Other Commonly Used Energy-Saving Operation Methods

Abstract

Some of the electrical equipment used in the industry are resistive loads, such as resistance heating furnaces, reactor heating.

24.1 Reactive Power Compensation of Motors

24.1.1 Reactive Current and Reactive Power

Some of the electrical equipment used in the industry are resistive loads, such as resistance heating furnaces, reactor heating rods, chemical reaction vessel heating jackets, etc., while more electrical equipment is electric motors, transformers, etc. For resistive electrical loads, the phase of the current in the line is the same as that of the working voltage. For inductive electrical loads, due to the limitation of power in the circuit, the current on the inductance cannot change abruptly, so the phase of the current in the inductive line lags behind working voltage 90°.

Taking a three-phase motor as an example, assuming that the motor is in a Y connection, the phase current is I, the line current I_i is equal to the phase current I, the phase voltage is U, the line voltage U_i is equal to U, and the phase current I lags φ behind the phase angle of the phase voltage U, we decompose the phase current I in the line into two parts I₁ and I₂, as shown in Fig. 24.1.

Fig. 24.1

Decomposition of current

In Fig. 24.1, the current I₁ is in the same direction as the phase voltage U, I₁ is the active current, I₁ and U generate single-phase active power P₁, and the active power P₁ is converted into mechanical energy and heat energy, as shown in Eq. (24.1).

$$ P_{1} = U \times I_{1} = U \times I \times COS\varphi $$

(24.1)

In Fig. 24.2, the current I₂ is perpendicular to the phase voltage U, and I₂ is a reactive current, which is caused by the coil inductance L. I₂ and U generate single-phase reactive power P₂. The P₂ is used for the connection between the electric field and the magnetic field although it does not do work, this energy conversion is necessary for the operation of the motor, so the reactive current is also necessary in the motor. The reactive power P₂ is shown as follows

$$ P_{2} = U \times I_{2} = U \times I \times \sin \varphi $$

(24.2)

When the motor is in no-load operation, the active current component of the motor is very small, and the current of the motor is basically the reactive excitation current. At this time, cos_φ tends to 0, and sin_φ tends to 1.

Seen from the power supply side, the total capacity (also called apparent power) transmitted by the line is S, as shown in Eq. (24.3).

$$ S = \sqrt 3 \times U_{i} \times I_{i} $$

(24.3)

In Eq. (24.3), Ui is the line voltage of the three-phase motor, and I_i is the line current of the three-phase motor.

The three-phase total active power of the motor is P, which is also the power consumption of the electric motor we often say, such as Eq. (24.4).

$$ P = 3 \times U \times I_{1} = 3 \times U \times I \times COS\varphi = \sqrt 3 \times U_{i} \times I_{i} \times COS\varphi = S \times COS\varphi $$

(24.4)

The three-phase total reactive power of the motor is Q, such as Eq. (24.5).

$$ Q = 3 \times U \times I_{2} = 3 \times U \times I \times \sin \varphi = \sqrt 3 \times U_{i} \times I_{i} \times \sin \varphi = S \times \sin \varphi $$

(24.5)

The reactive current I₂ is necessary to establish a rotating magnetic field in the motor, but the reactive current in the transmission line will generate heat loss I₂² × R, and these losses will be wasted. The reactive current flowing through the transformer will also occupy the capacity of the power supply transformer, and this part of the capacity does not do work, which reduces the power supply capacity of the transformer.

24.1.2 Compensation of Reactive Current and Reactive Power

Generally, the reactive current needs to be compensated in the line. Most of the compensation measures are carried out by connecting capacitors in parallel, because the current on the capacitor is ahead of the voltage by 90° and can be offset by the current on the inductor lagging behind the voltage by 90°. The relationship of current after connecting capacitors in parallel is shown in Fig. 24.2.

Fig. 24.2

Compensation of reactive current

In Fig. 24.2, if the current I_c of the compensation capacitor is equal to the amplitude of I₂, but the phase is opposite, I_c = -I₂, then the current in the power supply line after compensation changes from the original I to I₁, and Fig. 24.3 supplies power to the motor current representation before and after line compensation.

Fig. 24.3

Current before and after compensation

In Fig. 24.3, before compensation, the current in the motor power supply line is I, and after compensation, the current in the line is reduced to I₁, and the heat loss is reduced from I² × R to I₂² × R. In actual compensation measures, 100% compensation is generally not performed, that is, the power factor cos_φ after compensation is not required to be 1, and of course overcompensation cannot occur.

