This work is concerned with the small signal stability problem in multi-machine systems. By means of H∞ theory, firstly the math model with disturbances is constructed;and secondly, the excitation control law for eac...
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ISBN:
(纸本)7900719229
This work is concerned with the small signal stability problem in multi-machine systems. By means of H∞ theory, firstly the math model with disturbances is constructed;and secondly, the excitation control law for each generator is designed based on solving Riccati Equation. Finally, simulations performed on 4-machine system shows that the proposed H ∞ method has more advantages over LQR method in both damping ratio and H∞ norm of the corresponding closed-loop system and so can enhance the small signal stability of power system greatly.
The shape change of electrical tree propagating in ice-water quenched high-density polyethylene (HDPE) film under AC voltage of different frequency ranging from 50 Hz to 90 kHz as well as the breakdown phenomena cause...
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The shape change of electrical tree propagating in ice-water quenched high-density polyethylene (HDPE) film under AC voltage of different frequency ranging from 50 Hz to 90 kHz as well as the breakdown phenomena caused by the treeing degradation under high frequency condition were studied. The electrical treeing aging experiment is carried out at room temperature. The shape change of electrical tree and the arcing process during the experiment is observed via a digital micro-observing system. It is found that the arcing process can be obviously observed under a high frequency voltage compared with that under low frequency voltage. It is also found that under different frequency voltages the electrical tree initiation shape is different. Most of the electrical trees are branch-shape tree under lower frequency voltage. When the frequency is higher than 5 kHz, trunk-shape tree and bosk-like tree appears. Once the frequency is higher than 50 kHz, breakdown tree can be found out. It is shown that the tree shape conversion is influenced by the frequency. The electrical tree usually has a simple shape and rarely changes under low frequency voltage in one hour or more. However, under a high frequency voltage, the electrical tree shape changes more frequently and has a large probability to breakdown. The influence of frequency on material polarization process, fatigue and thermo effect is considered as the main causes of the experiment results. The more serious destruction caused by high frequency electrical treeing degradation can well explain the reason of insulation premature inactivation in mid-frequency or high-frequency electrical equipment.
A risk based method is proposed to design under voltage load shedding (UVLS) scheme. Different with traditional methods, the proposed one employs a series of risk indices, which are obtained based on a full-scale cont...
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A risk based method is proposed to design under voltage load shedding (UVLS) scheme. Different with traditional methods, the proposed one employs a series of risk indices, which are obtained based on a full-scale contingencies analysis, to determine the operating parameters of load shedding. According to this method, the load bus, in which the UVLS can exert itself with the highest efficiency to prevent voltage collapse, is selected as the first candidate to execute load shedding. And the amount of loads to be shed is identified though a relationship between risk values and shedding amount. The selection of shedding time conforms to the principle that the compound risk brought by failed shedding and unexpected shedding must be the minimum. Experiments conducted for IEEE 39-bus system reveal that the proposed method redound to identify the location, amount and time of load shedding more accurately and reasonably due to taking into account a great deal of uncertain factors.
In order to make up the deficiency of traditional analytical method used in the research of voltage stability problem, we need to know the probability information concerned with voltage instability. Therefore, this pa...
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In order to make up the deficiency of traditional analytical method used in the research of voltage stability problem, we need to know the probability information concerned with voltage instability. Therefore, this paper proposes a method to calculate the probability of voltage instability based on the stochastic characteristic of load margin index. This method firstly determines the stochastic characteristic of load margin index through an analysis about the randomicity of parameters which tie up with the tracing of critical point in continue power flow computation, and then figures out the probability of voltage instability by using moment and cumulate method. Owing to take into account more uncertain factors' influence on the voltage stability, the result acquired by this method is much more accurate and reasonable. A numerical simulation based on IEEE 39-bus system reveals that the proposed method works properly.
The characteristic of the transient response of the grounding system takes on a fast rising and slow damping with the lightning excitation. An improved simultaneous time and frequency domain extrapolation method is pr...
