Because of its high-capacity, low losses and no electromagnetic interference, the gas-insulated transmission line (GIL), which is a replacement of an overhead line in special environments, has been used for over 40 years, mainly as bus ducts of gas-insulated substations or underground connections in power plants. The insulated and cooling gas in GIL is mainly SF 6 or its mixtures, which have high global warming potential (GWP) and are listed as restricted gases in the 3 rd Conference of the Parties to the United Nations Framework Convention on Climate Change in 1997. Therefore, a lot of researches have been made to find a substitute gas for SF 6 . In this paper, the cooling capability of gas mixtures with fluorocarbon, which has a lower GWP than SF 6 and outstanding insulating performance, is investigated. Heat transfer coefficients of gas mixtures are calculated by measuring the surface temperature of a metal pipe under a certain current. The heat transfer coefficients of gas mixtures with fluorocarbon are analyzed and compared with that of SF 6 mixtures. Based on the heat transfer coefficients, the maximum permissible currents of our GIL model with fluorocarbon mixtures or SF 6 mixtures are also calculated and compared.
because of its high dielectric strength, good partial discharge capability, low global warming potential (GWP), none ozone depletion potential (ODP) and nontoxicity, fluorocarbon gas is possible substitute for SF6, and can be used hopefully in electrical equipment, such as circuit breaker. In this paper, we calculate the pressure characteristic of circuit breaker using gas mixture containing c-C4F8 as arc quenching gas based-on the first law of thermodynamics and the law of hydrokinetics. The pressure characteristic curve of the gas chamber and the gas mass flow pass the nozzle are obtained through computation. In addition, the influences of mixtures ratio and nozzle throat diameter to the pressure and gas mass flow rate is achieved. It shows that the bigger ratio of fluorocarbon corresponding to the bigger chamber pressure and relative bigger mass flow as to the same structural factor. And the nozzle throat diameter has a large impact on the pressure and gas mass flow rate. Besides, we also compared the gas pressure and gas mass flow rate of mixture gas with that of SF6 gas. These results provide a helpful reference for the design of the new type circuit breaker.
Abstract Microdevice integrating energy storage with wireless charging could create opportunities for electronics design, such as moveable charging. Herein, we report seamlessly integrated wireless charging micro-supercapacitors by taking advantage of a designed highly consistent material system that both wireless coils and electrodes are of the graphite paper. The transferring power efficiency of the wireless charging is 52.8%. Benefitting from unique circuit structure, the intact device displays low resistance and excellent voltage tolerability with a capacitance of 454.1 mF cm −2 , superior to state-of-the-art conventional planar micro-supercapacitors. Besides, a record high energy density of 463.1 μWh cm −2 exceeds the existing metal ion hybrid micro-supercapacitors and even commercial thin film battery (350 μWh cm −2 ). After charging for 6 min, the integrated device reaches up to a power output of 45.9 mW, which can drive an electrical toy car immediately. This work brings an insight for contactless micro-electronics and flexible micro-robotics.
In the voltage source inverter applications, inverter nonlinearities would affect the parameter identification process in many ways. Hence, this article proposes an offline identification method for resistance and dq -axis inductance surface by considering the inverter nonlinearity characteristics. A variable amplitude square-wave injection (VASI) scheme is proposed for the dq -axis inductance identification. The VASI method achieves the inductance identification with a novel data sampling strategy. Meanwhile, it can also establish the inductance surfaces by only a few identified data points with a polynomial fitting algorithm, which greatly reduces the identification time compared with the existing methods. The resistance identification is realized by a slope signal injection method, in which the effect of IGBT voltage drop is analyzed. In order to improve the identification accuracy, the inverter nonlinearities are compensated by a self-learning method considering the zero-axis voltage at different rotor positions. At the same time, the sampling error in zero current zones of abc-phases is researched. In order to verify the effectiveness and generality, the proposed method is carried out on two different test machines and confirmed by finite element analysis.
As the increasing demand for large capacity, high voltage and high reliability power transformers in urban power grid, oil-free, non-flammable and non-explosive equipment is recommended. For this reason, evaporative cooling transformers, gas insulated transformers and other electrical equipment using fluorocarbon as coolant and dielectric have been developed. This paper presents an experimental survey of the main components of decomposition products generated by several faults of electrical equipment using fluorocarbon; here evaporative cooling transformer and gas insulated transformer are taken as example. All experimental studies are carried out by simplified testing setups. The gaseous decomposition products formed during the tests are analyzed and assayed by means of GC/MS (gas chromatography/mass spectrometry) method. The amount of decomposition products varied with temperature, time and discharge capacity are studied. Based on these results, criterions for judging the fault type of this kind equipment is suggested, and it could be helpfulness to develop a diagnostic method for the new electrical equipment using fluorocarbon.
When the grid impedance changes, the performance of active damping strategies for electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives may decay. A novel harmonic energy regulation strategy for grid currents is proposed to improve the robustness to the grid impedance. The quality of grid currents can be improved when the DC-link capacitors and the motor inductance serve as the main harmonic energy storage elements. Based on this concept, the harmonics in the DC-link voltage are extracted to reconstruct the sampled DC-link voltage in Space Vector Pulse Width Modulation (SVPWM) for harmonic energy regulation. Specifically, the phase and amplitude processing units are applied to regulate the harmonics in the motor current and DC-link voltage based on system model to achieve the theoretical harmonic energy exchange state. By comparing the stability criterion of the cascaded system with the active damping strategy, the proposed method shows better robustness to the grid impedance. Finally, experiments are carried out on a platform of 5.5kW electrolytic capacitorless PMSM drive to verify the effectiveness of the proposed control strategy.
With the increased demand for wireless communication systems for unlicensed indoor applications, the FCC in February 2002, allocated unlicensed bands ranging from 3.1 GHZ to 10.6 GHz with fractional bandwidth of about 109 %, because it plays a key role in the radiofrequency (RF) front ends devices and has been widely applied in many other microwave circuits. Targeting the proposed band defined by the FCC for the UWB system, this article presents a UWB bandpass filter with three stop bands for the mitigation of wireless bands that may interfere with the UWB range. For this purpose, two resonators are utilized for the implementation of triple-notched bands. The C-shaped resonator is used for the first notch band creation at 3.4 GHz to suppress the WiMAX signal while the H-shaped resonator is employed in the initial UWB design to introduce the dual notched characteristic at 4.5 GHz and 8.1 GHz to reject the WLAN and Satellite Communication signals. The overall circuit area covered by the proposed design is 30.6 mm × 20 mm or in terms of guided wavelength at the first stopband its size is 0.06 λg × 0.02 λg. The presented structure shows a good return loss under -10 dB over most of the passband and greater than -15 dB for the notched frequency bands. Finally, the filter is simulated and analyzed in HFSS 15.0. All the bands for the rejection of wireless signals are independently controlled which makes this work superior to the rest of the UWB filters presented in the literature.
For the position sensorless permanent magnet synchronous motor (PMSM) drive system, the online identification of temperature is of great significance for safe operation. Generally, the motor temperature can be obtained directly from the stator resistance, the identification of which is, however, affected by the position estimation error of sensorless control. In order to deal with this problem, a stator temperature identification method for the interior PMSM is proposed with the position error adaptive compensation. The influence of position error on the stator resistance and temperature identification is analyzed and then compensated based on the minimum current vector online tracking (MCVOT) scheme for improving the identification precision. For further improving the accuracy and the convergence rate of MCVOT, a current vector angle tracking strategy based on the adaptive variable tracking step value is adopted in the rotating reference frame. The validity of the proposed method is verified on two experimental platforms.
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