Low-voltage dynamic reactive power compensation device

"Dynamic reactive power compensation" refers to a type of reactive power compensation with a very short delay time (the delay time is generally no more than 5 seconds). It is mainly applied in scenarios where the load changes rapidly. Therefore, the dynamic reactive power compensation device can be understood as: a reactive power compensation device that uses semiconductor electronic switches or composite switches for switching, or a reactive power compensation device that uses other methods for switching but with a delay time no more than 5 seconds.

The compensation capacitor is a key component of the thyristor switching capacitor (TSC) system. By means of switching on or off the capacitors, the system can dynamically balance the inductive load and capacitive load, thereby maintaining a high power factor.

(1) Grouping method.

In many industrial production practices, apart from large motors that are compensated locally, a large number of dispersed inductive loads need to be compensated centrally in the low-voltage distribution room. At this time, since the compensation capacity varies over time, in order to avoid over-compensation or under-compensation, the capacitors need to be divided into several groups and operated in an automatic switching manner.

The specific method for grouping capacitors is quite flexible. The common methods include the following:

① Equal-capacity method: This involves dividing the capacitors that need to be compensated into several equal parts.

② The ratio is 1:2:4:8. That is, the capacitance value of each unit is set in a manner of doubling successively. This way, 15 levels of compensation values can be obtained.

③ Binary system, which uses N-1 capacitors each with a capacitance of C and one capacitor with a capacitance of C/2, enables the adjustment of the compensation amount to have 2N levels. Comparing with the above methods, Method ① has the simplest control mode, but the relatively large compensation level difference limits the accuracy. While Methods ② and ③ improve the effect by adopting a multi-level differential compensation method, they are both cumbersome and not convenient for automatic control. In contrast, Method ③ is not without being a beneficial compromise solution.

(2) Switching mode.

Since dynamic reactive power compensation requires frequent switching on and off of capacitors, in order to ensure the lifespan and quality of the capacitors, the switching mode of the compensation capacitors needs to be considered. There are typically the following two modes:

① The cyclic switching mode involves arranging each group of capacitors in a circular formation according to their group numbers, and then sequentially switching them on or off according to their sequence numbers. If capacitors are removed, they are removed from the tail of the already switched-on capacitor queue. Thus, as the power factor changes, the switched-on capacitor queue moves counterclockwise within the circular queue, ensuring that each group of capacitors has an equal chance of being used, effectively reducing the failure rate of the capacitor groups. This method is typically used for equal-capacity grouping.

② Temperature-based switching mode: Each group of capacitors is arranged in a straight line queue according to their group numbers. By switching on or off the capacitors, the already switched-on capacitor group will rise or fall in the straight line queue, similar to the rise and fall of the mercury column in a thermometer. This method is often used for variable capacity grouping.