1 reduce transformer loss during power transformation
Transformer losses are divided into no-load losses and load losses. The no-load loss mainly depends on the material of the transformer core and the internal structure of the transformer. The load loss is mainly determined by the material of the coil and the conductor cross section.
1. 1 using energy-saving transformer
Due to the continuous development of material technology and the continuous improvement of the structure of the transformer factory, the development of energy-saving transformers is also very fast, and is currently developed to type 10 (design number) or even type 11. The Type 9 transformer, which is characterized by energy saving, has become a cost-effective type compared to the 10 type with better energy saving effect.
The following is a comparison of the losses of the commonly used type 7, 9, and 10 10 kV distribution transformers (for example, a 1 600 kVA capacity transformer).
Loss comparison table for 10 kV distribution transformers Model no-load loss / kW load loss / kW S7- 1600/10 2. 65 16. 5 S9- 1600/10 2. 4 14. 5 S10- 1600/10 1. 8 14
It can be seen that the energy-saving effect of the energy-saving transformer is still very good, so the energy-saving type 10 transformer or the new type of energy-saving transformer should be preferred.
1. 2 adjust the transformer operation mode to save energy
Minimize the number of transformers running at no load. We know that thermal power plants generally have large-capacity high-voltage start-up transformers. As a backup for high-voltage factory transformers, they also serve as power plants. The capacity is generally the same as that of the largest high-voltage factory transformers. The capacity is large and the no-load losses are also Very big. The starting capacity of the 2 300 MW power plant is generally 40 MW, and the no-load loss is generally 46 kW. According to the calculation of 8 000 h of no-load operation for the whole year, it is necessary to purchase 370,000 kWh of electricity from the grid. If the start/standby change can be designed as a cold standby (not powered when in standby), it can save a lot of power and expenses. Of course, whether to use cold standby has to follow the specific regulations of the regional power grid and listen to the owner's operational opinions. In order to make the start-up change to the cold standby operation mode, the plant power plan should be designed to become normal without public load, and the utility load should be designed for the high-voltage plant transformer of the No. 1 unit, or be allocated to No. 1 and On the high-voltage factory transformer of Unit 2. However, it should be noted that the reliability of the plant electricity should meet the requirements of the code.
Under the premise of meeting the reliability of the plant, the low-voltage factory power wiring should be wired as far as possible by the dark standby power center. In the dark standby power center wiring mode, during normal operation, the two mutually standby transformers are each loaded with half load, and the load loss of each transformer is reduced to 1/4 of the total load, and the energy saving effect is obvious.
Although the use of the Ming spare power center wiring can save the investment of the transformer, but the investment in the cable and cable channel is increased, and the economic advantage is not large. From the perspective of long-term operation, the wiring mode of the dark standby power center is economically more advantageous.
2 reduce line loss and ferromagnetic loss during transmission
2. 1 Select the current carrying conductor surface with economic current density
When the conductor is selected, in addition to the bus bar of the power distribution device, the circuit has a large number of hours of utilization throughout the year, a long busbar (more than 20 m in length), and a circuit with a large transmission capacity (such as a generator to the main transformer and the generator to The mains distribution circuit), the conductor cross section should be selected according to the economic current density. This can reduce the line loss energy consumption under the premise of investment optimization.
2. 2 using closed busbars
In addition to the economic current density selection, the current-carrying conductor of the generator lead-out line should also be based on the phase-closed busbar on the basis of the possibility of layout and installation. In order to make the main building and the front of the A row compact, shorten the conductor length and reduce the loss of the transmission line. At the same time, due to the good shielding effect, the ferromagnetic loss on the transmission path is greatly reduced. In addition, there is a big improvement in operational reliability, reduced maintenance workload and aesthetics. For the traditional design idea, 200 MW and above units use off-phase closed busbars as generator outlets, but in recent years, many 150 MW units, 135 MW units, 100 MW units, 60 (50) MW units have been phased closed. As the generator outlet, the busbar replaces the traditional bare busbar method, and the effect is very good, which is greatly welcomed by the operating unit and the construction unit.
2. 3 reduce ferromagnetic losses during transmission
Under the action of alternating magnetic field, steel materials will produce eddy current loss and hysteresis loss, collectively referred to as ferromagnetic loss. If the ferromagnetic loss is too large, it will cause local overheating of the steel material, which may threaten personal safety, equipment safety or structural safety, and also cause a large amount of power loss. To reduce ferromagnetic losses, we should start from reducing the use of steel materials in alternating magnetic fields, increasing shielding, avoiding the formation of closed loops, and improving the spatial relationship between steel materials and current-carrying conductors.
The specific measures are briefly introduced as follows:
Conductor fittings should be designed with more advanced models and fittings made of non-magnetic materials as much as possible. This reduces losses and also reduces temperature rise and extends the safe life of the fittings.
