Reactive Power Compensation Buying Guide | Steps, Reactors and Control
1. Measure the reactive load before sizing
Start from the load profile, not from the transformer rating. Record the active and reactive power through a full production cycle, then calculate the kVAr needed to reach the target power factor. Oversizing causes leading power factor at light load, which raises voltage and can trip protection; undersizing leaves a penalty on the electricity bill.
2. Choose the compensation voltage and connection
High-voltage compensation connects at the 6kV or 10kV bus and corrects the load before it reaches the transformer, which reduces transformer and cable losses. Low-voltage compensation at 400V is easier to switch in small steps but does not relieve the transformer. The right level depends on the load location, the network layout and the utility metering point.
3. Add reactors for harmonic-rich networks
| Configuration | Effect | When to use |
|---|---|---|
| Capacitor only | Simple correction at the fundamental frequency | Clean networks with low harmonic content |
| Detuned reactor 7% | Shifts resonance below the 5th harmonic | Networks with 5th and 7th harmonic loads |
| Detuned reactor 14% | Shifts resonance below the 3rd harmonic | Networks with strong 3rd harmonic content |
A capacitor bank on a harmonic-rich network can amplify the harmonic and fail early. Ask for a harmonic study, or at least the measured harmonic spectrum, before choosing the reactor.
4. Set the switching steps and controller
Automatic compensation divides the total kVAr into steps so the controller can follow the load without hunting. Confirm the step size, the number of steps, the switching interval and the controller target power factor. Vacuum contactors or thyristor switches are chosen for the switching frequency; frequent switching needs components rated for the duty.
5. Confirm protection, discharge and ventilation
Each capacitor step needs a fuse, a discharge resistor and over-voltage protection. Discharge resistors bring the terminal voltage down to a safe level within the specified time after switching off. The enclosure needs ventilation for the capacitor and reactor losses, and the internal temperature must stay within the capacitor rating.
6. RFQ checklist
- System voltage and measured reactive load
- Target power factor and required kVAr
- Harmonic spectrum and reactor percentage
- Number and size of switching steps
- Controller target, protocol and metering
- Enclosure, ventilation and installation location
- Quantity, destination and delivery date
Send the load data and harmonic measurements and the compensation design can be confirmed in one round.
