Reactive Power (Q) Calculator for AC Systems

This tool calculates the protected area between two lightning rods based on the IEC 62305 standard and the Rolling Sphere Method, suitable for building, tower, and industrial facility lightning protection design. Parameter Description Current Type Select the type of current in the system: - Direct Current (DC) : Common in solar PV systems or DC-powered equipment - Alternating Single-Phase (AC Single-Phase) : Typical in residential power distribution Note: This parameter is used to distinguish input modes but does not affect the protection zone calculation directly. Inputs Choose input method: - Voltage/Power : Enter voltage and load power - Power/Resistance : Enter power and line resistance Tip: This feature may be used for future extensions (e.g., ground resistance or induced voltage calculation), but it does not influence the geometric protection range. Height of Lightning Rod A The height of the primary lightning rod, in meters (m) or centimeters (cm). Usually the taller rod, defining the upper boundary of the protection zone. Height of Lightning Rod B The height of the second lightning rod, same unit as above. If the rods are of different heights, an unequal-height configuration is formed. Space Between Two Lightning Rods Horizontal distance between the two rods, in meters (m), denoted as (d). General rule: \( d \leq 1.5 \times (h_1 + h_2) \), otherwise effective protection cannot be achieved. Height of the Protected Object The height of the structure or equipment to be protected, in meters (m). This value must not exceed the maximum allowable height within the protection zone. Usage Recommendations Prefer equal-height rods for simpler design Keep spacing less than 1.5 times the sum of rod heights Ensure the protected object's height is below the protection zone For critical facilities, consider adding a third rod or using a meshed air-termination system

Calculation of voltage

Calculate resistance (Ω) from V, I, P, or Z in DC and AC circuits using Ohm’s Law. Includes power factor handling for real-world accuracy. “Tendency of a body to oppose the passage of an electric current.” This is the fundamental definition of resistance: the property of a material that resists the flow of electric current. Accurately calculating resistance is essential for circuit design, troubleshooting, and energy efficiency analysis—whether in direct current (DC) or alternating current (AC) systems. Who Is This Tool For? Electrical engineers : for load modeling, protection coordination, and pre-simulation parameter estimation. Electricians and field technicians : to quickly verify equipment resistance and diagnose short circuits, ground faults, or insulation degradation. Students and electronics hobbyists : to understand practical applications of Ohm’s Law across different circuit conditions. Energy auditors and efficiency consultants : to evaluate operational efficiency using resistance and power factor relationships. Automation and control engineers : for precise impedance matching in sensor loops or PLC input modules. Typical Use Cases Scenario Application Motor winding inspection Measure voltage and current to back-calculate equivalent resistance and detect inter-turn short circuits. Heating element verification Given rated voltage and power (e.g., 220V / 1500W), compute theoretical resistance to assess aging or failure. Lighting system design Calculate equivalent resistance of LED drivers or incandescent loads to ensure voltage drop stays within limits. UPS and inverter testing In single-phase AC output, combine apparent power and power factor to isolate the resistive component of the load. Educational labs Help students visualize why V/I ≠ R in AC circuits due to reactance and phase shift. Calculation Principle The calculator is based on Ohm's Law and its derived forms. Resistance (R) can be computed using any of the following equivalent formulas: R = V / I R = P / (I^2) R = (V^2) / P R = Z / Power Factor Where: R : Resistance (Ω) V : Voltage (V) I : Current (A) P : Power (W) Z : Impedance (Ω) Power