kV Gas Insulated Switchgear Research Articles

Three-dimensional X-ray imaging system and its application in power equipment

The medical computed tomography (CT) technique cannot be directly applied to power equipment, such as gas-insulated switchgear (GIS), because of its huge size and immovability. In this research, a three-dimensional X-ray imaging system is developed for GIS equipment. The three-dimensional X-ray imaging system includes machinery, motion control, data acquisition, image reconstruction and three-dimensional image display subsystems. The principle of three-dimensional X-ray imaging is based on the Radon transform and the inverse transform. The rotary scanning device successfully collects 360 sets of projection data. The tomographic image is reconstructed using the acquired projection data. Shown in this paper is what is believed to be the world's first three-dimensional structure photograph of GIS that can be sliced and displayed using X-ray imaging. The application of the three-dimensional X-ray imaging system to the 110 kV GIS equipment at the Shayao Station of the Dongguan Power Supply Bureau shows that the overall accuracy of the system can reach up to 200 microns and the highest resolution of the output tomogram can reach up to 3160 × 3160 pixels.

Mechanical stress distribution and risk assessment of 110 kV GIS insulator considering Al 2 O 3 settlement

The growing application of gas insulated switchgear (GIS) in electric power system asks for higher reliability of epoxy (EP) insulators, thus it is important to seek effective methods to improve the operating reliability of GIS insulators. On the basis of the 110 kV GIS insulator, this study studied the aluminium oxide (Al2O3) settlement in the curing process and the stress distribution of the horizontally laid GIS. Besides, the risk coefficient was defined to evaluate the operating reliability of insulators laid by different methods (I–V). Some conclusions are shown below: the Al2O3 settlement in the curing process causes the insulator density to have a large variation from 2.13 to 2.32 g/cm3. The Al2O3 content has a great influence on the mechanical performances of EP/Al2O3system. The first principle stress is localised on the upper interface between the insulator and the conductor, which is the main threat to the mechanical damage of insulator. The laying method V appears to be optimal with a pretty low risk coefficient of 31.5. In actual application, for the horizontally laid GIS, the insulator should be laid with the mould gate downward to improve its mechanical reliability.

Research on the RBF‐PID control method for the motor actuator used in a UHV GIS disconnector

To improve the reliability and intelligent level of the AC transmission system, the radial basis function-based proportional-integral-derivative (RBF-PID) control method for the motor actuator used in the 550 kV gas-insulated switchgear (GIS) disconnector is proposed. According to the dynamic mathematical model of the motor actuator, the main structure of the RBF neural network based on the gradient descent method for learning algorithm is constructed. An identification function is formed by taking values of the output error square, and then by gathering information on the real-time tuning parameters of PID. Based on that, the simulation of the control system is constructed. The comparative analyses of the tracking control characteristics and the servo following error of the disconnector's contact speed between double-loop PID and RBF-PID are done through the computational and experiment methods, respectively. The results show that 550 kV GIS disconnector with the motor actuator by the RFB-PID control method has better controllability, and the servo following error is controlled within 0.1 m/s.

A Novel GIS Partial Discharge Detection Sensor With Integrated Optical and UHF Methods

A novel gas insulated switchgear (GIS) partial discharge (PD) sensor with integrated optical fiber and ultrahigh frequency (UHF) method is developed in this paper. The integrated sensor is formed by placing an optical fiber on the surface of the UHF sensor. The novel sensor can be mounted inside the GIS and measure the PD through optical and UHF signals at the same time. The validity and sensitivity of the sensor are proved by experiments on a physical 110 kV GIS. This PD detection sensor solves the problem that the optical fiber is difficult to be mounted inside GIS and provides a novel method for PD detection in GIS.

