1 The necessity of split-phase automatic compensation
Automatic reactive power compensation is divided into three-phase capacitor automatic compensation and split-phase capacitor automatic compensation according to the nature.
Three-phase capacitor automatic compensation is suitable for three-phase load balanced power supply and distribution system. Because the three-phase circuit is balanced, the reactive current in the circuit is the same, so when compensating, the signal to adjust the reactive power parameters is taken from any of the three phases, and according to the detection results, the three-phase simultaneous switching can ensure the quality of the three-phase voltage. Three-phase capacitor automatic compensation is suitable for a large number of three-phase power equipment in factories and mining enterprises.
In civil buildings, a large number of single-phase loads, lighting, air conditioning, etc., due to the randomness of the load change is large, it is easy to cause a serious imbalance of the three-phase loads, especially in the operation of residential buildings in the three-phase imbalance is more serious. As the sampling signal for regulating and compensating reactive power is taken from any one of the three phases, the two phases that are not detected are either overcompensated or undercompensated. If over-compensation, the over-compensation phase of the voltage rise, resulting in control, protection components and other power equipment due to over-voltage and damage; if under-compensation, the compensation phase of the circuit current increases, lines and circuit breakers and other equipment due to the increase in the current caused by the heat is burned. In this case, the traditional three-phase reactive power compensation, not only energy saving, but also a waste of resources, it is difficult to effectively
compensate for the system reactive power compensation, compensation process generated by the over- and under-compensation and other drawbacks is the normal operation of the entire power grid has brought serious harm.
According to the information, a local complex is a set of shopping malls, banks, offices, garages, hotels as one of a class of high-rise buildings, with a total floor area of 3.2 million m2. The main power equipment are air conditioning units, pumps, fans and lighting fixtures, etc., which lighting fixtures are single-phase loads, the power factor in the 0.45 to 0.75. The low voltage active load 2815 calculated, the power factor is 0.45 to 0.75 between. The low-voltage active load is calculated to be 2815kW, of which the active load for lighting is 1086.5kW, and the other loads are basically three-phase loads such as air conditioners, fans, pumps, elevators, etc. The reactive power before compensation is 3182kW. The reactive power before compensation is 3182kvar, and if the overall power factor is compensated to 0.92, it needs to be compensated 1982kvar, and the reactive power after compensation is 1200kvar. The original design adopts the three-phase centralized automatic compensation of shunt capacitor bank in the low-voltage distribution room, and after the completion of the project and putting it into use, there are often cases that the instruments, lamps and other electric equipments are burnt out or can't be used normally, which affects the normal operation and work. After the project was completed and put into use, there were frequent cases of burnt-out or inoperative electrical equipment such as instruments and lamps, which affected normal operation and work. After the scene test, found that the low-voltage feeder circuit three-phase load imbalance, the gap is very large, the current difference is large, the maximum phase current difference of 900A; detection of bus voltage, three-phase bus voltage, some as high as 260V, and some as low as 190V. through the analysis of three-phase capacitor auto-compensation caused by the results.
For three-phase imbalance and single-phase distribution system using split-phase capacitor automatic compensation is a better way to solve the above problems, the principle is to adjust the reactive power parameters by the signal taken from each of the three-phase, according to the size of the inductive load in each phase and the power factor for the corresponding compensation, the other phases do not affect each other, so it will not produce under-compensation and over-compensation of the situation.
The control module and data acquisition module of this device adopt new type of microcontroller and large-scale integrated circuit, and the switching module adopts high-power thyristor, which realizes zero-voltage input and zero-current removal of capacitor bank, no closing surge current impact, no sparks and harmonic interference. The features of the product are as follows:
(1) digitalization and intelligence of the control module is realized, and the switching execution unit has no contact, which ensures the control precision and operation reliability;
(2) fully automatic split-phase and graded on-demand compensation;
(3) the parameters of over-voltage, under-voltage, and under-current delay can be flexibly set, and it has a perfect over-limit alarm and over-voltage, under-voltage, phase-loss, zero, harmonic overrun protection shrinking and closing functions, to ensure the safe operation of the system;
(4) real-time digital measurement and display of the main parameters in the power grid: power factor, voltage, current, harmonic voltage and current, active power and power, reactive power and power, etc.
(5) with harmonic analysis, measurement of the total harmonic distortion (THD) and the 1st to 31st harmonic voltage and current, to provide accurate harmonic analysis and analysis for the management of harmonic. (6) Adopting "self-healing" capacitor, which has the advantages of long service life, high reliability, small temperature rise and no need for special heat dissipation device, etc.; (7) Equipped with data acquisition function and standard communication interface (RS232), which can realize remote real-time monitoring and computer network management;
(8) Adopting "self-healing" capacitor, which has the advantages of long service life, high reliability, small temperature rise and no need for special heat dissipation device, etc. (7) With data acquisition function and standard communication interface (RS232), it can realize remote real-time monitoring and computer networking management;
(8) It adopts modular structure design, easy to maintain and upgrade.
