Keywords: measures to reduce the line loss rate
Introduction to 0
Power loss (referred to as line loss rate) is an important economic and technical index for the national assessment of the power sector, and it is also a comprehensive reflection of the design level, production technology level and management level of the power system. Therefore, it is of great significance to adopt and popularize new technologies, strengthen line loss management and reduce power grid loss, so as to do a good job in energy conservation and improve the economic benefits of power enterprises. Taking 1987 as an example, the national average line loss rate is 8.48%, and the line loss power is as high as 36.775 billion kW·h, while the average line loss rate of the United States, Japan and West Germany is 6. 1%, 6. 0% and 3.7% respectively. If China's average line loss rate drops by 2%, it will save 8.673 billion kW·h of electric energy every year, which is equivalent to the annual power generation of a power plant with installed capacity of 1.200 MW, and the economic benefits are very considerable. So how to reduce the line loss rate? This must start with the composition of line loss, find out the source of power loss, and then take effective measures to reduce the line loss rate.
Cause and composition of 1 line loss
1. 1 Causes of line loss In the power system, electric energy is generated by the transformation of generators through the consumption of primary energy and transmitted to thousands of households through the power grid. In this process, the transmission and conversion elements from the generator to the power grid, such as lines, transformers, reactive power equipment, phase modulation and voltage regulation equipment, insulating media, measuring and metering equipment, protective devices, etc. Consume electricity. In addition, there are some unknown losses. For example, in view of the causes of the above line loss rate and combined with many years of line loss management experience, reducing line loss should start from two aspects: technology and management. First, we should carefully analyze the composition of line loss, and formulate targeted measures according to the specific reasons of line loss to effectively reduce the line loss rate.
1.2 Composition of power loss Power loss is the loss of power in the process of transmission, transformation, distribution and power consumption, which can be divided into three parts: fixed loss, variable loss and other losses.
The fixed loss of 1.2. 1 generally does not change with the load. As long as the equipment has voltage, it will consume electric energy, and there will be losses, regardless of the power or current passing through the equipment. So it is also called no-load loss (iron loss) or basic loss. It mainly includes iron loss, insulator loss, corona loss, dielectric loss of capacitors and cables, voltage coil loss of electric energy meter, etc. of transformers, cameras, voltage regulators, reactors, arc suppression coils and other equipment.
1.2.2 change loss It changes with the change of load and is proportional to the square of current, so it is also called variable loss or short-circuit loss (copper loss). It mainly includes copper losses of transformers, cameras, voltage regulators, reactors, arc suppression coils and other equipment, copper losses of power transmission and distribution lines and household lines, and copper losses of current coils of electric energy meters.
1.2.3 Other losses refer to some unknown factors in the process of transmission, transformation, distribution and use of electric energy, as well as losses caused by stealing, leakage, throwing and sending in the process of power supply and use, which are customarily called unknown losses or management losses.
Cause analysis of high line loss
2. 1 technical reasons analysis
2. 1. 1 line loss is too high ① the power grid planning is unreasonable, the power supply point is far from the load center, and the long-distance transmission increases the loss; Or the loss increases due to unreasonable line layout, near power supply and far power supply, circuitous power supply, long power supply radius and other reasons; (2) If the conductor section is too large or too small, the line will run under light load, no load or overload for a long time, which will not reach the optimal economic operation state, resulting in increased loss. ③ The aging of lines, serious defects, dirty porcelain and other reasons lead to lower insulation grade, increased impedance and leakage, and increased loss. ④ Undercompensation or overcompensation of reactive power leads to reactive power crossover, which affects power supply capacity and increases line loss.
2. 1.2 The loss of main equipment in substation is too high. ① The main transformer with high energy consumption cannot be updated in time. (2) The unscientific operation mode causes the main transformer to fail to operate according to the economic operation curve, resulting in overload operation or light load operation of the main transformer. ③ The reactive power compensation ability is insufficient, and the reactive power ride-through is serious, which is transmitted through lines and transformers, resulting in low power factor, poor voltage quality and increased active power loss. (4) The main equipment is aging, the defects are not eliminated in time, the dielectric loss and the leakage of porcelain bottles and porcelain sleeves increase, and the contact resistance and loss of wiring equipment clamps increase.
