Gas Insulated Substation Research Articles

Analysis of Very Fast Transients Using Black Box Macromodels in ATP-EMTP

Modelling for very fast transients (VFTs) requires good knowledge of the behaviour of gas insulated substation (GIS) components when subjected to high frequencies. Modelling usually takes the form of circuit-based insulation coordination type studies, in an effort to determine the maximum overvoltages and waveshapes present around the system. At very high frequencies, standard transmission line modelling assumptions may not be valid. Therefore, the approach to modelling of these transients must be re-evaluated. In this work, the high frequency finite element analysis (FEA) was used to enhance circuit-based models, allowing direct computation of parameters from geometric and material characteristics. Equivalent models that replicate a finite element model’s frequency response for bus-spacer and 90° elbow components were incorporated in alternative transients program-electromagnetic transients program (ATP-EMTP) using a pole-residue equivalent circuit derived following rational fitting using the well-established and robust method of vector fitting (VF). A large model order is often required to represent this frequency dependent behaviour through admittance matrices, leading to increased computational burden. Moreover, while highly accurate models can be derived, the data extracted from finite element solutions can be non-passive, leading to instability when included in time domain simulations. A simple method of improved stability for FEA derived responses along with a method for identification of a minimum required model order for stability of transient simulations is proposed.

Two-stage Partial Discharge Location Method Based on Defect Recognition Pre-screening

Partial Discharge (PD) detection of gas insulated substation (GIS) must be done before commissioning, this is an important guarantee to reduce the incidence of post-commissioning faults. Fast and accurate partial discharge location is the key to improve test efficiency. Therefore, a two-stage partial discharge location method based on pre-screening of defect recognition is proposed in this paper. The convolution neural network (CNN) is used to supervise and train the signal atlas recorded by GIS withstand voltage test. By identifying the discharging atlas, the types of defects can be distinguished. Based on analysis of the typical discharging defects in GIS and their affiliated area, a law of partial discharge detection area screening is established which can be used to exclude some gas chambers from consideration. Ultra High Frequency Time Difference of Arrival (UHF TDOA) positioning method is then used to carry out further positioning analysis to determine the accurate position of PD. The analysis shows that, combined with the pre-screening of defect recognition in GIS, the location judgment area can be effectively reduced and the complexity of positioning can be lowered.

Experimental and numerical study on heavy gas contaminant dispersion and ventilation design for industrial buildings

Heavy gases, in particular sulfur hexafluoride (SF6), are used extensively in the gas insulated substations (GISs) of various industrial buildings, such as nuclear power plants. Although the construction and operation of these facilities are closely monitored and regulated, accidents are possible. A hazardous situation may arise if the SF6 gas in a GIS leaks without effective measures to remove the contaminants in time. In this study, a chamber experiment and CFD numerical simulation were carried out to study SF6 gas dispersion characteristics and the optimal ventilation design for its accidental leakage in industrial buildings. The influence of leakage angle (α= 90°, 45° and 0°) on the SF6 dispersion and concentration distribution was analyzed. Several different ventilation design parameters, i.e., air outlet layout, size and air change rate, were proposed to evaluate the ventilation performance. The findings indicated that different leakage angles could result in different space concentration distributions of SF6 and that any leakage angle deviating from 90° could result in an uneven SF6 concentration distribution; a deviation angle of 45° caused the maximum concentration variation in the lower part of the chamber. The removal of SF6 was more effective when the air outlets and inlets were arranged on the same side of the wall. Vent openings and air outlets had a remarkable influence on the removal rate of SF6. It was found that high-efficiency ventilation could be achieved with a 10 h−1 air change rate, meeting the needs of SF6 emergency ventilation. The current study can serve as a reference for ventilation design and establishment of standards for the accidental leakage of heavy gas in industrial buildings.

Simulation Analysis on Partial Discharge Signals Produced by Multiple Insulation Defects in GIS

In this paper, the simulation analysis on partial discharge (PD) signals produced by multiple insulation defects in gas insulated substation (GIS) has been researched by the simulation software of electromagnetic field (XFDTD). The theoretical analysis and simulation results show that the single partial discharge signal is the linear convolution of the partial discharge current signal and its corresponding impact response in GIS. The mixed partial discharge signals are the linear mixtures of every partial discharge signal.

