电力系统静态安全分析new
电力系统静态安全分析综述
事故。对系统安全性的分析，涉及到系统故 障后的稳态行为和暂态行为，相应地安全 分析也分为静态安令分析和动态安全分析 两个领域。电力系统的静态安全分析仅考 虑事故后稳态运行情况的安全性，它研究 系统中的元件开断引起支路有功潮流及母 线电压越限，如果出现越限，就要采取相应 的校正控制策略消除越限，保证系统的正 常运行。静态安全分析是电力系统调度部 门在调度过程中必须进行的一项重要工 作，其目的是提高系统运行的安全性。在本 文中。我们将重点讨论静态安全分析的问
后果。自２０世纪６０年代以来，大面积停电事 故时有发生，在经济上造成了巨大的损失， 因此，各国对电力系统的安全性分析，开始 给予了足够的重视，成为七、八十年代非常 活跃的研究领域。特别是２００３年８月１４日发 生的美加大停电事故，造成的经济损失和 社会影响更加严重，引起了人们对电力系 统安全性的强烈关注。如何提高系统的安 全性，将重点放在了如何对系统进行安全 分析，必须从系统规划、系统调度操作以及 系统维修计划等方面做统一而全面的考 虑，并最终集中体现在系统的运行条件上。 当互连系统运行中发生故障时，保证 对负荷持续供电的能力，即系统保证避免 引起广泛波及性供电中断的能力，这就是 电力系统的安全性问题，它涉及到系统的
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国民经济发展水平的重要标志是电力
工业。现代社会的不断发展，促使用电需求
率供需必须平衡，一类是不等式约束条件， 即系统中的某些变量必须在一定限值以 内，如各节点的电压模值、机组的有功和无 功出力、支路潮流等。同时满足等式和不等 式条件的系统，才可以认为是处于正常状 态。在考虑预想事故集的情况下，根据系统 对以上两类约束条件的满足情况，可将电 力系统分为四种运行状态： （１）安今正常状态－（２）不安全正常状态。 （３）紧急状态，（４）待恢复状态。
Power System Contingency Analysis电力系统静态安全分析
Power System Contingency Analysis: A Study of Nigeria’s 330KVTransmission GridNnonyelu, Chibuzo Joseph Department of Electrical Engineering University of Nigeria, Nsukkachibuzo.nnonyelu@.ngProf. Theophilus C. MaduemeDepartment of Electrical EngineeringUniversity of Nigeria, Nsukka AbstractsAs new sources of power are added to the Nigeria’s power system, an over-riding factor in the operation of the power system is the desire to maintain security and expectable reliability level in all sectors –generation, transmission, and distribution. System security can be assessed using contingency analysis. In this paper, contingency analysis and reliability evaluation of Nigeria power system will be performed using the load flow method. The result of this analysis will be used to determine the security level of the Nigeria power system and suggestions will also be made on the level of protection to be applied on the Nigeria power system with aim of improving system security.Keywords: Contingency Analysis, Contingency, Power System Security, Overload Index1.INTRODUCTIONPower system protection is an important factor of consideration in all sectors of a power system during both planning and operation stages. This is because any loss of component leads to transient instability of the system and can be checked immediately by the help of protective devices put in place. As we propose and source new sources of power in order to meet up the Nigeria energy demand, it is important to access the security level of the existing grid in order to devise a more defensive approach of operation.Currently, the Transmission Company of Nigeria (TCM), projected to have the capacity to deliver about 12,500 MW in 2013, has the capacity of delivering 4800 MW of electricity. Nigeria has a generating capacity of 5,228 MW but with peak production of 4500 MW against a peak demand forecast of 10,200MW. This shows that if the generation sector is to run at full production, the transmission grid will not have the capacity to handle the produced power reliably [7]. This goes a long way to tell that the 330 KV transmission system is not running effectively as expected. Therefore to maintain and ensure a secure operation of this delicate system, the need for contingency analysis cannot be over emphasized.Contingencies are defined as potentially harmful disturbances that occur during the steady state operation of a power system [1] Contingencies can lead to some abnormalities such as over voltage at some buses, over loading on the lines, which if are unchecked, can lead to total system collapse.Power system engineers use contingency analysis to predict