In order to keep the power factor at a high level and maintain acceptable voltage quality in distribution systems, a novel dynamic reactive compensation equipment is proposed. This equipment, which consists of a speci...
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ISBN:
(纸本)0863412467
In order to keep the power factor at a high level and maintain acceptable voltage quality in distribution systems, a novel dynamic reactive compensation equipment is proposed. This equipment, which consists of a special regulating autotransformer with a vacuum on-load tap-changer and an intelligent power factor controller (IPFC), adopts step-voltage- regulating control method. It bases on the principle of the capacitor bank's output is in direct ratio with the square of the voltage works on it. In the course of tap- changer switching, the capacitor bank is not cut-out from the powersystem all along, it is proved in theory that dangerous over-voltage and associated inrush current will not occur. Thus security of the operation on capacitor bank is improved greatly and its natural life will increase much too. Compared with any other dynamic reactive compensation this novel equipment is less expensive and would be more likely to be put to be practical use. In the end, experimental results are given to verify that the proposed equipment has good characteristic of dynamic reactive compensation.
Induction-motors are the main component of the compositive load especially of the industry load and air- condition loads have been uppermost dynamic load in summer with the fast economy development, which are very imp...
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Induction-motors are the main component of the compositive load especially of the industry load and air- condition loads have been uppermost dynamic load in summer with the fast economy development, which are very important to analysis and controlpowersystem. So induction-motors and air-condition loads are studied seriously as dynamic loads in this paper. This paper studies the function mechanism and the influence of static and dynamic load characteristic on voltage stability by comparing the voltage stability simulation result of different loads based on a simple case of powersystem. The small disturbance analysis method is used and static load, induction-load and air-condition load are modelled in this paper. It is proved that powersystem get more and more voltage instability with induction-motor or air-condition load increasing, especially air-condition load.
Both static and dynamic electric load characteristics have considerable effect on short circuit ratio (SCR) or effective short circuit ratio (ESCR). This paper gives emphasis on the relationship between static/dynamic...
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Both static and dynamic electric load characteristics have considerable effect on short circuit ratio (SCR) or effective short circuit ratio (ESCR). This paper gives emphasis on the relationship between static/dynamic load characteristics and SCR (ESCR). Different power level with different power factor is considered for the impacts on SCR or ESCR of static load characteristics. Three-phase short-circuit current of induction motors is qualitative analyzed and simulation of the feeding current is carried out for the dynamic process of induction motor in the consideration of dynamic load characteristics. Case studies are carried out on WEPRI-36 system and Hunan power grid. Simulation results with powersystem analysis software package (PSASP) illustrates that load should be considered in calculating SCR.
Secondary voltage controlsystem is a significant segment of the hierarchical voltage control in powersystems. Though voltage controller has both constant voltage regulators, such as generators and static reactive po...
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Secondary voltage controlsystem is a significant segment of the hierarchical voltage control in powersystems. Though voltage controller has both constant voltage regulators, such as generators and static reactive power compensators, and discrete voltage regulators, such as OLTC and shunt capacitors/reactors, traditional secondary voltage control (SVC) only consider constant voltage regulators. A few of the papers consider discrete voltage regulators, but they are also treated as constant variable. In this paper, Considering the trait of continuous and discrete devices in secondary voltage control co-existing, a mixed secondary voltage control optimal model including continuous and discrete variables is established. The solution is gained by multi-agent particle swarm optimization algorithm. This method concerned with the advantages of multi-agent system and particle swarm optimization algorithm can get every setting value of regulator exactly and quickly. The proposed method is applied to the New England 39 nodes system. It is shown that by contrast to the traditional secondary voltage control, this method can achieve satisfactory controlling effort involved both constant and discrete controllers at the same time.
When relays trip a faulted line in powersystem, the flow on the faulted line will be transferred to the other lines. Those lines might be overloaded and then cascading tripped by the backup relays, which worsen the s...
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When relays trip a faulted line in powersystem, the flow on the faulted line will be transferred to the other lines. Those lines might be overloaded and then cascading tripped by the backup relays, which worsen the system state and even cause blackout. Generally, these kind of cascading trips are the origins of a lot of well-known blackouts. In this paper, by analyzing the defects of traditional backup protections, a new wide area backup protection scheme based on WAMS is presented to identify flow transferring. A new concept of flow transferring relativity factor (FTRF) is proposed to estimate the flow distribution after flow transferring occurs; and the method of calculating FTRF matrix online is also deduced. The simulation of 10-unit and 39-bus New England network shows that the proposed wide area backup protection scheme can identify flow transferring successfully and hence be superior to the traditional backup protection.
In substations, shielded cables are widely used to reduce transient electromagnetic interference to the relay and control equipments due to the switch operation. Both the transfer impedance and transfer admittance are...
