This paper introduces a new arrester protection scheme for ±800 kV UHVDC converter station by considering both reliability and economy. In the new scheme, M2 arresters are proposed to use at the DC side of converter station and M2 and V3 arresters are suggested to install in series to replace the A2 arresters. Smooth reactors are suggested to install equally on pole bus and 400 kV DC bus and CB1B and E1H arresters be abandoned. By comparing the typical scheme and the economical scheme for ±800 kV UHVDC converter station, the reason why the economical scheme can optimize the economical efficiency is analyzed. The arrester parameters are selected according to the selection principle of the arrester DC reference voltage. The new arrester protection scheme and its parameters have played some guiding roles in ±800 kV UHVDC transmission projects.
Air-cooled condensers (ACCs) of direct air-cooled plant with unit capacity of 1 000 MW have huge size and more cells, and the inhomogeneity of system performance in space distribution by ambient wind is obvious. The optimization of the structure and layout can provide feasible technical approach for 1 000 MW ACCs to replay to ambient wind. On the basis of 2×1 000 MW direct air-cooled units, this paper constructed physical and mathematical models with considering the coupling effect of ambient wind and air flow from unit fans, and presented the three-dimensional distribution of flow and temperature fields by using numerical simulation method. Then the variation mechanism of the cooling ventilation flow rate and heat transfer performance of ACCs with wind speed and distance between ACCs and the main buildings was explained, especially for the wind from boiler house which was most unfavorable. The results show that the heat thermo-flow performance of ACCs is decreased with the increase of the wind speed. With the increase of wind speed, the heat capacity decreases more rapidly when the distance between ACCs and the main buildings increases. When the wind speed is over 6 m/s, the exhaust plume recirculation flow ratio increases with the distance increases; the heat transfer performance of 15 m is better than other more lager distance. Therefore it’s benefit to resist adverse effect by strong wind with tight air-cooled plant layout at high wind speed.
Energy storage system (ESS) has the advantages of fast absorption and release electricity, which can compensate for the shortcomings of renewable energy fluctuation. So, ESS has been widely used as a spinning reserve. This paper established a bi-level optimization model for the optimal supply of power producer with considering ESS, in which the upper level considered the interests of the diesel generation, and the lower level was to maximum the interests of energy services provider (ESP). According to the unsmooth characteristic of the lower-level optimization model, the method of smoothing processing was applied. In order to solve the model, the bi-level optimization was transformed into a single-level optimization by Karush-Kuhn-Tucker (KKT) conditions, and the nonlinear constraints were transformed into the linear constrains by using nonlinear complementary slackness conditions. Finally, numerical experiments show the effectiveness of the proposed model and algorithm.
The consistent and active control strategy was proposed for optimally controlling the distributed energy storage devices. Each control objectives only needed to interact with the neighboring target, and it could achieve the goal of global optimal consistency control without global information. The consistent and active control strategy could make the system energy storage device in the same proportion of discharge state to meet the requirements of practical application, which was based on the monitoring of the Leader node and combined with the interaction between local energy storage devices. The efficiency and feasibility of the consistent and active control algorithm for distributed energy storage system in distribution network were demonstrated by the example results of IEEE3 and IEEE32 bus systems.
The influence of the indeterminacy of intermittent new energy on power system should be considered in wind-solar-battery hybrid power system. Based on this, the stochastic scheduling model of energy storing device and thermal power station was developed with considering wind/photovoltaic power’s indeterminacy and load’s stochasitic. The constraint condition of energy storing device’s charge-discharge was considered in the model. Assuming that the wind speed followed the Weibull distribution and the solar irradiance followed the Beta distribution, the average variance expression of equivalent load in wind-solar-battery hybrid power system was derived, which was used as objective function to build the stochastic optimization dispatching model of energy storing device, and measure the fluctuation inhibition ability of thermal power. The double chains quantum genetic algorithm was employed to solve this optimization problem. Finally, the efficiency and feasibility of the model were demonstrated by IEEE30 bus system.
