To improve the efficiency of electrical systems and cut energy costs, it is essential to understand reactive power and compensation properly. In this article, we look step by step at what reactive power is, its effects on low-voltage networks, how it is calculated and how compensation improves it. We also show the compensation requirement with a worked example.
1. What Is Reactive Power?
Reactive power (Q) is a component of power in alternating current (AC) systems that is needed to create magnetic fields but does no direct work. On low-voltage networks, it is consumed mainly by inductive loads such as motors, transformers and fluorescent ballasts.
Reactive power is part of the total apparent power (S) and is measured in volt-ampere reactive (VAR). The power drawn is returned to the system without being converted into active energy.
- Active power (P): The real power that does work (watts)
- Reactive power (Q): The power needed for magnetic fields (VAR)
- Apparent power (S): The combination of P and Q (VA)
2. The Effect of Reactive Power on Low-Voltage Networks
Low-voltage networks (0–1000 V) are directly affected by reactive loads. Excess reactive power can cause the following problems:
- Overheating cables
- Transmission losses
- Transformers exceeding their capacity limits
- A higher risk of reactive penalties on the electricity bill
The power factor (cos φ) should therefore be monitored and reactive power kept under control with suitable compensation systems. A power factor close to 1 indicates a more efficient system.
Reactive Power Calculation and Compensation Example for Three-Phase Systems
3. Reactive Power Calculation in Three-Phase Systems (Example)
Data measured at a facility:
- Line voltage (VL): 400 V
- Line current (IL): 100 A
- Power factor (cos φ): 0.80
Active power (P) calculation:
Reactive power (Q) calculation:
This system draws approximately 40 kVAr of reactive power.
4. Compensation Calculation (Example)
Goal: raise the power factor from 0.80 to 0.95.
Required compensation power:
In conclusion, this system should be compensated by adding approximately 25 kVAr of capacitive load, which can be provided with capacitor banks.
Controlling reactive power on low-voltage networks is critical both for lowering energy costs and for keeping the system healthy. Reactive power consumption should be monitored regularly and compensation systems serviced periodically.