the effect of any component failure. Periodically, maintenance operation are carried out on generating units or transmission lines. During this, a unit is taken offline for servicing. The effect of this forced outage on other parts of the system can be observed using contingency analysis.As demand for power increases, more generating units are installed in Nigeria with no corresponding increase in transmission capacity. This makes the transmission lines run at their maximum power capacity which is very dangerous as there is too much power in the system at any moment. This power will be shifted to any available portion of the transmission system in case of any contingency thereby overloading the available portion. This effect can be analysed by the calculation of Line Outage Distribution Factor (LODF). Also, the overloading index of the remaining lines will can be obtained equally.2.POWER SYSTEM SECURITYOne of the most important factors in the operation of any power system is the desire to maintain system availability and reliability. This ensures a secure operation of the system and improved economic operation. Power system security is the ability of the system to withstand one or more component outages with the minimal disruption of service or its quality. System security involves practices designed to keep the system operating in emergency state when components fail and to restore it to its preventive state. For instance, a generating unit may break down or have to be taken off-line for maintenance purposes. This leads to frequency and voltage instability as the available generating unit experiences more loads than usual, hence frequency drops and bus voltages lowers. If this is not foreseen and defensively prevented by use of protective devices such as relays for load shading, it can lead to the collapse of the concerned system. Therefore the control objective in the emergency state is to relieve system stress by appropriate actions while economic consideration becomes of secondary.2.1CONTINGENCY ANALYSISContingency analysis is the study of the outage of elements such as transmission lines, transformers and generators, and investigation of the resulting effects on line power flows and bus voltages of the remaining system. It represents an important tool to study the effect of elements outages in power system security during operation and planning. Contingencies referring to disturbances such as transmission element outages or generator outages may cause sudden and large changes in both the configuration and the state of the system. Contingencies may result in severe violations of the operating constraints. Consequently, planning for contingencies forms an important aspect of secure operation [2].There are various methods of contingency analysis which include the following:a.AC Load flow methodb.DC Load flow methodc.Z-Matrix methodd.Performance Index methodOf all the above listed methods, methods based on AC power flow calculations are considered to be deterministic methods which are accurate compared to DC power flow methods. In deterministic methods line outages are simulated by actual removal of lines instead of modelling. AC power flow methods are accurate but they are computationally expensive and excessively demanding of computational time. Because contingency analysis is the only toolfor detecting possible overloading conditions requiring the study by the power system planner computational speed and ease of detection are paramount considerations. [1]Results of contingency