Wind turbines convert wind energy into mechanical work and drive generators to generate electricity. Broadly speaking, it is a heat energy utilization engine with the sun as the heat source and the atmosphere as the working medium. Wind power generation uses natural energy. Much better than diesel power generation. But if it is used in an emergency, it is still not as good as a diesel generator. Wind power generation is not a backup power source, but it can be used for a long time.
Operation management:
The control system of wind turbine is controlled by industrial microprocessor, and generally it is run by multiple CPUs in parallel. Strong anti-interference ability, remote control by connecting with computer through communication line, greatly reducing the workload of operation. Therefore, the operation of the fan is to carry out remote troubleshooting, statistical analysis of operation data and analysis of fault causes.
Remote troubleshooting:
Most faults of the fan can be reset remotely and automatically. The operation of the fan is closely related to the quality of the power grid. Two-way protection, the fan is equipped with multiple protection faults such as high and low grid voltage and high and low grid frequency, which can be automatically reset. Due to the uncontrollable wind energy, the limit value of excessive wind speed can also be automatically reset. There are also temperature limits that can be automatically reset, such as high generator temperature, high and low gearbox temperature and low ambient temperature. The overload fault of the fan can also be automatically reset.
In addition to automatic reset failure, other remote reset control failures may be caused by the following reasons:
1, fan controller false alarm fault;
2, each detection sensor misoperation;
3. The controller thinks that the fan is unreliable.
Statistical analysis of operation data:
Detailed statistical analysis of wind farm equipment operation is an important content of wind farm management. Through the statistical analysis of operation data, we can evaluate and quantify the operation and maintenance work, and also provide an effective theoretical basis for the design of wind farms, the evaluation of wind resources and the selection of equipment.
The monthly report of power generation statistics is one of the important contents of operation, and its true reliability is directly linked to economic benefits. Its main contents include: monthly power generation, on-site electricity consumption, normal working hours, failure time, standard utilization hours, power grid blackout, failure time and so on.
Statistics and analysis of power curve data of wind turbine can provide practical basis for improving the output of wind turbine and improving the utilization rate of wind energy. Through the statistics and analysis of wind condition data, we can master the output law of various fans changing with seasons, make reasonable regular maintenance plans and reduce the waste of wind resources.
Small wind turbines:
A wind turbine is a machine that converts wind energy into electric energy. From the point of view of energy conversion, the wind turbine consists of two parts: one part is the wind turbine, whose function is to convert wind energy into mechanical energy; The second is the generator, whose function is to convert mechanical energy into electrical energy.
The structure of small wind power generation system is generally composed of wind wheel, generator, tail rudder and electrical control part. Traditional small wind turbines are mostly composed of induction generators or permanent magnet synchronous generators plus AC /DC converters, batteries and inverters. Driven by the wind, the wind wheel rotates, converting aerodynamic energy into mechanical energy (speed+torque). The hub of the wind wheel is fixed on the generator shaft, and the rotation of the wind wheel drives the generator shaft to rotate and drives the permanent magnet three-phase generator to generate three-phase alternating current. With the constant change of wind speed, the current and voltage generated by the generator also change. The generated electricity is rectified by the controller and changed from alternating current to direct current with a certain voltage to charge the battery. The direct current output by the battery pack, after passing through the inverter, becomes 220V alternating current, which is supplied to the user's household appliances.
Wind turbines are divided into grid-connected wind turbines and off-grid wind turbines according to different application occasions. Off-grid wind turbine, also known as independent operation wind turbine, is a wind turbine applied in areas without power grid, and its power is generally small. In general, an independent wind turbine needs to be combined with storage batteries and other control devices to form an independent wind turbine power generation system. This independent operation system can be several kilowatts or even dozens of kilowatts to solve the power supply system of a village, or tens to hundreds of watts of small wind turbines to solve the power supply of a family.
Because of the randomness of wind energy, the frequency and voltage of the power generated by the generator are unstable, and the storage battery can only store direct current energy, but cannot directly supply power to the AC load. Therefore, in order to provide stable and high-quality electric energy to the load and meet the demand of AC load, it is necessary to add a power conversion device between the generator and the load, which is mainly composed of rectifier, inverter, controller and battery.
As a part of rural energy, the popularization and application of small-scale wind power generation system will play a positive role in improving the electricity consumption structure, especially in remote mountainous areas, and promoting the development of ecological environment construction, with broad market prospects. Wind energy is random and uncertain, and wind power generation system is a complex system. Simplifying the structure of small wind power generation system, reducing the cost, improving the reliability and realizing the optimal operation of the system are of great significance for the popularization of small wind power generation system.