2. 1.3 The loss of distribution network is too high ① The capacity of distribution transformer does not match the load, resulting in "big horse-drawn cart" or "small horse-drawn cart", which leads to increased loss. (2) The installation position of distribution transformer shall not deviate from the load center. ③ Unreasonable low-voltage reactive power compensation, under-compensation during peak hours and over-compensation during valley hours. ④ The voltage level setting is unreasonable. The high energy consumption distribution transformer was not replaced in time. ⑤ Unbalanced three-phase load of low-voltage line leads to the increase of neutral current and loss; Because the low voltage line is too long, the terminal voltage drop is too high, which increases the loss; The connecting wire is too thin and too long, which is seriously damaged and increases the loss.
2. 1.4 Large measurement error ① The angle error of current transformer does not meet the specified requirements, and the accuracy is not enough. The cross section of the secondary pipeline is too small and the secondary pressure drop is too large. (2) The electric load is small, the capacity of metering equipment is large, and long-term light load or no-load metering increases the metering error.
2.2 Analysis of management reasons ① The management of copying, checking and receiving in business work is not in place, and the phenomenon of missing copying, estimating copying, missing calculation and miscalculation is serious. (2) There is no electricity meter to measure the domestic and production electricity. (3) Seasonal distribution transformers such as irrigation and drainage and heating cannot be stopped in time. (4) The measuring equipment is not regularly overhauled, calibrated and rotated. ⑤ Users use electricity illegally and steal electricity.
3 Measures to reduce line loss rate
In order to ensure the operating results, reduce the line loss and improve the economic benefits of enterprises, in view of the specific reasons for the high line loss rate, the loss reduction measures are formulated from two aspects of technology and management.
3. 1 Technical measures Technical measures to reduce line losses include measures that require a certain increase in investment for technical transformation of power grids and measures that only need to improve the operation mode of power grids without increasing investment.
3. 1. 1 Improve the power distribution in the network. We know that when the power of the system is inversely proportional to the resistance in the ring network, the power loss is the smallest. We call this kind of power distribution economic distribution. In order to reduce the network loss, measures such as changing the system operation mode, adjusting the operation parameters and load rate can be taken to make the network power distribution close to the economic distribution, make the network operation more economical and minimize the network loss. While the active power is reasonably distributed, the reactive power should also be reasonably distributed. Arrange compensation according to the principle of proximity to reduce the long-distance transmission of reactive power. Adding reactive power compensation device and reasonable configuration can improve the power factor of load, change the distribution of reactive power flow, reduce the active power loss and voltage loss, reduce the reactive power sent by generators and transmitted through lines and transformers, greatly reduce the line loss, and also improve the voltage quality and transmission capacity of lines and transformers. According to the formula Δ p% = [1-(COSφ 1/COSφ2) ]×100% When the power factor is increased from cos φ1to cos φ 2, the power loss reduction rate in the line is Δ p%, and it can be calculated that when the power factor is increased from 0.7 to 0.9,
3. 1.2 Reasonable arrangement of operation mode
(1) Economic operation of power system and power grid. The economic operation of power system is mainly to determine the optimal combination of units and distribute the load economically. On the premise of economic distribution of active load, it is an effective measure to reduce line loss to realize the economic operation of power grid and its equipment. The economic operation of substation is mainly to determine the best combination mode and the best load rate of transformer operation. The determination of the reasonable operation mode of the ring network, whether it is joint operation or open operation, and at which point the ring network is open are related to the safety, reliability and economy of the power grid. In order to enhance power supply reliability and improve power supply economy, closed loop operation should be carried out, but closed loop operation will complicate relay protection and thus affect reliability. In open-loop operation, the best disconnection point should be selected according to the calculation results of network loss and considering the principle of safety and reliability.
