Gas-insulated Switchgear Disconnector Research Articles

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.

Research on Electromagnetic Interference of Smart Device Acquisition Unit under GIS Disconnector Operation

With the continuous improvement of substation voltage level and the wide use of GAS insulated SWITCHGEAR (GIS), switching overvoltage, especially the very fast transient overvoltage (VFTO) caused by disconnector operation, has attracted more and more attention. According to the demonstration project of a new generation intelligent substation with the highest voltage grade (330kV) in operation in China, analysing the physical process of VFTO generation and propagation in high voltage substation by combining simulation calculation with test detection. Taking the electronic current transformer of intelligent secondary equipment as an example, its exploitation is established. We got the output signal waveform of the acquisition unit port under the action of VFTO by the high frequency transient model of the unit. By comparing the distribution parameters and the measured signal waveforms, the high frequency characteristics of the acquisition unit of the electronic current transformer under the action of VFTO are reflected. The results show that the EMI of the acquisition unit of electronic current transformer is in the form of pulse group. The amplitude of EMI is about 900V and the stable impact frequency is about 50 kHz. The impact frequency directly related to the arc reburning frequency.

Finite Element Analysis on Forces, Currents, and Magnetic Fluxes of Misaligned GIS Disconnector

This paper provides an effective misalignment fault diagnosis method of the gas-insulated switchgear (GIS) disconnector. Relationships between contact forces and the surrounding magnetic field in various mechanical assembly conditions were studied by the 3-D electromagnetic-mechanical coupled finite-element model and physical experiments. First, spring deformation and contact forces on individual contact elements were obtained by mechanical field analysis. Holding springs were modeled by equivalent elastic rings during analysis. Second, the magnetic field around the GIS disconnector was obtained by electromagnetic-field analysis. Contact resistances on contact interfaces were modeled by cylindrical bridges, which use mechanical contact forces as parameter inputs. Physical tests have been carried on the prototype GIS disconnector with various artificial misalignment faults. In different situations of misalignment faults under ac current, surrounding magnetic flux densities were measured by the Hall sensor array. Calculated and measured results have the same trend that the mechanical misalignment fault could change distributions of contact forces then make distortion of currents and the surrounding magnetic field. Magnetic-field behaviors of the GIS disconnector with different mechanical assembly conditions were studied. The results show that the deviation of magnetic flux density becomes larger while reducing holding spring stiffness, decreasing movable conductor insert depth, and increasing the movable conductor docking angle.

Improving GIS Disconnectors for Future HVDC Applications

The use of standard HVac disconnectors for bus-transfer switching in future HVdc gas-insulated switchgear (GIS) has been demonstrated successfully in past research through simulation and testing. Prolonged arcing times through reignitions caused by high frequency harmonics as well as the proposed extension of GIS disconnector switching cases, however, create an HVdc-specific demand for more advanced disconnector concepts capable of withstanding higher switching stresses and increased recovery voltages. A spring-loaded disconnector designed for use in HVac mixed technology switchgear was found to shorten the time to first current zero through an accelerated increase of the arcing voltage compared to standard disconnectors. Despite its increased switching performance, the reignition characteristics of this fast-acting disconnector were found to largely follow the previously established extinction criterion, which enables further simulation of similar technologies for HVdc applications. To additionally combat the issue of contamination of HVdc GIS by electrode erosion products, a prototype disconnector was improved using permanent magnets to evoke arc rotation. Erosion tests in air have shown an effective reduction of electrode erosion for long arcing times at currents typical for disconnector switching, whereas bus-transfer tests revealed promising enhancements of the reignition behavior.