If the power factor before compensation is cosφ₁, and the power factor required after compensation is cosφ₂, assuming that the active power of the load is P_a (kW), the capacity Q_a (kvar) to be compensated is shown in Eq. (24.6).

$$ Q_{a} = \sqrt 3 \times U_{i} \times I_{i} \times sin\varphi_{1} - \sqrt 3 \times U_{i} \times I_{i} \times sin\varphi_{2} = P_{a} \times \left( {tan\varphi_{1} - tan\varphi_{2} } \right) $$

$$ = P_{a} \times \left( {\sqrt {\frac{1}{{\cos^{2} \varphi_{1} }} - 1} - \sqrt {\frac{1}{{\cos^{2} \varphi_{2} }} - 1} } \right) $$

(24.6)

When performing compensation according to Eq. (24.6), it is necessary to measure the actual active power Pa of the electric load and the power factor cosφ1 before compensation, and then calculate the compensation capacity Q_a.

Under rated operating conditions, the relationship between the actual active power Pa, the rated output power Pe of the electrical load, and the rated efficiency ηe is shown in Eq. (24.7).

$$ P_{a} = \frac{{P_{e} }}{{\eta_{e} }} $$

(24.7)

24.1.3 Reactive Power Compensation of Motors

If the distance between the motor and the power distribution room is relatively close, we can adopt the method of centralized compensation in the power distribution room. For the situation far away from the power distribution room, the reactive current of the motor will cause loss in the line, and this part of the loss cannot be distributed in the power distribution room. It is compensated by reactive power compensation in the room, so it is necessary to perform local compensation next to the motor.

According to the requirements of reactive power in-situ compensation for small and medium-sized motors, it is generally required to compensate 90% of the no-load current of the motor. Several commonly used calculation methods are introduced below.

• (1) Compensate according to Eq. (24.6), and the power factor cosφ2 after compensation is generally required to be 0.95–0.97.

• (2) In order to avoid overcompensation, it is generally compensated according to 90% of the no-load current, and the compensation capacity Q_a (kvar) is calculated according to Eq. (24.8).

  $$ Q_{a} = 0.9 \times \sqrt 3 \times U_{i} \times I_{0} \times 0.001 $$

  (24.8)

In the Eq. (24.24–24.8), Ui is the rated voltage of the motor, and I0 is the no-load current of the motor, which can be found out from the samples of the motor.

Compensation capacity Qa calculated according to Eq. (24.7), and then calculated power factor cosφ2 after compensation according to Eq. (24.6) and Eq. (24.7), pay attention Compensation has occurred.

• (3) Calculate the compensation capacity according to the data on the motor nameplate, such as Eq. (24.9).

  $$ Q_{a} = \left( {2.12.7} \right) \times \left( {1 - \cos^{2} \varphi_{e} } \right) \times I_{e} \times U_{e} \times 0.001 $$

  (24.9)

In the Eq. (24.8–24.9), cosφe is the rated power factor, I_e is the rated current of the motor and U_e is the rated voltage of the motor, the coefficient in front of the 2-pole motor is 2.1. The coefficient in front of the 4-pole motor is 2.4, and the coefficient in front of the 6-pole motor is 2.55, and the coefficient in front of the 8-pole and 10-pole motors is 2.7.

Issues to be aware of:

• (1) We cannot simply calculate the power by multiplying the ratio of the actual current to the rated current of the motor by the rated power. Unless the actual current of the motor is near the rated current. The no-load current of the motor is not too small.

• (2) The compensation methods mentioned above are all calculated for fixed-speed motors. If a frequency converter is used for speed regulation, compensation is not required.

• (3) Capacitor switching of the capacitor compensation device on the power supply side of the inverter may lead to a sudden drop in voltage, sometimes resulting in a malfunction of the inverter and a protective shutdown.

• (4) The compensation capacity calculated by Eq. (24.6) is suitable for other power lines and loads.

24.2 Reduce Voltage and Save Electricity When the Motor is Lightly Loaded

• (1) For some fixed-speed motors with large load changes, they often work under no-load, light-load or even power generation conditions, such as various industrial conveyors, port belt conveyors, coal mine belt conveyors, cement belt conveyors, steel rolling equipment, machine tools, grinding machines, punching machines, polishing machines, cutting machines, compressors, oil well pum** units, forging machines, presses, concrete molding machines, rubber molding machines, etc.