The space extent of the steel structure should be limited around the reactor in strict accordance with the space dimensions given by the manufacturer. At the same time, we must also pay attention to minimize the use of steel materials around the reactor, and try to increase the distance between the steel structure and the reactor within a reasonable range.
In a space with a strong alternating magnetic field (such as around a reactor and around a large current-exposed conductor), the closed-circuit magnetic circuit should not be constructed using a single-phase conductor supporting steel structure and a conductor-supporting splint in the steel structure design. Reasonably increase the distance between the steel structure and the busbar. The distance (mm) from the center of the busbar to the center of the steel structure is 0.7 times or more of the bus current (A). Other facilities may not be used. Reasonably choose the relative position of the steel structure and the busbar so that the steel structure is as perpendicular as possible to the conductor so that no induced potential and circulation occur. Avoid longer steel structures parallel to the busbars. For the steel structure in large-area reinforced concrete, the steel structure should be cut into discontinuous small sizes or wrapped at the intersection of vertical and horizontal steel bars to reduce the circulation.
Disconnect the closed loop. In the design, the steel members near the high-current busbar should be avoided to form a closed loop that encloses one phase or two phases. If it is unavoidable, a brass weld or an insulating plate can be used to isolate the magnetic circuit. A shield plate (or shielded grid) made of a non-magnetic permeability material with a low resistivity between the high-current open bus and the steel structure can significantly reduce the ferromagnetic loss of the steel structure. The shielding ring is made by adding a non-magnetic permeability material with low resistivity to the high-current open busbar support steel structure, which can significantly reduce the ferromagnetic loss of the steel structure.
3 reduce the loss during power drag
The electric motor used in the power plant is basically a squirrel cage type asynchronous AC motor, which has the advantages of simple structure, reliable operation, low price and easy maintenance, and is the absolute main force of electric drag. However, due to its structural reasons, the efficiency is low and the efficiency power curve is low.
Asynchronous motor efficiency power curve In order to reduce the loss of asynchronous motor in electric drive, first choose high-efficiency motor with high power factor; secondly, adopt speed control technology, use motor to run at low speed at low load, and then improve efficiency and reach The purpose of energy saving and consumption reduction.
According to the formula of the speed of the asynchronous motor: n = n 1 ( 1- s) = 60 f 1 p ( 1- s) It can be known that the method of adjusting the speed of the asynchronous motor is: changing the pole pair number p of the winding; changing the frequency of the power supply f 1; change the slip of the motor s.
According to the above theory, the electric speed control technology of the three-phase asynchronous motor obtained in practice is as follows: 3. 1 variable pole speed regulation
The motor uses a multi-speed motor (generally a two-speed motor), and different pole pairs are obtained through different windings to obtain different speeds. For example, a 2-pole motor becomes a 4-pole motor, and the synchronous speed is changed from 3,000 rpm to 1,500 rpm.
High-voltage multi-speed motors are generally used in high-power fans and high-power pumps. Low-voltage multi-speed motors are generally used in ventilators, machine tools, driving, cranes, etc.
The advantages are: simple equipment, reliable operation and low initial investment. The disadvantages are: the speed change rate is small, and there is a step speed regulation (only two-stage or three-stage speed regulation), which is not suitable for occasions with large load changes and high speed regulation requirements. Compared with single-speed motors, it also has better energy saving effects.
3. 2 frequency control
The AC motor variable frequency speed control system consists of an AC motor, a static frequency conversion device that can be converted by frequency conversion, and its control circuit. Static frequency conversion devices can be divided into two major categories: AC frequency conversion and AC line frequency conversion. Among them, the cross-over frequency conversion application is widely used.
Hand over the frequency converter: also known as direct frequency converter or cycle inverter. It consists of several phase-controlled rectifiers connected to the same AC power supply. The control angle of each phase-controlled rectifier is controlled according to a certain law, so that the rectifier works in the rectified or active inverter state, and multi-phase rectification can be obtained at the output end. The envelope of the wave consists of a lower frequency alternating current. This method is only suitable for high power and low speed AC drag.
AC-DC converter: also known as indirect inverter. It first converts the AC frequency of the grid frequency into a DC power with a controllable or uncontrollable rectifier. After passing through the intermediate DC circuit (DC link), the inverter is converted into AC power with adjustable frequency to control the speed of the motor. The advantages of this kind of frequency converter are: large speed regulation range (generally 0 100% synchronous speed), good smoothness (stepless speed regulation), high efficiency, good power saving effect (average power saving 20% ​​60%), speed regulation Accurate (comparable to DC motor speed control), flexible speed control mode, software control can adapt to various load characteristics of motor speed control requirements, can achieve soft start, reduce motor start disturbance to the grid, can achieve motor overheating, overcurrent Protection against overload, overvoltage, undervoltage, phase loss, grounding, etc., makes the motor run safer and more reliable.