Factor : Ratio of active power to apparent power, ranging from 0 to 1 Note: In AC circuits, these formulas are only fully equivalent when the power factor equals 1 (purely resistive load). Parameter Details Current Type Direct Current (DC) : Current flows steadily in one direction from positive to negative pole. Frequency is zero. In this case, impedance Z equals resistance R, and power factor is always 1. Alternating Current (AC) : Current direction and amplitude vary periodically at a constant frequency. Single-phase system : Two conductors — one phase and one neutral (zero potential). Two-phase system : Two phase conductors; neutral may be present in three-wire configurations. Three-phase system : Three phase conductors; neutral is included in four-wire systems. This calculator currently supports DC and single-phase AC inputs. For three-phase systems, convert line-to-line voltage to phase voltage first: V_phase = V_line / sqrt(3), then treat as single-phase. Voltage Voltage is the difference in electric potential between two points. Input method depends on system type: Single-phase : Enter Phase-Neutral voltage. Two-phase / Three-phase : Enter Phase-Phase voltage. Example: A standard 220V household outlet is single-phase → input 220V. An industrial 380V supply is three-phase → for per-phase calculation, use 380 / sqrt(3) ≈ 220V. Current Current is the flow of electric charge through a conductor, measured in amperes (A). It is one of the most direct inputs for resistance calculation via R = V / I. Power Electric power is the rate at which energy is supplied or consumed by a component, measured in watts (W). In AC systems, distinguish between: Active Power (W) : Real power that performs useful work. Reactive Power (VAR) : Power used to establish magnetic/electric fields; does no real work. Apparent Power (VA) : Vector sum of active and reactive power: S = sqrt(P^2 + Q^2). Important: The "P" in the formulas above refers to active power (W) . If you input apparent power (VA), you must also provide the power factor; otherwise, results will be inaccurate. Power Factor Power Factor = cos(phi), where phi is the phase angle between voltage and current. Pure resistive load (e.g., heater, incandescent lamp): Power Factor = 1 Inductive or capacitive loads (e.g., motors, transformers): Power Factor < 1 (typically 0.7–0.95) In AC circuits, resistance is derived from impedance and power factor: R = Z * Power Factor = Z / (1 / Power Factor) Impedance Impedance (Z) is the total opposition to alternating current flow, combining resistance (R) and reactance (X), measured in ohms (Ω). The relationship is: Z = sqrt(R^2 + X^2) Therefore, resistance can only be extracted from impedance if the power factor (or phase angle) is known. People Also Ask (FAQ) Why can’t I use R = V / I directly in AC circuits? Because V / I gives you impedance (Z) , not pure resistance (R). To get R, multiply by the power factor: R = (V / I) * cos(phi). Do I need to enter power factor for DC circuits? No. In DC, there is no phase shift, so power factor is always 1, and Z = R. Can I calculate resistance if I only know reactive power (VAR)? No. Resistance relates only to active power. You need either active power (W), or apparent power (VA) plus power factor. Can this tool be used for three-phase motors? Yes, but treat it per phase. Measure phase voltage and phase current, or convert line values using V_phase = V_line / sqrt(3), then apply single-phase formulas. Usage Tips Prefer voltage + current input : Most accurate and least prone to error. Ensure unit consistency : V in volts, I in amps, P in watts. Always enter power factor for AC : If omitted, the calculator assumes cos(phi) = 1, which overestimates resistance. Validate results : Example – a 1000W heater at 220V should have R ≈ (220^2)/1000 = 48.4 Ω. Large deviations suggest input errors. This tool adheres to international electrical standards (IEC 60050) and is suitable for education, engineering design, and field maintenance—helping users quickly and accurately determine the effective resistance in real-world circuits.