Partial discharge detection by extracting UHF signal from inner grading electrode of insulating spacer in GIS

In this study, a novel ultra-high frequency (UHF) sensor using an inner grading electrode inside an insulting spacer is employed to detect gas-insulated switchgear (GIS) partial discharge (PD). The simulation of the waveguide modes of the 252 kV GIS and the frequency response characteristics of this UHF sensor are performed by using the finite difference time domain (FDTD) method. Three kinds of typical defects are employed to investigate the PD detection characteristics of this UHF sensor. It is shown that the resonance frequencies of this sensor are extremely abundant below 3 GHz, and the major resonance frequencies around 0.5–1.2 and 2.2–3 GHz. The phase-resolved PD (PRPD) images accumulated by using this UHF sensor present the typical PRPD images of defects. The main frequency spectrum of the metal protrusion on a high-voltage conductor and floating potential defects are distributed below 1.5 GHz, which is consistent with waveguide mode simulation. A resonance frequency of a grading electrode UHF sensor appears at about 115 MHz, which is close to the simulation value of a resonance frequency at 140 MHz. The PD detection sensitivity of this sensor is much higher than that of an external sensor; however, it is a little lower than that of an internal sensor.

Surface charge distribution on GIS insulator under DC/AC voltage

The Gas Insulated Switchgear (GIS) equipment observes surface charge accumulation under DC or AC voltage in real operation, which could distort the electric field and incur flashover eventually. With a 3D high-resolution surface charge measurement system established on actual 220 kV GIS basin insulator, the present research captured the surface charge distribution characteristics of the insulator under DC and AC voltage through high-precision probe scanning on the insulator surface. The test results show that: 1) Surface charge demonstrates obvious polarity effect under DC voltage. Under positive DC voltage, there accumulated mainly positive surface charges. Under negative DC voltage, the polarity of accumulated surface charges is all negative. Regardless of charge polarities, the surface charge density increases as the voltage amplitudes mounts and the voltage application duration prolongs. 2) Surface charge accumulation also takes place under AC voltage application. All charges are negative and distribute in a uniformed manner but in smaller density comparing to the DC scenario. As the voltage amplitudes increase, the surface charge density first increases, then decreases and finally reaches a near saturation state. As voltage application goes on, the surface charge accumulation becomes more obvious. Above all, the insulation issues in relation to surface charge accumulation require due attention in the application and maintenance of GIS equipment, and the present research attempts to provide useful reference for the optimal design of GIS/GIL insulators.

Experience with Construction of 500 kV Gas Insulated Switchgear at the Votkinsk Hydroelectric Power Plant

Experience with Construction of 500 kV Gas Insulated Switchgear at the Votkinsk Hydroelectric Power Plant

Full-Maxwell Simulations of Very Fast Transients in GIS: Case Study to Compare 3-D and 2-D-Axisymmetric Models of 1100 kV Test Setup

Development and type testing of gas-insulated switchgear (GIS) disconnectors are supported with the simulation-based analyses of very fast transients (VFTs) that are associated with the disconnector switching operations. In order to analyze local field values in the entire GIS geometry, the full-Maxwell approach needs to be involved for simulating the VFT generation process. According to power substation layout studies, 90 ${}^{\circ }$ -angled GIS disconnectors are often used in GIS projects, since they offer most layout options and, at the same time, require the lowest number of GIS components. This implies that the test setups are asymmetric, thus the direct use of the full-Maxwell approach requires 3-D models, the application of which is considered to be highly demanding from a numerical point of view. The paper shows a comparison of the results obtained from full-Maxwell numerical simulations for a development test setup of 1100 kV GIS. The analyses are conducted for full 3-D geometry and for the corresponding 2-D-axisymmetric geometry. Example simulations of the VFT overvoltage (VFTO) waveforms are presented for both geometries, together with a comparison of the numerical effort needed for solving the associated field equations. The presented approach based on the 2-D-axisymmetric GIS model allows one to significantly reduce the numerical effort involved to support design work and development tests.

