it was required to reduce the rate of insulation failure. In this work, Conventional cone type spacer geometry is taken for which field study has been done. Electric field stresses developed by the cone type spacer on the surface of the spacer and also at the triple junction is determined. It is found that the electric field stress at the surface of the spacer is maintained uniform, the electric field stress at the critical junctions formed by the conductor, solid insulator and SF6 gas is not maintained at minimum value. Metal inserts are considered as a means to reduce the stress at the triple point junction. The impact of Lightning Impulse on the Electric Field Stress along the spacer is carried and the reduction of stress is mitigated with the insertion of Metal Inserts.

Comparison between suppressing approaches of very fast transient over voltages in gas insulated substation

Very Fast Transient Over-Voltage (VFTO), which is a unique electromagnetic transient phenomenon generated by SF6 gas discharge in disconnector gap in Gas Insulated-Substation (GIS), could bring damage to power devices, especially to power transformers. The peak magnitude and high-frequency oscillations of VFTO cause reduction of dielectric of gas insulation, high inter-turn voltages and internal resonance in the transformer windings. Due to all of these disadvantages related to VFTO, VFTO becomes a criterion to determine the insulation level of the GIS, and VFTO damping is rising as an essential issue to be solved. However, the researchers concern on finding the optimum technique for suppressing VFTO, this paper aims to discuss the most feasible methods for mitigation of the overvoltage magnitude of VFTO and determine the most efficient approach for VFTOs attenuation by presenting the advantages and disadvantages of each approach. In this review paper, some suppression methods of very fast transients in GIS are presented, including adopting a resistor-fitted disconnector, ferrite rings, surge arresters, and high-frequency resonator. The results show that the peak value of VFTOs can be decreased to a great level by employing the proposed damping methods. Finally, the best approach for the suppression of VFTOs is chosen based on deep discussion for each method with its features.

A Non-Intrusive Electrical Discharge Localization Method for Gas Insulated Line Based on Phase-Sensitive OTDR and Michelson Interferometer

To overcome the high cost and low-spatial resolution of the electrical discharge localization systems for the gas insulated line (GIL), a non-intrusive distributed optical fiber sensing system based on the phase-sensitive optical time domain reflectometer (phi-OTDR) and the optical fiber Michelson interference is proposed. In the system, the Michelson interference provides a trigger signal since it has a better sensitivity and a higher frequency response, and the phi-OTDR localizes the ultrasonic vibration induced by a discharge. First, the principle of the proposed discharge localization system is introduced. Then, the bandwidth and multi-points distributed sensing performances of the system are investigated based on the ultrasonic signal induced by a piezoelectric transducer. Furthermore, the localization results of experiment using gas insulated switchgear spacer discharges indicate that the sensing distance of the sensing system can reach 1 km and the positioning accuracy of the discharge is smaller than 15 m. Thus, the system meets the requirement of the GIL discharge localization. Contrary to the traditional GIL discharge methods, the system has several advantages, such as non-intrusive, better spatial resolution, lower cost, and greatly simplified structure.

Interruption of Medium-Voltage Direct-Currents by Seperation of Contact Elements in Mineral Oil Using an Ultra Fast Electro-Magnetic Actuator

The increasing usage of medium-voltage direct-current in upcoming electrical energy grid topologies requests novel solutions for MVDC switching. The interruption of direct-currents is accomplished by enforcing a current zero crossing by adequate means and preventing reignition due to the recovering dc voltage. This paper evaluates the rapid separation of the contact elements in mineral oil leading to a liquid flow around the contact elements and the switching arc. The energy turnover of dielectric liquids interacting with an electric arc is considerably higher leading to heavily increased arc voltages compared to dielectric gases. This paper confirms results of earlier publications and carries them further towards a possible usage in an MVDC switching or protection device. Thus a contact arrangement surrounded by mineral oil in combination with an ultra fast electro-magnetic actuator is introduced and performed measurements are discussed.