Aiming at the shortcomings of the traditional fault diagnosis method for transformer, this paper introduced the applications of several intelligent methods in the fault diagnosis of power transformer based on dissolved gas-in-oil analysis (DGA), including the artificial neural network, the fuzzy theory, the expert system, the grey relational analysis and other intelligent methods. This paper analyzed these intelligent diagnosis methods and obtained the relative merits and improved solutions, which could provide a reference for the researchers to choose the optimal fault diagnosis method of oil-immersed power transformer. At last, the DGA-based intelligent fault diagnosis method for transformer was discussed, and its future development direction was analyzed.
Most of southwest mountainous areas are underlying bedrock ground cover layer, and the terrain is steep. In the transmission line engineering, the influence of the site stability under seismic action on the safety of upper tower structure is obvious. At present, there are some researches on the influence of different site conditions on seismic effect, but there are few researches for the southwest steep terrain, especially for the influence of the bedrock strength in the rock sites on the seismic effect of the site. Taking a typical transmission line site in southwestern mountainous area as research object, with using numerical analysis software FLAC3D and time history analysis method, this paper analyzed the seismic peak acceleration amplification coefficient on site, the variation characteristics of the permanent displacement on site along with the cover thickness and bedrock strength, and discussed the seismic effect of different site conditions in southwest mountainous area. The results show that: with the increase of cover thickness, the peak acceleration amplification coefficient gradually decreases, and the permanent displacement gradually increases; with the increase of bedrock strength, the vertical peak acceleration amplification coefficient gradually increases, and the horizontal peak acceleration amplification coefficient and the permanent displacement gradually decrease.
With the development of power system communication automation, various kinds of information collection systems have been widely used, which is beneficial to analyze the spatial-temporal characteristics of power grid faults. Taking 500 kV transmission network in H province as example, this paper researched the long-time behavior characteristics of 500 kV transmission line faults in recent 5 years. Firstly, on the time series level of transmission line fault, statistical analysis was carried out on the interrelation between fault timing (unit: day) and fault cumulative frequency and probability under same time point. Kolmogorov-Smirnov (K-S) method was adopted to testify the normality of the distribution, and Hurst exponent based on time series of 500 kV transmission network in H province during 5 years was calculated according to R/S time series analysis. Thereby the long-term correlation under time series was estimated. Then, on the level of space, statistical analysis was carried out on the interrelation between fault times of each 500 kV transmission line in H province during 5 years and its fault cumulative frequency and probability, and it was proved that transmission line faults coincided with power-law distribution characteristic. The research on the spatial-temporal distribution characteristics can provide the basis of assistant decision for the risk management and prediction of power system.
IEEE gives deeper research on the resonance mechanism and impact factors of passive interference resonance (PIR) for transmission lines at medium-wave frequency. However, the resonance phenomenon existing at short-wave frequency (SF) can’t be explained by above research conclusions. In order to research the decisive impact factors of PIR for transmission lines at SF, the possible impact factors of interference resonance, such as tower spans, tower number, conductor, grounding wire and other single macro structure were considered, and the passive interference level in the electromagnetic open system composed of transmission line and antenna was studied. Grey system theory and correlation analysis were introduced to calculate the sensitivity of impact factors to interference change, and the correlation degree of various macro structure and interference was obtained. The results show that the decisive impact factor of PIR at SF is tower spans, which can be adjusted to evade the resonance frequencies at line design stage.
In the light of the problem that chronological load model could not be directly used in reactive power optimization, a new load modeling method was proposed based on the pivotal quantity. Because the multiple random parameters in distribution network were in parallel, a temporal and spatial decoupling scenario partition strategy was proposed based on the Bayes formula, and then the multi-objective reactive power optimization model was established with multiple random parameters for distribution network. At last, the improved IEEE33 standard node test system was used to verify the effectiveness of the proposed model, and the results proved that this method was efficient and flexible.
With the continuous expansion of power grids, the limit-exceeding problems of short-circuit current has become one of the prominent factors restricting the growth and development of power grid load. The traditional limiting measures have been difficult to meet the development of modern power system. Along with the rapid development of superconducting material, the fast and effective current limiting devices—superconducting fault current limiter has emerged as the times require. Due to the outstanding performance, the saturated iron-core superconducting fault current limiter (SICSFCL) has been applied in transmission lines and distribution systems. Considering the actual structure of SICSFCL, a new equivalent magnetic circuit method was proposed, which could accurately and effectively analyze the transient characteristics of the current limiter. The equivalent magnetic circuit method is important for the theoretical analysis on SICSFCL and its actual application.
