Compressed air foams (CAFs) system has proved to be highly effective to generate uniform and highly stable foam, showed a great potential application in ultra-high voltage (UHV) substation. But the key parameters of the system are not focused deeply. In this paper, an experimental platform was established to study the effect of system parameters of CAFs on foam jet capability, including the nozzle aperture, flowrate, liquid–gas ratio, jet angle, and ambient wind speed. Also, fire extinguishing performance of the CAFs was evaluated after parameter optimization. The results show that there is an optimal nozzle aperture range, and the foam jet distance can be increased by increasing the flowrate, liquid–gas ratio, and angle. The offset degree of foam jet path increases with the increase of wind speed. The methods to improve the wind resistance of foam include increasing the nozzle aperture, decreasing the flowrate, and changing the jet angle. The CAFs have a high performance of extinguishing transformer oil fire, but it gradually decreases with the increase of fire source position under ambient wind. This paper can provide guidance for the design of CAFs system used in UHV substation.

Compressed air foam (CAF) system has been proposed as an excellent method for fighting liquid fuel fires, where the foam flow rate is the critical factor in determining the efficiency. However, the existing research of the effect of foam flow rate on CAF system limited to extinguishing time, while ignoring the detailed quantitative study on some characteristic parameters during the extinguishing process, particularly the flame height. Aiming at investigating the influence of foam flow rate on these parameters, a series of CAF extinguishing tests were carried out in the range of different foam flow rates from 10 to 80 L/h. Results indicate that with an increase in the gas-liquid ratio, the extinguishing time for AFFF, FP, and S initially decreases by 69.9 %, 47.1 %, and 59.0 %, respectively. This reduction continues until reaching a minimum at a gas-liquid ratio of 10:1. When foam is released onto the fuel surface at a low flow rate of 10 L/h, flame height increases rapidly by approximately 50 to 100 mm caused by air entrainment, whereas at a higher flow rate of 45 L/h, this parameter decreases quickly over time. Further, the extinguishing time decreases gradually with increasing foam flow rate, dropping from over 100 s to around 30 s in the range of 10 to 80 L/h. Based on experimental data of this study, the extinguishing time model on foam flow rate has been developed for typical foam of AFFF, FP and S. The findings of this study provide valuable insights for optimizing the effective utilization of the CAF system.

Organic fireproof plugging material (OFPM) is commonly applied in buildings to prevent the spread of smoke and flame. Its pyrolysis characteristics, reaction mechanisms and gas emission were studied by thermogravimetric analysis coupled with Fourier infrared spectroscopy and mass spectrometry (TG-FTIR-MS). The thermogravimetric analysis showed that the pyrolysis process of OFPM in nitrogen might be divided into four stages, which could be attributed to the dehydrogenation of polychloroprene (PCP), depolymerization of PCP and decomposition of kaolinite and carbonate. The reaction mechanism of OFPM in nitrogen atmosphere was further investigated by various kinetic methods. The average activation energy of the four stages was 92.47, 166.47, 239.69 and 232.72 kJ mol −1 . In addition, ( g(a) = [1−(1– a ) −3 ]/ (−3)) was responsible for Stage I, and ( g(a) = [−ln(1– a )] 2 ) was responsible for Stage IV. The characteristic parameters and kinetic triplets were verified by predicting the experimental data at an extra heating rate. The predicted conversion rate curve was consistent with the experimental conversion rate curve, which manifested the accuracy of the obtained parameters. In addition, the evolved gas consisted of ethane, HCl, 1, 3-butadiene, 2-chloro-1, 3-butadiene and CO 2 by the FTIR-MS analysis. Eventually, the pyrolysis pathway was proposed based upon thermogravimetric and gas analysis results.

The ITIC curve standard evaluates the impact of voltage sag by counting the voltage sag characteristic distribution on the receiving side of low voltage sensitive devices. However, direct use of medium and high voltage sag data for power quality on-line monitoring may result in large evaluation errors. To solve these problems, this paper presents an on-line monitoring system ITIC curve sag severity assessment method to improve the accuracy of voltage sag severity assessment in the absence of low voltage side voltage data. Firstly, the transient transfer between power grid side and equipment side is analyzed according to the sequence component transfer characteristics of transformer. Secondly, the recording data is processed by DFT to obtain the voltage sag data of the equipment side. Then the ITIC curve is used to evaluate the voltage sag severity of the low-voltage side equipment and the state after the voltage sag of the equipment. Finally, the validity of the method is verified by the measured data.

