1.1 The three-level generator set maintenance plan of the unit maintenance plan can solve the power plant power company and the interconnected power system from three levels. In terms of power plant floor, the goal of the generator set maintenance plan is to give each unit the most complete inspection interval to achieve a satisfactory level of equipment availability. This level of constraints is related to the availability of the operator's repair shop. Too little overhaul will result in huge economic losses in the future, while over-frequency will cost more maintenance. In order to balance, a probabilistic model based on reliability-based maintenance is proposed from the power company level. The goal should be to minimize the economic cost of power generation. In addition to the power plant layer, the constraints should be added to the constraints related to the load supply in the area, and exchange of power contracts with the area. At present, many generator set maintenance plans consider this level of questions. In the interconnected system layer, in addition to the constraints of the power plant and the single area, the line exchange capacity limit should be added to meet the requirements of the reliability of the interconnected system. The mutual support policy and the operational unit with load sequence and seasonal factors.
1.2 Application development of generator set maintenance plan The development of power system has greatly promoted the research and development of generator set maintenance plan, and put forward higher requirements for reliability and economy. This is mainly reflected in the fact that more and more power plants are beginning to adopt pilot-based inspections to reduce maintenance costs and extend the maintenance cycle. 2 The nuclear power industry has achieved rapid development. The special feature of the nuclear power plant lies in the National Natural Science Foundation of the Nuclear Power Transportation Fund Project, 59,977,004. It is impossible to refuel during the reincarnation. It is necessary to stop the refueling of the atomic reactor for at least 4 weeks. 3. In the actual production, the unit is overhauled and rebuilt. Refueling takes place at the same time, which requires a fairly rigorous optimization of the unit maintenance plan. 3 The development of interconnected systems has made the interconnection system maintenance a necessary feasibility course. Interconnected systems enable higher reliability and lower production costs for the entire power system, and multi-zone joint maintenance in the case of interconnection is imperative. 4 In the process of transition to the power market, the power plant is all set up, and the power grid management is the consensus of the world power industry restructuring. 4. In the power market where the plant network is separated, there is an overall coordination of economics and reliability. From a system perspective, the plan to make the system most reliable is not to make the generator set owner consume the lowest cost of the maintenance plan, so there is a decentralized coordination question. Independent system operators Independent power company transmission suppliers need to develop a comprehensive long-term plan, and the unit maintenance plan is an important and basic part.
1.3 Maintenance methods involved in the maintenance plan The power plant level maintenance plan involves 6 types of maintenance methods. 1 Reliability-centered maintenance 1 Determines effective economic preventive maintenance tasks for equipment and components through special procedures. Or a systematic approach to monitoring intervals. 2 State inspection According to the analysis of measurement data such as temperature vibration, the state of the equipment is diagnosed, so that timely and appropriate maintenance can be performed. 8 Corrective maintenance is the method of repair only when the equipment fails. 4 Preventive maintenance Regularly overhaul the equipment to increase the usefulness of the power generation equipment. 5 Active maintenance to monitor whether various parameters are abnormal. At this time, the equipment has not deteriorated or the performance has declined. Look for the root cause caused by the fault, design or modify the equipment to eliminate the possibility of failure. 6 Regular maintenance The complete maintenance plan consists of different maintenance categories and their maintenance cycles, and regular maintenance.
2.1 Reliability Model The user's power outage loss has a very close relationship with the system reliability. The generator set maintenance plan must consider the system reliability. Although the maintenance plan is actually a multi-objective and multi-constrained optimization question, due to the complexity, only the optimization index is selected as the objective function in the practical application, and other specific requirements are considered in the constraint. Whether as an objective function or as a constraint, reliability must be considered. Economics may not appear in mathematical models, such as the risk method. Reliability model takes reliability as the objective function and can be divided into two categories: deterministic and random. The determined reliability objective function is to consider the maximum net backup of the system after the unit is shut down, and the standby method belongs to this category. Since this concept is simple and easy to implement, it is often used in practice. However, the determined reliability objective function ignores the uncertainty of the generator set availability and load. Therefore, having different periods of the same net backup does not mean that the reliability is the same, which is its main disadvantage. The random reliability objective function can make up for the above defects by considering the influence of random forced outage of the generator unit. The equivalent risk method falls into this category. The random reliability objective function generally uses a reliability index such as 101 yang as the target value.
