Basic knowledge of wind power

impeller

Wind farm wind turbines usually have 2 or 3 blades, tip speed 50 ~ 70m / s, with such tip speed, 3-blade impeller can usually provide the best efficiency, while the 2-blade impeller is only reduced by 2-3% effectiveness. It is even possible to use a single-blade impeller with a balanced weight, which in turn reduces its efficiency, which is typically 6% lower than a 2-vane impeller. Although there are fewer blades, the cost of the blades is naturally reduced, but this comes at a price. For well-balanced blades, impellers with fewer blades will spin faster, which can cause problems such as tip noise and corrosion. More people think that the 3 blade is more satisfactory from the aesthetic point of view. The force on the impeller is more balanced and the hub can be simpler. However, the hub of a 2-bladed and 1-bladed impeller is usually more complicated because the speed is changed when the blade sweeps through the wind. In order to limit the fluctuation of the force, the hub has an upward-turning direction. The characteristics of the board. The seesaw hub, with the impeller attached to the hub, allows the impeller to tilt back or forward a few degrees in the plane of rotation. The oscillating motion of the blades significantly reduces the load generated by the gusts and shears on the blades during weekly rotations.

The blades are made of reinforced glass plastic (GRP), wood and wood, carbon fiber reinforced plastic (CFRP), steel and aluminum. For small wind turbines, if the impeller diameter is less than 5 meters, the material of choice is usually concerned with efficiency rather than weight, hardness, and other characteristics of the blade. For large wind turbines, the blade characteristics are usually difficult to meet, so the choice of materials is more important.

The blades of most of the world's large wind turbines are made of GRP. Most of these blades are coated with polyester resin by hand, as is the usual method of manufacturing hulls, gardening, gaming facilities and consumer goods worldwide. The process requires a very high level of technology to get the desired results, and if people are less concerned about weight, such as blades less than 20 meters in length, the design is not very complicated. However, there are many very advanced ways to use GRP, which can reduce the weight and increase the strength. We will not go into details here. The glass fiber is to be placed more accurately. If it is placed in a prepreg sheet, high-performance resins, such as controlled epoxy ratios, are used and processed at high temperatures. Nowadays, simple hand-placed polyesters have emerged, providing a cost-reducing path for GRP blades by carefully selecting and placing fibers.

Yaw system

The yaw system of a wind turbine is also referred to as a wind device, and its role is to be able to quickly and smoothly align the wind direction when the direction of the wind speed vector changes, so that the wind wheel can obtain maximum wind energy.

Small micro wind turbines commonly use rudder rudder wind, which consists of two parts. One is the tail wing, which is mounted on the tail shank parallel to the wind wheel axis or at a certain angle. In order to avoid the effects of wakes, the tail can be upturned and mounted at a higher position.

The small and medium-sized wind turbines can use the steering wheel as the wind-guiding device. Its working principle is roughly as follows: When the wind direction changes, the two steering wheels (its rotation plane is perpendicular to the rotation plane of the wind-wheel) located behind the wind-wheel rotates, and wind is transmitted through a set of gear transmission system. The wheel is deflected. When the wind wheel is redirected to the wind direction, the steering wheel stops rotating and the wind process ends.

Large and medium-sized wind turbines generally use an electric yaw system to adjust the wind wheel and align it with the wind direction. The yaw system generally includes a wind direction indicator, a yaw motor, a partial planetary gear reducer, and a large gear of a revolving body. Its working principle is as follows:

The wind vane, as a sensing element, transmits the change of the wind direction to the processor of the control circuit of the yaw motor through an electric signal. After comparison, the processor sends a clockwise or counterclockwise yaw command to the yaw motor in order to reduce the yaw time. Gyroscope torque, motor speed will be reduced through the coaxial reducer, the yaw moment will act on the large gear of the rotary body, drive the wind turbine yaw to the wind, when the wind is completed, the wind vane loses the electric signal, the motor stops working The yaw process ends.

Wind turbine generator

All grid-connected wind turbines convert mechanical energy into electrical energy through three-phase alternating current (AC) motors. There are two main types of generators. Synchronous generators operate at exactly the same frequency as their connected power grids. Synchronous generators are also known as alternators. Asynchronous generators operate at a slightly higher frequency than the grid frequency, and asynchronous generators are often referred to as induction generators.

