HVDC transmission lines system has some advantages, but it can generate an effect on the environment nearby due to the corona, especially the ionized field. Based on the electromagnetic field theory, a simple method t...
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HVDC transmission lines system has some advantages, but it can generate an effect on the environment nearby due to the corona, especially the ionized field. Based on the electromagnetic field theory, a simple method to analyze the ionized field generated from the bundled conductors of bipolar lines is proposed. And then, after the validity of the method is testified, some examples are analyzed and some conclusions are drawn finally. The results have been used in the design of plusmn800 kV HVDC transmission lines system in China
A new algorithm based on waveform characteristics is presented for fast discrimination between inrush current and fault current of power transformers. The method is based on that the waveform of inrush current (concav...
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A new algorithm based on waveform characteristics is presented for fast discrimination between inrush current and fault current of power transformers. The method is based on that the waveform of inrush current (concave) distorts seriously, while the fault current nearly keeps sinusoid (convexity). Utilizing the sample data within 5 ms after fault initiation and extending the data windows from 5 ms to 10 ms, the approximate current formula can be extracted from fault current or inrush current using least square fitting method. According to the curvature and convex-concave characteristic of the fitting curve, inrush current and fault current of power transformers can be distinguished. Experimental results indicate that this algorithm is not only effective under various fault conditions but also can be realized easily and hardly to be affected by current transformer saturation and decaying DC components. Moreover, fault clearance time can be limited within 5 ms.
Acquiring the dynamic parameters based on computer vision instead of manual patrol, and via comparing power meter reading with its preliminary definition threshold, which is a new automatic monitoring scheme of power ...
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Acquiring the dynamic parameters based on computer vision instead of manual patrol, and via comparing power meter reading with its preliminary definition threshold, which is a new automatic monitoring scheme of powersystem running. In the process of power meter automatic recognition, three particle feature invariants, include length ratio, compactness and simplicity factor have been extracted. The RBFNN is utilized in the dial plate elements recognition. The meter identifying experiments proved that the RBFNN input invariants are stable and proper, and it is insensitive to the background noise. It can optimize the powersystemmonitoring with the image-analyzing introducing.
In resonant grounded system when single-phase earth fault occurs, for arc suppression coil cannot compensate the active current of the zero-sequence grounding current passing through the fault point, the zero-sequence...
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In resonant grounded system when single-phase earth fault occurs, for arc suppression coil cannot compensate the active current of the zero-sequence grounding current passing through the fault point, the zero-sequence active current passing through the fault line is the sum of those passing through the non-faults. Therefore in theory the zero-sequence active current passing through the fault line is greater than others in absolute value. Energy function is the integrating of product of zero-sequence voltage with zero-sequence current. The fault line's energy function value is negative, while the non-fault's is positive. If three-phase earth capacitance is imbalanced, zero-sequence voltage produces, which will produce zero-sequence current passing through all the line. This zero-sequence current is the key variable that influences the phase-angle between non-fault zero-sequence current and the zero-sequence voltage. This paper analyzes the influences in different compensation conditions in theory. Simulation results are presented to demonstrate that the validity of earth fault line detection based on energy function will be worse and worse accompanied with the increasing of earth resistance when single-phase earth fault occurs on the imbalanced phase, and indicate that energy function has its validity scope.
Voltage fluctuation and flicker are mainly caused by surge load with large capacity, which may lead to the unstable operation of the motor, the poor characteristics of electrical equipments and the mis-operation of th...
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Voltage fluctuation and flicker are mainly caused by surge load with large capacity, which may lead to the unstable operation of the motor, the poor characteristics of electrical equipments and the mis-operation of the electronic device even damage etc. Traditional SVC can adjust the reactive power ideally to maintain the system voltage of the connection point and play an excellent role in suppressing the voltage fluctuation and flicker. The minor defect is that it can not be directly applied to the ultrahigh or extra-high voltage system. This paper puts forward a topology of SVC based on the controllable reactor. It can be made into voltage at any level to connect to the ultra-high or extra-high voltage network directly, and can dynamically adjust the saturation degree of the controllable reactor according to the fluctuation of the reactive power of the system, smoothly change the reactive power it sends out, effectively suppress the voltage fluctuation and flicker. Meanwhile, H alpha control is taker as the main control strategy. The validity of proposed approach is verified by calculation and simulation.
Long-term powersystemdynamic simulation needs to reflect the dynamic process of the fossil fuel steam unit when occurring severely disturbances in the powersystem. A physically based detailed model of the fossil fu...
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Long-term powersystemdynamic simulation needs to reflect the dynamic process of the fossil fuel steam unit when occurring severely disturbances in the powersystem. A physically based detailed model of the fossil fuel steam unit for powersystem long-term dynamic simulation has been described in this paper. The model can reflect the dynamic variation of the internal parameters accurately. In particular, the detailed model considers the dynamic impact on the turbine output from the extraction system. The simulation is much closer to the reality in the powersystem long-term dynamic process. This detailed model of the fossil fuel steam unit can be used for the powersystem long-term dynamic simulation.