Electric Field Signal Recognition Method of DS Switching Operations Based on Wavelet Packet Analysis and PSO-HSVM

In order to monitor the state of Gas Insulated Substation (GIS), this paper established a fault simulation experimental platform for Disconnecting Switch (DS), and collected data through a 3D radiation electric field (E-field) measurement system. For extract the feature parameters, four-layer wavelet packet decomposition was performed on the data to obtain normalized energy, and the dimension of the eigenvector was reduced by principal component analysis (PCA) algorithm. Then, the model was trained with the hybrid kernel support vector machine (HSVM) algorithm, and the parameters was optimized with the particle swarm optimization(PSO) algorithm. The result shows that compared with the traditional SVM model, the method proposed in this paper improves the diagnosis accuracy of DS defect signals.

Insulation Fault Diagnosis of Disconnecting Switches Based on Wavelet Packet Transform and PCA-IPSO-SVM of Electric Fields

Previous studies have shown that switching operations of gas insulated substations (GIS) can generate transient radiation fields outside the enclosure, namely switching transient electric fields (STEF). The waveform features of STEF can reflect the functioning performance of the switch. To monitor online the working states of disconnecting switches (DS), in this paper, we built an experimental platform to simulate their typical faulty types. Then, under different faulty status, a non-invasive three-dimensional (3D) electric field measurement system was applied to obtain STEF produced by DS. It is difficult for conventional methods to establish an accurate fault-diagnosis model, so we presented a novel method to identify the condition of DS. This innovative approach is based on feature extraction and machine learning and combined signal analysis to classify different defect types of DS. Measured STEF signals were analyzed by the wavelet packet transform(WPT) method in the time-frequency domain, which was transformed to the multi-dimensional feature matrix. The principal component analysis (PCA) algorithm was employed to reduce the dimensionality of the obtained feature matrix, which was also compared to other feature extraction algorithms. In addition, a support vector machine (SVM) with an improved particle swarm optimization (IPSO) algorithm was designed to achieve a PCA-IPSO-SVM model which can be used for signal recognition. The proposed IPSO technique can improve the convergence performance of the PSO through the dynamic adjustment of inertia weight and learning factors. Results show that the proposed fault diagnosis method based on WPT and PCA-IPSO-SVM can effectively identify the insulation faulty signals in STEF.

Numerical Analysis of a Spiral Tube Damping Busbar to Suppress VFTO in 1000 kV GIS

Gas insulated substations (GISs) are broadly used for transmission and distribution in electric power networks. Very fast transient overvoltage (VFTO) caused by SF6 discharge during switching operations in a GIS may threaten the insulation of electrical equipment. In this paper, a novel VFTO suppression method with great prospects in engineering, called the spiral tube damping busbar, is proposed. The suppressing mechanism of the new method is analyzed. The structure and the design characteristics of the damping busbar are introduced as well. Moreover, a calculation method for the self-inductance of the damping busbar at high frequency is presented. According to the structural characteristics of the damping busbar, the inductance effect on suppressing VFTO is analyzed. A further improvement in damping VFTO is investigated by designing a spiral litz coil connected in series with the busbar, which increases the damping effect. The simulation results show that the improved damping busbar has a significant suppressing effect on the amplitude and the frequency of VFTO.

Experimental Study of Fast Transient Currents in Gas Insulated Substation

Abstract The increasing demand in transmitting electrical energy at very high voltages with low transmission losses and improved efficiency has led to the development of compact metal enclosed gas insulated substation. There are various advantages of gas insulated substations over conventional substations yet there are a few problems associated with the switching operation in gas insulated substation. The fast transient voltages arising due to the switching operation of disconnectors or circuit breakers may impair the service reliability. The fast transient currents are associated with these fast transient voltages. The main aim of this paper is to characterize the fast transient currents generated due to the switching operations in a gas insulated substation. The dominant frequency content has been identified for different rise times of the fast transient currents and the percentage attenuation in amplitude is determined at different distances from the source. The variation in the peak value of current with distance from the source is also analysed. The experimental work is carried out on 145 kV gas insulated substation models of different configurations and comparison of the results for different case studies are reported.