Maintenance of wind turbines:
Wind turbine is a comprehensive product integrating electrical, mechanical, aerodynamic and other disciplines, and all parts are closely related. The maintenance of wind turbines directly affects the level of power generation and economic benefits; The performance of the wind turbine itself should also be maintained through maintenance. Timely and effective maintenance can find hidden dangers, reduce the occurrence of faults and improve the efficiency of wind turbines.
Fan maintenance is divided into two ways: regular maintenance and daily fault maintenance.
1, maintain the fan regularly.
Regular maintenance can keep the equipment in the best condition and prolong the service life of the fan. The main contents of regular maintenance work include: bolt torque check between fan connectors (including electrical connection), lubrication between transmission parts and various functional tests.
When the fan is running normally, due to the resultant force of various vibrations for a long time, the bolts at each connection part are easy to loosen. In order not to cause uneven stress and shear after local bolts are loosened, the bolt torque must be checked regularly. When the ambient temperature is lower than -5℃, the torque should be reduced to 80% of the rated torque for fastening, and when the ambient temperature is higher than -5℃, it should be rechecked. Bolt fastening inspection is generally arranged in windless or windy summer to avoid the high power season of fans.
The lubrication system of fan mainly includes two ways: thin oil lubrication (or mineral oil lubrication) and dry oil lubrication (or grease lubrication). Fan gear box and yaw reduction gear box are lubricated with thin oil, and their maintenance methods are replenishment and sampling. If the test results show that the lubricating oil can no longer be used, it should be replaced. Dry oil lubrication components include generator bearings, yaw bearings and yaw teeth. Because of the high working temperature, these parts are easy to deteriorate, leading to bearing wear, so they should be replenished every time during regular maintenance. In addition, the supplementary dose of generator bearing must be added according to the required amount, not too much, to prevent too much from squeezing into the motor winding and burning the motor.
The function test of regular maintenance mainly includes overspeed test, emergency stop test, fixed value test of hydraulic system components, vibration switch test and stranded wire switch test. You can also do some routine tests on the limit settings of the controller.
In addition to the above three items, regular maintenance should also check the hydraulic oil level, whether the sensor is damaged, whether the sensor power supply works reliably, and the wear of brake pads and brake discs.
2. Daily troubleshooting and maintenance
During the operation of the fan, there will also be some faults that must be handled on site.
First, carefully observe whether the safety platform and ladder in the fan are firm, whether the connecting bolts are loose, whether there is a smell of paste in the control cabinet, whether the cable is displaced, whether the splint is loose, whether the pull ring of the stranded wire sensor is worn and broken, whether the lubrication of the yaw gear box, hydraulic oil and gear box is dry and deteriorated, whether the gauge pressure of the hydraulic station is normal, whether there is wear between the rotating parts, whether there is leakage of each oil pipe joint, and whether the gear oil and hydraulic oil filter indication is normal.
The second is to listen to whether there is a discharge sound in the control cabinet. If there is sound, it may be loose terminals or poor contact. When listening to yaw, carefully check whether the sound is normal, whether there is dry grinding sound, whether there is abnormal sound in generator bearing, whether there is abnormal sound in gearbox, whether there is abnormal sound between brake disc and brake pad, and whether the wind cutting sound of blades is normal.
Third, clean up your work site and wipe all the components and pipe joints of the hydraulic station so as to observe whether there is any leakage in the future. Synchronous motors operate as generators. It is the most commonly used alternator. In modern power industry, it is widely used in hydropower, thermal power, nuclear power and diesel power generation. Because synchronous generators generally adopt DC excitation, when they operate independently, the voltage of generators can be easily adjusted by adjusting the excitation current. If it is connected to the power grid, the voltage is determined by the power grid and cannot be changed. At this time, the result of adjusting the excitation current is to adjust the power factor and reactive power of the motor.
The stator and rotor structure of synchronous generator is the same as that of synchronous motor, and generally adopts three-phase form. Only in some small synchronous generators, the armature winding adopts single phase.
High-speed synchronous generator;
Because most generators and prime movers are coaxially linked, thermal power plants use high-speed steam turbines as prime movers, so turbine generators usually use high-speed 2-pole motors with a rotation speed of 3000 rpm (3600 rpm when the grid frequency is 60 Hz). Four-pole motors are mostly used in nuclear power plants, and the rotating speed is 1500 rpm (1800 rpm when the grid frequency is 60 Hz). In order to meet the requirements of high speed and high power, high-speed synchronous generator adopts hidden pole rotor and special cooling system.
