Power station load and power transformer capacity, number of units selected - Database & Sql Blog Articles

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According to the situation of the substation supply and output in the power supply area, the safety type of the transformer type, quantity and capacity and the economic operation conditions and requirements are compared and analyzed. Combined with the actual operation examples on the site, the economic operation and capacity and quantity selection of the power transformer are introduced. The relationship between safety and economic benefits is raised and relevant precautions are raised.
1 Introduction In order to meet the requirements of social power consumption and power supply safety and reliability, in the specific work of substation construction, expansion and transformer capacity expansion, the primary consideration is to select the capacity of the transformer according to the power supply load of the substation (1) and The number of units used; the capacity selection is too large, increasing the investment of the transformer itself and related equipment purchase and installation, operation and maintenance, resulting in waste of funds; the capacity selection is too small to meet the demand of power supply, overloading the transformer, causing equipment damage, affecting the substation externally Safe and reliable power supply; while the quantity is too small, it can not meet the requirements of wiring mode and power supply reliability, affecting maintenance and lack of necessary spares; too many quantities, increasing investment in supporting facilities, difficulty in substation layout, increasing maintenance and repair workload, transformer capacity and quantity Proper selection, not only saves the construction of one-time investment, but also can help the safe and economic operation of the transformer, reduce the cost of operation and maintenance; this paper combines the relevant rules and regulations of the transformer overhaul operation, combined with the actual experience of the author's field work, proposes the transformer capacity. The principle of selecting the number of units to be followed and the conditions and requirements for economic operation, comparing the economic and technical and safety of different schemes, analyzing the factors to be considered in the selection of transformer capacity and number of units, and comprehensively determining the power supply load and the capacity and number of transformers. Safety and benefit analysis.
2 Principles of power transformer capacity and number selection follow The transformer capacity and number of substations are important factors affecting the structure of the power grid, power supply reliability and economy (2), and the choice of the size and number of units often depends on the current status of the regional load. And the rate of growth, depending on the size of the one-time construction investment, depends on the ability of the surrounding upper-level grid or power plant to provide the load, depending on the power distribution equipment technology and performance indicators associated with it, depending on the nature of the load itself and The reliability requirements of power supply depend on the unit cost of transformers, system short-circuit capacity and transportation installation conditions. In recent years, with the continuous improvement of transformer manufacturing technology, the quality and safe operation level of transformers have been greatly improved; The rate of loss reduction is large, the load rate of transformer economic operation is continuously reduced; and the national energy conservation and emission reduction policy encourages enterprises to carry out economic operation; the number of units and capacity for construction, expansion and transformer capacity increase is not clear in China. Regulations are also constantly increasing with the level of technology
(1) The rated capacity of the transformer should be able to meet the needs of the electric load in the power supply area, that is, to meet the total calculation load of all the electric equipment, and avoid the long-term overload operation of the transformer. The capacity of the new substation transformer should meet the needs of 5~10 years of planned load, prevent unnecessary expansion and capacity expansion, and reduce large-area and long-term power outages caused by expansion and capacity increase; It is good to put two transformers, and the normal load ratio of the transformer is not more than 50%.
(2) For substations with important users in the power supply area, one transformer should be considered in the state of fault or power failure maintenance, and the other transformers ensure the primary and secondary loads of the user within the allowable time after taking into account the overload capacity. For a substation of general load, any one transformer should be shut down, and it should be able to ensure that 70%~80% of the total power supply is not affected. The number and capacity of transformers in urban substation should meet the requirements of N-1.
(3) Although the unit capacity of large-capacity transformers is low, building a large-capacity substation in a high-load-density power supply area can save investment. The larger the capacity, the more obvious the effect; but to ensure the flexible operation mode, multiple transformers should be considered. The selection of the capacity of a single transformer should not be too large or too small. It is necessary to reserve the development of the load and expand the capacity of the substation from small to large. The number of transformers is from small to large. The operation mode of the three transformers in the urban substation is the most flexible and reliable. .
(4) In order to ensure the flexible and reliable operation mode of the substation, reduce and facilitate the spare capacity reserve, facilitate the cooperation with the phase-connected power distribution device, facilitate the maintenance and repair, and achieve the unified specification of the substation. The type of transformer capacity should be minimized, generally not exceeding Two, here, it is recommended to harmonize the transformer capacity level in a substation that supplies electricity to the city.
(5) Within a certain capacity range, the capacity increase and loss will be reduced, but the saved electricity cost may be difficult to compensate for the increase of investment cost, and the switching capacity of the matching switch and other equipment is large, so the choice of transformer capacity should be considered. One-time investment in transformers and their associated equipment (3), implementation of national reduction and energy conservation policies, if necessary, the calculation of economic operation mode.
(6) Since the power supply enterprise requires the urban power supply to meet the reliability criterion of N-1, the selection of the transformer capacity, in addition to meeting the above conditions, should consider the economic loss and social impact caused by the power supply under the accident and maintenance conditions, at least After a transformer is powered off, part of the load can be transferred to the surrounding substation without affecting the normal power demand of all users.