Static Synchronous Series Compensator (SSSC) is a sort of FACTS equipments based on the series Voltage Source Converter (VSC). The small-step ( less than or equal 2 μs) model of SSSC is built in RTDS in this paper. T...
Static Synchronous Series Compensator (SSSC) is a sort of FACTS equipments based on the series Voltage Source Converter (VSC). The small-step ( less than or equal 2 μs) model of SSSC is built in RTDS in this paper. The main circuit structure of SSSC consists of cascaded H-bridge units and single-phase coupling transformer. Because of the simple and independent connection among three phases, it is easy to present the unbalanced compensation. The modulation strategy of SSSC which adopts staircase modulation can be got on-line;it uses equal area principle to calculate the trigger angels in this way. Constant impedance strategy is also applied, namely the output voltage of SSSC is proportional to the line current in amplitude and leads or lags the line current by π/2. Details for building cascaded multilevel SSSC model in RTDS are shown in this paper;in addition, there are also some tips about how to present the small-step simulation of VSC. Firstly, the VSC module must be arranged suitably on the allowable simulation scale. Secondly, the special transformer has to be used at the interface between large step model and small step one. Thirdly, in order to avoid the 'stiff' instance of the interface, the VSC breaker must substitute for the large step side breaker. Finally, the division module must be set properly in that the dividend may equal to zero. Moreover, the results including indices such as P, Q, current of line, modulation index and output voltage under different running conditions have proved that the model in RTDS is almost perfect by comparing with the results got in EMTDC/PSCAD4.02.
Grounding characteristics of linear, star-type and toroidal electrodes are discussed in this paper. Based on the analysis of the performance of double-ring in uniform and horizontal two-layer soils, an electrode model...
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Grounding characteristics of linear, star-type and toroidal electrodes are discussed in this paper. Based on the analysis of the performance of double-ring in uniform and horizontal two-layer soils, an electrode model of standard triple concentric rings buried with different depth is presented for plusmn800 kV Xiluodu and Xiangjiaba converter stations in the first period of Jinsha River DC projects. Considering the three sending converter stations in the projects close to each other relatively, an initial analysis of sharing electrodes has been made, including the operation mode of converter stations, choice of rated current and the design model of electrodes. Simulation results obtained from the electrode sites primarily selected for Xiluodu right-bank converter station show that the above model can satisfy the operation requirements with a better economical performance and sharing electrodes by multi-converter stations is also feasible. They may supply some reference to the practical projects.
Low frequency oscillations in the interconnected powersystems are observed all around the world. Besides conventional PSS to suppress Low frequency oscillation, there are other modern FACTS devices to damp oscillatio...
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Low frequency oscillations in the interconnected powersystems are observed all around the world. Besides conventional PSS to suppress Low frequency oscillation, there are other modern FACTS devices to damp oscillation, among which flywheel energy storage system (FESS) is a comparative valid way. The theory on restraining low frequency oscillation used by flywheel energy storage system is described through transfer function diagram and complex torque coefficient. A numerical model of flywheel energy storage asynchronous motor controlled by VVVF inverter is derived from its mathematical model in alpha-beta coordinate system. Then the total model eigenvalue is analyzed. Based on analysis, attach control strategy using two parallel independent parts for active powercontrol and reactive powercontrol is designed in FESS to restrain low frequency oscillation. The calculation result shows that flywheel energy storage system is an effective way to restrain low frequency oscillation and enhance powersystemdynamic performance.
The communication of power line carrier (PLC) in the frequency of 20-500 kHz in the ultra-high voltage direct current (UHVDC) transmission line with ±800 V rated voltage and the radio communication range from 500...
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The communication of power line carrier (PLC) in the frequency of 20-500 kHz in the ultra-high voltage direct current (UHVDC) transmission line with ±800 V rated voltage and the radio communication range from 500 kHz-20 MHz near the converter substation and along the ultra-high voltage direct current transmission line are interfered strongly by high order harmonics from converters and direct current transmission line and neutral line of ultra-high voltage direct current transmission system. It's a virtual way to reduce power line carrier interference (PLCI) and radio interference (RI) to install PLC/RI filters at the terminals of the polar line and neutral line at the direct current side of converter substation. The power line carrier interference and radio interference from the ultrahigh voltage direct current transmission system with two series of 12 pulse converters in a pole line are produced by the chopping of valve voltage of converters and the discharging of electric corona and insulators. The limitation values for power line carrier interference and radio interference from the converter substation of ultra-high voltage direct current transmission system are analyzed in the paper. After calculating the total power line carrier interference and radio interference at the terminal of the direct current pole line and neutral line in the circumstance of PLC/RI filter schemes with a harmonic analysis program, a economical and practical PLC/RI filter scheme for limiting power line carrier interference and radio interference at the direct current side of ultra-high voltage direct current converter substation is produced.
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