油中溶解气体分析是变压器状态检测最为常见且可靠的方法,油气分离技术则是溶解气体分析中重要的一环.在油气分离技术中,渗透膜是一种较为新颖且颇具前途的分离技术.相较于传统的油气分离方法,渗透膜技术具有结构简单、体积较小、免于维护等优点,因此该方法是油中溶解气体分析研究的热点之一.该文首先对近年来应用于油气分离的高分子渗透膜材料及其结构进行了综述;然后,结合现有研究对几种常见的不同类型的高分子渗透膜进行归纳、总结和对比;最后,在总结当前研究的基础上,提出并讨论高分子渗透膜在变压器油中溶解气体分析领域中未来的发展方向.

研究直流接地极周边交流系统变压器偏磁直流分布特征及其影响因素能够为治理变压器直流偏磁提供理论依据.首先,基于变电站偏磁直流分布模型,分析了各影响因素的作用机理;其次,利用主成分分析法对影响因素进行处理,在此基础上,提出基于神经网络的变电站偏磁直流估测模型;最后,利用某电网变电站监测直流数据对上述分析方法进行验证,分析了偏磁电流对影响因素的敏感性,结果表明,所建模型的有效性,能够为规划阶段避免或降低中性点偏磁直流提供有用参考.

利用火焰蔓延仪开展了不同油层厚度和外加辐照强度对典型换流变压器KI50X型绝缘油的点燃时间、热释放速率、CO及烟气生成速率等燃烧特性影响的试验研究,并计算了绝缘油的火灾增长系数.结果 表明:KI50X型绝缘油的点燃时间随着外加辐照强度的增大先迅速缩短,而后缓慢缩短,且随着油量的增加其点燃时间先增加后下降,随后保持在40 s左右;本试验中,当油层厚度为4.4 mm以上时,能够完整观察到池火5个典型的燃烧状态,并且绝缘油的热释放速率(HRR)的变化趋势能够与之对应;随着油量的增加,绝缘油燃烧效率先降低后保持不变;随着外加辐照强度的增加,绝缘油燃烧效率下降;就火灾增长系数而言,外加辐照强度的增加导致绝缘油的火灾危险性增大,而油量的增加并未导致其火灾危险性持续增加;峰值HRR在5 mL油量下不到400 kW/m2,随着油量的快速增加,峰值HRR增速放缓,在50 mL油量时,峰值HRR不到900 kW/m2,而随着辐照强度的增加,在辐射强度为5～10 kW时峰值HRR出现了显著增长,但随后峰值HRR在800 kW/m2附近微弱波动.

Wind energy is developed intensively and is distributed in reverse with load in China. One of the key reasons for high curtailment rate is the shortage of transmission lines. Moreover, the configuration of energy storage in wind farms can suppress power fluctuation and reduce the capacity demand of transmission lines. Therefore, a complete information static game model of energy storage and line planning between a wind farm and a grid company is established. In the model, the government affects the result by setting different penalty coefficients of wind abandoning to achieve the target of wind abandoning rate. This model can reflect the conflict of interest between the two rational players. The result of case study partly explains why abandoned wind energy rate is high and shows the necessity of the government's interference in the game. In addition, the sensitivity of the equilibrium to the parameters is analyzed.

大型油浸式变压器作为核心电力设备已广泛应用于电厂和变电站,但近年来国内外油浸变压器火灾事故频发,造成了严重的后果.基于近年来国内外发生的油浸式变压器火灾事故案例,从火灾模式和燃烧形式方面划分了油浸式变压器火灾事故的类型,总结出油浸式变压器火灾具有爆炸性、快速性、破坏性、多变性和火灾形式多样性等特点,归纳了油浸式变压器火灾事故的发生机理,指出可燃的变压器绝缘油是油浸式变压器火灾的重要事故因素,并提出了防止和控制油浸式变压器火灾事故的灭火对策与防火技术措施.

To deal with the problems including complex setting and coordination, a new method for wide-area backup fault identification with the use of Stacked Auto-encoder (SAE) is put forward in this paper. The directional elements of line fault, the measurement elements of distance protection section II and action state of main protection are taken as SAE network’s input, and state information matrix for all certain fault is made as the training sample to train SAE. Then, the element state information vector under random failures is used as the test sample, and a lot of fault identification results under inaccurate state are simulated. The results of experiment prove that the wide-area backup protection based on SAE has good ability of fault tolerance and high accuracy.

