Reactive Power Compensation, Harmonic Control Schemes and Selection of Components (1)

Abstract: This paper briefly describes the solutions of reactive power compensation and harmonic suppression in low-voltage distribution networks and the selection of components needed in complete sets of equipment.
Keywords: filter reactor filter complete set harmonic control harmonic suppressor
1 Foreword With the rapid development and continuous growth of the national economy, electric power construction has made remarkable achievements. By the end of 2004, the installed capacity of China’s power stations has reached 440 million kW, and the annual power generation capacity has reached 2187 billion kW/h. Increased by 14.8%. However, the growth in electricity demand is even more rapid. The contradiction between power supply and demand is becoming increasingly prominent. In the peak period of last year, there were 24 provinces and regions in the country that used electricity during the peak period. At the same time, as most of the power facilities are in a state of overload for a long time, there are many potential safety hazards. There have also been many accidents that have caused great losses to the property of the country and people. This year (2005) still saw a substantial increase in electricity consumption, and the gap in electricity supply at the peak was even greater (only Beijing (2005) still saw a significant increase in electricity consumption, and the electricity supply gap at the peak was even greater (Beijing 2005 only. There is still a substantial increase in electricity consumption, and the electricity supply gap at peak hours is even greater (only when the electricity supply gap in the Beijing region this year is high when the electricity supply gap reaches more than one million KW). The situation of tight power supply is even more severe.
The serious shortage of electricity supply has restricted the speed of the national economy. In order to alleviate the contradiction between current and future power supply and demand, and fundamentally solve the problem, save the use of power and rational use of electricity, in addition to the main channels for increasing national and local investment in power construction and increasing power generation. Electricity - Using various power-saving measures, it is also very important and necessary to maximize the use of existing power facilities. It is to open source and save money. As we all know, the use of reactive power compensation technology to tap the potential of existing power resources is one of the measures that can be quickly and effectively implemented, and it can also save a lot of power energy.
2 Determination of application scheme of reactive power compensation technology
2.1 The concept of reactive power compensation 2.1.1 The reactive power is the indispensable part of the transmission and distribution network as well as the active power. The reactive power is very important and necessary for the normal operation of the power supply system and the load system.
2.1.2 Since there are a large number of inductive loads in the power grid, the power supply department needs to provide sufficient reactive power. If these reactive powers are generated by generators (plants) and transmitted to the required places through long-distance transmission lines, this is obviously unreasonable and uneconomical, and it is practically impossible. The most reasonable and most effective method is to generate (issued) reactive power at or near the place where reactive power is needed, that is, reactive power compensation.
2.2 The role of reactive power compensation 2.2.1 Due to the existence of reactive power, the grid will also have an adverse impact, mainly in the following aspects:
(1) The increase in reactive power leads to an increase in current and an increase in apparent power, thereby increasing the capacity of electrical equipment such as generators, transformers, start-up and control equipment, and conductors.
(2) Increased loss of power supply equipment and lines.
(3) The voltage drop of the transformer and the line increases, causing the supply network voltage to fluctuate. In the power grid, the fluctuation of the active power generally has little effect on the grid voltage, and the grid voltage fluctuation is mainly caused by the fluctuation of the reactive power. If it is an impact reactive power load, it will also cause severe fluctuations in the power grid, and even accidents.
2.2.2 The role of reactive power compensation is to minimize the impact of reactive power on the grid. Its main functions are:
(1) Improve the power factor of the power supply system and load, reduce the capacity and load of transmission lines and power equipment, and reduce power consumption.
(2) Stabilize the voltage of the power supply and power grid, improve the quality of power supply, increase the stability of the power transmission system, and increase the transmission capacity.
(3) Balance the three-phase load and reduce the impact of reactive power on the power grid.
2.3 Method of reactive power compensation With the gradual maturity of power electronic control technology and computer application technology, methods for reactive power compensation are increasing, and the compensation effect is more and more obvious. The economic and social benefits it brings. It is also huge.
2.3.1 Synchrotron camera Synchrotron camera is an early reactive power compensation method. It has been used for decades and has played a very important role in voltage and reactive power control. Synchrotron camera can not only compensate for fixed reactive power. The power can also perform dynamic continuous compensation for changing reactive power, and can also compensate for capacitive and inductive reactive power. However, due to its own shortcomings, it has become less and less application, and it has basically been eliminated and replaced by a new compensation method.
2.3.2 Parallel capacitors and their devices Among the various reactive power compensation methods, shunt capacitors have been characterized by their simple structure, convenient and flexible installation methods, low operating costs and low product prices. It has become the dominant product used in today's reactive power compensation technology. In particular, with the increasing maturity of capacitor manufacturing technologies, indicators such as quality levels, life levels, and reliability for safe operation have been greatly improved; varieties and specifications have become increasingly complete, bringing great benefits to the design and manufacture of compensation devices. convenient. Therefore, the application fields of various capacitor compensation and filtering devices manufactured by the company are becoming more and more extensive. Has gradually replaced the traditional synchronous camera.
However, shunt capacitors also have their disadvantages: for example, only fixed reactive power can be compensated stepwise (the compensation accuracy is determined by the capacitance of a single capacitor in the capacitor bank), and continuous and linear compensation cannot be achieved. In addition, in the presence of harmonics in the system, it may also generate parallel resonance with the inherent reactance in the system, so that harmonic currents are amplified (up to several times or even several times the rated current), resulting in serious capacitors and related components and lines. Overloaded and burned.
2.4 The method of reactive power compensation According to the working mode of the compensation device, it can be divided into: (1) three-phase common compensation; (2) three-phase compensation; (3) comprehensive compensation with a combination of total compensation and supplementary compensation; (4) Three-phase imbalance compensation and several other.
2.5 Determination of reactive power compensation scheme Based on the actual demand of reactive power of the power supply and power system, when deciding to use a shunt capacitor for reactive power compensation, the type, configuration scheme of the device to be used shall be planned, designed and confirmed. When determining the final plan, it is necessary to consider various factors, and to learn from the experience and lessons of the existing various devices.
Because the location of the reactive power compensation needs to be different, the expected goals to be achieved are different, and the nature of the load and the quality of supply and consumption are also different. At the same time, it is also necessary to consider from an economic point of view (investment cost). The actual situation starts with a comprehensive assessment of various options, from which to choose the appropriate program.
2.5.1 In the conditional or necessary condition, the power quality of the system to be compensated shall be tested, analyzed and evaluated. This work requires dedicated test equipment and is completed by professional technicians. This point is very important, and it can be said to be an indispensable link for a complete and effective solution and the design and production of the entire installation. Most of the compensation devices before and even now do not carry out this work seriously before designing, or there are quite a few manufacturing companies that do not have the technology and the ability to do this work at all. It is only based on past experience or before the installation of the device. Reference counterparty factory prototype. This is one of the main causes of fire accidents. Most of the reactive power compensation devices currently in operation have unsatisfactory compensation performance, fail to achieve the design function, and often malfunction, fail to work properly (some have been abandoned). . In addition, when the device is designed, the quality of the selected components and the matching of parameters between various components are reasonable or the assembly process is also an important reason.