If the load is not allowed to reduce the speed when it is lightly loaded, you can consider reducing the voltage of the motor to save power, such as some belt conveyors. In the state of power generation, it may be necessary to take measures to feedback electric energy to the grid. If the equipment is allowed to change the speed, such as the dust removal fan in a steel mill, you can consider speed regulation and power saving measures.

Because factors such as voltage fluctuations and equipment overload must be considered when selecting a motor, its power margin usually has a certain ratio. A certain amount of electric energy is wasted. Therefore, when the motors of these devices are under light load or no load, appropriately reducing their operating voltage can reduce their loss and improve the operating efficiency of the motor.

Reducing the voltage of a light-load or no-load constant-speed motor can reduce the excitation current and iron loss of the motor, thereby producing a power-saving effect. The way to reduce the voltage can be through transformer step-down, thyristor step-down or series partial voltage reactance implemented in the form of a device. The power supply voltage of the motor should not be reduced too much, otherwise the torque of the motor will drop too much. Under the condition of constant load, it may cause the slip rate to rise and the rotor current to rise. The total consumption of the motor will increase instead if the rate at which the copper loss rises is increased.

Ways to reduce voltage by using inductance coils and transformers:

• (1) Three inductance coils are connected in series at the three input terminals of the three-phase motor (similar to the governor of a household electric fan). There are two types of adjustable and non-adjustable inductance of the inductance coil for voltage reduction.

• (2) The stepwise reduction of voltage can be realized by changing the position of the tap connected to the transformer coil, or by stepless adjustment of the self-coupling voltage regulating transformer output tap position to continuously and smoothly adjust the output voltage. The method of using series inductors and transformers to divide voltage has no harmonic pollution, but the disadvantage is that it is bulky and the adjustment speed is slow by switching contacts.

The method of using the thyristor to step down the voltage is to change the conduction angle of the bidirectional thyristor on the three-phase power line, so as to achieve the purpose of reducing the voltage. The power saver in this way can also easily realize the soft start and Soft stop function. The disadvantage of this method is that there is harmonic interference to the power grid, and the advantage is that the adjustment speed is fast and the volume is small.

Figure 24.4 shows two implementations of voltage reduction. U, V, and W are connected to the input voltage of the power line. By detecting the magnitude of the motor current and the phase angle between the current and voltage, the load rate of the motor can be judged. When the electric motor is in light-load operation, for the series inductance mode, open the contact of KM1, and connect the inductance L1, L2, L3 to the power supply circuit of the motor in series. Due to the voltage drop of the inductance, the working voltage on the motor is reduced. For thyristor step-down mode, open the contact of KM1, control the conduction angle of bidirectional thyristor SCR1, SCR2, SCR3, and change the average effective voltage value on the motor.

Fig. 24.4

Two ways of step-down regulation

What needs to be reminded is that if the variable load equipment that does not require the motor to run at a constant speed, such as hydraulic presses, injection molding machines, dust removal fans in steel mills, etc., when maintaining, cooling or venting, it is to ensure the oil pressure and not stop the machine. This power-saving method is far less effective than the method of frequency conversion speed regulation and speed reduction.

2. When the △-connected motor running at a constant speed is in a light-load working state, the slip of the motor is less than the rated value, and the rotor current is not large. At this time, the line voltage of the winding can be reduced to 1/2 of the original by changing the Y connection, so that the iron loss and the no-load current decrease. Because the torque of the motor is proportional to the square of the voltage, the torque decreases to 1/3 of the original, the slip increases slightly, and the rotor current increases slightly, but the total motor losses are reduced. However, the definition of light load means that when the motor with △ connection is changed to Y connection, the total loss of the motor must be reduced. The load rate when the losses in the two ways are equal is the critical load rate βΔY, and the critical load rate of the △ connected motor can be calculated according to the relevant parameters of the △ connected motor are obtained as follows.

$$ \beta_{\Delta Y} = \sqrt {\frac{{\frac{2}{3} \times P_{Fe} + 0.75 \times P_{0Cu} }}{{2 \times \left[ {\left( {\frac{1}{{\eta_{e} }} - 1} \right) \times P_{e} - P_{0} } \right]}}} $$

(24.10)

In Eq. (24.10), P_Fe is the iron loss of the motor (kW), P_0Cu is the no-load copper loss of the motor (kW), P_e is the rated power of the motor (kW), P₀ is the no-load loss of the motor (kW), η is the rated efficiency of the motor (kW).