The integration of the distributed generations and DC network has aggravated the complexity of fault characteristics of distribution systems, and the traditional protection strategy cannot meet the security and stability requirements of distribution systems under new conditions. In this paper, a centralized backup protection strategy which is suitable for AC/DC hybrid power grid is proposed. The scheme extracts the direction of fault current component of each IED (Intelligent Electronic Device) in the grid and obtains the corresponding fault correlation coefficient based on the fault current value. A matrix that can evaluate the severity of the fault can be obtained by combining the information above, helping the protection strategy to realize fault location and isolation. Finally, a simulation example is given to verify that the protection scheme can effectively adapt to the changes of the operation conditions with high-permeability DGs, being able to identify the fault quickly and accurately, which is of great significance for the secure and reliable operation of AC/DC hybrid system.

With the rapid increasing of resident photovoltaics, the power utility is hard to effectively manage them, and the voltage at the end of the feeder always exceed the voltage limit. This paper takes the National Key Research and Developing Program—Jinzhai Photovoltaic Demonstration Project as an example, and a dispatching device is developed and installed on the low voltage side of 10kV/380V transformer, which is equipped with a telecontrol dispatching strategy with communication and a local adaptive control strategy without communication. The dispatching strategy mainly aims at the master station instructions, improving the generation capacity of distributed photovoltaics. The local adaptive strategy controls the voltage not exceed limits. Through the active power and reactive power coordinated control of the photovoltaic and energy storage system(ESS), the utility can control the power generation of PVs and the local voltage is optimized. Simulation validates feasibility and effectiveness of the proposed method.

This paper presents a novel dynamic clustering equivalent modeling method for a two-staged photovoltaic (PV) station cluster, which is a key tool to analyze the dynamic responses of the distribution network with high PV penetration. In this paper, a dynamic affinity propagation (DAP) clustering algorithm is proposed after studying the indexes that can describe the dynamic characteristics of two-staged PV power station. Then this algorithm is used to group the PV stations in the PV cluster according to their dynamic characteristics. Finally, the dynamic equivalent model of PV cluster is obtained by parameters aggregation of PV stations in the same group and simplification equivalent of the network. The proposed method is verified by a PV cluster distribution network with 20 two-staged PV stations and the simulation results show that the proposed dynamic equivalent model can accurately reflect the dynamic response characteristics of the PV cluster. At the same time, the simplified PV cluster model would reduce the computational complexity and the simulation time significantly.

In this paper, a practical analytical switching loss model that depends on curves provided by datasheets is used to predict its power losses during hard-switching operation. In order to analyze and apply it easily, the transmission delays introduced by Si MOSFET and interconnection inductances are ignored in modeling. Meanwhile, the nonlinear junction capacitances of the device and circuit stray inductances are also incorporated to increase the accuracy of model. Moreover, the implement method of the totem-pole PFC converter efficiency calculation is introduced in detail. Finally, the accuracy of the model is validated with simulation and experiment results, and a peak efficiency of 99.26% is achieved for a 3.6 kW single phase CCM Totem-Pole PFC AC/DC converter switching at 50 kHz based on 650V cascode gallium nitride high electron mobility transistors (GaN HEMTs).

The insulation failure time and failure temperature of aged cables under external radiation heat flux were investigated experimentally in the present study. The effects of ageing type and ageing time on the insulation failure time and failure temperature of cables were explored. The ozone aging, the xenon arc ageing and the high and low temperature cycle ageing of cables were considered. Results show that the insulation failure time decreased with the ageing time of cables under external heating. It means that the long-term used cable had serious insulation failure hazard. Among the three types of aged cables investigated in this study, the insulation failure time of xenon arc aged cables and the high and low temperature cycle aged cables were lower than the ozone aged cables. Therefore, the insulation failure hazard of the xenon arc aged cables and the high and low temperature cycle aged cables need more attentions.