analysis are usually ranked based on some indices calculated during the analysis. The choice of performance index to calculate depends on the engineer. In a deregulated power system, a discernibly purely profit driven, economic operation is of utmost importance hence Available Transfer Capability (ATC) is normally calculated to ascertain the available transfer capability of the system in case of any contingency. Other Indices include Voltage Stability Index (VSI), Active Power Loading Performance Index (APLPI), Line Outage Distribution Factor (LODF), Line loadability, etc.Generally, once the current working state of a system is known, contingency analysis can be broken down into the following steps:a.Contingency definitionb.Contingency selectionc.Contingency evaluationContingency definition involves preparing a list of probable contingencies. This typically includes line outages and generator outages.Contingency selection process consists of selecting the set of most probable contingencies; they need to be evaluated in terms of potential risk to the system. Usually, fast power flow solution techniques such as DC power flow are used to quickly evaluate the risks associated with each contingency. But in this work, the Newton-Raphson load flow method will be used to ensure higher accuracy.Finally, the selected contingencies are ranked in order of their security, till no violation of operating limits is observed.The algorithm for a typical contingency analysis is shown in Figure 1.Figure 1: Algorithm of a typical contingency analysis2.2 LINE LOADABILITYLine Loadability can be defined as Transmission-line voltages decrease when heavily loaded and increase when lightly loaded. When voltages on EHV lines are maintained within ±5% of rated voltage, corresponding to about 10% voltage regulation, unusual operating problems are not encountered. Ten percent voltage regulation for lower voltage lines including transformer-voltage drops is also considered good operating practice.In addition to voltage regulation, line loadability is an important issue. Three major line-loading limits are:a.the thermal limit,b.the voltage-drop limit, andc.the steady-state stability limit.The maximum temperature of a conductor determines its thermal limit. Conductor temperature affects the conductor sag between towers and the loss of conductor tensile strength due to annealing. If the temperature is too high, prescribed conductor-to-ground clearances may not be met, or the elastic limit of the conductor may be exceeded such that it cannot shrink to its original length when cooled.Conductor temperature depends on the current magnitude and its time duration, as well as on ambient temperature, wind velocity, and conductor surface conditions.The loadability of short transmission lines (less than 80 km in length) is usually determined by the conductor thermal limit or by ratings of line terminal equipment such as circuit breakers.For longer line lengths (up to 300 km), line loadability is often determined by the voltage-drop limit. Although more severe voltage drops may be tolerated in some cases, a heavily loaded line with V R/V S ≥ 0.95 is usually considered safe operating practice. For line lengths over 300 km, steady-state stability becomes a limiting factor [4].3.METHODOLOGYIn this paper, the AC load flow method of contingency analysis was adopted. The Newton-Raphson load flow algorithm, an algorithm under the AC load flow method, was used to solve the power flow problems during the analysis using MATLAB. This