In the power supply system, reactive power compensation can improve the power factor of the power grid, reduce the loss of power transformers and transmission lines, and improve the power supply environment. Reasonable selection of compensation devices can minimize the loss of the power grid and improve the quality of the power grid. If the selection or use is improper, it may cause many problems such as voltage fluctuation and increased harmonics in the power supply system. So what are the common compensation, separate compensation, and mixed compensation of reactive power compensation?
Traditional contactors act on three phases together, that is, when they are attracted, all three phases are attracted, and when they are disconnected, all three phases are disconnected. In this case, the capacitor used for compensation is a three-phase capacitor, which compensates the entire three-phase circuit at the same time. We call it common compensation, also known as "three-phase common compensation".
The advantages of common compensation are simple control, low price, good reliability, and convenient maintenance; the disadvantage is that in the case of three-phase imbalance, it cannot be compensated, or the more it is compensated, the more unbalanced it becomes.
Because most of the high-power and high-load equipment in the power grid is very easy to cause three-phase imbalance when they are running. These devices only need to use two phases of voltage when working, and the other phase is not used at all, which causes three-phase imbalance. At this time, if compensation is required, only two phases can be compensated, otherwise there will be a problem of reactive power imbalance.
Therefore, some switching switches can work independently for the three phases A, B, and C, and switch which phase needs to be switched. This kind of compensation for a single phase is called "split compensation".
If the maximum power imbalance does not exceed 15%, there is basically no need to use split compensation. The reason is that the power supply bureau assesses the average power factor. If the imbalance is within 15%, it is easy to meet the standard after the common compensation is averaged.
The advantage of split compensation is that it has high compensation accuracy for unbalanced occasions; the disadvantage is that it is expensive, complex control, and complex lines. It is difficult to inspect and maintain.
When there are both common compensation branches and split compensation branches in the compensation, we call this compensation method "mixed compensation", which means that "split compensation" and "common compensation" work together. In fact, in the case of three-phase unbalance, when the shortage of each phase is inconsistent, the solution of separate compensation is adopted. However, if all separate compensation branches are used, the cost will be very high, so it is hoped that the shortage of the basic part will be compensated by the common compensation branch, and the shortage of the unbalanced part will be compensated by the separate compensation branch. The compensation system with common compensation and separate compensation is arranged at the same time. Usually, the separate compensation accounts for 20% to 40%.