Hidden-pole rotor: the shape is cylindrical, DC excitation winding is placed on the cylindrical surface and fastened with metal slot wedge to make the motor have uniform air gap. Due to the huge centrifugal force when rotating at high speed, the rotor is required to have high mechanical strength. The hidden-pole rotor is generally forged by high-strength alloy steel, and the groove shape is generally open to install the excitation winding. About 1/3 of each polar distance is not slotted, forming large teeth; The other teeth are narrow and called small teeth. The center of the big tooth is the center of the rotor magnetic pole. Sometimes the big teeth also open some smaller ventilation slots, but the windings are not embedded; Sometimes a narrow and shallow groove is milled at the bottom of the groove as a ventilation groove. The hidden pole rotor is also provided with metal retaining rings and central rings at both axial ends of the rotor body. The retaining ring is a thick-walled cylinder made of high-strength alloy to protect the end of the excitation winding from being thrown out by huge centrifugal force; The center ring is used to prevent the axial movement of the winding end and support the retaining ring. In addition, in order to make the excitation current flow into the excitation winding, the collector ring and brush are also installed on the motor shaft.
Cooling system: Because the energy loss in the motor is directly proportional to the volume of the motor, its size is directly proportional to the cubic power of the linear metric level of the motor, and the size of the motor cooling surface is only the quadratic power of the linear metric level of the motor. Therefore, when the size of the motor increases (limited by materials, it is necessary to increase the size to increase the capacity), the heat that needs to be dissipated per unit surface of the motor will increase, and the temperature rise of the motor will also increase. In high-speed turbo-generator, centrifugal force will produce great tangential stress on the surface of rotor and the surface of rotor center hole. The larger the rotor diameter, the greater the stress. Therefore, within the allowable stress limit of forging materials, the diameter of rotor body of 2-pole turbogenerator should not exceed1250 mm. To improve the capacity of large turbogenerator, only by increasing the length of rotor body (that is, using slender rotor) and increasing electromagnetic load can it be solved. The rotor length can reach 8 meters, which is close to the limit. To continue to increase the capacity of a single machine, only the electromagnetic load of the motor can be increased. This makes the heating and cooling problems of large turbogenerators particularly prominent. For turbo-generators below 50,000 kilowatts, a closed-circuit air cooling system is often adopted, and the fan in the motor blows air to cool the heating parts. Hydrogen cooling is widely used in 500,000 ~ 600,000 kW generators. The heat dissipation performance of hydrogen (purity 99%) is better than that of air. Replacing air with it not only has good heat dissipation effect, but also can greatly reduce the ventilation friction loss of the motor, thus significantly improving the efficiency of the generator. However, explosion-proof and leakage-proof measures must be taken when hydrogen cooling is used, which makes the structure of the motor more complicated and increases the consumption and cost of electrode materials. In addition, liquid media can also be used for cooling. For example, the relative cooling capacity of water is 50 times that of air, and the flow rate of water required is much smaller than that of air. Therefore, using a part of hollow wires in the coil and cooling water in the wires can greatly reduce the temperature rise of the motor, delay insulation aging and prolong the life of the motor.
Low speed synchronous generator;
Most of them are driven by low-speed turbines or diesel engines. The number of poles of the motor varies from 4 to 60 or even more. The corresponding speed is 1500 ~ 100 rpm and below. Due to the low rotating speed, salient-pole rotors with low requirements on materials and manufacturing processes are generally used.
Each magnetic pole of salient-pole rotor is usually made of steel plate with a thickness of 1 ~ 2mm, which is assembled into a whole with rivets, and the magnetic pole is covered with excitation windings. The excitation winding is usually made of flat copper wire. Damping windings are usually installed on pole shoes of magnetic poles. It is a short circuit formed by the bare copper bar in the damping groove of the pole shoe and the copper rings welded at both ends. The magnetic poles are fixed on the rotor yoke, which is made of cast steel. Salient pole rotors can be divided into horizontal and vertical types. Synchronous motors, synchronous cameras and generators driven by internal combustion engines or impulse turbines mostly adopt horizontal structures; The low-speed and large-capacity hydrogenerator adopts vertical structure.
