To achieve a fast approach to the dynamic reactive power optimization model, a mixed integer nonlinear programming model was set up, with consideration of the discrete reactive power equipment operation limit and powe...
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Low voltage distribution network usually operates under three-phase unbalanced conditions. And the distributed generators (DGs), integrated with distribution network, show different behaviors under different control s...
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Impedance method and single terminal travelling wave method are analyzed in paper, applicable scope of optimized solution is presented. Impedance method is of high robustness but low accuracy. Single terminal travelli...
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Impedance method and single terminal travelling wave method are analyzed in paper, applicable scope of optimized solution is presented. Impedance method is of high robustness but low accuracy. Single terminal travelling wave method offers high accuracy but poor robustness. Optimized solution combines these two methods together, takes advantages of both methods. It is a great enhancement to single terminal fault location. This paper analyzed theoretical basis of optimized solution, proposed the calculation algorithm of fault location range using impedance method. Analyses of impedance method and single terminal travelling wave method show that the optimized solution is suitable for engineering application. Error analysis is proved correct by simulation.
With the trend of electricity market deregulation for recent decades, the consumers at demand-side are progressively encouraged to trade the power in competitive market environment. Conventionally, only large-scale co...
With the trend of electricity market deregulation for recent decades, the consumers at demand-side are progressively encouraged to trade the power in competitive market environment. Conventionally, only large-scale consumers participate directly in the wholesale market that adopts spot energy pricing. Most small-scale consumers are involved in the retail market that offers non-varying tariff predefined by retailers or utility companies. In this work, we investigate a framework of coordinated wholesale and retail market structure that enables consumers in the retail market to reflect the spot price and improve the power system flexibility for the high penetration of renewables. Then, market behaviors of demand-side participants with the proposed market mechanism and some related business models are discussed. The following participation modes for consumers could be opted including: direct trade, trade agented by retailers or organized in virtual power plant (VPP). For a pool-based trade at demand-side, a bi-level market clearing mechanism at transmission and distribution levels is explained. This mechanism seeks to optimize the global demand profile for hosting renewables while solving the operating constraint of loads and local networks. This study can offer constructive advises to promote further development of China's electricity market.
Shielding failure of lightning is the key problem for safe operation of transmission lines. Compare to Electro-geometry Method, Leader Progress Method more suitable for lightning protection analysis because the physic...
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Shielding failure of lightning is the key problem for safe operation of transmission lines. Compare to Electro-geometry Method, Leader Progress Method more suitable for lightning protection analysis because the physical model is used instead of empirical formula. The relationship between amplitude of lightning current and other parameters, such as wires position, ground tilt angle, was analyzed.
Electrical tree break-down is the major failure problem in cable accessories, however, mechanisms of the electrical tree initiation and propagation are still lack of deeply research, especially in silicone rubber (SIR...
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Electrical tree break-down is the major failure problem in cable accessories, however, mechanisms of the electrical tree initiation and propagation are still lack of deeply research, especially in silicone rubber (SIR) which is widely used as insulation material for cable accessories. Long-term aging (0- 1000 h) experiments under the different voltages were conducted to observe electrical tree initiation and propagation processes. In trees initiation stage, with increasing of applied voltage, electrical tree initiation probability becomes larger, while tree initiation time dramatically decreases. The experiment observations demonstrated four shapes of trees which are dominated. As applied voltage increasing, the numbers of electrical trees life-cycles increased and exponential relationship was found between tree length and magnitude of applied voltage. It is noted that charges, whose energy exceeding a certain critical value, destroy microstructure of dielectric accumulatively via injection and extraction, and cause electrical trees initiate when it accumulates to a visible extent.
Fault locator for power distribution system with neutral non-effectively grounded should locate phase-to-phase fault and single-phase-to-ground fault respectively. For phase-to-phase fault, the point can be located by...
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Fault locator for power distribution system with neutral non-effectively grounded should locate phase-to-phase fault and single-phase-to-ground fault respectively. For phase-to-phase fault, the point can be located by power-frequency impedance. However, for single-phase-to-ground fault with limited power-frequency current not more than load current, a novel fault location technology should be developed. The paper will present a practical single-phase-to-ground fault location based on fault generated traveling waves acquired from one phase current transducer and zero sequence current transducer at first. Then implementation of the novel fault locator is proposed including hardware design and software flowchart. At last field tests will be made to verify the feasibility of the fault locator.
This paper analyzes the general process of power flow transferring and divides it into four parts: 1) the process of first phase selection after fault occurs; 2) the process of selective action at the first time; 3) t...
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This paper analyzes the general process of power flow transferring and divides it into four parts: 1) the process of first phase selection after fault occurs; 2) the process of selective action at the first time; 3) the process of second phase selection and status confirmation; 4) the process after status confirmation. It points out that the issue of asymmetrical flow transferring is a critical process which must be put emphasis on. Then it proposes a method to identify this process, and discuss different solution methods.
LCL filter can improve the output current of the shunt active power filter. The paper proposes a resonant LCL filter structure with a LC high-frequency filter branches adding to LCL filter with damping resistor. By LC...
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LCL filter can improve the output current of the shunt active power filter. The paper proposes a resonant LCL filter structure with a LC high-frequency filter branches adding to LCL filter with damping resistor. By LC resonance effect, the switching frequency harmonics are filtered more efficiently and the loss of the system is reduced. The paper also builds the system modeling and analyzes the stability of the grid filter with the deadbeat control, then gives parameter selection methods and simulates with PSCAD/EMTDC. All these are verified through the experiments on a 70-KW shunt APF prototype using deadbeat controller.
High impedance faults (HIFs) are easy to occur in collective feeders in wind farms and may cause the cascading of wind generators tripping. This kind of faults is difficult to be detected by traditional relay or fuse ...
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High impedance faults (HIFs) are easy to occur in collective feeders in wind farms and may cause the cascading of wind generators tripping. This kind of faults is difficult to be detected by traditional relay or fuse due to the limited fault current values and the situation is worse in wind farms. The mostly adopted HIF detection algorithms are based on the 3rd harmonic characteristic of the fault zero-sequence currents, whereas these 3rd harmonics are very easy to be polluted by wind power back-to-back converters. To solve this problem, the typical HIF arc flash based on Mayr's arc model is first built, and the typical fault waveforms of HIF in wind farm are presented. Then the characteristics of high impedance faults are analysed to distinguish the occurrence of HIF from other harmonic interference. After that, the performance of the traditional harmonic based HIF detection algorithm is discussed, and a novel detection algorithm is presented to prevent harmonic interference influence in wind farms.
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