is because the NRLF method has more accuracy than other AC Load flow methods and converges faster. Newton-Raphon’s Load flow method is discussed more in [3, 4].3.1 Calculating System Line Overload Index (SLOI)To obtain the overall system overload index, a new performance index was proposed and calculated based on the Line Loadability discussed in Section 2.2. As stated, for safe operation, the ratio of the receiving end voltage and the sending end voltage must be greater than 0.95. This newly proposed index relies on this to calculate the system line overload index. It helps tell the system designer at a glance, the lines that should be given utmost attention in terms of protection. SLOI is computed by equation (1):SLOI=1− [min(V RV S )]k(1)whereV R, V S are the receiving end and sending end voltages respectively, andk the number of lines whose V R/V S < 0.95The Nigerian transmission grid is shown in Figure 2 with the single line diagram shown in Figure 3.Figure 2: the Nigerian power system. Blue lines indicate the 330-KV lines(Source: Nigeria System Operator)Figure 3: one-line diagram of the Nigeria 330-KV transmission gridThe network parameters – generator data, load data, and line & transformer data, of the Nigeria power system as used in this work were collated from [8, 9, 10] and are shown in tables 1, 2, and 3 respectively.Table 1: Generator data3.1 Simulation of Line OutageSimulation of transmission line outage is carried out by the formulation of the corresponding admittance matrix [5]. For instance, after outage of a line connecting bus ‘a’and ‘b’, the components of the Y bus that will be affected are Y aa, Y bb, Y ab, and Y ba. For a ‘π-modelled’transmission line, the admittance values after this outage is obtained by subtracting the admittance of the line a-b and the shunt susceptance jb ab/2 and jb ba/2 from Y aa and Y bb.Line outages was simulated by simply removing the line information from the line data matrix. This is similar to the line not existing initially as the information no longer exists.3.2 Simulation of Generator OutageThis simulates mainly outage of one unit (or more) in a power station. Let the total generation for the station at bus ‘m’ be P gm, and assume that there exist identical (g) units, then [6]:)(2) P gm′=P gm−n(P gmgwhereP’gm: Active power generated at bus m after the outageP gm: Active power generated at bus m before the outagen: Number of outage generation units in the stationP gm/g: Active power generated at bus m per generator unitIn this work, generator outages were not simulated as only the effect of line outages were desired.4.Results and DiscussionThe results of the analysis (the SLOI) is shown in Table 4 ordered by the SLOI from the most critical to the least critical.The result as shown in Table 4 contains the SLOI values of the different lines for line outages. It has been organised in the order in descending order.This shows that the outage of line 11 to 14 (Oshogbo to Aiyede) will have the most critical effect on the system followed by 11 – 15, 16 – 20, 20 – 24, 25 – 16. These lines have been shown to pose serious danger on the system stability if they fail, and therefore should be secured defensively to avoid the level of system instability caused by the outage of any of the lines.5.ConclusionFrom this study, it is has been shown with values, the importance of operating the transmission system defensively to avoid system collapse due to overloading. Also, the writer suggests that the Transmission Company of Nigeria (TCN) should