Transformer KVA Sizing Calculator
ANA›Life Services Authority›National Calculator Authority›Transformer KVA Sizing Calculator
.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }
Transformer KVA Sizing Calculator
Determine the minimum KVA rating required for a transformer given your load characteristics, supply voltage, and power factor. Results include a recommended standard KVA size with a safety margin.
Total Load (kW)
kW
Power Factor (PF)
0–1
System Phase
Single-Phase (1Ø) Three-Phase (3Ø)
Primary Voltage (V)
V
Secondary Voltage (V)
V
Safety Margin (%)
%
Calculate
function traCalc() { var loadKw = parseFloat(document.getElementById('tra-load-kw').value); var pf = parseFloat(document.getElementById('tra-power-factor').value); var phases = parseInt(document.getElementById('tra-phases').value); var primaryV = parseFloat(document.getElementById('tra-primary-v').value); var secondaryV = parseFloat(document.getElementById('tra-secondary-v').value); var margin = parseFloat(document.getElementById('tra-margin').value); var resultDiv = document.getElementById('tra-result');
// --- Validation --- var errors = []; if (isNaN(loadKw) || loadKw 1) errors.push("Power Factor must be between 0.01 and 1.00."); if (isNaN(primaryV) || primaryV 100) errors.push("Safety Margin must be between 0 and 100.");
if (errors.length > 0) { resultDiv.style.display = 'block'; resultDiv.innerHTML = '⚠ ' + errors.join('⚠ ') + ''; return; }
// --- Core Formula --- // KVA_required = kW / PF var kvaRequired = loadKw / pf;
// Apply safety margin var kvaWithMargin = kvaRequired * (1 + margin / 100);
// Standard KVA sizes (ANSI/IEEE common ratings) var standardSizes = [1, 1.5, 2, 3, 5, 7.5, 10, 15, 25, 37.5, 50, 75, 100, 150, 167, 200, 250, 333, 500, 750, 1000, 1500, 2000, 2500, 3000, 3750, 5000, 7500, 10000]; var recommendedKva = null; for (var i = 0; i = kvaWithMargin) { recommendedKva = standardSizes[i]; break; } } if (recommendedKva === null) { recommendedKva = Math.ceil(kvaWithMargin / 1000) * 1000; }
// Full-load current on secondary side // Single-phase: I = KVA × 1000 / V // Three-phase: I = KVA × 1000 / (√3 × V) var sqrt3 = Math.sqrt(3); var flaCurrent; if (phases === 1) { flaCurrent = (recommendedKva * 1000) / secondaryV; } else { flaCurrent = (recommendedKva * 1000) / (sqrt3 * secondaryV); }
// Primary full-load current var primaryCurrent; if (phases === 1) { primaryCurrent = (recommendedKva * 1000) / primaryV; } else { primaryCurrent = (recommendedKva * 1000) / (sqrt3 * primaryV); }
// Turns ratio var turnsRatio = primaryV / secondaryV;
// Reactive power (kVAR) var kvar = kvaRequired * Math.sqrt(1 - pf * pf);
// --- Output --- var phaseLabel = (phases === 3) ? "Three-Phase (3Ø)" : "Single-Phase (1Ø)";
resultDiv.style.display = 'block'; resultDiv.innerHTML = '### Results ' + '' + 'Required KVA (no margin)' + kvaRequired.toFixed(2) + ' KVA' + 'Required KVA (with ' + margin + '% margin)' + kvaWithMargin.toFixed(2) + ' KVA' + '✅ Recommended Standard KVA Size' + recommendedKva.toLocaleString() + ' KVA' + 'Reactive Power (kVAR)' + kvar.toFixed(2) + ' kVAR' + 'Turns Ratio (Primary : Secondary)' + turnsRatio.toFixed(3) + ' : 1' + 'Secondary Full-Load Current' + flaCurrent.toFixed(2) + ' A' + 'Primary Full-Load Current' + primaryCurrent.toFixed(2) + ' A' + 'System Configuration' + phaseLabel + '' + ''; }
#### Formulas Used
Required KVA:
KVA = kW ÷ Power Factor (PF)
KVA with Safety Margin:
KVAdesign = KVA × (1 + Margin% ÷ 100)
Secondary Full-Load Current:
Single-Phase: I = (KVA × 1000) ÷ Vsecondary
Three-Phase: I = (KVA × 1000) ÷ (√3 × Vsecondary)
Turns Ratio:
a = Vprimary ÷ Vsecondary
Reactive Power:
kVAR = KVA × √(1 − PF²)
#### Assumptions & References
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