Effect of Metallic Particle Movement at Different Positions of Particle on Spacer in a 1-Ø GIB

Gas Insulated Substation has been more credible than Air Insulated Substation thus increasing its application in the electrical industry. Though being more advantageous there are some areas in the system where there is a need for study. Metallic particle contamination is one of the areas where there are chances for the risk or failure; the particles reduce the dielectric strength of the insulating medium i.e. the SF6 gas. The metallic particles can be formed from the enclosure, conductor or the insulating material during various operations such as assembling, operating, and transporting etc. The particles can exist anywhere on the enclosure, conductor and the spacer. In this paper a single phase Gas Insulated Busduct with conductor diameter of 55mm and outer enclosure of diameter 152 mm with a spacer inclined at an angle of 450 to the enclosure is considered. Movement of aluminum and copper particles are studied which are present on the spacer at a certain distance from the enclosure.

Accelerated Ageing Tests of Rubber O-rings for Gas-Insulated Substation Equipment

Accelerated Ageing Tests of Rubber O-rings for Gas-Insulated Substation Equipment

UHF PD signal transmission in GIS: Effects of 90° bends and an L-shaped CIGRE step 1 test section

When applying radio-frequency (RF) techniques to measure and monitor partial discharges (PD), the CIGRE ‘sensitivity verification’ recommendation details a methodology for achieving a specified equivalent PD charge sensitivity for the combination of RF PD sensors and the measurement or monitoring system installed in a gas-insulated substation (GIS). The recommendation allows some flexibility in the GIS set-up used to perform the test. For the work covered in this paper, second in a series, a CIGRE step 1 laboratory test was conducted using an ‘L’ -shaped section between sensors 'C1' and 'C2', in order to present a more challenging propagation path between them. RF network analyzer (RFNA) measurements and finite-element modeling (FEM) were performed on the section and compared. The RF propagation properties of GIS sections with similar topologies in both lab and field were investigated through both models and measurements and these results compared with prior work in the field. Refinements to FEM modeling techniques result in a closer match to actual measurements, but an exact match probably remains out of reach. We discuss these results and our recent observations, the implications for PD sensor placement to satisfy the CIGRE recommendation, and outline anticipated next steps.

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.

Partial discharge detection and diagnosis in gas insulated switchgear: State of the art

Power utilities are struggling to reduce power failure incidents in substations and their components to operate more reliably and economically [1]. Many power failures are produced directly or indirectly because of the insulation system of utility components [2], [3]. The selection of the insulation should ensure power plant operational continuity along with completely resolving or significantly limiting the actual power system's failures [4]. Gas insulated substations (GIS) have the best insulation performance which ensures achieving minimum failure incidents, although at high installation cost. The most common insulating gas used in GIS is Sulfur hexafluoride (SF 6 ) gas, which is widely used as an effective electrical insulation as well as an arc-quenching medium [5]. Basic GIS and gas insulated transmission lines (GITL or GIL) consist of a conductor supported by solid insulators inside an enclosure filled with SF 6 gas or its mixture [6].

Field-dependent charging phenomenon of HVDC spacers based on dominant charge behaviors

Spacers are key components that are used to support high voltage conductors in gas-insulated substations or gas-insulated lines. The analysis of the surface charge patterns on spacers remains a difficult task, which requires a comprehensive understanding of the physical mechanism of the gas-solid interface charging phenomenon. In this letter, we reported a field dependent property of surface charge accumulation patterns on spacers under DC stress. We verified this finding through experiment, and further, we put forward a field-dependent charging model based on dominant charge transport behavior under different electric fields. It was found that the charging characteristics of the spacer are dominated by the Ohmic conduction from the volume below an electric field of 2.5 kV/mm. When the electric field stress is higher than 2.5 kV/mm, the charging property of spacers is dominated by the enhanced gas ionization according to Townsend's law. The correctness of this model was verified by surface charge measurement results in literature studies, and a method for determining the dominant mechanism of charge accumulation under different electric fields was proposed.

