Pick to: this paper introduces the typical faults of the main equipment in power plants and the method of fault diagnosis, this paper expounds the existing fault diagnosis system and the problems existing in the power plant equipment fault diagnosis, and points out the development trend of fault diagnosis system, puts forward the research direction.
Large coal-fired power plant main equipment including boiler, steam turbine and generator, etc., finish from heat energy into mechanical energy to electrical energy conversion process. Coupling between the devices and equipment, the complexity of the system, as well as the equipment in high temperature and high pressure, high speed rotating under special working conditions, determine the coal-fired power plant is a high failure rate and harmfulness of big production place, these failures will cause great economic losses and social consequences. Therefore, through the use of advanced technology, the equipment state parameter monitoring and analysis, judge whether the equipment is abnormal or fault, fault reasons and positions, the deteriorating trend of the fault, in order to determine reasonable repair time is necessary.
One, the typical fault and diagnostic methods of the main equipment in power plants
1. The main faults and diagnosis methods of the boiler
(1) the main fault
1 the superheater leakage. Leakage of superheater explosive district concentration under the high temperature superheater bend outer ring this side, the main reason is that furnace is low, in the overheating, here also have insufficient material allowance and welding quality problems.
(2) the economizer leakage. The main reason is caused by fly ash abrasion wall thinning, especially in the wall tube, air leakage and elbow for common furnace wall.
(3) water wall leakage. The main reason is that local overheating and corrosion, local overheating is caused, destruction of water cycle and tube fouling and flame deflection or burning area smoking temperature is too high, make water wall high temperature corrosion.
(4) filter failure. Main reason for the flue gas velocity is too fast, ash grain size is larger, dust concentration, exhaust smoke temperature is lower than the dew point temperature, etc.
(2) the diagnosis method
In fault diagnosis of boiler, physical diagnosis methods are: the infrared temperature measurement technology, specific application areas have boiler flame and combustion state units to identify and control, thermal fatigue damage, thermal equipment heat mechanics characters, diagnosis and evaluation on the thermal system heat leakage and heat preservation, boiler heat pollution control, etc; Ultrasonic diagnosis method, which can be used to monitor the upper chamber of a stove or furnace area of the flue gas temperature, deciding when to blowing operation, the performance of the boiler is a good, each burner area near the flue gas temperature monitoring furnace, helps to identify and remove the burner failure caused by abnormal combustion conditions, at the same time can have important effects on pollutants generated the optimization control of temperature, achieve clean combustion; No damage detection technology is to point to to the nondestructive testing of materials, components, in order to find a technology of surface and internal defects. Mathematics diagnostic methods such as fault tree diagnosis method, the fuzzy diagnosis method. In terms of diagnosis system, mainly with tsinghua university, research and development of large-scale power plant boiler remote monitoring and fault diagnosis system, huazhong university of science and technology research and development state of circulating fluidized bed boiler on-line monitoring and diagnosis expert system, etc.
2. The major faults and diagnosis of steam turbine unit method
The main failure (1) steam turbine
1) don't balance. There is mainly due to the rotor machining error and the permanent drift partial bending, leaf falls off, coupling, long axis manufacturing, uneven heating or material defects caused by the heat deflection, etc.
(2) in the wrong. Main reason is unsmooth slide pin system, cylinder temperature overrun, set up quickly, vacuum drop too much, foundation uneven subsidence, such as uneven expansion not free and bearing seat of generating unit, and the eccentric shaft coupling, etc.
(3) rotor rubbing. Main reasons are improper design and adjust the seal clearance, poor expansion cylinder, cylinder thermal deformation is too large, the unit vibration and axial displacement increases, and so on.
(4) leaf loss. Is mainly due to the design of the strength is insufficient, volatile steam parameters, unit larger changes in the power grid frequency and long running under low load, and the unit in less than rated speed under a certain speed for a long time, and so on.
(5) the steam excitation. The main reason is because of the high pressure rotor critical speed is low, and the high pressure rotor deflection under thermal state change is bigger, bearing elevation change is bigger, to answer the long axis of the fabrication and installation quality bad, coupling center radial or axial error is too great, shafting balance and the deteriorated, etc., make the high pressure rotor instability.