2.2 Economic model The economic cost objective function mainly includes two parts: maintenance cost and production cost. The total maintenance cost of the generator set consists of two parts, which is the maintenance investment loss of Zhu wear. It is caused by the repair unit being too early; the other part is the actual maintenance cost, which is a function of the time of the last inspection. The total maintenance cost is basically a convex function. The production cost is the fuel cost required to produce a fixed electrical energy. The objective functions commonly used in optimizing maintenance plans only include production expense items. The optimization of the minimum production cost plan is quite difficult because it is a nonlinear function of the operating unit. 5.9. It is worth emphasizing that economic research shows that the most reliable planning method is not necessarily the least costly. An optimized maintenance plan that considers production costs is better than simply considering reliability. In the case of electricity market conditions, economic costs should also include reliability costs and electricity purchases from outside the region.
The ways to solve the generator set plan are divided into two categories: heuristic optimization method and mathematical optimization method.
3.1 Heuristic optimization method Heuristic algorithm is a technique that finds the best solution within the acceptable computational cost, but may not guarantee the feasibility and optimality of the solution obtained, even in most cases. It is impossible to explain the degree to which the obtained solution is similar to the optimal solution. The generator set maintenance plan is a combination optimization problem, which is characterized by dimensional discretization and nonlinearity. Accompanied by the current taboo search and other solutions. 1 asked the rise of the global optimization heuristic algorithm, the heuristic algorithm is widely used in the maintenance plan.
3.1.1 The standby method, such as the standby method, is to make the maintenance plan of the system as equal as possible in the whole period of the year after taking into account the maintenance and shutdown of the generator set. The basic principles are very intuitive and are the traditional method of arranging maintenance plans, but do not reflect the uncertainty of unit availability and load.
3.1.2 Equal Risk Method 8 This is a method with a random reliability objective function. Through the optimization of the maintenance plan, the system risk degree is close to the same goal in each period of the research cycle. Its implementation steps are similar to the alternate method, which is also a flat process. It overcomes the alternate method 3.1.3 simulated annealing method. This method is a random algorithm, with a probability 1 progressive convergence to the global optimal solution. The advantage is that it can prevent the local optimization from being more effective, but it takes a long time and is a single point optimization. Using this method, the system deterministic optimization of the 60 units of the force capsule has reached a time-consuming optimization of about 21, which is not ideal for large systems.
3.1.4 Evolutionary Algorithms Typical evolutionary algorithm models include genetic algorithm evolutionary strategies and evolutionary programming. The advantage is that it is suitable for numerical solution with multi-variable multi-parameter multi-objective and multi-regional but poor connectivity. It is quite suitable for generator set maintenance planning, and it is multi-point optimization and compatible with other heuristic algorithms. It has the disadvantages that the calculation speed is slow and sometimes the convergence of the local optimum convergence parameters is difficult to grasp. The literature uses evolutionary strategies and fuzzy decision-making to solve the overhaul plan including generator sets and transmission equipment. It is a human-machine interactive optimization program similar to the expert system, in which fuzzy decision-making is used to evaluate the resulting maintenance plan. In particular, it also considers the real-time maintenance demand status of the generator set and transmission equipment, so that it can be handled flexibly according to the actual situation.
3.1.5 Tabu search algorithm The tabu search algorithm is the successful application of artificial intelligence in the combinatorial optimization algorithm. The advantage is that the convergence speed is fast, and the disadvantage is that the convergence is affected by the initial solution, and the skill is very strong. The literature combines genetic algorithm simulated annealing taboo search in the optimization of thermal power unit maintenance plan, using their respective advantages to achieve a certain result.
3.1.6 Lagrangian relaxation method Simulated annealing tabu search genetic algorithm and other heuristics give the upper bound of the optimal value, while the Lagrangian relaxation method gives the lower bound of the optimal value. The basic principle is to absorb the constraints that cause difficulty and to absorb the objective function, and keep the linearization of the objective function, making it easy to solve. The Lagrangian relaxation heuristic algorithm mainly includes the feasibility of the gradient optimization calculation and solution. The literature uses the Lagrangian relaxation method to develop a nuclear power unit maintenance plan, and gives the inspection sequence of 58 nuclear power units in France.