(2) Reasonable grid operating voltage The grid operating voltage has an influence on the no-load loss of components in the grid. Generally, in the power supply network of 35kV and above, increasing the operating voltage 1% can reduce the loss by about 1.2%. In order to improve the voltage level of the power grid, in addition to increasing the generator outlet voltage, it is mainly to do a good job of reactive power balance in the whole network, including improving the user power factor and adopting reactive power compensation devices. It is also an important means to adjust the transformer tap on the premise of reactive power balance.
In 6 ~ 10 kV rural distribution network, the no-load loss accounts for about 50% ~ 80% of the total loss, especially in the middle of the night, because of the low load, the proportion of no-load loss is larger, so the voltage should be reduced appropriately according to the user's requirements for voltage offset. For low-voltage power grid, its no-load loss is very small, so it is advisable to increase the operating voltage. Therefore, in the operation of power grid, a large number of on-load voltage regulating devices can be used to reasonably adjust the operating voltage of power grid under different load conditions. (3) Adjust the load curve to balance the three loads, with large peak-valley difference and large loss under the same power supply. When the three-phase load of transformer is unbalanced, especially in low-voltage power grid, it will not only affect the safe operation of transformer, but also increase the line loss. For the load with large peak-valley difference, double-circuit power supply should be adopted. For three-phase unbalanced load, load regulation is the main technical means. Three-phase imbalance often occurs in distribution lines. If the unbalance is large, it will not only increase the loss of phase line and neutral line, but also endanger the safe operation of distribution transformer. In order to reduce this loss, the three-phase load should be adjusted in time, and the power load and time should be arranged and planned reasonably according to the power consumption law of each user to improve the power grid load rate. By adjusting the three-phase unbalanced current, the current in the neutral line is reduced, so as to achieve the purpose of reducing line loss and safe operation.
3. 1.3 Economic operation of transformer According to statistics, the loss of transformer in power grid accounts for 30% ~ 60% of the total system bus loss, and reducing transformer loss is an important content of power grid loss reduction. According to the change of load, the power loss can be reduced by properly adjusting the number of transformers in operation. When the load is less than the critical load, it is more economical to reduce one transformer. On the contrary, when the load is greater than the critical load, parallel operation is more economical. Generally, more than two transformers should be designed and installed in substations, which is the technical basis for changing the operation mode of the system. This not only improves the reliability of power supply, but also can reasonably stop the number of transformers running in parallel according to the load and reduce the transformer loss. At the same time, energy-saving transformers are generally used. For agricultural distribution transformers whose load is greatly affected by seasonal changes, denominator transformers can be used, and the switching capacity can be selected according to the load conditions in different seasons to reduce no-load loss.
3. 1.4 power grid reconstruction The power grid planning is unreasonable due to various reasons, such as insufficient power transmission and transformation capacity and "stuck neck" phenomenon; Or the power point is far away from the load center, and the power transmission is long-distance; Because of unreasonable line layout, power supply is nearby, circuitous and long power supply radius, which not only affects the safety and reliability of power supply, but also increases the power grid loss.
① Adjust the unreasonable network structure: transform the power grid, by erecting new transmission and distribution lines, transform old lines, appropriately increase the conductor section according to the economic current density, and transform circuitous lines, so as to eliminate the "bottleneck" phenomenon under the conditions of voltage drop, construction investment, mechanical strength and heating. Make power grid planning, develop and construct on schedule, and ensure the safe and economic operation of power grid. (2) Power grid boosting transformation: Power grid boosting transformation simplifies voltage level and substation level, reduces duplication and substation capacity, which not only improves power supply capacity, but also receives good loss reduction effect. Because transformer loss accounts for a large proportion in the total loss of power grid, it is feasible to reduce the capacity of repeated substations and adopt energy-saving transformers, which has obvious economic benefits. ③ Optimizing power distribution: Different power distribution modes will lead to great differences in power loss and voltage loss. The power supply should be arranged in the load center as far as possible, and two or more points should be given priority in the heavy load area with high load density and large power supply range. This not only has obvious loss reduction and energy saving benefits, but also effectively improves the voltage quality. ④ Popularize and apply new technologies, new processes, new equipment and new materials: if new energy-saving transformers and new alloy wires are adopted, the energy-saving effect will be remarkable.