25.8kV급 GIS에 Matrix System을 적용한 전력설비 최적화 연구

Recently, more electric power facilities have been miniaturized and it is noted that the facilities maintenance will be essential through operation optimization. In this paper we applied and examined the operation optimization of electric power facilities by applying Matrix system which can improve reliability to minimize outage and recover failure rapidly when blackouts happen at 25.8kV Gas Insulated Switchgear(GIS). The fundamental problem for facilities maintenance of GIS can happen due to indeterminable internal state in real time. Matrix optimization organizes action states in all containers which contain pressurized SF 6 Gas such as circuit breaker, disconnector switch, bus for utilizing them each area. Then, we connect it with power system to monitor and control internal state remotely in real time, and we can minimize blackout zone or outage. Considering above process, we improved stability of overall facilities.

Partial discharge diagnosis by simultaneous observation of discharge pulses and vibration signal

Protrusion defects on inner conductor can seriously weaken the dielectric strength of gas insulated switchgear (GIS). In practice, pulse current method (IEC 60270) and vibration method sometimes are ineffective for this type of defect. Clarification of coincidence of partial discharge (PD) characteristics measured with both methods is very important for further application of the vibration method. In this paper, PD pulses and vibration signal recorded on enclosure generated from artificial protrusions mounted on inner conductor with different lengths and diameters were measured synchronously by using a 252 kV GIS PD test system. The test GIS was filled with the gas SF6 of the standard atmosphere pressure (i.e. 101 kPa), and the power frequency of the test voltage was 50 Hz. The pulse repetition frequency (PRF) characteristics and frequency-resolved vibration (FRV) characteristics under different discharge level were investigated. The dynamic response (DR) characteristics of the experimental GIS are also obtained by using the force hammer test. For a good understanding of PD vibration characteristics, the relationship between FRV, PRF and DR was analyzed in detail. To make more reliable operations of GIS, an improvement vibration method for protrusion defect detection was developed and applied.

Transient Electromagnetic Disturbance Induced on the Ports of Intelligent Component of Electronic Instrument Transformer Due to Switching Operations in 500 kV GIS Substations

Switching operations in gas-insulated switchgear (GIS) substations generate transient electromagnetic fields in the GIS pipes. These fields leak out discontinuities of the GIS and induce electromagnetic disturbance voltages on the cables and ports of secondary circuits. In smart GIS substations, secondary devices especially, such as the intelligent component of electronic instrument transformer, are vulnerable to electromagnetic interference. In this paper, the disturbance voltages induced on the ports of intelligent component of electronic instrument transformer had been measured in three 500-kV GIS substations, respectively. The disturbance was generated either during disconnector (DS) switching operations or circuit breaker (CB) operations. Then, the time-domain and frequency-domain characteristics of the disturbance waveforms have been analyzed. The micro-pulses of disturbance voltages have been extracted from the raw data. The waveform parameters, including peak voltage, rise-time, dominated frequency, and duration, have been calculated by the statistical analysis. The comparison between disturbance during DS switching operations and that of CB operations has been made. Also, the differences and similarities of disturbances between the three GIS substations have been displayed. Furthermore, the differences between measured waveforms and the IEC 61000-4-18 immunity test standard waveform have been discussed.

Damping of VFTO in Gas-Insulated Switchgear by a New Coating Material

Several methods of attenuation of very-fast transient overvoltages (VFTOs) in gas-insulated switchgear (GIS) are under development. An approach that is currently gaining high attention among researchers is based on the application of magnetic cores dissipating the energy associated with VFTO due to eddy current losses and magnetic hysteresis losses. This paper presents an advancement in this approach by introducing a new material type (denoted in this paper as “nanoflakes”). This new material comprises macro pieces of nanocrystalline ribbons (with the size ranging in square millimeters), acquired from crumbled nanocrystalline cores of a standard design. The material is characterized by relatively high magnetic permeability, poor electrical conductivity, and high saturation flux level. The material is suitable for application as a coating layer applied to the surfaces of an inner and/or an outer GIS conductor, as a fill-in material in the GIS shielding elements, or as a standard shaped core. This paper presents the material major features, outlines its development process, and reports on validation of the material effectiveness in real VFTO conditions. The validation is based on the measurement of VFTO attenuation in a full-scale 550 kV GIS test setup.

