.p3-calc-box {
background: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
margin-bottom: 40px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.p3-input-group {
margin-bottom: 20px;
}
.p3-label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #2c3e50;
}
.p3-input {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.p3-input:focus {
border-color: #007bff;
outline: none;
box-shadow: 0 0 0 3px rgba(0,123,255,0.1);
}
.p3-btn {
background-color: #007bff;
color: white;
border: none;
padding: 14px 24px;
font-size: 16px;
font-weight: 600;
border-radius: 4px;
cursor: pointer;
width: 100%;
transition: background-color 0.2s;
}
.p3-btn:hover {
background-color: #0056b3;
}
.p3-results {
margin-top: 25px;
padding-top: 20px;
border-top: 2px solid #e9ecef;
display: none;
}
.p3-result-item {
background: #fff;
padding: 15px;
border-radius: 4px;
border-left: 5px solid #28a745;
margin-bottom: 10px;
display: flex;
justify-content: space-between;
align-items: center;
box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}
.p3-result-label {
font-size: 14px;
color: #6c757d;
font-weight: 500;
}
.p3-result-value {
font-size: 20px;
font-weight: 700;
color: #2c3e50;
}
.p3-error {
color: #dc3545;
font-size: 14px;
margin-top: 5px;
display: none;
}
.p3-article h2 {
color: #2c3e50;
border-bottom: 2px solid #007bff;
padding-bottom: 10px;
margin-top: 30px;
}
.p3-article p {
line-height: 1.6;
margin-bottom: 15px;
}
.p3-article ul {
margin-bottom: 20px;
padding-left: 20px;
}
.p3-article li {
margin-bottom: 8px;
line-height: 1.5;
}
.formula-box {
background: #e8f4fd;
padding: 15px;
border-radius: 4px;
font-family: monospace;
margin: 15px 0;
border-left: 4px solid #007bff;
}
function calculateThreePhasePower() {
var voltageInput = document.getElementById('p3_voltage');
var currentInput = document.getElementById('p3_current');
var pfInput = document.getElementById('p3_pf');
var errorMsg = document.getElementById('p3_error_msg');
var resultsContainer = document.getElementById('p3_results_container');
var volts = parseFloat(voltageInput.value);
var amps = parseFloat(currentInput.value);
var pf = parseFloat(pfInput.value);
// Validation
if (isNaN(volts) || isNaN(amps) || isNaN(pf) || volts <= 0 || amps <= 0) {
errorMsg.style.display = 'block';
resultsContainer.style.display = 'none';
return;
}
if (pf 1) {
errorMsg.textContent = "Power Factor must be between 0 and 1.";
errorMsg.style.display = 'block';
resultsContainer.style.display = 'none';
return;
}
errorMsg.style.display = 'none';
// Constants
var sqrt3 = Math.sqrt(3); // Approx 1.732
// Calculations
// 1. Apparent Power (S) in kVA = (sqrt3 * V * I) / 1000
var apparentPowerKVA = (sqrt3 * volts * amps) / 1000;
// 2. Active Power (P) in kW = S * PF
var activePowerKW = apparentPowerKVA * pf;
// 3. Reactive Power (Q) in kVAR = S * sin(acos(PF))
// Calculate phase angle theta
var theta = Math.acos(pf);
var sinTheta = Math.sin(theta);
var reactivePowerKVAR = apparentPowerKVA * sinTheta;
// Update UI
document.getElementById('res_kw').textContent = activePowerKW.toFixed(2) + " kW";
document.getElementById('res_kva').textContent = apparentPowerKVA.toFixed(2) + " kVA";
document.getElementById('res_kvar').textContent = reactivePowerKVAR.toFixed(2) + " kVAR";
document.getElementById('res_amps_disp').textContent = amps.toFixed(2) + " A";
resultsContainer.style.display = 'block';
}
Understanding the Power Calculation Formula for 3-Phase Systems
In industrial and heavy commercial electrical systems, three-phase power is the standard method for transmitting and distributing alternating current (AC). Unlike single-phase systems found in residential homes, three-phase systems provide more consistent power delivery and allow for the use of smaller wires for the same load.
Calculating the power in a three-phase circuit requires specific formulas that account for the three distinct alternating currents and the square root of 3 ($\sqrt{3} \approx 1.732$).
The Core Formulas
Depending on whether you need to calculate Real Power, Apparent Power, or Reactive Power, the formulas differ slightly. The standard calculations assume a balanced load and use Line-to-Line voltage ($V_{LL}$).
1. Active (Real) Power ($P$)
Active power is the actual power consumed by the equipment to do useful work (like turning a motor or heating an element). It is measured in Kilowatts (kW).
P (kW) = ($\sqrt{3} \times V \times I \times PF$) / 1000
2. Apparent Power ($S$)
Apparent power is the vector sum of active and reactive power. It represents the total power supplied to the circuit. It is measured in Kilovolt-Amperes (kVA).
S (kVA) = ($\sqrt{3} \times V \times I$) / 1000
3. Reactive Power ($Q$)
Reactive power is the power that oscillates between the source and the load, used to maintain magnetic fields in inductive loads like motors. It is measured in Kilovolt-Amperes Reactive (kVAR).
Q (kVAR) = ($\sqrt{3} \times V \times I \times \sin(\theta)$) / 1000
Key Variables Explained
- Voltage ($V$): This is typically the Line-to-Line voltage (e.g., 400V, 480V). If you only have Line-to-Neutral voltage, multiply it by $\sqrt{3}$ to get Line-to-Line.
- Current ($I$): The current flowing through the lines, measured in Amperes.
- Power Factor ($PF$): A measure of efficiency, ranging from 0 to 1. Resistive loads (heaters) have a PF of 1.0, while inductive loads (motors) typically have a PF between 0.8 and 0.9.
- $\sqrt{3}$ (Square Root of 3): A constant approximately equal to 1.732. It arises from the geometry of the three phases being offset by 120 degrees.
Example Calculation
Let's say you have a 3-phase motor running on a 480V system drawing 50 Amps with a power factor of 0.85.
- Calculate kVA: $1.732 \times 480 \times 50 = 41,568 \text{ VA} = 41.57 \text{ kVA}$.
- Calculate kW: $41.57 \text{ kVA} \times 0.85 = 35.33 \text{ kW}$.
This means while the utility must supply 41.57 kVA of capacity, the motor is only performing 35.33 kW of useful work.