3.2 Management measures In addition to technical measures to reduce line losses, strengthening organizational management is also an important measure to reduce losses.
3.2. 1 Improving the line loss management system Line loss work is a full-time, whole-process and all-round work. Strengthening line loss management should start with strengthening the leadership system. Power supply enterprises should establish and improve a three-level line loss management network headed by the director in charge personally, with leaders of biotechnology, dispatching, measurement and business departments and line loss commissioners of various power supply stations, hold regular line loss analysis meetings, focus on key issues, and discuss topics at any time to ensure timely and accurate information feedback and smooth channels for analysis and research. Form a management system to implement loss reduction measures quickly, quickly and efficiently.
3.2.2 Theoretical calculation and analysis of strengthening line loss. Theoretical line loss is the most basic data of line loss management, the basis for analyzing the composition of line loss and formulating technical loss reduction measures, and also the yardstick for measuring the quality of line loss management. Therefore, it is necessary to strengthen the calculation of theoretical line loss and carefully analyze the gap between theoretical line loss and actual line loss. Comparing the actual line loss with the theoretical line loss, when the actual line loss rate is much greater than the theoretical line loss rate, it shows that the management line loss is too large. Starting from the phenomena of "stealing, leaking, poor and wrong" and "copying, checking and collecting", we should formulate targeted management measures to reduce line loss. Through the theoretical calculation and practical analysis of the fluctuation of line loss and line loss rate, the problems existing in management, as well as the weak links and irrationalities of power grid structure layout are found in time, and specific measures are formulated to promote the all-round development of line loss management.
3.2.3 Management Measures In view of these management loopholes analyzed above, the following specific measures should be taken: ① Improve the management system, vigorously carry out business investigation, investigate and deal with illegal electricity use and electricity theft, install anti-theft watt-hour meters for key users, adopt high-voltage and low-voltage metering boxes according to different users and loads with different electricity properties, and strengthen the management of metering points. (2) replace the zero value and damaged porcelain bottles, clean up the polluted porcelain bottles, properly handle the trees within the specified range of the line channel, and improve the insulation level of the line. ③ Strictly guard against and promptly correct the phenomenon of "estimation, leakage and delivery" in the work of copying, checking and collecting electricity charges, improve the electricity management system, further strengthen business management and standardize the electricity market. (4) Under economic and reasonable conditions, the fixed loss and variable loss in theoretical line loss are basically equal. When the fixed loss is greater than the variable loss, it shows that the line is in a light load operation state and does not reach the economic and reasonable value, resulting in large theoretical and actual line losses, and efforts should be made to increase the power load of the line; When the load has no development potential, adjust the transformer of "big horse-drawn car" to improve the comprehensive load rate of transformer and reduce no-load loss. When the fixed loss is less than the variable loss, it means that the line is overloaded and does not reach the economic and reasonable value. As a result, both theoretical and practical line losses are large, so the reactive power compensation capacity on the line should be increased, the power factor of the load should be appropriately increased, and the transmission amount of reactive power on the line should be reduced. Appropriately increase the actual operating voltage of the line; Adjust and transform circuitous and "stuck neck" lines; Shorten the power supply radius; Adjust the three-phase load to make it as balanced as possible; Adjust the transformer to make its capacity match the power load.
4 conclusion
Reducing line loss is an important way for power supply enterprises to improve economic benefits. Line loss management workers should organically combine strengthening management with technical loss reduction, that is, while strengthening line loss management, they should also choose appropriate technical measures according to the actual needs of local power grids in order to achieve higher social and economic benefits.