Propogation characteristics of PD‐induced UHF signal in 126 kV GIS with three‐phase construction based on time–frequency analysis

Partial discharge (PD) detection of the gas-insulated switchgear (GIS) is an effective method for substation security. The GIS with three-phase construction is widely used for substations. The propagation characteristics of PD-induced ultra-high-frequency (UHF) signal in three-phase GIS is investigated in this study by time–frequency analysis method. The variation of peak-to-peak value (V pp) and cumulative energy, and especially the energy density in the time–frequency plane are used to represent the feature of the UHF signal. Furthermore, the different situation of the insulation defects and the detection point positions are compared, and the reason for the difference is explained as well. As a result, this study identified a novel method to determine the PD source position in the GIS with three-phase construction.

Behavior of metallic particles in GIS under DC voltage

The paper investigated the behavior and partial discharge (PD) characteristics of a metallic particle under residual dc voltage, using the setting conditions and length of the particle, the applied dc voltage, and other factors as parameters and a gas insulated switchgear (GIS) bus bar model equivalent to that of an actual 300 kV GIS. A metallic particle repeated reciprocating movement at a relatively high frequency of about 5 times per second between the high-voltage conductor and the sheath when the electric field at the bottom surface of the tank exceeded its lift-off electric field. It emerged that, in the process of this reciprocating movement, PD occurred at the moment when the particle collided with the high-voltage conductor. In addition, when a particle collided with the electrode, the electrical charges moved and the residual dc voltage was damped. Conversely, where the sheath side was insulation-coated, the particle did not move at the normal operating voltage level, and even though it moved if vibration was applied, its movement stopped relatively soon. If a metallic particle exists in GIS and moves, there is concern that the insulating performance may decline significantly. When a metallic particle moves under dc voltage, a relatively stable PD is generated and consequently, for example, the PD measurement is considered an effective way to detect a particle. It is also considered effective to take physical measures, such as using an insulating sheath at the bottom surface of the tank to restrain the behavior of particles.

Design of permanent magnet motor actuator used in 550 kV gas-insulated switchgear disconnector

To improve the operating characteristics of disconnector, a limited rotating angle permanent magnet motor actuator is presented in this article. The mathematical relationship between the moving contact stroke and rotation angle of motor is obtained by analyzing the dynamical coordination characteristics of motor actuator used in 550 kV gas-insulated switchgear disconnector. The electromagnetic field equation of motor, motive equation of rotor, and circuit equation of winding are solved simultaneously for acquiring dynamical characteristics of motor. The electromagnetic-mechanical coupled calculating model of motor is established by finite element method, and magnetic saturation of stator tooth is calculated and analyzed. According to the operating principle of motor, the double-closed control system which collects the motor speed and contact stroke signal during the operation of disconnector is developed. The experimental results show that the opening and closing speeds of disconnector are 1.1 and 1.2 m/s, respectively, which meet design requirements. The speed-regulating operation of disconnector is also carried out so that the switching speed of disconnector can adjust by motor actuator and control system.

Partial Discharge Pattern of Various Defects Measured by Spiral Antenna as UHF External Sensor on 66 kV GIS Model

This paper deals with partial discharge (PD) measurement in gas insulated switchgear (GIS) using spiral antenna as UHF external sensor. PD detection in UHF band is effective because it detects electromagnetic (EM) wave induced by PD with high S/N ratio. External sensor was used to detect leaked EM wave signals from insulation spacer of GIS tank. The experiment was conducted in 66 kV GIS model with metal type spacer. There is insulation window in the spacer. PD was generated by some artificial defects in GIS and an external PD source. The leaked EM wave propagated through spacer aperture was measured using spiral type sensor without filter and amplifier. The peak to peak value (Vpp) and the transmission rate of electromagnetic wave signals were evaluated. The PD patterns were observed. The results showed that the PD was detected by the spiral antenna. PD pattern was unique for each defect. These results are considered to be useful for enhancement of database PD diagnosis.

