Common Compensation vs. Separate Compensation in Reactive Power Compensation
What They Are
To put it simply, common compensation and separate compensation refer to whether the compensation device is switched on a three-phase capacitor or a single-phase capacitor.
Why It Matters
The traditional contactor operates with three phases together, that is, when it is energized, all three phases are energized, and when it is disconnected, all three phases are disconnected. In this way, the capacitor switched on is a three-phase capacitor, and the three-phase circuit is compensated at the same time, which we call "common compensation" or "combined compensation". Since there are often some special equipment in the power grid, they will cause three-phase imbalance when they work. For example, a 380V single-phase welding machine uses two line voltages to work, and the other phase is not used, which causes three-phase imbalance. At this time, if compensation is required, only two phases can be compensated, otherwise it will cause reactive power and imbalance. In order to solve this problem, some new switching switches, such as compound switches, thyristor modules, etc., can work independently for phases A, B, and C, and switch which phase needs to be switched. This kind of artificial compensation for single phase is called "separate compensation".
Pros and Cons
Advantages of common compensation: simple control, low price, good reliability, easy maintenance. Low requirements for compensation controller.
Disadvantages of common compensation: in the case of three-phase imbalance, compensation is impossible, or the more compensation, the more unbalanced.
Advantages of separate compensation: can deal with unbalanced occasions, high compensation accuracy.
Disadvantages of separate compensation: expensive price, complex control, complex circuit. Difficult maintenance. High requirements for compensation controller. Three control lines are required for separate compensation of each group of ABC capacitors.
Only one control line is needed for common compensation of each group of capacitors.
The number of routes for common compensation and separate compensation should be allocated according to actual needs. According to past experience, if the balance of electricity consumption is relatively good and the maximum imbalance does not exceed 15%, there is basically no need to use separate compensation. The reason is that the power supply bureau assesses the average power factor. The imbalance within 15% can easily meet the standard after the common compensation is averaged.
Unbalance: Among the three phases, the current of the phase with the largest current minus the current of the phase with the smallest current, divided by the smallest current of the phase.If the imbalance is high, separate compensation should be used.
Determination of the split compensation capacity: The unbalance degree is usually used to determine the split compensation capacity. For example, if the total capacity is 420Kvar and the maximum unbalance degree is 20%, then the split compensation capacity should be close to 20%. That is: 420×20%=84KVar.
Determination of the number of split compensation paths: The number of split compensation paths should not be too many, because the number of output paths of the compensator is limited.
According to the above example: it can be like this:
Total compensation: 35Kvar per phase, 35×10 paths=350Kvar
Split compensation: 2 paths per phase×11Kvar, 6 paths in total. The total is 16 paths.
Total compensation amount: 350+6×11=416Kva, approximately equal to 420Kvar.
Guang Dong Hao Cheng Electric Co., Ltd. A smart power system solution service provider, Hao Cheng Electric is located in Gaoming, Foshan, Guangdong, covering an area of 80 acres with a construction area of over 50,000 square meters.
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