The low voltage reactive power compensation device is widely used in the power supply system. The purpose is to improve the power factor of the power grid, reduce the loss of power transformers and transmission lines, improve the efficiency of power supply and improve the power supply environment.
At present, there are many types of compensation devices and different performance. Different compensation devices have different characteristics and are suitable for use in different power grid and load conditions. Therefore, a reasonable selection of compensation devices can minimize the loss of the network and improve the quality of power supply. On the other hand, improper selection or use may result in poor compensation effect, and even cause adverse phenomena such as voltage fluctuation and increase of harmonics, resulting in the decline of power supply quality.
The following is a brief introduction to the classification, characteristics and scope of application of low-voltage compensation devices commonly used in China.
1. Classification of common compensation methods
The common compensation methods are divided into four kinds of static compensation MSC (using ordinary controller + special contactor), quasi dynamic compensation TSC, quasi dynamic compensation MSC+TCR and full dynamic compensation TSC+TCR.
Two, the choice of the way of compensation
In the application of the reactive power compensation device, the compensation method is chosen, which is determined by the working conditions of the power grid and load. First, it is necessary to analyze the compensated lines, and the dynamic compensation for the loads with larger load and faster change (such as the electric welding machine, high power motor and so on) and the energy saving effect. Obviously. For the relatively stable load line, the static compensation method should be adopted. For some special working environment, it is necessary to choose the compensation method carefully, especially in the case that the transient high voltage and high current impact can not be compensated dynamically. The working time of the general electric welding machine is more than a few seconds, and the motor starts for more than a few seconds, and the response time of the dynamic compensation is tens of milliseconds. According to 40 milliseconds, it is a relative steady process from 40 milliseconds to 5 seconds, and the dynamic compensation device can complete this process. If there is no such a relative steady state process in the line and there is a big change in the energy (called transient or flicker), the use of dynamic compensation will cause problems and may cause accidents.
From the perspective of price factors, the input cost of dynamic compensation is about 1-2.5 times of static compensation for the same capacity.
Three, the choice of reactive power compensation controller
The reactive power compensation controller has three sampling modes, power factor type, reactive power type and reactive current type.
Choosing the physical control mode is actually the choice of the reactive power compensation controller. The controller is the command system of the reactive power compensation device, which is sampled, operated and sent out, and the functions of parameter setting, measuring and component protection are all completed by the compensation controller. Over the past decade, it has experienced a rapid development process of discrete components, integrated circuits, monolithic integrated circuits, DSP chips, and its functions are more and more perfect. As far as the overall situation of the domestic market is concerned, because of the large demand for the market, more and more manufacturers are also, their performance and internal quality differences are very large, many products are not worthy of the name, and should be taken seriously when they are selected. Another problem that needs to be paid attention to in selection is that the name of the domestic production controller is all "XXX reactive power compensation controller", and the meaning of "reactive power" in the name is not the physical quantity of the controller. The physical quantity of sampling depends on the type of the product, not the name of the product.
1. power factor controller
Generally, it has the following functions.
The "delay" setting time should be adjusted in the range of 10s-120s to adjust the sensitivity. The sensitivity of the current is not greater than 0-2A.
The power factor should be set at 0.85 (lag) -0.95 (lead) in the input and reset.
Overvoltage protection setting
Display settings, cycle switching and other functions
This sampling method should not only ensure the stability of the line system and the phenomenon of no oscillation, but also give consideration to the effect of compensation. This is a pair of contradictions and can only work in a better state when the parameters are set in the scene. Even if the adjustment is better, it will not be able to remedy the defects of this way, especially when the line is heavy. For example: set the input threshold; cos (lag) =0.95 (lag) the line heavy load at this time, even if the reactive power loss is very large at this time, the reinvestment capacitor bank will not be compensated, but cos phi is not less than 0.95, the controller will not have compensation instructions, and there will be no input in the electric container group, so this control should be used carefully. mode
2. reactive power (reactive power current) controller
The controller of reactive power (reactive current) has solved the defects of power factor type better. A well designed reactive power controller is intelligent, has a strong adaptability, can take into account the stability and compensation effect of the line, and can improve the protection and detection of the compensator. These controllers generally have the following functions:
Four quadrant operation, automatic, manual switching, self identification of the power of various capacitor banks, automatic adjustment of switching time according to the load, harmonic overvoltage alarm and protection, line resonant alarm, overvoltage protection, line low current alarm, voltage and current distortion rate measurement, display electric container power, display cos phi, U, I, S, P Q and frequency.
Some products have combined the controller with the power distribution monitor, and have a standard communication interface.
From the above functions, we can see that its control function is complete. Because of the reactive power controller, the effect of the compensation device is most effective. If the line is in heavy load, it is afraid that cos [Phi] has reached 0.99 (lagging), and a set of capacitors will be put into a set of capacitors so that the compensation effect is best. Some of them adopt DSP chip controller, and its operation speed is greatly improved. Fourier transform is implemented and the anti-interference ability is very strong. Of course, not all reactive power controllers have such a complete function.
3. controller for dynamic compensation
The demand for this kind of controller is higher, which is generally considered with the trigger pulse forming circuit, which requires the controller to have strong anti-interference ability, fast operation speed, and more important is to have a good dynamic compensation function. This kind of controller is also based on reactive power.
At present, the domestic controller used for dynamic compensation has a large gap compared with the similar products abroad. One is that the dynamic response time is slower and the dynamic response time is not good. The two is that the compensation power can not be carried out in one step, which should be the key problem for manufacturers. In addition, the corresponding national standards have not yet been seen, which is lagging behind development.
Four. Conclusion
When choosing the reactive power compensation device, it is necessary to make a comprehensive comparison between the load and the power grid working conditions, considering the effect of the device on the power grid, especially the size of the negative influence and the size of the input cost. Finally, the reactive power of the load is compensated with the accurate capacitive reactive power to make the power factor reach the high level. And improve the quality of power supply. It is particularly important to choose a reasonable compensation method and a good controller and compensation device. Now the power sector acceptance equipment or check the meter is also in accordance with the old mode, that is to see whether the power factor is up to standard. This is not in line with the requirements of the development of electric power technology today. It is hoped that the relevant departments will introduce new policies as soon as possible so as to encourage the adoption of advanced and reasonable compensation devices, and to promote and apply vigorously.