Field Stress Control of a Functionally Graded Disk Type Spacer in a Gas Insulated Bus Duct with Metal Inserts

High voltage electric utilities are hindered with certain difficulties like high stress distribution and insulation damage that are needed to be taken care for reliable operation of the system. In a Gas Insulated bus duct, high field stress along the spacer surface especially at the contact point of the conductor, insulator and gas (called triple junction) is a major factor affecting the insulation strength. Research studies of shaping the spacer were found effective in controlling the stress distribution but found to be complicated in real time application. In this paper, functionally graded materials of disc type spacer with different permittivity are proposed for controlled field stress distribution at the spacer surface. Electric field calculations with different gradings from high to low and U shape are done. Properly shaped metal inserts are incorporated to have a uniform stress distribution along the spacer.

Developing a lean model to reduce the design process cost of gas insulated switchgear foundation using value stream mapping – a case study

Construction industry across the world has been facing immense challenges in improving its productivity and efficiency. In the path of continuous improvement, the companies are forced to impart new technologies and methods into their work culture. But still there is a fine line between what they have achieved and what they wanted to achieve. Lean Construction is an ideology designed to fill this fine line. The aim of this paper is to discuss the application of Lean techniques in construction management. A case study where the Lean concept is applied using Value Stream Mapping tool to reduce the cost of the design process of foundation for Gas Insulated Switchgear by improving the process productivity has been discussed. The current state of the activities in the design process was mapped first which was followed by preparing the future state map of the activities after eliminating the non-value adding tasks. The results exhibited a promising increase in productivity of about 30% after the application of Lean tool.

An Approximate Calculation Method of Broadband Impedance of GIS Pipe Brackets

In Gas Insulated Switchgear (GIS) substation, the grounding bracket of GIS pipe is used to support GIS pipe, meanwhile, it’s a part of grounding system connecting GIS pipe to grounding grid. The frequency of transient enclosure voltage(TEV) generated during switching operation of disconnector in gas insulated switchgear (GIS) with no-load short busbar can be up to tens or even hundreds of megahertz(MHz). Because of the impact of skin effect and proximity effect, the impedance of bracket will vary considerably with frequency. A simple and effective method of broadband impedance modeling was proposed based on electromagnetic field numerical calculation method and the physical structure of the grounding bracket in this paper. At last, the validity of the method was verified through calculating and analyzing some typical grounding bracket.

Through-Process Finite Element Modeling for Warm Flanging Process of Large-Diameter Aluminum Alloy Shell of Gas Insulated (Metal-Enclosed) Switchgear.

The large diameter metal shell component (LDMSC) is an important part of gas insulated (metal-enclosed) switchgear (GIS). The LDMSC with multi branches is filled with gas under certain pressure. The plastic forming process is an efficient approach to manufacturing the high reliability LDMSC. The warm flanging process has been widely used to form LDMSC using aluminum alloy. The forming process is characterized by local heating, and the distribution of temperature is strongly inhomogeneous. Although the wall thickness of the shell is 10 mm to 20 mm, the ratio of outer diameter to thickness is more than 40. These present some difficulties in the flanging process and result in some forming defects. Detailed forming characteristics are hard to obtain by analytical and experimental methods. Thus, the through-process finite element (FE) modeling considering heating, forming, unloading, and cooling is one of the key problems to research the manufacturing process of LDMSC. In this study, the through-process FE modeling of the warm flanging process of LDMSC using aluminum alloy was carried out based on the FORGE. The thermo-mechanical coupled finite element method was adopted in the modeling, and the deformation of the workpiece and the die stress were considered together in the modeling. A full three-dimensional (3D) geometry was modeled due to inhomogeneous distribution in all directions for the temperature field. The simulation data of local flame heating could be transferred seamlessly to the simulations of the deforming process, the unloading process, and the cooling process in the through-process FE model. The model was validated by comparison with geometric shapes and forming defects obtained from the experiment. The developed FE model could describe the inhomogeneous temperature field along circumferential, radial, and axial directions for the formed branch as well as the deformation characteristic and the unloading behavior during the warm flanging process. By using the FE model, the forming defects during the flanging process and their controlling characteristics were explored, the evolution of the temperature field through the whole process was studied, and deformation and springback characteristics were analyzed. The results of this study provide a basis for investigating deformation mechanisms, optimizing processes, and determining parameters in the warm flanging process of a large-diameter aluminum alloy shell component.