adopts the (Flexible AC Transmission), FACT devices as they can improve the lines active power capability in any contingency event as have faster switching than the traditional compensation devices. Also additional lines should be used to connect Oshogbo to Aiyede through different routes to create more links for power to be transmitted through to Lagos area in order to reduce the SLOI value of Oshogbo to Aiyede line.References[1] Chary, D. M., “Contingency Analysis in Power Systems, Transfer CapabilityComputation and Enhancement Using Facts Devices in Deregulated Power System.”Ph.D. diss., Jawaharlal Nehru Technological University, 2011[2] Wood, A. J.; Wallenberg, B. F., “Power Generation, Operation and Control”. 2nd ed.,New York/USA: John Wiley& Sons, 1996, pp. 410-432.][3] Saadat, H., Power System Analysis, New Delhi: McGraw Hill, 2002, pp 189 – 256.[4] Glover, J. D., Sarma, M. S., Overbye, T. J., Power System Analysis and Design, 5h ed.Stamford: Cengage Learning, 2012.[5] Nara, K.,Tanaka,K., Kodama, H., Shoults, R. R., Chen, M. S., Olinda, P. V. andBertagnolli, D., “On-Line Contingency Selection for voltage Security Anal ysis”, ibid, Vol.PAS – 104, pp. 847-856, April 1985.[6] Mohamed, S. E. G., Mohamed, A. Y., and Abdelrahim, Y. H., “Power SystemContingency Analysis to detect Network Weaknesses”, Zaytoonah UniversityInternational Engineering Conference on Design and Innovation in Infrastructure, Amman, Jordan, pp. I3-4 Jun., 2012.[7] “Nigeria's Power Generation hits 5,228 Mega Watt”, Nigeria Compass, May 4, 2013.[Online]. Available: /index.php/special-desk/business-news/12769-nigerias-power-generation-hits-5228-megawatts [Accessed July 15, 2013]. [8] Ogbuefi, U. C., “A Powerflow Analysis of Niegria Power System with Compensation onSome Buses”,PhD thesis, University of Nigeria, Nsukka, Nigeria, 2013.[9] Nigeria System Operator, “Profile of Transmission”, 2011. [Online]. Available:/spread/profile/ [Accessed: July 15, 2013].[10] Onohaebi, O. S., “Power Outages in Nigeria Transmission Grid,” Research Journal ofApplied Science, vol. 4, Issue 1, pp 1- 9, 2009.。
现代电力系统分析静态安全分析
基于物联网的安全分析技术
定义：基于物联 网的安全分析技 术是一种实时监 测和预警系统， 通过传感器网络 采集电力系统的 运行数据，并进 行安全评估和预
警。
特点：能够实现 远程监控和实时 预警，提高电力 系统的安全性和
稳定性。
应用场景：广泛 应用于智能电网、 风力发电、太阳 能发电等领域的 电力系统安全监
电力系统安全预警与控制案例
案例名称：某地区电网安全预警系统
案例简介：该系统通过实时监测电网运行状态，运用静态安全分析方法，实现对电网 安全风险的预警和控制。
案例效果：有效降低了电网运行风险，提高了电网稳定性和可靠性。
案例应用：适用于各类电力系统，尤其适用于复杂电网的安全预警与控制。
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现代电力系统静态安全 分析发展趋势与挑战
现代电力系统分析静 态安全分析
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目录 /目录
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点击此处添加 目录标题
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现代电力系统 静态安全分析 技术
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现代电力系统 概述
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现代电力系统 静态安全分析 应用案例03Leabharlann 静态安全分析 方法06
现代电力系统 静态安全分析 发展趋势与挑 战
01 添加章节标题
02 现代电力系统概述
电力系统组成
云计算技术在静态安全分析中的发展前景
云计算技术为电力系统静态安全分析提供了强大的计算能力和存储资源，提高了分析效 率和准确性。
云计算技术可以实现实时数据采集、处理和分析，为预防性维护和故障预测提供了有力 支持。
云计算技术可以降低电力系统静态安全分析的成本，提高经济效益。
云计算技术可以促进电力系统静态安全分析的标准化和规范化，提高分析结果的可靠性 和可重复性。
电力系统静态安全分析方法研究
电力系统静态安全分析方法研究电力系统是现代社会的基础设施之一，它不仅提供了电力服务，同时也对工业生产、商业发展、社会稳定起着至关重要的作用。
因此，保障电力系统的安全是非常重要的任务。
在电力系统运行中，静态安全分析是一项重要的工作。
本文将介绍电力系统静态安全分析的方法，分析其优缺点，并探讨未来的发展方向。
一、静态安全分析方法静态安全分析是指在电力系统正常运行状态下，研究其稳定性、断电容忍能力、电压控制能力等，从而保证电源的可靠性和稳定性。
静态安全分析的主要方法包括潮流分析、潮流限制分析、电压稳定裕度分析、可靠性评估等。
1、潮流分析潮流分析是电力系统静态安全分析的基础工具，它是用来计算电力系统各节点的电压、电流、功率等技术参数的一种数学方法。
潮流分析可以用来确定输电线的负载率、测量变压器的功率损耗、计划电力系统的运行条件等。
它不仅可以满足工程实际操作需要，还可以提供对电力系统的可靠性和稳定性的静态分析。