Induction generators and synchronous generators have a non-rotating part called the stator. The stators of the two motors are similar. The stators of the two motors are connected to the grid and they are all three-phase windings on the laminated core. The composition, after energization, produces a magnetic field that rotates at a constant rotational speed. Although both motors have similar stators, their rotors are completely different. The rotor in the synchronous motor has a DC-directed winding called field winding. The field winding establishes a constant magnetic field to lock the rotating magnetic field established by the stator winding. Therefore, the rotor can always rotate at a constant, constant speed that is synchronized with the stator field and grid frequency. In some designs, the rotor magnetic field is generated by a permanent magnet machine, but this is not commonly used for large generators.

The rotor of an induction motor differs, for example, in that it consists of a squirrel-cage winding short-circuited at both ends. The rotor is not electrically connected to the outside world. The rotor current is generated by the relative motion of the rotor cutting stator rotating magnetic field. If the rotor speed is exactly equal to the speed of the magnetic field of the stator speed (as with a synchronous generator), there is no relative movement and there is no rotor induced current. Therefore, the total speed of the induction generator is always slightly higher than the rotating magnetic field speed of the stator, and the speed difference is slip, which is during normal operation. It is probably 1%.

Synchronous generators and asynchronous generators

Generators that convert mechanical energy into electrical energy devices commonly use synchronous excitation generators, permanent magnet generators, and asynchronous generators. Synchronous generators are widely used. Synchronous generators are used in conventional power grids such as nuclear power, hydropower, and thermal power. In wind power generation, synchronous generators can be independently powered and can be connected to the grid for power generation. However, synchronous generators must have synchronous detection devices to compare the frequency, voltage, and phase of the generator side and the system side during grid connection. The wind turbines are adjusted so that the frequency of the generator's electrical energy is consistent with that of the system. The voltage regulator adjusts the generator voltage to be consistent with the system voltage; at the same time, the speed of the fine tuning wind turbine is monitored from the periodic inspection disk so that the voltage of the generator coincides with the voltage phase of the system, which is at the same time in frequency, voltage and phase. At a moment, the breaker was incorporated into the system. In the same period, the device can be manually synchronized and connected to the grid during the same period. However, in general, synchronous generators are rarely used in grid-connected wind turbines due to their relatively high cost of construction and troublesome grid connection.

Control monitoring system

The operation and protection of the wind turbine requires a fully automatic control system, which must be able to control the automatic start-up, the mechanical adjustment of the blade pitch (on the variable-pitch wind turbine) and shut down under normal and abnormal conditions. In addition to control functions, the system can also be used for monitoring to provide information such as operating status, wind speed, and wind direction. The system is based on a computer. In addition to a small wind turbine, control and monitoring can also be performed remotely. The control system has the main function of passing:

1. Sequence control start, stop and alarm and running signal monitoring 2. Low speed closed loop control of yaw system 3. Pitch device (if variable pitch wind turbine) Quick closed loop control 4. Wind park controller or remote computer <br> <br> fan drive system of communication

The mechanical energy generated by the impeller blades is transmitted to the generator in the drive system of the nacelle, which includes a gear box, clutch and a brake system that enables the wind turbine to be reset in an emergency when the wind turbine is stopped. Gearboxes are used to increase the impeller speed from 20 to 50 rpm to 1000 to 1500 rpm, which is the speed required to drive most generators. The gearbox can be a simple parallel shaft gearbox, where the output shaft is a different shaft, or it can be a more expensive one, allowing the input and output shafts to be collinear, making the structure more compact. The drive system is designed for output power and maximum dynamic torque load. Due to fluctuations in the power output of the impeller, some designers try to control the dynamic load by increasing the mechanical adaptability and cushioning drive, which is very important for large-scale wind turbines due to its large dynamic load and the induction generator's The cushion is smaller than the small wind turbine.

Asynchronous generator

The permanent magnet generator is a generator that changes the rotor of an ordinary synchronous generator into a permanent magnet structure. The commonly used permanent magnetic materials include ferrite (BaFeO), samarium cobalt 5 (SmCo), etc., and the permanent magnet generator is generally used. In a small wind turbine.

Induction generator refers to the asynchronous motor is in the working state of power generation. There are two kinds of excitation modes: excitation of the grid power source (excitement) and self-excitation of the shunt capacitor (self-excitation).

1 Grid power excitation and power generation: It connects the asynchronous motor to the power grid. The stator windings in the motor generate a rotating magnetic field that rotates at a synchronous speed, and then drags with the prime mover to make the rotor speed greater than the synchronous speed and the direction of the magnetic torque provided by the grid. Must be opposite to the direction of speed, and the direction of the mechanical torque is the same direction as the speed, then the mechanical energy of the prime mover is converted into electrical energy. In this case, the active power generated by the asynchronous motor is transmitted to the grid; at the same time, the reactive power of the grid is used for excitation, and the reactive power consumed by the magnetic flux leakage of the stator and the rotor is supplied, so when the asynchronous generator is connected to the grid for power generation It is generally required to add a reactive power compensation device, usually using parallel capacitor compensation.