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The characteristic of the transient response of the grounding system takes on a fast rising and slow damping with the lightning excitation. An improved simultaneous time and frequency domain extrapolation method is presented based on Hermite function expansion, which takes the above mentioned characteristic of the transient signal into account, using early time response and low-frequency data, the complete electromagnetic response is generated. By using mutually complementary data, simultaneous extrapolation in time and frequency domains are carried out by using the Hermite polynomials as the basis function. However, the extrapolation method is not suitable to deal with the transient response with the fast pulse excitation. The improvement for the extrapolation method is to pre- and post-process the transient response data with the fast pulse excitation. As a pre-processed procedure, in order to reduce the condition number of the matrix used for determined the coefficient of basis function, the scale transformation is used in time and frequency domain respectively, and the data in time domain is smoothed and padded with zero. An adaptive algorithm to determine the order of Hermite function is also proposed. As a post-processed step, the transient data are smoothed by using GPOF to obtain a convergent result. The numerical example and the field measurement are presented to illustrate the application of this methodology. The method proposed enhances the ability of the simultaneous time and frequency extrapolation techniques.
The indirect boundary element method has some special advantages for the 3D linear magnetostatic field calculation by using the equivalent magnetic surface charge. In order to improve the accuracy of solutions and dec...
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The indirect boundary element method has some special advantages for the 3D linear magnetostatic field calculation by using the equivalent magnetic surface charge. In order to improve the accuracy of solutions and decrease the computational costs, an adaptive Galerkin approach to solve the magnetostatic integral equation is presented by using the h-type refinement technology. The basic idea of the proposed approach can be summarized as follows. The error of magnetic flux density is globally minimized in the Galerkin sense in the implementation, so the continuity error of magnetic flux density of each element can be served as a criterion to guide the adaptive refinement. The singularity of geometric corners and edges can be overcome due to the scheme of the discretization of the integral equation with Galerkin's approach. In addition, a local resolution technology is proposed, which leads to the minimal refined unknown. The numerical examples show the proposed method is efficient and accurate by comparison to the analytical solutions and the measured results.
To research the influence of multi-phase winding to generators and calculate the losses in solid rotors, the stator mint of a 12-phase asynchronous generator have been well analyzed and finite element method by ANSYS ...
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ISBN:
(纸本)7506274078
To research the influence of multi-phase winding to generators and calculate the losses in solid rotors, the stator mint of a 12-phase asynchronous generator have been well analyzed and finite element method by ANSYS software has been applied to get the accurate losses in the rotor through both harmonic and transient 2-D analysis. The relationship between stator harmonic current and stator harmonic mint has been deduced and proved through ANSYS software to some extent, and rotor losses produced by both stator fundamental current and stator total current have also been obtained and compared. The results show that 12-phase stator winding with appropriate short pitch can effectively eliminate or reduce many mmf produced by stator fundamental and harmonic current and rotor losses are mainly produced by stator fundamental current.
Combined with a single circuit UHV power transmission project in one million voltage from Jincheng to Jingzhou via Nanyang which is reasoned by statepower Grid Corp. of China, its switching overvoltages, including th...
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Combined with a single circuit UHV power transmission project in one million voltage from Jincheng to Jingzhou via Nanyang which is reasoned by statepower Grid Corp. of China, its switching overvoltages, including three-phases closing with no load and single-phase auto-reclosing, are considered. The switching overvoltages are calculated with Electromagnetic Transient Program (EMTDC). The calculation shows that the switching overvoltage is too high up to 1.80 pu if only with parallel resistor in circuit breaker or high performance ZnO arrester. Combining arrester and parallel resistor is a good measure to limit switching overvoltage without such high requirement on arrester's or resister's thermal capacity.
The concept of a digital power system (DPS) is set forth in the paper. The definition, the contents, the function, the hardware and the software conditions for implementing it are discussed. Moreover, the necessary ba...
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The concept of a digital power system (DPS) is set forth in the paper. The definition, the contents, the function, the hardware and the software conditions for implementing it are discussed. Moreover, the necessary basic research work for implementing a DPS is also discussed. The DPS may be defined like this: the digital power system is the digital, figuration and real time description and reappearance of physical structure, technical characteristic, management system as well as personal information system of a real power system which is in operation. The DPS will be able to make a significant contribution to administrating and decision-making more scientifically, improving security and stability online, online making and implementing economical operation strategy and carrying out emergency and anti-fault control, etc.
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