Multi-spark modeling of very fast transient overvoltages for the purposes of developing HV and UHV gas-insulated switchgear and of conducting insulation co-ordination studies

AbstractVery fast transient overvoltages (VFTO) originate from steep voltage breakdowns in SF6gas that are inherent to operation of any switching device of the gas-insulated switchgear (GIS) type. For power stations with voltage ratings exceeding 500 kV, the ratio between equipment rated- and withstand-voltage levels becomes relatively low, which causes the VFTO peak values to reach the component’s insulation withstand-voltage levels, thus becoming a design factor for high- and ultra-high voltage GIS. While well-established approach to VFTO analyses involves only single VFTO events (the so-called single-spark approach), there is often the need to analyze the entire VFTO generation process, for which the multi-spark approach to VFTO modeling is to be employed. The multi-spark approach allows one to evaluate the VFTO impact on the GIS disconnector design along with the impact of the VFTO on selection and dimensioning of the VFTO damping solutions. As the multi-spark approach to VFTO modeling is now being increasingly used in UHV GIS developments as well as for the insulation co-ordination studies of power stations, the present paper is motivated by the need to report on the VFTO multi-spark modeling approach and to lay a common ground for development works that are supported extensively with VFTO simulations. The paper presents physical assumptions and modeling concepts that are in use in such modeling works. Development of the multi-spark GIS disconnector model for VFTO simulations is presented, followed by an overview of examples of the model application for the GIS development works and for insulation co-ordination studies.

Characteristics of Electromagnetic Disturbance for Intelligent Component Due to Switching Operations via a 1100 kV AC GIS Test Circuit

Switching operation of the disconnector in gas-insulated switchgear (GIS) results in very fast transient overvoltage in GIS pipes. In a smart substation, this process induces disturbance voltage on the port of the intelligent component fixed on GIS pipes or placed in the local cabinet nearby, which then may lead to the failure of the equipment. The experimental results of the port disturbance voltage during the switching operation via a 1100 kV test circuit are first reported in this paper. The test arrangement, including both 70 opening operations and 70 closing operations, had been performed. The influences of different grounding schemes of cable shield on port disturbance had been investigated. Three different cases of the terminal load had also been considered: open circuit, short circuit, and 50 Ω. Over 100 000 micro-pulses had been extracted from the disturbance voltage waveforms. The waveform characteristics including peak voltage, rise-time, oscillation frequency, and decaying had been obtained by statistical analysis of these micro-pulses. Furthermore, the differences between measured waveforms and the IEC 61000-4-18 immunity test standard waveform had been discussed.

Controlled Voltage Breakdown in Disconnector Contact System for VFTO Mitigation in Gas-Insulated Switchgear (GIS)

Several methods have been proposed and investigated so far on mitigation of very fast transient overvoltages (VFTO) in gas-insulated switchgear (GIS). The state-of-the-art methods are primarily based on dissipation of the energy associated with electromagnetic waves that the VFTO originate from and are composed of. Present paper reports on an alternative concept of VFTO mitigation based on the principle of controlling voltage conditions preceding voltage breakdown in SF6 gas that leads to VFTO generation. The paper introduces different control algorithms and shows how the algorithms can limit VFTO maximum value and total number of voltage breakdowns during operation of the GIS disconnector. The concept is applied for mitigation of VFTO in ultra-high voltage GIS. As the study case, an 1100 kV test set-up is used as recently reported for Wuhan (China) GIS station, with the disconnector characteristics obtained from 1100 kV development tests.

New Concept for VFTO Attenuation in GIS with Modified Disconnector Contact System

This paper investigates on a new concept for very-fast transient overvoltages (VFTOs) attenuation in gas-insulated switchgear (GIS). The concept, first introduced by the authors in this paper, involves modification of the GIS disconnector contact system in order to dissipate the VFTO energy in damping elements placed inside the GIS busbar conductor. The concept is an alternative to the state-of-the-art method where magnetic rings are placed in the space between the GIS conductor and the enclosure. The proposed arrangement has no impact on the damping element on the dielectric design of the GIS busbar, and it highly reduces the impact on the GIS thermal design. This paper presents analyses which show feasibility of the concept, through 1) principles which govern voltage conditions inside the GIS busbar and 2) full-Maxwell finite-element method electromagnetic simulations of VFTO attenuated with the use of the proposed concept.