The ignition characteristics and fire growth indexes of the PVC cable (Cable 1), the flame retardant PVC cable (Cable 2), the cabtyre cable (Cable 3), and the cabtyre cable with fireproof coating (Cable 4), were investigated experimentally. Twenty experiments were conducted by cone calorimeter, and the ignition time and fire growth index under different external radiation heat fluxes were focused primarily. Results showed that the ignition time of Cable 2 was longer than that of Cable 1, and the ignition time of Cable 4 was longer than that of Cable 3. The critical heat flux, under which the cable could be ignited for any length of time, was derived through data fitting. In the present study, the critical radiation heat fluxes for Cable 1–4 are 3.5, 9.5, 13.4 and 18.5 kW/m2. The ratio of peak heat release rate (HRR) to the time reached the peak HRR is defined as fire growth index. The fire growth index of Cable 1 is larger compared with that of Cable 2, and the fire growth index of Cable 3 is larger than that of Cable 4. The fire growth index of cables has well linear relationship with the external radiation heat flux in the present study.

This paper investigated the combustion behaviors of live PVC cables with overload currents experimentally. The smoke coefficient of released smoke and the released gas concentration were examined. The results indicate that the combustion of live PVC cables can be divided into four stages, i.e., core exposed with a little smoke, obvious flame, maximum smoke and smoke depress. For most cases, using blue laser is better than using rad laser, since the extinction coefficient of the rad laser was larger than that of the blue laser. The response time of the detection of the released typical gases due to cable pyrolysis decreased and the peak values of the typical gases increased with the overload currents. In addition, the time to reach the peak value of gas concentration also decreased with the overload currents.

An embodiment of the invention provides a reactive power scheduling method for a photovoltaic-energy storage cluster of a power distribution network. The method comprises steps as follows: a reactivepower operating interval is judged, and a to-be-adjusted value delta Q of reactive power is determined according to a scheduling value Q and actually measured reactive power Qpcc at a grid connectionpoint and in combination with local voltage threshold-crossing conditions; reactive power of each energy storage equipment and each small photovoltaic power station are scheduled according to the sizeof delta Q; when delta Q is larger than zero, scheduling of increasing the reactive power is performed on each energy storage equipment and each small photovoltaic power station, otherwise, delta Q is equal to absolute delta Q, and scheduling of decreasing the reactive power is performed on each energy storage equipment and each small photovoltaic power station. A power grid scheduling departmentobtains originally absent reactive power scheduling capacity, the voltage exceeding problem is reduced and even avoided, and the method can cope with complicated and variable field working conditions.

The localization of partial discharge (PD) sources using the acoustic emission(AE) technique has attracted increasing research attention. Previous studies have focused on applying different optimization algorithms to solve the time difference of arrival equations. Some simple iteration algorithms and some intelligent optimization algorithms are used to solve the time difference of arrival equations. Moreover, a new localization method using transformer model is proposed. In this paper, experiments are performed in a 35kV transformer to compare quantitatively those different localization methods. Five different localization methods are introduced in detail about their algorithm theory, advantages and disadvantages. After that, those algorithms are tested using data from a three-phase 35kV transformer. To generate predictable PD signals, an artificial protrusion defect model was used. This defect was placed at different positions in the transformer and the localization results of various algorithms can be gathered. Both the Newton-Raphson algorithm and the Chan algorithm suffer non-convergence or localization outside the transformer. The GA and ICA have better performance but large errors are induced because those two methods treat direct paths as the fastest routes. Moreover, the algorithm based on the transformer model shows the best accuracy but its calculation time is the longest while other methods can response quickly.

The effects of insulating material ageing on the fire performance of flame retardant cables were investigated experimentally by cone calorimeter in the present study. The ageing time and ageing type of the insulating material were concerned, and the fire hazard of cables was represented by the ignition time and the heat release rate (HRR). The results show that both the ignition time and the peak of HRR increase with the ageing time first and then decrease slightly for the flame retardant control cables with polyvinyl chloride insulated and polyvinyl chloride sheathed (ZR-KVV). For the flame retardant control cables with crosslinked polyethylene insulated and polyvinyl chloride sheathed (ZR-KYJV), the ignition time increase and the peak of HRR decrease with the ageing time. The effects of ageing type of insulting material on fire hazard of cables were investigated with the ZR-KVV cables. The ignition time and the HRR of the thermal aged cables were higher than those of the xenon arc aged cables, the ozone aged cables and the hydrothermal aged cables. The results of fire hazard assessment of aged flame retardant cables according to the ignition time might be opposite to those derived from the HRR of cable fires, which should be paid attentions in cable fire safety evaluations.