This paper presented a novel design of insulator detecting robot for EHV/UHV transmission line. With the features of compact in size, easy operation and applicability for the zero value detecting of insulator string, the proposed robot had efficient walking and detection methods. Maintenance personnel only needed to cooperate with the detection procedures of the robot, and placed the robot on the insulator that needed to be overhauled. Then the robot would automatically detect one by one, and immediately triggered intelligent insulator detection unit, calculated the resistance value of each insulator. Software simulation and hardware experiment show that this insulator detecting robot can achieve intelligent security detection, which has important social and economic benefits for ensuring the safe and stable operation of power system.
According to the GIS, materials, craft structures and processing characteristics of UHV primary equipment, ultrasonic testing method based on time of flight diffraction (TOFD) was presented for the weld detection of primary equipment. Firstly, the adaptability and parameters selection principle of TOFD ultrasonic testing method were analysed from aspects of equipment material, base metal thickness, etc. Then, two briquettes with different thickness: aluminium alloy and carbon steel, were used for experimental verification. The results show that the welds of aluminium alloy and carbon steel with thickness of about 6 mm and 10 mm above can be detected by high frequency probe with using TOFD method, which can clearly and accurately determine the size, nature, height of defect.
Single simulation software was difficult for complex power system containing traditional elements, new element and complex control system, so the interface technology of co-simulation of Matlab/SimPowerSystems and power system analysis software package (PSASP) was proposed. This paper used multi-port equivalent circuit to study the interface of software models, and called the Matlab engine API function to implement the co-simulation between these two simulation programs, through the user program interface (UPI) of PSASP. Through controlling the co-simulation process, the simulation with finer step was carried out in Matlab/SimPowerSystems to realize the simulation with mixed-step. Finally, PV simulation example was built to prove the feasibility and correctness of the co-simulation method, which could provide a new approach for the transient stability calculation after new components and the control devices of power system connected into large-scale systems.
Distributed power system is widely used in electric vehicle, industrial control, communication industry, etc. Connecting converters in cascade is a typical configuration in distributed power system. Because of the interaction between individually design converters, the cascaded converter system may be unstable. The present studies focuses on the stability criterion, impedance measurement, and design of voltage-voltage type cascaded converter system. This paper systematically studied the small signal models for different types of cascaded converter systems, and then obtained the stability criteria. Firstly, the two-port small signal models for the voltage type and current type converters were established. And then, according to the types of source converter and load converter in the cascaded converters, the cascaded converter systems could be divided into four types as follows: voltage-voltage type, voltage-current type, current-voltage type, current-current type, whose small signal models were discussed and stability criteria were deduced individually. Finally, taking the voltage-voltage type cascaded converter system as example, the correction of the established small signal model were verified, through the comparison and analysis on the simulation and theoretical calculation results.
Based on the analysis on power generation technologies related to microgrid, this paper established a multi-objective optimization model, aiming at minimizing the generation cost, pollutant emission cost, the compensation cost of load shedding and microgrid network loss, and used super efficiency data packet analysis evaluation methods to transform multi-objective optimization problem into a single-objective programming one. The traditional bat group easily gathered in local minima, which would lead to premature. So the chaotic sequence and adaptive adjustment strategy were applied into bat optimization algorithm, and a improved multi-objective bat optimization algorithm was proposed, in which the characteristics of chaos theory and dynamic adaptive adjustment mechanism were used to adjust the parameters of the bat algorithm, in order to overcome the defect that the algorithm itself was lack of variation mechanism. Finally, the good practicability and adaptability of proposed algorithm were verified through numerical example, as well as the practical significance of the proposed model.