Insulation condition monitoring of epoxy spacers in GIS using a decomposed gas CS2

The epoxy spacers in SF6 Gas Insulated Switchgear (GIS) are vulnerable to discharge. Once the surface of the epoxy spacers is deteriorated under discharge, insulation break down may occur subsequently. From a number of experiments carried out on 110 kV GIS, a new gas CS2 was detected when creeping discharges occur on the epoxy spacer surface. In order to verify the correlation between CS2 and the degradation of epoxy spacers, the quantum chemistry analysis was used to investigate the mechanism of CS2 development. Based on the results, the relation between CS2 and spacer insulation degradation was determined.

Gas-insulated switchgear PD signal analysis based on Hilbert-Huang transform with fractal parameters enhancement

This study proposes a novel method of partial discharge (PD) electrical signal analysis based on the Hilbert-Huang transform (HHT) with fractal feature enhancement. Firstly, this study establishes four defect types of 15 kV gas-insulated switchgear (GIS) and uses a commercial high-frequency current transformer (HFCT) to measure the electrical signals caused by the PD phenomenon. Second, the authors applied HHT for the PD electrical signal process. The HHT can represent instantaneous frequency components through empirical mode decomposition (EMD) and then transform to a 3D Hilbert energy spectrum. Finally, this study extracts the fractal parameters from the 3D energy spectrum and uses a neural network (NN) for PD recognition. To demonstrate the effectiveness of the proposed method, this study uses 160 sets of field-tested PD patterns generated by GIS, and then compares the recognition rate of the signal with and without the EMD process. The result shows that the proposed method can easily separate various defect types. The method can also be employed by the construction unit to verify the GIS quality and determine the GIS insulation status.

Insulation characteristics of 1100 kV GIS under very fast transient overvoltage and lightning impulse

Very fast transient overvoltage (VFTO) in gas insulated switchgear (GIS) is of great concern at the higher rated voltages because the difference between the rated lightning impulse (LI) and the VFTO withstand voltage decreases. In order to clarify VFTO withstand level of 1100 kV GIS, a simulation system was designed for generation of VFTO. The breakdown characteristics of sphere-plane gap and rod-plane gap in SF6 under VFTO and LI were investigated for different gas pressures. Experimental results show that the breakdown voltages in slightly inhomogeneous field gaps under VFTO are higher than that under LI. However, for the rod-plane gaps, the breakdown voltages and voltage-time curves under VFTO fall below that of LI at higher pressure in the case of negative polarity. The polarity effect of rod-plane gaps under LI is reversed at a certain pressure. Based on the analyses, it is concluded that the different breakdown characteristics of SF6 gaps may be attribute to the difference between space charge behaviors during the discharge development under the impulse with different wave front and oscillation tail of VFTO and LI.

Propagation properties of PD-induced electromagnetic wave in 66 kV GIS model tank with L branch structure

The authors investigated the effects of a corner that affects the transmission characteristics of a partial discharge (PD) induced electromagnetic (EM) wave, using a gas insulated switchgear (GIS) model with an L-shaped branch. The authors also experimentally investigated the change of amplitude of PD-induced EM wave around the passage of the Lshaped part using a disc-type ultra-high frequency (UHF) sensor located in a 66 kV model GIS. In addition, the effects of transverse electric (TE) mode were examined using a low pass filtering process, and a finite difference time domain (FD-TD) simulation with a simple model was performed. Subsequently, the effects of the L-shaped part that affected the EM wave transmission characteristic were discussed based on a comparison of the results with the analysis. It was found that the effects of the L-shaped part that affected the transmission characteristics of the PD-induced the EM wave did not affect the transverse electromagnetic (TEM) wave mode component, and reflection was generated with a higher frequency component above TE11 mode. It was also shown that the amplitude of the propagating EM wave changed significantly around the L-shaped part due to the superimposition of the reflected TE mode on the latter part of the incoming EM wave.