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In substations, shielded cables are widely used to reduce transient electromagnetic interference to the relay and control equipments due to the switch operation. Both the transfer impedance and transfer admittance are quantities for expressing numerically the mechanism that allows the passage of electromagnetic energy across the cable shield. Theoretical models to compute both the quantities often rely on simplifying assumptions. This, together with the fact that the transfer impedance and admittance can vary considerably between cable samples of the same type, means that measurements become necessary. In this paper, based on the transmission line theory we present a simple method to measure the transfer impedance and admittance of shielded cable in magnitude as well as in phase over the frequency range (0.1 MHz-10 MHz) which covers the main interference frequencies in powersystem. To illustrate this method a coaxial cable with a braided shield has been measured and compared with the existing method. As an application, the proposed method is used to predict the induced voltage and current on the shielded cable due to the switch operation in substation
The power line tower lightning surge impedance is computed using an electromagnetic field approach. After comparing the results computed by our method and those tested with both a vertical conductor and reduced scale ...
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The power line tower lightning surge impedance is computed using an electromagnetic field approach. After comparing the results computed by our method and those tested with both a vertical conductor and reduced scale 4-poles model of tower, the method we used is proved to be right and more practical as the soil and the grounding system of the tower can be considered in the method. Using this method, the lightning surge impedance of the full scale UHV tower with grounding system is analyzed and the results show that the lightning surge impedance of a tower on the perfect ground has a little difference with those of an actual tower considering both its grounding system and soil resistivity, and when the soil resistivity is changed, the surge impedance changes slightly. Furthermore, a circuit model of the tower is obtained by vector fitting method based on the results we computed. Using the circuit model, the lightning surge performance of a power transmission line can be analyzed more accurately by EMTP or other methods
In load forecasting of a bulk powersystem, the geographical scope of forecasting region is large, the main electrical load effecting factors in sub districts are different greatly. So it is very significance to estab...
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In load forecasting of a bulk powersystem, the geographical scope of forecasting region is large, the main electrical load effecting factors in sub districts are different greatly. So it is very significance to establish different load forecasting model according to self-feature of each sub district of a large area, by which the forecasting load is closer to the fact load than establishing one model in whole to forecast electrical load. This paper presents a grid model in terms of geographical division for short-term load forecasting in a bulk powersystem. The subset model in each geographical grid, considering its own historical loads and meteorological conditions, is more effective and could lead to more accurate results. Therefore, every subnet model is established based on the mining default rules on rough sets (MDRBR) algorithm. First, the MDRBR algorithm is discussed, and the constructing process of the multi-layered rule-network of daily load forecasting is then analyzed in detail. Furthermore, the whole process of load forecasting based on the MDRBR algorithm is presented. Finally, an example using actual historical data shows that the grid forecasting model can yield high accurate results, reduce noises effectively, and is efficient in computation and rule searching
The black start restoration of a powersystem after a complete blackout is a very important issue to safety of the powersystem. The reasonable network reconfiguration strategy is necessary for establishing the main n...
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The black start restoration of a powersystem after a complete blackout is a very important issue to safety of the powersystem. The reasonable network reconfiguration strategy is necessary for establishing the main network and restoring loads as soon as possible. A skeleton-network reconfiguration strategy is proposed in this paper. Through determining the skeleton network, the burden of network reconfiguration can be reduced effectively. The reconstructing processes are evaluated by a comprehensive index of network reconfiguration efficiency. Furthermore, discrete particle-swarm optimization is employed in reconstructing network skeleton and several relatively-optimal schemes can be obtained as the guidance of the system restoration. Application to the IEEE 30-bus powersystem shows that reconfiguration schemes derived from the strategy are effective under uncertain system situations and ensure that the following restoration be successful
Conventional HVDC has the advantages of mature state of art and lower cost and the disadvantages of absorbing large reactive power and the danger of commutation fault. Voltage source converter (VSC) based HVDC (VSC-HV...
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Conventional HVDC has the advantages of mature state of art and lower cost and the disadvantages of absorbing large reactive power and the danger of commutation fault. Voltage source converter (VSC) based HVDC (VSC-HVDC) has the advantages of flexible operation and control and the disadvantages of high cost. Combining the advantages of the two kinds of transmissions, a novel hybrid HVDC transmission type is analyzed in this paper, which the sending terminal adopts phase control converter (PCC) and the receiving terminal adopts VSC. The hybrid HVDC system can supply to passive network, supply reactive power to AC system and expediently extend to two bi-terminal or multi-terminal systems from conventional HVDC system. The expressions of voltage, current and power in rectifier and inverter sides are deduced. The relationship between the operational variables and control variables is analyzed. The basic regulation characteristics are gotten. The simulation model is founded based on the simulation software PSCAD/EMTDC. Simulation results show that the hybrid HVDC system could be operated steadily when the system active power changes slowly and quickly. It has the application prospect in scope of long distance small load supplying, multi-terminal DC system connection and system black-start etc.
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