Standby vs Prime Power Calculator
ANA›Life Services Authority›National Calculator Authority›Standby vs Prime Power 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; } }
Standby vs Prime Power Calculator
Compare standby and prime power ratings for generators. Calculate derating factors, continuous vs emergency power capacity, and determine the right generator sizing for your application.
Rated Power (kW)
kW
Input Rating Type
Standby Power Rating Prime Power Rating Continuous Power Rating
Power Factor
—
Altitude
m
Ambient Temperature
°C
Average Load Factor (Prime)
%
Calculate
function staCalc() { const ratedPower = parseFloat(document.getElementById('sta-rated-power').value); const ratingType = document.getElementById('sta-rating-type').value; const powerFactor = parseFloat(document.getElementById('sta-power-factor').value); const altitude = parseFloat(document.getElementById('sta-altitude').value); const temperature = parseFloat(document.getElementById('sta-temperature').value); const loadFactor = parseFloat(document.getElementById('sta-load-factor').value);
const resultDiv = document.getElementById('sta-result');
// --- Validation --- if (isNaN(ratedPower) || ratedPower ⚠ Please enter a valid rated power greater than 0 kW.'; return; } if (isNaN(powerFactor) || powerFactor 1.0) { resultDiv.style.display = 'block'; resultDiv.innerHTML = '⚠ Power factor must be between 0.1 and 1.0.'; return; } if (isNaN(altitude) || altitude ⚠ Altitude must be 0 or greater.'; return; } if (isNaN(temperature) || temperature 60) { resultDiv.style.display = 'block'; resultDiv.innerHTML = '⚠ Ambient temperature must be between -20°C and 60°C.'; return; } if (isNaN(loadFactor) || loadFactor 100) { resultDiv.style.display = 'block'; resultDiv.innerHTML = '⚠ Load factor must be between 1% and 100%.'; return; }
// --- Derating Factors --- // Altitude derating: ~3% per 300 m above 1000 m (ISO 3046 / ISO 8528) let altitudeDerate = 1.0; if (altitude > 1000) { altitudeDerate = 1.0 - ((altitude - 1000) / 300) * 0.03; altitudeDerate = Math.max(altitudeDerate, 0.5); // floor at 50% }
// Temperature derating: ~1% per °C above 25°C (ISO 3046) let tempDerate = 1.0; if (temperature > 25) { tempDerate = 1.0 - (temperature - 25) * 0.01; tempDerate = Math.max(tempDerate, 0.5); }
const combinedDerate = altitudeDerate * tempDerate;
// --- Rating Conversions (ISO 8528 / NFPA 110 relationships) --- // Standby = Prime × 1.10 (standby is ~10% higher than prime) // Prime = Continuous × 1.10 (prime is ~10% higher than continuous) // Standby = Continuous × 1.21 let standbyKW, primeKW, continuousKW;
if (ratingType === 'standby') { standbyKW = ratedPower; primeKW = ratedPower / 1.10; continuousKW = ratedPower / 1.21; } else if (ratingType === 'prime') { primeKW = ratedPower; standbyKW = ratedPower * 1.10; continuousKW = ratedPower / 1.10; } else { // continuous continuousKW = ratedPower; primeKW = ratedPower * 1.10; standbyKW = ratedPower * 1.21; }
// Derated values const standbyDerated = standbyKW * combinedDerate; const primeDerated = primeKW * combinedDerate; const continuousDerated = continuousKW * combinedDerate;
// kVA conversions const standbyKVA = standbyKW / powerFactor; const primeKVA = primeKW / powerFactor; const continuousKVA = continuousKW / powerFactor;
const standbyKVADerated = standbyDerated / powerFactor; const primeKVADerated = primeDerated / powerFactor; const continuousKVADerated = continuousDerated / powerFactor;
// Prime power overload capacity (10% overload for 1 hr in 12 hrs) const primeOverload = primeKW * 1.10; const primeOverloadDer = primeDerated * 1.10;
// Effective prime output at given load factor const effectivePrimeOutput = primeDerated * (loadFactor / 100);
// Fuel efficiency note: prime ~better efficiency than standby at partial load const altitudePct = ((1 - altitudeDerate) * 100).toFixed(1); const tempPct = ((1 - tempDerate) * 100).toFixed(1); const totalDerPct = ((1 - combinedDerate) * 100).toFixed(1);
// --- Recommendation --- let recommendation = ''; if (ratingType === 'standby') { recommendation = 'Standby rating is for emergency use only — typically limited to 200 hours/year with no sustained overload. Do not use standby-rated generators as primary power sources.'; } else if (ratingType === 'prime') { recommendation = 'Prime rating allows unlimited hours of operation at variable load (avg ≤ ' + loadFactor + '% of rated). A 10% overload is permissible for up to 1 hour in every 12 hours.'; } else { recommendation = 'Continuous rating allows unlimited hours at 100% load with no overload permitted. Ideal for base-load or critical continuous applications.'; }
resultDiv.style.display = 'block'; resultDiv.innerHTML = ` ### Results
Rating Type kW (Nameplate) kVA (Nameplate) kW (Derated) kVA (Derated)
Standby ${standbyKW.toFixed(2)} ${standbyKVA.toFixed(2)} ${standbyDerated.toFixed(2)} ${standbyKVADerated.toFixed(2)}
Prime ${primeKW.toFixed(2)} ${primeKVA.toFixed(2)} ${primeDerated.toFixed(2)} ${primeKVADerated.toFixed(2)}
Continuous ${continuousKW.toFixed(2)} ${continuousKVA.toFixed(2)} ${continuousDerated.toFixed(2)} ${continuousKVADerated.toFixed(2)}
Derating Detail Factor Reduction
Altitude Derating (${altitude} m) ${altitudeDerate.toFixed(4)} ${altitudePct}%
Temperature Derating (${temperature}°C) ${tempDerate.toFixed(4)} ${tempPct}%
Combined Derating ${combinedDerate.toFixed(4)} ${totalDerPct}%
Additional Outputs Value
Prime 10% Overload Capacity (nameplate) ${primeOverload.toFixed(2)} kW
Prime 10% Overload Capacity (derated) ${primeOverloadDer.toFixed(2)} kW
Effective Prime Output at ${loadFactor}% Load (derated) ${effectivePrimeOutput.toFixed(2)} kW
Power Factor Used ${powerFactor.toFixed(2)}
📋 Application Note: ${recommendation}
`; }
#### Formulas Used
Rating Conversions (ISO 8528-1):
Altitude Derating (ISO 3046-1):
Temperature Derating (ISO 3046-1):
Combined Derating:
Prime Overload Capacity:
Effective Output at Load Factor:
#### Assumptions & References
- ISO 8528-1:2018 — Reciprocating internal combustion engine driven alternating current generating sets: Application, ratings and performance.
- ISO 3046-1:2002 — Reciprocating internal combustion engines: Performance — Standard reference conditions, declarations of power, fuel and lubricating oil consumptions.
- NFPA 110:2022 — Standard for Emergency and Standby Power Systems.
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