The disadvantage is that the price is higher, but due to the obvious energy-saving effect, the energy cost saved in a few years can recover the equipment investment, and the long-term energy-saving effect is extremely obvious. Since the frequency conversion speed regulation has many advantages, the electric power dragging machinery with large load changes in the power plant or the electric power dragging machinery often running under low load should be adopted after the technical and economic analysis and the possibility of installation. The frequency conversion speed control device can save a lot of electric energy.
3. 3 change the slip rate speed
The rotor is connected in series with the speed variable resistor. The motor adopts a wound-type asynchronous motor, and the number of series resistors in the rotor circuit is switched by the control circuit. As the rotor resistance increases, the slip rate s becomes larger, and the asynchronous motor speed decreases. The advantage of this method is that it is simple and high torque can be obtained. The disadvantage is that the rotor copper consumption increases and the motor efficiency is low.
This method can't save energy, it is rarely used, but it has applications on the lifting machinery. Heavy-duty machinery that is often used should not adopt this type of speed control. Frequency control should be used to save energy.
When cascade speed regulation changes the rotor loop resistance speed, it will consume a lot of power in the regulation resistor. In order to make this part of the power not consumed, a speed control method for adding an additional potential in the rotor circuit is proposed, which is called cascade speed regulation.
Now the cascade speed regulation method is to rectify the slip frequency alternating current of the asynchronous motor rotor circuit from the semiconductor rectifier to the direct current, and then convert the direct current into the same frequency communication with the grid through the static inverter, and feedback back to the alternating current grid through the transformer to improve The efficiency of the speed control system. The advantages are: stepless speed regulation, high efficiency, constant torque, and obvious power saving effect. The disadvantages are: low power factor, small speed range (speed ratio 2 1 4 1), complicated equipment, high investment, and the use of wound-type motors. Generally only used in high power fans, pumps, air compressors, etc. where the speed ratio is less than 2 1 . As the price of high-voltage inverters gradually declines, the high-voltage cascade speed control device will also withdraw from the market and be replaced by high-voltage inverters.
Electromagnetic slip speed regulation. The electromagnetic speed regulation cage motor is used to change the excitation current of the electromagnetic clutch, thereby changing the slip of the asynchronous motor to achieve the purpose of speed regulation. The disadvantage is that the efficiency is low and the energy saving effect is not obvious.
Electromagnetic speed regulation is generally used in coal feeders and powder feeders of boilers. Due to its low efficiency, it has been gradually replaced by frequency converters. It is not recommended in the design.
In combination with the characteristics of the above-mentioned asynchronous motor speed control methods, it is recommended to use variable pole speed regulation or frequency conversion speed regulation. Rotor string resistance speed regulation, cascade speed regulation and electromagnetic speed regulation are not recommended. In the actual design work of electrical professional, it should be based on the load characteristics and speed regulation requirements provided by the process professional, through the technical and economic analysis, flexible selection of speed control mode, and finally achieve the good purpose of energy saving.
4 reduce lighting loss
4. 1 using special lighting regulator
The thermal power plant lighting power generally takes the automatic power supply, the power supply requires the high voltage of the power grid, so that the motor-like power drag load is easier to start, the general supply voltage is 400 / 230 V.
The lighting fixture requires a power supply voltage of 380 / 220 V. There is a contradiction between the two. For the power plant, the power load is more important than the lighting. In actual operation, the power supply voltage of the lighting fixture is moved to the power voltage (400 / 230 V ). The lighting fixture is a resistive load and the power is approximately proportional to the square of the voltage. Therefore, lighting with 400 / 230 V power supply will waste about 10% of energy when using 380 / 220 V power supply, and the waste is very serious. The lighting regulator saves power by maintaining a stable supply voltage of 380 / 220 V. In addition, due to the reduced operating voltage, the power plant lamps have a short life span and frequent replacement of ills. It can be said that it is more than one thing.
4. 2 using energy-saving lamps
With the continuous development of technology, the life of energy-saving lamps has gradually increased, prices have been declining, and its comprehensive economic indicators have obvious advantages. Therefore, the lighting design of power plants should closely follow the development of lighting technology, and actively promote the use of new energy-saving lamps to save energy.
4. The power factor of the gas-discharge lamp with a low power factor is generally between 0. 4 0. 6 and the power compensation factor can be compensated to 0. 85 or higher. The working current is lower than that before the compensation (in accordance with the power factor uncompensated 0.44, after the compensation is calculated as 0.85), the lamp line loss is lower than before the compensation (in accordance with the power factor uncompensated 0. 4, after compensation 0. 85 Calculation), the power saving effect is obvious.
5 Conclusion
Energy-saving transformers, variable frequency drives, energy-saving lighting technology, optimized electrical wiring scheme design, optimized conductor selection, and optimized installation are the main means of electrical energy conservation. As electrical designers, they should adapt to the requirements of new forms and use energy saving and consumption reduction. The guiding ideology of design actively promotes the development of electrical energy-saving technologies.
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