(7) For the substation dense area of ​​the power supply enterprise, because there is a contact power supply line between the substations, the substation can handle mutual supply, and the capacity selection of the transformer can be appropriately reduced. Under normal conditions, the sub-areas are separately powered, when the power supply output cannot be met. It is possible to rely on the surrounding substation to carry part of the load through the tie line, but in the end, it is necessary to increase the substation layout or increase the number of transformers to gradually meet the requirements of load supply and output.
(8) For the substation with the generator set connected to the low-voltage side, the transformer capacity can also be appropriately reduced, but the capacity selection should be considered: 1 Meet the rated capacity of the generator set. When the regional load is minimum, the transformer can be output to the power system through the transformer. The capacity of the transformer must be greater than the generating capacity of the unit; 2 The sum of the rated capacity of the transformer and the generator set is greater than the maximum load in the area; 3 When the generator set is out of service, the transformer should be able to guarantee 70%~80% of the total power supply of the entire load. Affect and ensure that the primary and secondary loads are used normally; 4 and the equipment parameters of the upper-level power grid are properly matched to meet the requirements of the system short-circuit capacity.
3 Conditions and requirements for economic operation of power transformers The economic operation of power transformers is based on ensuring the safe operation of transformers and satisfying the quality and reliability of power supply to users. Fully utilize the equipment conditions of substations, select the operating mode of transformers, and reduce transformers. The energy loss of itself increases the power factor of the power supply side, achieving the goal of reducing energy consumption. The determination of power supply load and transformer capacity and number is related to the way of transformer economic operation. The implementation of transformer economic operation is closely related to the number and capacity of transformers in the substation and the performance and loss parameters of the transformer. It is based on the premise of ensuring safe and reliable power supply. An integrated economic and technological activity runs through the entire process of design, maintenance, and decommissioning of power transformers; factors and conditions must be considered in substation construction, expansion, and transformer capacity expansion; And the substation equipment itself should generally have and meet the following conditions, which should be fully considered in the design and selection of the transformer.
(1) New substation construction in phases, considering the increase of load, when there is only one transformer in the first phase, the capacity of the transformer should be determined according to the final scale. The load ratio of the transformer should be close to the optimal economic operation area, generally below 75%. If the expansion is not carried out in the short term, the transformer should not be operated at full capacity.
(2) Multiple transformers operating in parallel shall meet the parallel conditions, that is, the junction group has the same phase relationship; the voltage and transformation ratio are the same, the allowable deviation is the same, and the voltage of each stage in the voltage regulation range is the same; Due to the electromotive force difference, a circulating current is generated, which affects the capacity output and burns out the transformer. The short-circuit impedance is the same, the control is within the allowable deviation range of 10% (1); the capacity ratio is between 0.5 and 2; the load distribution is ensured to be uniform, the transformer with short-circuit impedance and small capacity is prevented from being overloaded, and the transformer with large capacity and short-circuit impedance is owed. Load, the size of the short-circuit impedance must meet the requirements of the system short-circuit current, otherwise it should take restrictions.
(3) The technical parameters of the power transformer should be selected based on the overall reliability of the transformer, taking into account the advancement and rationality of the technical parameters, taking into account the impact on the system safety, taking full account of the inherent loss of the transformer itself, and the load loss. When basically the same, try to use a transformer with low no-load loss, and the load loss meets the national standard "three-phase oil-immersed power transformer technical parameters and requirements" (4).
(4) When the power transformer is operated in the load area, the temperature of its windings, clamps, leads, insulating oil and insulating parts should not be too high. In the temperature limit specified by the transformer load guide, avoid high temperature operation and insulation aging. Accelerate and shorten the life of the transformer and cause damage (3). It is also necessary to prevent the transformer from operating at a high temperature, causing excessive loss of the transformer itself, affecting the output efficiency, and causing unnecessary waste of electrical energy.
(5) In a substation equipped with a standby transformer, it is necessary to select a small transformer with integrated power loss (which should be included in the cooling power of the transformer) to be put into operation. According to the change law of the load, the optimal combination mode should be selected reasonably. The load, increase the load rate, increase the power factor, and make the transformer work in the preferred section of the economic operating zone.
(6) The average load factor of the economic operation zone of a single transformer, the upper limit of β is 1, and the lower limit is Pk/Po, (where Pk is the no-load loss of the transformer and Po is the rated load loss); the average load of the operating section is preferred in the economic operation zone. The coefficient, the upper limit of β is 0.75, and the lower limit is 1.33 (Pk/Po).
(7) The economic operation of the transformer must be established under the premise of safe and reliable power supply. The standby transformer should be equipped with reliable automatic input devices to ensure automatic operation when the transformer is faulty, ensuring that the normal power supply is not interrupted.
(8) Arrange the parallel operation mode of the transformer, and calculate the rated breaking capacity of the tie switch to prevent the system from being damaged due to insufficient switch interruption capacity when the system is short-circuited, affecting the automatic isolation of the fault point; When self-propelled, it should be able to automatically disconnect the other power supply connected to the bus side.