Free online calculator for active (real) power in DC and AC circuits. Supports voltage, current, resistance, impedance, power factor, or apparent/reactive power inputs. Active power, also known as real power, is the portion of electrical power that performs useful work in a circuit—such as producing heat, light, or mechanical motion. Measured in watts (W) or kilowatts (kW), active power represents the actual energy consumed by a load and is the basis for electricity billing. This tool calculates active power based on voltage, current, power factor, apparent power, reactive power, resistance, or impedance. It supports both single-phase and three-phase systems, making it ideal for motors, lighting, transformers, and industrial equipment. Parameter Description Parameter Description Current Type Select circuit type: • Direct Current (DC) : Constant flow from positive to negative pole • Single-phase AC : One live conductor (phase) + neutral • Two-phase AC : Two phase conductors, optionally with neutral • Three-phase AC : Three phase conductors; four-wire system includes neutral Voltage Electric potential difference between two points. • Single-phase: Enter Phase-Neutral voltage • Two-phase / Three-phase: Enter Phase-Phase voltage Current Flow of electric charge through a material, unit: Amperes (A) Power Factor Ratio of active power to apparent power, indicating efficiency. Value between 0 and 1. Ideal value: 1.0 Apparent Power Product of RMS voltage and current, representing total power supplied. Unit: Volt-Ampere (VA) Reactive Power Energy alternately flowing in inductive/capacitive components without conversion to other forms. Unit: VAR (Volt-Ampere Reactive) Resistance Opposition to DC current flow, unit: Ohm (Ω) Impedance Total opposition to AC current, including resistance, inductance, and capacitance. Unit: Ohm (Ω) Calculation Principle The general formula for active power is: P = V × I × cosφ Where: P : Active power (W) V : Voltage (V) I : Current (A) cosφ : Power factor Other common formulas: P = S × cosφ P = Q / tanφ P = I² × R P = V² / R Example Calculation If voltage is 230V, current is 10A, and power factor is 0.8, then active power is: P = 230 × 10 × 0.8 = 1840 W Usage Recommendations Monitor active power regularly to assess equipment efficiency Use data from energy meters to analyze consumption patterns and optimize usage Consider harmonic distortion when dealing with nonlinear loads (e.g., VFDs, LED drivers) Active power is the basis for electricity billing, especially under time-of-use pricing schemes Combine with power factor correction to improve overall energy efficiency Common Input Combinations The calculator supports multiple input methods depending on available measurements: Voltage/Resistance : Use when current is not directly measurable Voltage/Impedance : For AC circuits with known Z and cosφ Current/Resistance : Direct calculation via P = I² × R Current/Impedance : Requires power factor to extract resistive component Voltage/Current : Most direct method, requires power factor for AC Apparent power/Reactive power : Use trigonometric relationship to find active power Apparent power : Only valid if power factor is known Reactive power : Must be combined with power factor or apparent power Supported Circuit Types Direct Current (DC) : No phase shift, power factor = 1, impedance = resistance Single-phase AC : Common in homes and small commercial buildings Two-phase AC : Less common, used in specific industrial applications Three-phase AC : Standard for motors, transformers, and industrial power systems People Also Ask (FAQ) What is the difference between active power and apparent power? Active power (P) is the real power doing useful work (in watts). Apparent power (S) is the vector sum of active and reactive power (in VA). The ratio P/S is the power factor. Why is active power important for electricity billing? Utilities charge based on active power because it represents the actual energy consumed. Reactive power increases current but does no useful work, so it’s not billed directly. Can I calculate active power without knowing the power factor? Only if you know the resistance (for DC or purely resistive AC loads). Otherwise, you need either power factor or a combination of apparent/reactive power. How does this tool handle three-phase systems? For three-phase systems, enter line-to-line voltage and per-phase values. The tool assumes balanced loads and applies the standard three-phase formula: P = √3 × V_line × I_line × cosφ. Is this calculator suitable for non-linear loads like LED drivers? Yes, but keep in mind that non-linear loads may have distorted waveforms and lower power factors. Use measured RMS values and actual power factor for best accuracy. Calculation Example Given: Current type: Direct Current Voltage: 220 V Resistance: 20 Ω Using the formula: P = V² / R P = 220² / 20 = 48400 / 20 = 2420 W = 2.42 kW Result: Active power = 2.42 kW This matches the example shown in the interface screenshot. This tool adheres to international electrical standards (IEC 60050) and is suitable for engineers, technicians, students, and facility managers who need to calculate real power in various electrical systems.