When the actual load rate of the △connection motor is greater than βΔY, the motor remains in △connection, and when the actual load rate of the △connection motor is less than βΔY, the motor switches to Y connection.

If there is no variable load equipment that requires the motor to run at a constant speed, the Y-Δ conversion method may not be as effective as the frequency conversion speed regulation and speed reduction method to save electricity.

3. For light-load motors with variable frequency operation, at the same frequency, the iron loss of the motor can be reduced by reducing the output voltage of the frequency converter. Because the product of voltage and current has decreased to realize the energy-saving operation of the motor, many inverters provide energy-saving operation mode options. When the load is likely to be in light-load operation, the "energy-saving" operation mode should be selected.

24.3 Power-Saving Control of Equipment Such as Hydraulic Presses, Injection Molding Machines, and Dust Removal Fans

In the industry, there are also many loads that are under load changes. However, due to the characteristics of the equipment itself, when the equipment does not need to provide liquid flow, the power consumption of the equipment increases instead, such as injection molding machines, hydraulic machines and other loads. The hydraulic oil pump will have a large load change under different working conditions. Since most of the oil pumps that transport hydraulic oil are positive displacement oil pumps, the characteristics of this oil pump are that the oil output is proportional to the speed, and the oil output is small, and the pressure is small. Therefore, in the standby and pressure maintenance sections of this type of oil pump, although the oil consumption decreases, the output pressure rises and the power consumption increases. The oil exceeding the safety pressure returns through the relief valve, resulting in a lot of waste of electric energy. Since the load allows the oil pump to reduce the speed of the oil pump while maintaining the oil pressure during the pressure maintaining stage, the frequency conversion transformation can have a very good power saving effect.

Due to the impact of the smelting cycle, the dust removal fan in the steel plant needs a large air volume during the oxygen blowing and steelmaking stages (about half the time) for the production of a furnace of steel. After the converter taps steel (about half the time), the required air volume is immediately reduced, and the fan is often in this alternate working mode. The fan adjusts the air volume by the damper at the light load stage, which wastes a lot of electric energy. This type of load can be adjusted in speed. In the blowing stage, the fan works at a higher speed level. When the load is light, the motor speed is reduced to a lower level, which can produce a significant power saving effect. In particular, the greater the proportion of time after tap** in a cycle, the greater the power saving ratio.

Taking injection molding machines as an example, most injection molding machines use hydraulic transmission and electro-hydraulic proportional control technology. The hydraulic system of the equipment is composed of positive displacement hydraulic oil pumps (vane pumps, plunger pumps, piston pumps, etc.) and related oil circuits and accessories. The flow rate of the hydraulic oil pump is directly proportional to the rotational speed. Under the power supply condition of power frequency 50Hz, the motor of the oil pump operates at the rated rotational speed. The power consumption of the hydraulic system accounts for about 80% of the total power consumption of the injection molding machine. The injection molding machine is in different sections such as mold clam**, mold locking, injection, pressure holding and cooling, mold opening and ejection, etc. The oil pressure and oil volume required by the injection molding machine vary greatly, especially during the cooling and holding time, the flow rate is almost zero. The oil pump motor runs at rated speed, the oil pressure rises, and the high-pressure oil overflows through the relief valve, causing a large amount of waste of electrical energy.

Use PLC and other control equipment to detect the current working status of the injection molding machine. When the injection molding machine is in different states such as mold clam**, injection, pressure holding, sol, cooling, mold opening, thimble, and standby, use a frequency converter to adjust the speed of the oil pump. Make the oil supply of the oil pump match the oil demand of the injection molding machine, so as to avoid the phenomenon of high-pressure overflow and reduce the power consumption of the oil pump. Figure 24.5 is the schematic diagram of the power saving control system of the injection molding machine.

Fig. 24.5

Energy saving of injection molding machine oil pump

Fig. 24.6

Two ways to reduce voltage

In Fig. 24.5, PLC is used to detect the running state of the injection molding machine. According to the different sections of the injection molding machine, such as mold clam**, mold locking, injection, pressure holding and cooling, and mold opening, the analog output of PLC controls the output frequency of the inverter. Use the frequency converter to adjust the speed of the oil pump. When the injection molding machine is at a low oil consumption, reduce the speed of the oil pump to avoid the problems of high oil pressure and too much energy consumption, so as to achieve energy-saving operation.

24.4 Lighting Step-Down and Power Saving

Lighting electricity consumption accounts for about 10% of the country's total electricity consumption. It can be said that since human beings entered the era of electrification, lighting has been everywhere. How to achieve energy-saving lighting is of great significance.

