Functions of Capacitors
Technical Support
In power systems, loads simultaneously possess active power (effective power) and reactive power (invalid power). The transmission of reactive power requires higher voltage, increases power loss in transmission lines, and elevates the total current (the total current squared equals the effective current squared plus the reactive current squared). From an economic perspective, supplying reactive power from the power source (generator) is quite disadvantageous. Therefore, installing capacitors near the load to supply reactive power is the most economical and effective method. In distribution systems, we almost always use power capacitors to supply the reactive power required by the load, which is referred to as power factor correction. The benefits are as follows:
1. Save on Electricity Costs
The power factor is related to the calculation of electricity costs. According to the Taiwan Power Company’s rate schedule, if the average power factor of a user’s monthly electricity consumption is below 0.80, every 0.01 decrease will increase the electricity bill by 0.1% for that month. Conversely, if it exceeds 0.80, every 0.01 increase will reduce the electricity bill by 0.1%. However, no deductions are made for portions exceeding an average power factor of 0.95. This billing information is noted in the monthly electricity bill under the power adjustment fee section.
2. Reduce Power Loss
In general, the power loss in factory power wiring varies based on load factors, cable size, and length, typically around 2% to 3%. By improving the power factor, the total current decreases, which helps reduce power loss.
3. Improve Power Quality
Enhancing the power factor can reduce the total load current and voltage drop. After installing capacitors, the reduction in voltage drop can be calculated as: (current before installation - current after installation) x line resistance. Installing capacitors on the secondary side of transformers can improve power factor and increase secondary voltage.
Vc=Voltage increase after capacitor installation
4. Extend Equipment Lifespan
Improving the power factor results in reduced total line current, which helps prevent saturation of transformers, switches, and other equipment. This reduction in current minimizes overheating, thereby increasing the lifespan of the equipment.