Experimental Research of Electromagnetic Interference Caused by Disconnector Operation in Gas Insulated Switchgear

In order to intensively study the exterior transient electromagnetic interference characteristics caused by disconnector operation in Gas Insulated Switchgear, experimental research of exterior transient electromagnetic interference under switching conditions is performed in this paper. Based on 330kV GIS test platform, with the method of resistive impedance divider, TEV is measured with Pintech P6039A high-voltage probe and Yokogawa DLM2054 oscilloscope by using resistor voltage divider GIS exterior radiation electromagnetic circuit is also established using antenna theories, biconical antenna and spectrum analyzer etc. The exterior transient electromagnetic interference waveform and characteristics are precisely measured. By the contrast analysis of TEV and radiation electromagnetic waveforms, results can be summarized as followed: ① The TEV waveform caused by opening and closing of disconnecting switch is front sparse and rear dense, and its amplitude is low at the fore and high over the back; The electric field strength is weaker compared to the electromagnetic compatibility of normal substation.

가스절연개폐장치의 SF6 대체가스 적용을 위한 부분방전 특성

가스절연개폐장치의 SF6 대체가스 적용을 위한 부분방전 특성

ANALISIS PENENTUAN SETTING DISTANCE RELAY PENGHANTAR SUTT 150 KV GIS PESANGGARAN – GI PEMECUTAN KELOD

The addition of UGC cable (Under Ground Cable) and equipment rating’s change for the reconfiguration from Air Insulated Swichgear into Gas Insulated Switchgear at Pesanggaran substation. Therefore need to reset distance relay settings so that relays can work more selectively and reliably. Using manual and simulation calculations, the results obtained from distance relay reset GIS Pesanggaran - GI Pemecutan Kelod, with impedance value 1 = 2.055 ?, zone 2 = 5.73 ? and zone 3 = 11.01 ? with time delay at zone 1 = 0 seconds, zone 2 = 0.4 seconds and zone 3 = 1.6 seconds. This setting shows that the reload setting value can secure the line from the 3 phase short circuit fault obtained from the simulation results.

Research on C4F7N gas mixture detection based on infrared spectroscopy

As a promising insulated gas to replace SF6, C4F7N gas mixture has gradually been put into practical application. It has great practical significance for condition monitoring and fault diagnosis of electrical equipment with C4F7N gas mixture. In this paper, molecular structure of C4F7N has been optimized by density functional theory using GGA-PBE functional with DZP basis set, and vibrational assignments have been calculated. The mixing ratio detection and leakage detection for the equipment based on infrared spectroscopy is proposed. The results show that: the calculated results and the experimental results have good agreement; the band of 750˜780 cm−1 can be used for mixing ratio detection, the error of mixing ratio inversion of 1˜10% C4F7N gas mixture using peak value as eigenvalue is less than 5%; after peak fitting processing, the error is less than 3% by using peak area as eigenvalue; 1240˜1290 cm−1 is the strongest infrared absorption band of C4F7N which has a good linear relationship between different concentrations, and it can be used for leakage detection. The calculated results and experimental results provide important theoretical support for the mixing ratio detection and leakage detection for the electrical equipment with C4F7N gas mixture.

Analysis of Gaseous By-Products of CF3I and CF3I-CO2 after High Voltage Arcing Using a GCMS.

Increasing demand for an alternative insulation medium to sulphur hexafluoride (SF6) has led to the investigation of new environmentally friendly insulation gases which could be used in high voltage equipment on the electrical power network. One such alternative, which is currently being explored by researchers, is Trifluoroiodomethane (CF3I) which could potentially be used in a gas mixture with carbon dioxide (CO2) as an insulation medium. In this paper an analysis of gaseous by-products detected as a result of high voltage breakdown through pure CF3I and a CF3I-CO2 gas mixture across a sphere-sphere electrode arrangement is given. Gas chromatography and mass spectrometry (GCMS) is used to identify the gaseous by-products produced as a result of high voltage arcing which causes the gas between the electrodes to dissociate. Analysing these gas by-products helps to identify the long-term behaviour of the gas mixture in high voltage equipment.