From the functions of the above products, it can be seen that the intelligent three-phase automatic reactive power compensation can automatically detect the power factor of each phase of the load, and at the same time, automatically phase by phase into the required amount of capacitor compensation for each phase, in order to make each phase of the reactive power compensation to achieve the best state, for the large number of single-phase loads, which is easy to produce the three-phase imbalance of the power consumption units such as residential districts, hotels, restaurants, shopping centers, and other civilian buildings, has the effect of improving the power factor of the power distribution system, the power factor of the power factor of the power factor. Distribution system has improved power factor, improve grid efficiency, improve voltage quality, saving electricity, increase the active capacity of the transformer and other significant effects, to a greater extent to meet the "greening of the grid" requirements. 2 group capacitance automatic compensation application in the low-voltage grid in a large number of power equipment for the inductive, especially in large areas, large openings in shopping malls, office buildings and other places of daily life and office space, most of the fluorescent lamps with good luminous effect for artificial lighting. Fluorescent lamps have good light effect, long life, no pollution and other characteristics, is a green light source. At present, civil construction projects in the large use of inductive ballast fluorescent lamps, it has a low cost, long life, low maintenance workload, less investment, etc., but its start-up time is long, the power factor is low, about 0.5 ~ 0.6, its own loss is large, increasing the supply and distribution system network loss, resulting in a waste of energy.
Capacitive compensation to solve the problem of low power factor of inductive loads in large shopping malls and office buildings is a common method in the current design.
We are in the design of the usual practice there are two: in the power distribution set up a centralized high-voltage or low-voltage compensation cabinet, the system front-end compensation, although to meet the power supply department on the grid power factor requirements, but the following levels of branch circuits are not compensated for, so the low-voltage distribution lines in the reactive current is large, resulting in the line cross-section and switching capacity of the distribution can not be reduced, and can not guarantee the quality of power supply for the entire low-voltage system; the other practice is the capacitive compensation, the power factor is low. The quality of power supply; another practice is to set up capacitors in each power equipment or each lighting fixture individually and separately for compensation, this way the effect is better for the factory and mining enterprises using a single large-capacity power equipment is more applicable, but for large shopping malls and other civilian buildings, compensation investment cost is too large, cost-effective and decentralized installation, resulting in a large amount of maintenance, maintenance difficulties, and capacitor utilization is low, the practical application is not ideal. Practical application is not ideal, so rarely used.
In the current low-voltage compensation capacitor technology and manufacturing quality, automatic switching device has improved greatly under the premise that the author believes that the distribution system in such civil buildings set up compensation capacitors in groups, that is, according to the functional partition of the building, the more centralized power, electrical equipment, lower power factor of the distribution box set up at the capacitor compensation device is more appropriate.
Group compensation can improve equipment utilization, reduce the capacity of the distribution system
Depending on its power S =, it can be seen in the active power under the premise of unchanged power factor can be improved to reduce the reactive power, reduce the capacity of the distribution system.
When the power factor from 0.65 to 0.92, equipment utilization:
η = × 100% = × 100% = 29.35% that is, after compensation, equipment utilization increased by 29.35%.
In the selection of the same type and cross-section of the cable, reducing the line loss
According to the formula: I =, line loss P = I2R, then:
ΔP = 2R-2R η = = = × 100% = × 100% = 50.08% that is, the compensation of the line loss reduced by 50.08%.
2 The feasibility of group compensation
The following engineering applications to illustrate the feasibility of group compensation.
A new bookstore building by the shopping mall, bookstore business hall, catering, hotels, underground garage, office composition, is a high-level, more complex functions. One of the 1 to 6 floors of the bookstore business hall, a single floor area of about 2800m2 (standard layer, each layer is the same), its lighting using inductive fluorescent lamps, power factor is low. Program design only in the substation to set up a centralized compensation cabinet.
1 to 6 layers of distribution lighting box from the substation using a circuit power supply, switch for 1250A, air-insulated busway selection of a section of 1250A, each layer of distribution lighting box inlet switch selection of 250A; grouped in each layer of capacitor compensation than the substation set up in a centralized compensation cabinet capacitor total capacity to be higher than about 20%. But reduce the switch, power supply line investment, this part of the cost relative to the capacitor investment is much higher. Each layer in the distribution lighting box set capacitor compensation and does not increase the number of distribution boxes, only the size of the distribution lighting box to increase the size of the capacitor installed in the box, which also saves the low-voltage distribution of capacitor compensation cabinets within the floor space. Another because the compensation capacitor configuration of the intelligent controller, product modularity, with data acquisition functions and standard communication interface (RS232), can realize remote real-time monitoring and computer networking management, easy to detect, maintain and upgrade.
From the above example can be seen, according to the setup of each layer of distribution lighting box group installed capacitor compensation better solve the centralized and individual setup compensation caused by the increase in reactive current in the line, the corresponding distribution line cross-section and switching capacity and compensation investment costs, installation and decentralization, large amount of maintenance, maintenance and other issues. For large shopping malls, office buildings and other large number of civil buildings using low power factor equipment design should be used according to the specific circumstances of the group set capacitor compensation is more reasonable