2、潮流限制分析潮流限制分析，指通过模拟各种故障和异常情况，评估电力系统在这些情况下的运行能力。
通过潮流限制分析，可以确定电力系统的最大电流、最大功率、最大负荷量等。
它可以帮助工程师找出电力系统中的故障点，并在紧急情况下制定合适的应对措施。
3、电压稳定裕度分析电压稳定裕度分析是指评估电力系统在负荷变化和扰动情况下的电压稳定性。
其分析结果可以用来指导电力系统的电压控制策略，以确保电力系统在正常工作条件下保持稳定和动态响应。
电压稳定裕度分析使电力系统管理人员能够更好地预测故障，并采取必要的措施，来避免电力系统的运行中断和不稳定因素的发生。
4、可靠性评估可靠性评估一般用来评价电力系统的负荷容量、发电机的使用年限、元件的可靠性、维护成本、电源的备用容量等问题。
可靠性评估可以从实践中获得足够的数据来确定电力系统的设计和运行要求，制定适当的运行和维护计划。
它在电力系统的长期规划和设计方面起着至关重要的作用，可对系统性能进行独立评估，从而优化可靠性、稳定性、安全性和经济性。
电力系统静态安全分析
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目录
静态安全分析概述
静态安全分析方法
静态安全分析的应用
静态安全分析的发展趋势
静态安全分析的定义
静态安全分析是一种对电力系统进行安全评估的方法
主要关注电力系统在正常运行条件下的稳定性和可靠性
通过对电力系统的拓扑结构、参数和运行状态进行分析，评估系统在故障情况下的稳定性和恢复能力
潮流计算可以分析电力系统的稳定性、可靠性和效率，为电力系统的规划、设计和运行提供依据。
潮流计算主要包括节点电压计算和支路电流计算，通过求解网络方程得到各节点的电压和各支路的电流。
潮流计算还可以用于分析电力系统的故障情况，为故障诊断和恢复提供支持。
灵敏度分析
灵敏度分析的定义：研究系统参数变化对系统安全性能的影响
应用效果：提高电力系统运行效率，减少故障损失，保障电力系统安全稳定运行
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考虑动态因素的静态安全分析
动态因素的影响：电力系统运行过程中，负荷、发电、输电等参数会发生变化，需要考虑这些动态因素对系统安全的影响。
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动态安全分析方法：传统的静态安全分析方法无法考虑动态因素的影响，需要采用新的分析方法，如动态潮流计算、状态估计等。
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静态安全分析的未来发展方向：与物联网、大数据、人工智能等技术的深度融合，实现电网的智能化、精细化管理。
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评估指标：包括电压稳定裕度、频率稳定裕度、功角稳定裕度等
评估步骤：首先确定系统的运行状态，然后计算系统的静态安全裕度，最后分析系统的稳定性和可靠性
电网规划设计
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静态安全分析在电网规划设计中的应用
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静态安全分析在电网规划设计中的作用
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电力系统静态安全分析
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网络
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对于线性网络，可以应用迭加原理把图3-6（a）分成两个网络即 . 图3-6（b）和3-6（c）。这时待求的节点电压 U 也可看成两个部 . . . ( 0) (1) 分
式中： U 相当于没有追加支路情况下的各节点电压，这个向量可 以用原网络的因子表求出，即:
. (0)
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补偿法
补偿法：将支路开断视为该支路未被断开，而在其两端节点 处引入某一待求的补偿电流，以此来模拟支路开断的影响。
特点：不必修改导纳矩阵，可以用原来的因子表来解算网络 的状态。
以单一支路开断为例说明补偿法的物理概念
当网络节点i、j之间发生支路开断，可以等效地认为在i、j节点间并 联了一个追加的支路阻抗Zij，其数值等于被断开支路阻抗的负值。 这时流入原网络的注入电流将由 I
Zij
. Iij
ZT Zij Zij
(53)
. 图3-7 用等效发电机原理求Iij的等值电路图
支路开断后的节点电压向量
通过等值电路络 ZT . E
电力系统静态稳定分析
δ a ↓ ⇒ Pe ↓ ⇒ w ↑ ⇒ δ ↑
P 不变 m w−1p0
δa
δb δb
1800
δ
b点： 不稳定
δ b ↑⇒ Pe ↓⇒ w ↑⇒ δ ↑
滑向深渊
δ b ↓⇒ Pe ↑⇒ w ↓⇒ δ ↓
t
滑向a点
2.静态稳定判据 2.静态稳定判据
决定。 两点有何不同？ δ、ω都由 Pe 决定。a、b两点有何不同？
P 0
均可提高系统的静态稳定性。 均可提高系统的静态稳定性。
具体措施： 具体措施：
采用自动调节励磁装置 减小元件电抗 改善系统的结构 采用中间补偿设备
采用自动调节励磁装置
发电机电势与励磁调节情况有关。 发电机电势与励磁调节情况有关。通过装设无 失灵区或者无时滞的比例型励磁调节器以及强力励 磁调节器，可以实现所谓的人工稳定区， 磁调节器，可以实现所谓的人工稳定区，即调节发 电机的功角 δ ，使之满足稳定要求。 使之满足稳定要求。
′ xd → xd → 0
减小元件阻抗 ——减小线路电抗 ——减小线路电抗
•采用分裂导线 采用分裂导线 • 提高线路额定电压等级 （可以等值地看作是减小线路电抗） 可以等值地看作是减小线路电抗） • 采用串联电容补偿 （在线路上串联电容器以补偿线路的电抗） 在线路上串联电容器以补偿线路的电抗）
串联电容补偿
二、电力系统静态稳定分析的小干扰法
所谓小干扰法， 所谓小干扰法，就是首先列出描述系统运动 的数学模型（通常是非线性的微分方程组）， 的数学模型（通常是非线性的微分方程组）， 然后将它们线性化，得出近似的线性微分方 然后将它们线性化， 程组， 程组，再根据其特征方程式根的性质判断系 统的稳定性。 统的稳定性。
电力系统静态安全分析2——杜晓风 (2)
以预想事故相邻级确定权重因子
预想事故自动筛选算法原理图
入口 取第一个预想事故 安全 自动选择 不安全 安全评估
行为指标计算及排队顺序 取下一个预想事故 否 是 输出预想事故一览表 出口
预想事故是否已经作完
图1 预想事故自动筛选算法的原理图
电力系统静态安全域
保证电力系统静态安全运行的条件是在当前网 络结构下，不但要保证正常运行状态，而且在 因偶然事故导致故障元件切除后的运行状态下， 仍然要保证发电机功率和负荷需求功率的平衡， 同时各设备运行在安全限值约束之内。 前面介绍的方法均为逐点法——在给定的运行 状态下，对预想事故集的所有预想事故逐一求 解潮流方程，以此来确定系统是否运行在安全 约束范围内。
-0.6
-0.8
接线图
例题
解： P B
0
1 1 0.6 0.25 0.2 0.8 1 0.2
1 9 5 2 0.2 2 15 3 1 1 3 5 2 0.4 0.2
潮流模型及安全约束条件
电力系统的安全运行，就是保证系统的功率平衡，同时 各设备运行在安全限值之内
潮流模型——保证功率平衡由功率平衡方程实现，即等式
约束条件
安全约束条件——设备运行在安全限值之内
若系统节点数为n，第n个节点为参考节点，负荷节 点编号为1~nL （共nL个），发电机节点编号为nL +1~n-1(共包括参考节点共Ng个)，支路数为m。此外 其潮流模型一般可采用P-Q分解潮流模型
概念
预想事故的自动筛选：在静态安全分析中，先 用简化潮流的计算方法对预想事故集中的每一 个预想事故进行近似计算，剔除明显不会引起 安全问题的预想事故，且按事故的严重性进行 排序，组成预想事故一览表，然后用更精确的 潮流算法去对表中的事故依次进行分析。