(2) generator main fault
(1) the oil film oscillation. Mainly because of the generator rotor of first order critical speed is too low, and three axis tile wedge stability, when load to reduce the instability rotating speed is too low.
(2) the stator winding insulation failure. Is mainly due to abrasion, aging, contamination and corrosion reasons make the insulation failure, caused by partial discharge and temperature, and the binding is not tight, cooling water leakage, fatigue wear makes insulation damage, such as wire rod displacement and turn-to-turn short circuit.
(3) of the stator coil overheating. Is mainly due to some defects in the manufacture or installation process turn-to-turn short circuit, cause local overheating.
(4) rotor winding fault. Including grounding, turn-to-turn short circuit and bolt failure. Grounding and interturn short circuit barrier is mainly due to the insulation to reduce and damage caused by open welding joint and the thermal deformation will cause disconnection.
(5) the cooling water system failure. Is mainly due to the cooling water leakage, piping foreign bodies blocked, false action and so on make the cooling water flow rate is reduced and the interruption, and the stator by the material and installation defects is leaking.
(3) the diagnosis method
In fault diagnosis of steam turbine unit, vibration method is one of the most common is more mature method. Application of thermodynamics analysis fault diagnosis of steam turbine unit performance is also an important means, in addition to oil analysis, the acoustic emission method and nondestructive testing technology, etc. Acoustic emission method is mainly used for movement to touch the ground fault detection, leak detection, etc. Hitachi is on the high pressure rotor of 350 mw turbine set specimens, at both ends of the bearing shell for acoustic emission and records, diagnosis of rotor touch the ground. Diagnosis of steam turbine unit lifespan, nondestructive testing technology is quite important, currently used in nondestructive evaluation method mainly includes the hardness measurement method, electric resistance method, ultrasonic method, comparison method, the crystal grain deformation method, microscope measurement, X ray analysis method and so on.
Today at home and abroad has developed dozens of fault diagnosis system for steam turbine unit. Abroad mainly include the development of turbo-generator set vibration diagnosis of Radial companies in the United States to use expert system, Westinghouse turbine generator fault diagnosis system, Bendy rotating machinery fault diagnosis system of the company. Domestic mainly developed by Shanghai university TPD thermodynamic parameters monitoring and fault diagnosis system, this system can improve the operation reliability of steam turbine unit, at the same time to optimize the operation scheme, improve operational efficiency, extend the life of the run. By tsinghua university, huazhong university of science and technology, Harbin industrial university, Harbin electrical instrument, such as institutes developed with 200 mm, 300 mw steam turbine generator condition monitoring and fault diagnosis expert system, the comprehensive monitoring vibration fault diagnosis of machinery, air gap can be vibration fault, fault caused by heat factor, mechanical and electrical coupling of shafting torsional vibration failure and adjust control system failure.
3. Main faults and diagnosis methods of transformer
(1) the main fault
1) coil turn-to-turn short circuit. The main reason is that poor insulation aging or heat or overload for a long time, due to the short circuit electric injury turn-to-turn insulation, winding of the defects in material or process of water be affected with damp be affected with damp, atmospheric or operating overvoltage.
(2) the winding wire break. Main reasons short-circuit electrodynamic force make the coil wire, welding, turn-to-turn short circuit.
(3) winding of breakdown. The ageing of the main reasons are the main insulation, insulation oil be affected with damp be affected with damp, winding with impurity enter, overvoltage coil deformation during short circuit, because of cooling system failure, cooling oil road congestion, the whole or partial overheat protection failure to produce insulation damage.
(4) and winding short circuit. Main reason for the like of breakdown, also may be lead or short circuit between casing, oil level is too low.
5. Local short circuit or partial melting iron chips. The main reason is that iron core or the conjugate screw insulation damage, had pieces of metal to make iron chip short-circuit fault, insulation was badly damaged, grounding method is not correct form current loop.
6 tap-changer poor contact, the contact surface melting. The main reason is that defects in structure and assembly, switch after the tap, contact unreliable, dynamic contact spring pressure is not enough, on-load regulating device is improper to install.
All landowners casing of flashover or explosion. The main reason is that the surface dust, dirt, cracks, untight seal, improper respirator configuration.
Normal oil temperature rise high end load. The main reason is winding interturn short circuit, loss increase, large current joint poor contact, oil level is too low, the cooling effect is poor.