3.1.7 Expert System The expert system stores the knowledge and experience of human experts into the computer in the form of a knowledge base, and imitates the reasoning methods and thinking processes of human experts to solve problems, making judgments and decisions on real-life questions. In large-scale power systems, if the transmission equipment maintenance load changes and other factors are taken into account, the maintenance plan becomes an extremely large optimization problem. Simple mathematical optimization techniques are difficult to solve, and expert systems can do it well.
3.2 Mathematical Optimization Method 3.2.1 Linear programming reaches power, thereby maximizing power backup. This is a deterministic method and can only be used to evaluate the genset overhaul plan. Document 3 applies the micro-increased risk method to the multi-regional generator set maintenance plan, mainly as a deterministic method. Document 4 combines linear programming with heuristic algorithms, first using linear programming to solve, and then using heuristics to correct. The advantage is that the maintenance period is changed from the original week to the day. However, the reliability of the latter part of the heuristic algorithm is worthy of research.
3.2.2 Dynamic Programming Dynamic programming is a mathematical method for solving the optimization of decision-making process. Its main idea is to transform the multi-stage process into a series of single-stage questioning decisions, which is discrete and complex. It is more appropriate to apply dynamic programming to find the best. of. However, the biggest shortcoming of dynamic programming is dimensionality, especially for high-dimensional numbers such as generator set maintenance plans. Document 5 utilizes a successive approximation method and solves all groups in groups. Document 6 incorporates the semi-invariant method on the basis of the former, and solves the objective function as the weighted sum of production cost and reliability cost.
3.2.3 Target Planning Objective planning is a type of multi-objective planning. The main idea is to grade and weight each target. It is worth mentioning that it uses a computer language designed for optimization and solves the optimization goal quickly and easily. Therefore, the research on the optimization of the generator set maintenance plan should start from many aspects.
3.2.4 Integer Programming Integer programming is a mathematical programming of the class requiring variables to take integer values, which is consistent with the integer nature of the generator set maintenance plan. But it builds a randomness model that requires a large amount of storage space and a long computation time. Document 6 uses mixed integer programming to consider the production of transmission pits for interconnected systems of two regions. Since integer programming takes a long time, although the algorithm established in Document 7 is an integer programming model, the solution is still done by a heuristic algorithm.
3.2.5 Benders Decomposition Method 819 Benders Decomposition Method Decomposes the generator set maintenance plan into integer plan and random plan for decentralized coordination. It can also contain integer randomness nonlinearity and other features without treatment. The result is quite high. Take into account the network constraint line maintenance plan and so on.
With the promotion of the power market, the power system is developing in a multi-regional direction of large systems, and the question of power transmission and maintenance is gradually exposed.
For practical questions, focus on finding a better way from the aspects of computational speed and convergence. In addition, consideration should be given to the overall overhaul and safety of the transmission and distribution network.
Li Bo, the editor-in-chief, stopped page 21, 1. The corrosion resistance of the 20-gauge carbon steel surface was evaluated by three methods: AC impedance and constant potential step phenanthroline spectrophotometry. Yes.
1 Huazhong Electric Power Administration went to Russia for inspection team. Brief Introduction to Anti-corrosion Technology of Thermal Equipment in Russian Thermal Power Plants 5. Huazhong Electric Power, 1993, 63.
5 Li Xing. Passivation technology for boiler cleaning process 1. Industrial water treatment, 1992, 125.
Xi'an Thermal Engineering Institute. Thermal power plant water vapor test method rib. Beijing Water and Electric Power Press, 1984.
2 Li Wei, Lin Haichao, Cao Chunan. The mechanism of interaction between organic amines and the behavior of corrosion inhibitors. Proceedings of the 10th National Corrosion Inhibitor Symposium. 1997.
8 weeks national. Electrochemical method applied to the corrosion and protection of power equipment, responsible for the corrosion of the editor, Jixiang Han Pan electric knife, live
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