To reduce the emissions of SO2 from the circulating fluidized bed (CFB) boiler to meet the increasingly stringent emission standards, this paper focused on the two-stage desulfurization system including the limestone desulfurization in the furnace of CFB boiler and the wet limestone-gypsum flue gas desulfurization (FGD). Relying on the investment equipment and operating costs in a 300 MW CFB unit with two-stage desulfurization system, this paper analyzed the impact of SO2 emission limits, sulfur content in coal, unit load, initial investment in desulfurization equipment and annual effective performance time on the economy of CFB-FGD two-stage intensified desulfurization system, finally obtained a reasonable scheme of desulfurization share.
Based on the transmission system model and submarine cable parameters of offshore wind farm, the reactive power compensation configuration mode of offshore wind farm and the calculation method of submarine cable loss were analyzed. A simplified model of offshore wind power transmission system was established; and the output cable loss under two different compensation schemes: both ends compensation and single-end compensation on land, were calculated for offshore wind farms with different scales and transmission distances; the power loss-wind farm output curves of submarine cable were obtained. Both ends compensation will have a lower cable power loss when the wind farm is in the low output level or with long distance transmission, while single-end compensation will have a little lower cable power loss when the wind farm is in the high output level or with short distance transmission.
Weather observation data of North China from 1973 to 2012 were investigated to analyze long term variation trend of haze related meteorological conditions which arised the frequency of pollution flashover on power system. The Mann-Kendall test was utilized to estimate a more flexible heating policy and reduce the frequency of pollution flashover on power system by analyzing the variation trends and mutation points of haze. It is uncovered that the escalated surface temperature in winter leads to the reduction in heating days and heating degree days (HDD) and the associated reduction in heating demand and the air pollution under the context of climate change. Traditionally, a fixed 120 heating days has been carried out in Shijiazhuang area all the time, however, the actual heating days and HDD calculated by the method of five days moving average put a reduction when compared to the fixed one. Therefore, for Shijiazhuang, the cancel of the traditional fixed heating first day, last day and the implementation of a flexible heating policy can have a notable reduction in heating demand and air pollution as well as a reduction in the pollution flashover on power system caused by heating haze.
To ensure the security and stability of the Gezhouba Power Plant, improve the utilization rate of water and increase power generation benefit, it plans to renovate and uprate 19 sets of 125 MW units including 14 sets in Gezhouba Dajiang Hydropower Plant and 5 sets in Gezhouba Erjiang Hydropower Plant. Base on the operation during peak-load flow period of Hubei power grid in 2015, this paper constructed the network structure model for Hubei Power Grid, calculated the power flow and stability of grid after the renovating and uprating of Gezhouba Hydropower Plant, and checked related mechanical and electrical parameters, with using BPA power system analysis program. The simulation results show that, after the renovating and uprating of Gezhouba Hydropower Plant, the transmission capacity of near-zone 500 kV power grid and the power supply of 220 kV power grid are unaffected and without system stability problem; the related mechanical and electrical parameters are reasonable and meet the system requirements.
Based on the principle of Bass model， a new model was established for the diffusion effects of the government investment, cost on supercritical units and ultra supercritical unit, with considering the the competition of supercritical units and ultra supercritical units . Research shows that ：（1） compared to the affect of government invest, the cost of supercritical units and ultra supercritical units has less effect to their diffusion trend; (2)in 1.5 times and 2 times of the current investment situation, under the different Q value, the supercritical units eventually installed capacity are about 494.585, 558.39, 622.20 GW and 434, 518, 602 GW while the ultra supercritical units eventually installed capacity are about 905.42, 841.61, 777.81 GW and 966, 882, 798 GW; (3)around 2025 supercritical units and ultra supercritical units will both complete the diffusion process.
The Mid & Low-voltage distribution network is an important part of power system, whose loss is around 50% of the power grid loss. Therefore, the benefit sharing energy management contract mechanism was introduced, and a distribution network optimization model for energy conservation and loss reduction was established. Energy saving optimization measures were replacing the high-efficiency transformer, adding 10 kV line reactive power compensation, changing the distribution network line wire, etc. In combination with the calculation of the present situation of a region distribution network operation, it is proved that the low-carbon optimization mode of distribution network based on energy management contract can reduce network loss effectively, improve power quality and reliability, and has good energy saving benefit, which is suitable for a wide range of promotion.