Study on the Influence of Disconnector Characteristics on Very Fast Transient Overvoltages in 1100-kV Gas-Insulated Switchgear

The very fast transient overvoltage (VFTO) generated during switching of the disconnector (DS) in gas-insulated switchgear (GIS) may threaten the insulation of electrical equipment. DS characteristics are important influence factors for VFTO. To study the influence of DS characteristics on VFTO in GIS, an experimental study was conducted in two established full-scale 1100-kV GIS test circuits. More than 1800 tests of switching of DS in test circuits were carried out. In one circuit, the effect of operating speed on VFTO amplitude and trapped charge voltage were studied by changing the operating speed of DS. The results show that the amplitude of the trapped charge voltage and VFTO decreases with a decrease of operating speed. Operating speed was proposed to be 0.5 m/s $ \sim $ 0.8 m/s to suppress VFTO. In the other circuit, VFTO characteristics were studied by tests under two connection ways of DS. One is that the moving contact is connected with the ac power source, and the other is that the fixed contact is connected with the ac power source. The results show that the connection way will affect the breakdown characteristics of the DS, and then affect the polarity of trapped charge voltage. However, the connection way has little influence on the amplitude of VFTO. The achieved results provide a reference for the design and optimization of DS in GIS.

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.

Experimental Research on Very-Fast Transient Overvoltage in 1100-kV Gas-Insulated Switchgear

Very-fast transient overvoltage (VFTO) generated during switching of the disconnector in gas-insulated switchgear (GIS) may threaten the safety operation of electrical equipment. As the rated voltage of GIS increases, the difference between the level of VFTO and its lightning impulse withstand voltage gradually decreases. Hence, VFTO becomes the main dielectric stress to switchgear optimization and insulation coordination for ultra-high voltage (UHV) systems. To obtain the characteristics of VFTO in UHV GIS, two full-scale 1100-kV GIS test circuits were established in China. Two types of capacitive sensors were developed to measure VFTO generated in two test circuits. The measurement systems based on both types of the sensors were calibrated by a special calibration device in laboratories and onsite. The measurable frequency range of the systems is 0.1 Hz ~ 100 MHz and their division ratios are stable. More than 2000 tests by switching the disconnector in GIS had been carried out in the test circuits, and VFTO waveforms were captured by the measurement systems. From the test results, the waveform properties, the striking number, the predominant frequency, and distribution of the trapped charge voltage for full-voltage waveforms, the typical characteristics and oscillation coefficient of single-strike waveform, the distribution of VFTO magnitude was analyzed. The mitigation of VFTO by a damping resistor in the disconnector was illustrated. The maximum magnitude of VFTO was 2.27 p.u., and it was mitigated to 1.33 p.u. by a damping resistor of 500 Ω. The achieved characteristics of VFTO in the UHV GIS have become the basis of VFTO simulation and insulation coordination for engineering design.

Influence of disconnecting part on propagation properties of PD-induced electromagnetic wave in model gis

Partial discharge (PD) detection using a UHF (ultra high frequency) band signal is a well known advanced insulation diagnosis method in gas insulated switchgear (GIS), and has been actively studied. Detailed investigation of electromagnetic (EM) wave propagation inside the GIS tank is required for significant improvement of detecting PD signal by UHF method. When practically applying the UHF method to GIS insulation diagnostics, it is necessary to examine the effects of GIS components such as circuit breakers, isolators and disconnectors on EM wave propagation properties. In this paper, attention is paid to the effects of a disconnecting part of a high voltage (HV) conductor like a circuit breaker or a disconnector in GIS. To examine the effects of disconnecting part, the gap length of the disconnecting part was set as parameter, and waveforms and frequency spectra of the propagation PD-induced EM wave were measured with UHF sensors. For the purpose of discussing the effects of the disconnecting part theoretically, a finite difference time domain (FD-TD) simulation was also carried out. The experimental results show that the PD-induced wave could propagate through the disconnecting part with higher frequency components over the cutoff frequency components of TE11 mode for disconnecting part, i.e. cylindrical shape formed by GIS tank without HV conductor. The propagation of the lower frequency components below the TE11 mode depended on the gap length of the disconnecting part.