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.
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.
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
The phase angle of the utility voltage plays a most important role for the operation of FACTS (flexible AC transmission system) and renewable energy systems, and PLL (phase locked loop) should be accurate, fast and ro...
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The phase angle of the utility voltage plays a most important role for the operation of FACTS (flexible AC transmission system) and renewable energy systems, and PLL (phase locked loop) should be accurate, fast and robust. Operation of a vector-based soft phase locked loop systemunder distorted utility conditions is presented in this paper. An intelligent PI controller is proposed to solve the conflict between tracing speed and filtering characteristics, which is to regulate the parameters of PI controller based on the phase error input. All analytical results are verified by simulations and experiments. The merits of high-speed, robust and strongly restraining ability to distorted voltage make it could be widely used in FACTS and renewable energy controlsystems
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 paper presents the dynamic model of doubly fed induction generator (DFIG) including the mechanical model, the generator model and the PWM voltage source converter model. The mechanical model uses two-mass model, a...
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The paper presents the dynamic model of doubly fed induction generator (DFIG) including the mechanical model, the generator model and the PWM voltage source converter model. The mechanical model uses two-mass model, and the generator model includes both the stator side and the rotor side dynamics. The PWM voltage source converter is modeled as an average model in which the action of power electronic switches is neglected. The paper features vector control of DFIG. On the rotor side converter, the control scheme enables the independent control of speed and reactive power from the stator. On the grid side converter, the control scheme is implemented to regulate the DC voltage and reactive power from the grid as well. In order to study the influence of the grid disturbances on the DFIG, grid voltage dip and quick frequency change are simulated with the engineering software, MATLAB/Simulink. Meanwhile, in the paper the pole-placement method and internal model control method are implemented for designing the PI controllers
Summary form only given. Dielectric barrier discharges in air are generally streamer-like discharges, however, a homogeneous discharge, called atmospheric pressure glow discharge, may be obtained in some noble gases s...
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Summary form only given. Dielectric barrier discharges in air are generally streamer-like discharges, however, a homogeneous discharge, called atmospheric pressure glow discharge, may be obtained in some noble gases such as helium and argon. Dielectric barrier discharges in nitrogen and argon are studied experimentally to determine mechanisms controlling the transition from glow to streamer discharge. The influences of the applied voltage, the gas gap distance, the gas pressure and other factors on the discharge are investigated. The characteristics of the dielectric barrier discharge in nitrogen and argon are analyzed and compared. The aim of the paper is to study the experimental conditions of obtaining an atmospheric pressure glow discharge in nitrogen and argon. The possibility of obtaining an atmospheric pressure glow discharge in air is examined by increasing the proportion of air in nitrogen gradually. The waveforms of the applied voltage and discharge current under different experimental conditions are reported, which is helpful to describe the characteristics of the discharge and judge whether the discharge is a glow discharge or not
In this paper, the influence of mobile signal in UHF PD monitoring is discussed in types of substation in China. To find the solving, the GSM mobile signal's spectrum are measured and analyzed both in laboratory a...
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In this paper, the influence of mobile signal in UHF PD monitoring is discussed in types of substation in China. To find the solving, the GSM mobile signal's spectrum are measured and analyzed both in laboratory and onsite. The results show that the mobile signal's spectrum is broad when the phone signal is emitted. It is hard to avoid this interfere only by using narrow measuring band. At the same time, the GSM mobile signal's transmission characteristic in GIS was simulated in our model underlaboratory conditions. In brief, our findings are discussed through two projects. The results show our finding is available and effective
作者:
XuBiHuangYangSi Fang Research Institute
Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control Ministry of Education North China Electric Power University Beijing China
Protective relays, pivotal devices that can quickly identify and isolate fault area in powersystems, is of great importance for power network security and reliability. When relays trip a faulted line in the network, ...
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Protective relays, pivotal devices that can quickly identify and isolate fault area in powersystems, is of great importance for power network security and reliability. When relays trip a faulted line in the network, 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. Studies on several well-known blackouts reveal that protective relays are involved and the most troublesome ones are backup protective relays. In this paper the defects of the existing backup protections are investigated in detail first. Then a new wide area backup protection scheme based on WAMS to identify flow transferring is presented. 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 on-line is also stated. The simulation of a three machines network shows that the wide-area backup protection scheme to identify flow transferring works well
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