The Function and Principle of Reactive Power Compensation Cabinet capacitor bank

I. Core Functions
1. Improve Power Factor and Avoid Electricity Fines
In industrial and commercial power usage, the power factor (a metric for measuring the efficiency of electrical energy utilization, with an ideal value of 1) is evaluated by the power grid. If the power factor is too low (e.g., below 0.9), the power supply department will impose additional fines. The compensation cabinet can increase the power factor to a qualified range (typically above 0.92), thus avoiding fines.
2. Reduce Line Losses and Save Electricity
Reactive current (generated by inductive loads such as motors and transformers) increases the current load on cables and transformers, causing line heating losses (losses are proportional to the square of the current). The reactive power provided by the compensation cabinet can offset part of the inductive reactive power, reduce line current, and lower electricity waste.
3. Enhance Grid Load-Carrying Capacity
The rated capacity of transformers and cables is fixed. If the reactive current proportion is high, it will occupy the transmission space for active power (the actual working electrical energy). After compensation, the reactive current decreases, allowing the grid to transmit more active power, which indirectly enhances the load-carrying capacity of the equipment.
4. Stabilize Voltage and Protect Electrical Equipment
When a large number of inductive loads start or operate, it can cause voltage fluctuations in the power grid (such as voltage drops). The compensation cabinet can quickly supply reactive power to suppress voltage fluctuations and prevent damage or abnormal operation of equipment such as motors and frequency converters due to unstable voltage.
II. Working Principle
The core logic is:
Using "capacitive reactive power" to offset "inductive reactive power" and balance the reactive power in the power grid. 

First, understand "reactive power". The loads in the power grid are divided into two categories:
Active load: directly consumes electrical energy to do work (such as resistance furnaces, lighting), corresponding to "active power" (P). 

Inductive load: It does not directly consume electrical energy but requires the establishment of a magnetic field to operate (such as motors, transformers, air conditioners). This type of load absorbs "inductive reactive power" (Q₁) from the power grid, causing the current to lag behind the voltage and reducing the power factor. 

The core of compensation: Capacitive reactive power offsets inductive reactive power
The core component of a reactive power compensation cabinet is the power capacitor (which can generate "capacitive reactive power Q₂"), whose characteristic is opposite to that of inductive loads: the current leads the voltage.
When there is excessive inductive reactive power Q₁ in the power grid, the compensation cabinet will automatically engage an appropriate amount of capacitors to release capacitive reactive power Q₂, allowing Q₁ and Q₂ to partially offset each other. Eventually, the total reactive power in the power grid is significantly reduced, and the power factor approaches 1, achieving "reactive power balance".
Automatic control logic (taking the commonly used "intelligent compensation" as an example)
The compensation cabinet achieves automatic compensation through the interlocking of "controller - contactor / thyristor - capacitor":
Detection: The controller continuously collects voltage and current signals from the power grid, calculates the current power factor and the reactive power that needs to be compensated. 

Judgment: If the power factor is lower than the set value (such as 0.9), the controller determines that capacitors need to be put into operation; if it is higher than the set value (such as 0.98), it is judged that some capacitors need to be disconnected (to avoid overcompensation, as overcompensation will cause the power factor to decrease in the opposite direction, which also affects the power grid). 

Execution: The controller sends instructions to connect or disconnect the corresponding capacitor banks through contactors or thyristors (with rapid response), precisely supplementing or reducing capacitive reactive power to maintain a stable power factor.