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Calculation of impedance

Description

Impedance is the total opposition of a circuit to the flow of alternating electric current, measured in ohms (Ω). It includes resistance, inductive reactance, and capacitive reactance, and is a key parameter in AC circuit analysis.

Parameter Description

Current Type
Select the type of current:
- Direct Current (DC): Constant flow from positive to negative pole
- Alternating Current (AC): Reverses direction and amplitude periodically at constant frequency
System configurations:
- Single-phase: Two conductors (phase + neutral)
- Two-phase: Two phase conductors; neutral may be distributed
- Three-phase: Three phase conductors; four-wire system includes neutral

Note: Impedance is only meaningful in AC circuits; in DC, impedance equals resistance.

Voltage
Electric potential difference between two points.
- For single-phase: Enter Phase-Neutral voltage
- For two-phase or three-phase: Enter Phase-Phase voltage

Current
Flow of electric charge through a material, measured in amperes (A).

Active Power
The power actually consumed by a load and converted into useful energy (e.g., heat, motion).
Unit: Watts (W)
Formula:

P = V × I × cosφ

Reactive Power
Power that alternately flows in inductors or capacitors without being transformed into other forms of energy.
Unit: Volt-Ampere Reactive (VAR)
Formula:

Q = V × I × sinφ

Apparent Power
The product of RMS voltage and current, representing total power supplied by the source.
Unit: Volt-Ampere (VA)
Formula:

S = V × I

Power Factor
Ratio of active power to apparent power, indicating efficiency of power usage.
Formula:

PF = P / S = cosφ

where φ is the phase angle between voltage and current. Value ranges from 0 to 1.

Resistance
Opposition to current flow due to material properties, length, and cross-sectional area.
Unit: Ohm (Ω)
Formula:

R = ρ × l / A

Impedance Calculation Principle

Impedance \( Z \) is defined as:

Z = V / I

For a series RLC circuit:

Z = √(R² + (XL - XC)²)

Where:
- R: Resistance
- XL = 2πfL: Inductive reactance
- XC = 1/(2πfC): Capacitive reactance
- f: Frequency (Hz)
- L: Inductance (H)
- C: Capacitance (F)

If XL > XC, the circuit is inductive; if XC > XL, it is capacitive.

Usage Recommendations

  • Impedance affects short-circuit current, voltage drop, and protection device selection in power systems
  • Low power factor increases line losses; consider reactive power compensation
  • Use this tool to back-calculate unknown impedance values from measured voltage and current

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