Calculator Inputs
Formula Used
Inductive reactive power is based on RMS voltage and reactance.
For one branch, use Q per branch. For three balanced branches, total Q is divided by three. For parallel inductors, each inductor carries a smaller share of branch reactive power.
How to Use This Calculator
- Enter the target reactive power.
- Select var, kvar, or Mvar.
- Enter the RMS voltage value.
- Pick the correct voltage basis.
- Choose single phase or three phase.
- Select wye or delta for balanced systems.
- Enter the frequency in Hz or kHz.
- Add parallel inductors per branch when needed.
- Press calculate and review the result.
Example Data Table
| Target Q | Voltage | Frequency | Setup | Approximate Result |
|---|---|---|---|---|
| 10 kvar | 400 V line-to-line | 50 Hz | Three phase wye | 50.93 mH per phase |
| 5 kvar | 230 V branch | 60 Hz | Single phase | 28.06 mH |
| 25 kvar | 480 V line-to-line | 60 Hz | Three phase delta | 73.34 mH per branch |
Inductance Sizing Guide
Why Inductance Controls Reactive Power
Inductance stores energy in a magnetic field. AC voltage keeps that field changing. The changing field opposes current flow. That opposition is called inductive reactance. Higher frequency raises reactance. Higher inductance also raises reactance. Reactive power then depends on voltage and reactance. A smaller reactance draws more reactive current. A larger reactance draws less reactive current. This calculator reverses that relationship. It finds the required inductance for a chosen target.
Balanced AC Design
Single phase loads use one voltage across one inductor path. Three phase systems use three balanced paths. The voltage across each branch matters most. A wye branch usually sees line voltage divided by root three. A delta branch usually sees full line voltage. This difference changes required inductance. The tool lets you choose the voltage basis. It also supports parallel inductors per branch. That helps when one device cannot handle current.
Reading The Results
The result shows inductance per inductor. It also shows branch voltage, reactance, and current. These values help check ratings before selection. Current rating is very important. An undersized inductor can overheat quickly. Voltage insulation must also match the circuit. The tolerance range estimates practical part variation. Real parts rarely match the exact calculated value. Use the range to compare catalog parts.
Practical Use Cases
Reactive inductors appear in filters and test benches. They can shape current at a chosen frequency. They can also simulate lagging reactive load. Power engineers may need kvar targets. Lab users may need var targets. Audio and radio builders may need small values. The same formula applies after correct unit conversion. Always use RMS voltage. Peak voltage will give the wrong result. Use the operating frequency, not a nameplate guess.
Choosing Useful Inputs
Start with the target reactive power. Use total three phase power for balanced systems. Enter the real supply voltage next. Select line voltage when using switchboard values. Select branch voltage when testing one coil alone. Choose the connection that matches the wiring plan. Keep the count at one for normal sizing. Add tolerance when part spread affects performance.
Why Frequency Matters
Inductive reactance rises directly with frequency. A coil sized at 50 Hz changes at 60 Hz. The required inductance becomes smaller at higher frequency. Low frequency work needs larger magnetic components. High frequency work needs attention to core losses. Winding resistance can also change real behavior. The calculator assumes ideal inductive behavior.
Safety And Accuracy Notes
Reactive power work can involve dangerous voltage and current. Calculations do not replace safe wiring practice. Use proper fuses, enclosures, and isolation. Measure the supply before final sizing. Three phase circuits need balanced construction. Unequal branches create neutral current or line imbalance. Keep inductors away from sensitive devices. Allow cooling space around every coil. Confirm local electrical rules before installation. Review ratings often. Use care. Use careful checks before wiring any real inductive load.
11 FAQs
1. What does this calculator find?
It finds the inductance needed to create a target inductive reactive power. It uses RMS voltage, frequency, phase setup, connection type, and branch sharing details.
2. Should I enter RMS voltage?
Yes. Reactive power formulas use RMS voltage. Do not enter peak voltage unless you convert it to RMS first.
3. What is reactive power?
Reactive power is power that moves between the source and magnetic field. Inductors absorb lagging reactive power in AC circuits.
4. Why does frequency change the result?
Inductive reactance equals 2πfL. Higher frequency raises reactance for the same inductance. That changes the reactive power.
5. What does branch voltage mean?
Branch voltage is the voltage directly across each inductor path. It may differ from line voltage in three phase circuits.
6. How is wye different from delta?
In wye, branch voltage is often line voltage divided by √3. In delta, branch voltage usually equals line-to-line voltage.
7. What does parallel inductors per branch mean?
It means identical inductors share the reactive current in one branch. The calculator returns the needed value for each inductor.
8. Can this calculator size a real coil?
It gives the ideal inductance. Real coils also need current, insulation, heat, core, and saturation checks.
9. Why is tolerance included?
Tolerance shows how part variation can shift the final inductance. It helps compare calculated values with available parts.
10. Does resistance affect the result?
The main calculation assumes ideal inductance. Winding resistance adds real power loss and heat. Test the final design carefully.
11. Is this safe for high voltage work?
High voltage work is dangerous. Use qualified supervision, rated parts, isolation, protective devices, and local code requirements.