Energy saving in the general sense refers to the comparison on the basis of completing the same work. According to the same point of view, energy saving work in the field of lighting needs to maintain the illuminance of lighting fixtures to save energy. In fact, due to human eyes, the response to the light intensity is related to the surrounding environment and the length of time in the dark, so it may not be the best to mechanically follow the method of maintaining the constant illuminance.

According to a large number of experimental statistical results, the acuity of human eyes to illumination is not linear, but logarithmic. According to the logarithmic theory of vision and light intensity, if the light intensity decreases by 10%, vision decreases by 1%. When it is 10%, the illuminance of commonly used electric light sources, such as fluorescent lamps, is only reduced by about 7%. The slight change in illuminance caused by a small reduction in light input power can hardly be felt by the human eye, but it is beneficial to prolonging the life of lamps, reducing maintenance costs and realizing energy-saving operation. But there is a positive meaning.

In the lighting power supply system, in order to avoid the terminal voltage being too low due to line loss and peak power consumption, it is often transmitted at a higher voltage. The design of street lamps also takes more consideration of the voltage and brightness of the lamps at the end of the line. After midnight, there are few pedestrians on the road, and because of the low power consumption, the grid voltage rises, resulting in an inversion of illuminance and demand, which not only shortens the life of the lamps, but also greatly increases power consumption.

In order to reduce this waste, we can use autotransformer step-down, series variable inductance coil step-down, thyristor chopper step-down or inverter step-down to reduce the supply voltage of street lamps to achieve energy saving. The magnitude of the voltage reduction depends on the lower limit of illumination allowed by the lighting and the fluctuation range of the circuit voltage. According to the different night time periods and the voltage level, the voltage of the lighting fixtures is properly reduced without affecting the lighting requirements of passers-by to achieve Power-saving operation. Figure 24.6 shows two ways to step down voltage by using transformer taps and step** down by using thyristor.

For the thyristor step-down method and the method of using the inverter to step down, harmonics will be generated, which will pollute the power grid. The advantages are small size, simple control, and the method of step** down by using transformer taps or variable inductance coils has no harmonics.

For some street lamps, a higher working voltage is only required when starting up, and the power supply voltage can be appropriately reduced after being ignited, so as to maintain its normal illuminance, effectively save electricity, and prolong the life of the lamp.

Taking AC220V powered lighting fixtures as an example, we can control them in this way. At the beginning, we can soft start with 90% of the voltage, and then slowly increase to 100% of the rated lighting voltage to preheat the lamps, which can also reduce the voltage to the lamps. Then reduce the lamp voltage to 95% for normal power supply. According to the flow of pedestrians on the local roads, determine a midnight time (such as 23:00). After this time, reduce the voltage to 90% of the rated voltage, and it will dawn in the early morning for a period of time before (such as the increase of pedestrians on the road starting at 5 o'clock), the voltage will be raised to 95% for power supply until it finally goes out. If there is a period when the grid voltage is too high in the middle process, we can increase the step-down range, and the power saving ratio will be greater. Of course, this is just an example. In practice, readers can implement other better power-saving control strategies according to the specific conditions of their own enterprises.

Energy-saving methods such as turning off lights when people go out are beyond the scope of this book.

24.5 Waste Heat Recovery

In steel, chemical, cement, textile, glass, ceramics, boilers, power generation and other industrial fields, a large amount of waste heat is wasted, including high-temperature product and slag waste heat, high-temperature waste gas waste heat, chemical reaction waste heat, waste steam and wastewater waste heat, cooling waste heat from media, waste heat from combustible waste gas, liquid waste, etc. The total waste heat resources of various industries account for about 17 to 67% of their total fuel consumption, and about 60% of the total waste heat resources can be recycled.

In the metallurgical industry, the waste heat that can be used includes: the waste heat in the billet heating furnace, the waste heat in the rolling steel continuous heating and soaking furnace. The waste heat in the wire rod annealing furnace, the waste heat in the sintering machine.

In the chemical industry, it can be used the waste heat used includes: the waste heat of synthetic ammonia blowing gas combustion, the waste heat of flue gas from the first (second stage) furnace of synthetic ammonia, and the waste heat of upstream and downstream gas of synthetic ammonia.

In the building materials industry, the waste heat that can be used includes: waste heat in cement kilns, the waste heat in various ceramic down-burning furnaces and tunnel kilns, the waste heat in glass kilns. The waste heat in kaolin spray drying hot blast furnace.