Study on break of thermal stratification in container targeted to thermodynamic vent system for future spacecraft

In the future space exploration mission, transfer vehicle using cryogenic propellant and oxidizer will be likely operated. Thermal management systems, such as thermal insulation, pressure control, and reduction of boil off gas must be installed on transfer vehicle since cryogenic fluid has high volatile characteristics. Final target of this study is the development of thermodynamic vent system (TVS) utilizing jet mixing. Numerical simulation and ground based experiment for thermal and fluid behaviours in tank partially filled with liquid nitrogen were conducted. Thermal stratification in tank was formed by creating heat input from side wall, and change of temperature field and break of thermal stratification by jet mixing were investigated. Numerical results were evaluated by comparing with experimental results.

Simulation on Propagation Characteristics of Ultra-High Frequency (UHF) Electromagnetic Wave Inside Typical Gas Insulated Switchgear (GIS) Structures

Simulation on Propagation Characteristics of Ultra-High Frequency (UHF) Electromagnetic Wave Inside Typical Gas Insulated Switchgear (GIS) Structures

Dynamic Temperature Calculation of Gas Insulated Bus Bars

As the key link of different voltage levels of power system, gas insulated bus bars have the important function of power transmission in large capacity. Temperature at the conductor is the highest when the bus bar gets overheat. As the conductor locates inside the metal shell, the usual thermal detection method can only measure the outer surface temperature and cannot obtain the temperature rise of the conductor inside. In this paper, a dynamic thermal analysis model of bus is proposed based on Thermal-electric analogy method. The thermal constant is calculated as the key parameter for conductor temperature prediction. An exponential function is obtained to model the temperature rise process of the conductor. The comparison between the temperature prediction results calculated by finite element model and dynamic model shows in good agreement. The research results provide theoretical basis and reference for the conductor temperature monitoring of gas insulated bus bars.

Influence of Molecular Properties on the Electric Strength of Potential SF6 Substitutes

SF6 gas has been widely used in power industry owing to its excellent insulation performances. However, due to its significant greenhouse effects, many scholars have carried out experimental and theoretical studies to search for the SF6 substitutes. In order to find the promising replacement of the insulation gas SF6, the basic physico-chemical properties and electronegativity of CF-x, HFC and HFO gases, which satisfy the safety and environmental requirements, are calculated based on the density functional theory (DFT). Relative electric strengths of these insulating gases are calculated by solving the Boltzmann equation. The influence of the molecular properties on the electric strength are studied by linear regression analysis. The calculation results show that the correlation coefficients of the molecular mass and electron number relative to the electric strength are 0.678 and 0.692, respectively. Furthermore, the electric strength is increased with higher electronegativity of potential gases and the magnitude of the electric dipole moment and polarizability are related to the electric strength. The correlation coefficient between polarizability and electric strength is 0.647. Considering the potential influential factors on the electric strength, a prediction formula is established through multivariate linear regression. The Pearson’s correlation between the calculated value and measured value is 0.948. Therefore, it can be used to predict the electric strength of the potential substituted gases when screening the enormous candidates of SF6.

A Novel System and Experimental Verification for Locating Partial Discharge in Gas Insulated Switchgears

Abstract Partial discharge location in gas insulated switchgears is important for timely identifying incipient problem and taking remedial actions to prevent later catastrophic breakdowns. This paper presents a new system including sensing terminals and hand-held intelligent terminals to locate partial discharge. Sensing terminals, housing the sensors, are attached to outside enclosure walls of the switchgear to collect acoustic signals, which are transmitted wirelessly to the hand-held terminals. The acoustic vibration caused by the discharge will propagate from the source, resulting in the highest intensity at the sensor closest to the discharge. By examining the signal signatures of the distributed sensors, the location of the partial discharge can be derived. The system is applied in both staged simulation environment and actual factory high voltage tests. The results have demonstrated that the system developed is highly effective in locating partial discharge in gas insulated switchgears and is suitable for practical applications.