The rotor of horizontal synchronous motor is mainly composed of main pole, yoke, excitation winding, slip ring and rotating shaft. Its stator structure is similar to asynchronous motor. The vertical structure must bear the gravity of the rotating part of the unit and the downward pressure of water borne by the thrust bearing. In a large-capacity hydro-generator, this force can be as high as 40-50 meganewtons (about 4,000-5,000 tons of gravity), so this kind of thrust bearing has complex structure and high requirements on processing technology and installation. According to the placement position of thrust bearing, vertical hydrogenerator is divided into suspension type and umbrella type. The floating thrust bearing is placed in the upper or middle part of the upper frame, which is mechanically stable under the condition of high rotating speed and small ratio of rotor diameter to iron core length. Umbrella thrust bearing is placed on the lower frame under the rotor or on the top cover of the steam turbine. The bearing frame is a smaller lower frame, which can save a lot of steel and reduce the height of the generator and workshop from the base.
Parallel operation of synchronous generators Most synchronous generators run in parallel and are connected to the grid to generate electricity. Synchronous generators running in parallel must be consistent in frequency, voltage and phase. Otherwise, internal circulation will be generated between generators at the moment of parallel switching, which will cause disturbance and even damage generators in serious cases. However, before two generators run in parallel, generally speaking, their frequency and voltage are not exactly the same in magnitude and phase. In order to make synchronous generators run in parallel, there must be a synchronous parallel process first. Synchronous juxtaposition methods can be divided into quasi-synchronous and self-synchronous. After synchronous generators are put into parallel operation, the load distribution of each generator depends on the speed characteristics of the generators. By adjusting the governor of the prime Mover and changing the speed characteristics of the generator set, the load distribution of each generator can be changed and the power generation of each generator can be controlled. By adjusting the excitation current of each generator, the reactive power distribution of each generator can be changed and the grid voltage can be adjusted.
Permanent magnet synchronous wind turbine;
Permanent magnet synchronous wind turbine (PMSG), with its advantages of low mechanical loss, high operating efficiency and low maintenance cost, has become another important wind turbine model after doubly-fed induction wind turbine, which has been widely concerned and gradually put into use. The basic structure of permanent magnet synchronous wind power generation system is shown in figure 1, which is mainly composed of wind generator, permanent magnet synchronous motor, frequency converter and transformer.
The basic principle of permanent magnet synchronous wind power generation is to use wind power to drive the blades of the wind generator to rotate and drag the rotor of the permanent magnet synchronous generator to rotate to realize power generation. The permanent magnet synchronous wind power generation system is similar to the cage-type variable-speed constant-frequency wind power generation system, except that the generator used is a permanent magnet generator and the rotor is a permanent magnet structure, so it is not necessary to provide external excitation power, which improves the efficiency. Its variable-frequency constant-speed control is realized in the stator loop. The variable-frequency alternating current of the permanent magnet synchronous generator is converted into alternating current with the same frequency in the power grid through the frequency converter, thus realizing the grid connection of wind power generation, so the capacity of the frequency converter is the same as the rated capacity of the system.
In the past decades, due to the improvement of the performance of permanent magnet materials and power electronic devices, permanent magnet synchronous generators have attracted more and more attention. Permanent magnet synchronous wind power generation system has the following characteristics:
1, permanent magnet synchronous generator system does not need excitation device, and has the advantages of light weight, high efficiency, high power factor and good reliability.
2. Wide range of variable speed operation, that is, supersynchronous operation or subsynchronous operation;
3, the rotor has no excitation winding, the magnetic pole structure is simple, the frequency converter capacity is small, and it can be made into a multipole motor;
4. Reduce the synchronous speed, so that the wind generator and the permanent magnet generator can be directly coupled, which saves the gear speed-increasing box in the wind power generation system, reduces the maintenance work of the generator and reduces the noise.
Applicable occasions:
1. In areas where power facilities are scarce, transportation is inconvenient, and conventional fuels are scarce, but wind resources are abundant, some power consumption problems can be solved, such as providing power for expressway lighting equipment;
2. In the wind farm with relatively small single unit capacity, the permanent magnet synchronous power generation system can be connected to the grid efficiently;
3. Provide AC or DC power supply for remote and light-load users such as rural areas, pastoral areas, border posts and meteorological stations. In daily life, when using alternator to supply power to electrical equipment, it often happens that electrical equipment can't work normally. The reason is that the alternating current output by the generator is not stable enough. At this time, a power regulator is needed to stabilize the voltage, that is, the AC regulated power supply commonly used in daily life. The AC regulated power supply can stabilize the output voltage accuracy of the generator within the range allowed by the normal operation of electrical equipment.