In petrochemical industry, the waste heat that can be used includes: waste heat in various heating furnaces, waste heat in hydrocarbon pyrolysis furnace (working temperature is about 750 ~ 900°C), waste heat in catalysis, waste heat in ethylbenzene dehydrogenation reactor, and waste heat in cyclohexanol dehydrogenation chemical reactor recycling.

In the textile printing and dyeing industry, the waste heat that can be used includes: boiler flue gas waste heat, setting machine waste heat, printing and dyeing hot sewage waste heat.

In the sulfuric acid industry, the waste heat that can be used is: SO₂ high temperature furnace gas from boiling Medium waste heat, waste heat in the boiling layer of the boiling roaster for sulfuric acid production, waste heat in hydrochloric acid and nitric acid furnaces.

There are many ways to recover waste heat, the efficiency of comprehensive utilization or direct utilization is high, and the efficiency of indirect utilization is low. The sequence of utilization of steam waste heat is: power heating, power generation and heating, production process use, direct replacement of motor-driven equipment, use of steam turbine to generate electricity, and domestic use. The utilization sequence of hot water waste heat is: for production process utilization, return to boiler utilization, and domestic use. The utilization sequence of air waste heat is: production utilization, HVAC utilization, power utilization, power generation utilization.

Figure 24.7 is the appearance of a power plant flue gas waste heat recovery and utilization equipment.

Fig. 24.7

Flue gas waste heat recovery and utilization equipment in a power plant

24.6 Solar Photovoltaic Power Generation Technology

Semiconductor Photovoltaic Effect: When the light shines on the solar cell, photons with sufficient energy excite electrons from covalent bonds in P-type silicon and N-type silicon, generating electron–hole pairs, and the electrons move to the positively charged N region, the holes move to the negatively charged P region, the charge is separated, and a voltage is generated between the P region and the N region. For solar silicon cells, the value of the open circuit voltage is about 0.5 to 0.6V.

Solar cells use the photovoltaic effect of semiconductors to directly convert light energy into electrical energy: silicon atoms have 4 electrons. If phosphorus atoms with 5 electrons are mixed into pure silicon, it becomes a negatively charged N-type semiconductor. Boron atoms with 3 electrons are doped in silicon to form a positively charged P-type semiconductor. When they are combined together, a potential difference will be formed on the contact surface, and sunlight will irradiate the P–N junction, and holes will flow from the N pole region to the P–N junction. The P pole area moves, and the electrons move from the P pole area to the N pole area to form a current, which becomes a solar cell. The more light-energy absorbed by the surface of the solar cell, the greater the current formed in the solar cell. A large number of solar cells are packaged in series to form a large-area solar cell module.

The shape of the solar cell is shown in Fig. 24.8.

Fig. 24.8

Solar cell

Off-grid photovoltaic power station: This system is composed of solar cell square array, system controller, battery pack, DC/AC inverter, etc. It is not connected to the public power grid and is mainly used in areas without public power grids, such as pastoral areas and remote People in mountain villages, plateaus, islands, and deserts provide electricity for lighting, television, broadcasting, and communications, and provide power for communication relay stations, weather stations, border posts, navigation marks, and highways.

Grid-connected photovoltaic power station: The power station is composed of a solar cell array, a system controller, and a grid-connected inverter.

Figure 24.9 is a photo of a solar photovoltaic power plant.

Fig. 24.9

A solar photovoltaic power station

24.7 Wind Power Technology

Wind power generation is to convert wind energy into mechanical work, and then generate electric energy. The principle is to use wind power to drive the windmill blades to rotate and drive the generator to generate electricity.

According to the orientation of the fixed axis of the blade, there are two types of wind turbines: horizontal axis type and vertical axis type. Horizontal axis wind turbines are currently the mainstream in the world.

The diameter of the blades of wind turbines can reach 216 m, and the power of a single machine can reach 11MW. There are lightning protection strips in the blades. When the blades are struck by lightning, the lightning protection strips will lead the lightning current into the ground.

Like the pump and fan equipment, the power generated by the wind turbine is proportional to the cube of the wind speed.

Because wind power does not use fuel, and does not produce radiation or air pollution, it is recognized as a green energy source.

The internal structure of the horizontal axis wind turbine is shown in Fig. 24.10, and a wind farm is shown in Fig. 24.11.

Fig. 24.10

Internal structure of horizontal axis wind turbine

Fig. 24.11

A wind farm