2. Self-excited generation of shunt capacitors: The shunt capacitors are divided into two types: star and triangle. Excitation Capacitor Access During the generator's use of its own remanence to generate power, the generator periodically charges the capacitor; at the same time, the capacitor is also periodically discharged through the stator windings of the asynchronous motor. The alternating charge and discharge process of this type of capacitor and the windings continuously plays the role of excitation, so that the generator can generate electricity normally. The excitation capacitor is divided into a main excitation capacitor and an auxiliary excitation capacitor. The main excitation capacitor is a capacitor required to establish a voltage under no-load conditions. The auxiliary capacitor is designed to ensure a constant voltage after the load is connected to prevent voltage collapse.

Through the above analysis, the start-up and grid-connection of asynchronous generators is convenient and convenient for automatic control, low price, reliable operation, convenient maintenance, and high operating efficiency. Therefore, in wind power generation, grid-connected generators basically use asynchronous power generation. Machines, while synchronous generators are often used for stand-alone operation.

Design of yaw system

According to the magnitude of the adjusting torque, the design of the gear transmission part can be calculated. When the strength of the driving pinion driving the large gear of the revolving body can not be satisfied, two sets of yaw motors---planetary planetary gear reducer can be selected and placed symmetrically on both sides of the main wheel of the wind wheel. The capacity of each motor is total. Half the capacity. The calculation of the gear transmission can be calculated according to the open gear drive. The main wear pattern is the tooth surface wear failure. If the steering torque is large, the tooth surface contact strength should be calculated in addition to the calculation of the bending strength.

It is noteworthy that the coaxial cable of the generator output power of most wind turbines rotates together when the wind turbine is yawing. In order to prevent cable rotation caused by yaw overrun, a cable untwisting device should be set up, and a twisted cable sensor should be added to monitor it. The twisted state of the cable. The wind wheel located in the downwind direction can automatically find the wind direction. In the overall layout, the weight in front of the tower should be considered slightly heavier, so that the balance will be better when the fan is running.

Motor switching

According to the determination of wind speed, whether to select small generators for grid-connected power generation or large generator idle, if the wind speed is lower than 8 meters/second, the small generators are connected to the grid and the fan operation status is switched to “input G2”. If the wind speed is higher than 8m/s, select the "idle G1" operating state.

Put in G2:

The small generator contactor is closed, and the generator grid-connected current is controlled by the SCR to 350A. Once the input process is complete, the thyristor is removed and the fan is switched to the "Run G2" state.

Wind power is put into small generators for power generation. If the average output power is too low for a certain unit of time, this is the state where the small generator is disconnected and the fan is switched to “waiting for re-arming”. If the average output power exceeds the limit value of 110 kW, the small generator is cut off and the fan operation status is switched to “G1 idle”.

G1 idling:

The fan waits for the wind speed to reach the wind speed of the large motor. Once this wind speed is reached, the fan will switch to the “G1” state.

Put in G1:

The contact of the large generator is switched on. The generator's grid-connected current is limited to 350A by SCR. At the end of the input process, the thyristor was removed and the fan was switched to the "Run G1" state.

Run G1

The large motor of the blower is put into power generation. If the power output is less than the limit value of 80 kW in a certain period of time, the large generator is cut off, and the operation state of the blower is switched to the state of “switching G11-G12”.

Switch G1-G2

The contactor of the large generator was cut off and the contactor of the small generator was turned on. The thyristor limited the current of the generator to 700A. Once the input process was completed, the thyristor was cut off and the fan was switched to the “running G2” state.

Wait for reinvestment If the output of the small generator is less than the limit value, this operating state is actuated. In this state, the contactor of the small generator is cut off. If the wind speed is effective, the fan will switch to the “G2” state. If the wind speed is lower than the limit, the fan will switch to the “idle G2” state.

The transition between the fan's working state and the fan's working state indicates how the conversion between the various operating states is achieved.

Raising the level of working status can only increase layer by layer, and the level of working status can be reduced to one or more layers. This method of transition between working states is a basic control strategy. Its main starting point is to ensure the safe operation of the unit. If the working status of the wind turbine needs to be converted to a higher level, it must be increased layer by layer. This process is used to determine if each fault in the system has been detected. When the system detects a fault during the state transition, it automatically enters the shutdown state.

When the system detects a fault in the operating state and the fault is fatal, the operating state has to go from running to tight stop, which can be realized immediately without the need to stop and stop.