Alternator structure
The structure of alternator is a bit complicated. But whether it is single-phase or three-phase, it is composed of the following main parts:
(1) Excitation part: including exciter and magnetic field part.
(2) Armature part.
⑶ Fence part: the frame including iron frame and equipment preparation part. Asynchronous generators are also called "induction generators". An alternator utilizes the interaction between the rotating magnetic field in the air gap between the stator and the rotor and the induced current in the rotor winding. The rotating direction of the rotor is the same as that of the rotating magnetic field, but the rotating speed is slightly higher than the synchronous rotating speed of the rotating magnetic field. It is often used as a low-power hydrogenerator.
Because the rotor of AC excited generator is excited by AC voltage, its operation mode is flexible, and it has unparalleled advantages in solving the problems of continuous power frequency overvoltage, variable speed constant frequency power generation and speed regulation of motor generator set in pumped storage power station. The main operation modes of AC excited generators are as follows:
1) runs in variable speed constant frequency mode;
2) operate in a wide range of reactive power regulation mode;
3) Run in the power generation-electric mode.
With the increase of transmission voltage in power system and the growth of lines, when the transmission power of lines is lower than natural power, there will be continuous power frequency overvoltage in lines and power stations. In order to improve the operation characteristics of the system, many countries with advanced technology began to study the application of asynchronous generators in large power systems at the beginning of the 6th century, believing that the use of asynchronous generators can improve the stability, reliability and operation economy of large power systems.
Because of its convenient maintenance and good stability, asynchronous generators are often used as low-power hydro-generators to run in the grid. When the rotor of asynchronous motor is dragged along the direction of magnetic field rotation by the prime mover, and its speed exceeds the synchronous speed, the motor enters the generator to run, and the mechanical energy input by the prime mover is converted into electrical energy and sent to the power grid. At this time, the excitation current of the motor is taken from the power grid.
Asynchronous generators can also be connected in parallel with capacitors, and generated independently by their own remanence excitation (see figure). At this time, the voltage and frequency of the generator are determined by the capacitance, the speed of the prime mover and the load. When the load changes, it is generally necessary to adjust the parallel capacitance value accordingly to keep the voltage stable. Because asynchronous motor can generate electricity independently without external excitation power supply when connecting capacitors in parallel, it is desirable under the condition of stable load. For example, it can be used as a lighting power supply for rural simple power stations, and it can also be used as a backup power supply. The tachogenerator is a kind of miniature generator for measuring the rotating speed. It converts the input mechanical rotational speed into a voltage signal for output, and the required voltage signal is proportional to the rotational speed.
Classification of tachogenerator: tachogenerator can be divided into DC tachogenerator and AC tachogenerator.
DC tachogenerator: DC tachogenerator is essentially a miniature DC generator, which can be divided into electromagnetic type and permanent magnet type according to the excitation mode of stator poles. The working principle of DC tachometer generator is the same as that of general DC generator.
Ac tachogenerator: The rotor structure of AC asynchronous tachogenerator is cage-shaped or cup-shaped, and the hollow cup rotor asynchronous tachogenerator is often used in the control system. There are two windings on the stator of the hollow cup rotor asynchronous tachogenerator, one is the excitation winding and the other is the output winding.
The errors of AC asynchronous tachogenerator mainly include:
Nonlinear error: the tachogenerator produces nonlinear error due to the change of direct-axis magnetic flux;
Residual voltage: in actual operation, when the rotor is stationary, the tachogenerator outputs a small voltage;
Phase error: Due to the leakage reactance of the excitation winding and the leakage reactance of the hollow cup rotor, the phase of the output voltage is different from that of the excitation voltage.
Ac synchronous tachogenerator is divided into permanent magnet type, induction type and pulse type. Diesel generator set is an independent power generation equipment, which refers to the power machinery that uses diesel as fuel and diesel engine as prime Mover to drive the generator to generate electricity. The whole unit is generally composed of diesel engine, generator, control box, oil tank, starting and control battery, protection device, emergency cabinet and other components. The whole can be fixed on the foundation for positioning and use, and can also be mounted on a trailer for mobile use. Diesel generator set belongs to intermittent operation power generation equipment. If the continuous operation exceeds 12h, its output power will be about 90% lower than the rated power.