Partial Discharge Detection and Characteristics of Gas-insulated Substation Free Metal Particles Based on Acoustic Emission

Partial Discharge Detection and Characteristics of Gas-insulated Substation Free Metal Particles Based on Acoustic Emission

Very Fast Transients in a 500 kV Gas-Insulated Substation

This paper performs thorough investigations of very fast transients (VFTs) in a 500 kV gas-insulated substation (GIS) by adopting complete earth-return impedance and admittance formulas. VFT simulations are performed with wideband models in a simulation tool for electromagnetic transients. The effects of various GIS parameters on VFTs are investigated. The maximum core and pipe voltages along the GIS are presented. The frequency spectra of VFT voltages are evaluated, and the effects of GIS length and transformer capacitances on the VFT frequencies are analyzed. The frequency decreases as the GIS total length increases. The frequency is decreased significantly by stray capacitances of transformers because those are far greater than the GIB capacitance. The effect of pipe grounding on the pipe voltage is a very noticeable, but on the core voltage and the oscillating frequency is minor. The position of an operating DS influences the VFT over-voltages and frequency significantly. Approximate analytical formulas are derived for physical and qualitative interpretation of simulation results.

Discharge Analysis of 1100kV GIS Equipment in Lightning Impulse and Power Frequency Withstand Voltage

The fully enclosed combined electrical appliance gas insulated substation (GIS) is an important large-scale substation equipment, which has been widely used in power systems. In order to ensure the safe and reliable operation of this equipment, UHV GIS will conduct the text of lightning impulse and power frequency withstand before delivery of this equipment. In this paper, the method of vibration was used to analyze the lightning phenomenon caused by lightning impulse and partial discharge of 1100kV GIS equipment. Put forward the problems that should be paid attention to when installing GIS equipment, in order to provide reference for troubleshooting GIS equipment in the future.

GIS UHF Partial Discharge On-line Monitoring Device Evaluation

The Ultra-high Frequency (UHF) partial discharge on-line monitoring system device is widely used in gas insulated substations (GIS), and has become one of the important detection methods for partial discharge of GIS. However, due to the lack of uniform standards within the industry, the equipment produced by the manufacturers is uneven, resulting in the performance evaluation problems of the UHF online monitoring device in the purchase and acceptance process. For this question, this paper proposes a measurement method, which has two parts: UHF sensor evaluation and complete device evaluation.A set of evaluation methods was established by using a signal simulation test method and a simulated fault evaluation method, and a more comprehensive understanding of the GIS UHF partial discharge on-line monitoring device were proposed.

Availability and Maintenance Modeling for GIS Equipment Served in High-Speed Railway Under Incomplete Maintenance

Gas-insulated substation (GIS) equipment served in the traction power-supply system (TPSS) of the high-speed railway (HSR) suffers from extremely severe traction load conditions during its lifetime. In this paper, three major issues related to the actual field maintenance operations of GIS equipment in TPSS are addressed: 1) $s$ -dependent degradation and shock process; 2) both spatial and temporal failure thresholds of shocks; and 3) incomplete maintenance (i.e., nonignorable maintenance time). To model the deterioration and failure process of GIS equipment, the hard failure model and the soft failure model are proposed. The characteristic function is utilized to bridge the s -dependent degradation and shock process in the soft failure model, while the extreme shock model (with spatial threshold) and $\delta $ -shock model (with temporal threshold) are introduced in the hard failure model. Furthermore, the index of availability, which combines both reliability and maintainability, is derived under the incomplete maintenance consideration. Based on the balance of availability and maintenance cost, the maintenance strategy with periodic inspections for GIS equipment in the long-run time span is developed. Optimizations of three decision parameters (i.e., inspection period, extreme shock threshold, and $\delta $ -shock threshold) are implemented to achieve the best performance (with high availability and low maintenance cost) of the maintenance strategy.

Environmentally Friendly Compact Air-Insulated High-Voltage Substations

This paper investigates the possible options for achieving a substantial reduction in a substation footprint using air-insulated switchgear as a more environmentally-friendly alternative to gas-insulated substations that use SF6 gas. Adopting a new approach to surge arrester location and numbers, International Electrotechnical Commission (IEC) minimum clearances can be successfully selected instead of the maximum clearances as currently adopted by many utilities, as is the case in the UK. In addition, innovative alternative compact busbar arrangements using vertical and delta configurations have been proposed by the authors. A further opportunity for compaction is offered by the application of compact and integrated technology offered from several manufacturers. The full overvoltage control within the entire substation under any surge condition is a key aspect of the feasibility of this type of substation. This work demonstrates that the new design option can be an attractive alternative for future substation configuration with minimum footprint.