(2) the diagnosis method
In the transformer fault diagnosis, the commonly used method is vibration analysis, gas analysis and method of partial discharge in transformer oil, the recovery voltage method, frequency response analysis method and infrared diagnosis technology, etc. The current application more mainly infrared diagnosis technology. In terms of diagnosis system, scholars and research institutes at home and abroad, a lot of work in this aspect, have developed which has the function of fault detection and preliminary diagnosis expert system, such as henan electric power test research institute development research of computer power transformer fault diagnosis expert system. In addition, there are many famous domestic colleges and universities are engaged in the research, has made great theoretical achievements.
Second, the current problems in power plant equipment fault diagnosis
Now although there are many diagnostic methods and diagnosis system is applied in the power plant equipment fault diagnosis, and obtained good application effect, but also there are many problems in practical application, mainly manifested in the following respects.
1. The test method
Fault diagnosis reasoning mechanism has reached very high levels, but signs of access has become a bottleneck, that is, the biggest problem is detection means can't meet the need of diagnosis, can not truly reflect the features of fault.
2. The failure mechanism of the complex
Understanding of the failure mechanism is the premise of accurate diagnosis fault. At present, some equipment complex fault in power plants, it is difficult to explain in theory, the understanding of its mechanism is not deep.
3. The application of artificial intelligence
As artificial intelligence expert system in power plant, the application of the main equipment fault diagnosis has been successful, but there are some key artificial intelligence application problems to be solved, mainly include the knowledge expression and acquisition, self-study, intelligent identification, information fusion, etc.
4. The diagnosis method of oneness
Current diagnostic methods used in the power plant equipment fault diagnosis system with fuzzy logic method, the fault tree analysis method, expert system and artificial neural network, etc. But a single diagnostic method is often difficult to achieve expected effect.
5. Fault location
The current fault diagnosis system is often just for this part to the fault type identification, cannot determine the location of the fault, and forecast the state of the equipment the function of the study was not enough.
Third, the development of the power plant equipment fault diagnosis
1. The development trend of fault diagnosis system
(1) the fault diagnosis system of hierarchical distributed structure
Thermal power unit of the structure and function of each subsystem is distributed and multi-level, the structure of hierarchical relationships, for its diagnosis system is a distributed and multi-level, consists of global diagnosis system and the diagnosis system. Global diagnosis system are responsible for the management of diagnostic tasks, including the overall task into subtasks and the tasks assigned to each diagnosis system, these tasks are often coupled to each other. Diagnosis subsystem is complete, and through the different conclusion diagnosis system of comprehensive, gives the final conclusion. Distributed fault diagnosis expert system reasoning with high efficiency, fast diagnosis, the system is reliable, good timing characteristics.
(2) the integrated fault diagnosis system
Due to the current diagnostic system on the reasoning method of oneness, in solving the diagnosis of complex systems is limited by a lot of problems. Fault diagnosis system for thermal power unit, in the future will be according to the characteristics of different subsystems with different reasoning model, using several different reasoning model for mixed reasoning, even will be give full play to the advantages of various kinds of propulsion model, thus improve the reasoning speed and accuracy.
(3) constructing large monitoring center
In the same grid, there are many types of thermal power units in operation at the same time. Constructing large monitoring center is the benefits are very obvious: (1) facilitates concentration save operating data of the unit and the unit's health data; (2) facilitate sharing between multiple units, multiple power plants of the existing knowledge, facilitate knowledge base WanShanHua; (3) to load dispatching of the unit.
(4) the closed-loop diagnosis system independently
The automatic fault diagnosis, the closed loop system will continue in the case of staff not to participate in complete fault diagnosis, making decisions, and the corresponding control commands issued by the diagnosis system to impose the appropriate control on unit. In order to achieve autonomous closed-loop diagnosis, must want to have a mature and advanced diagnostic technology. Diagnosis system knowledge base must be complete, diagnosis system should be learning mechanism, can diagnose the faults of unpredictable.
(5) of the remote fault diagnosis system based on Internet
With the development of computer network technology, making it possible to remote application system based on Internet. Combining fault diagnosis system and the Internet can not only get a lot of failure cases and diagnostic experience, able to share in the diagnosis of resources at the same time, realizing expert consultation, raise the level of fault diagnosis.
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