Demand-Factor Load Calculation
Compute active / reactive / apparent load and design current from installed capacity, demand factor, simultaneity factor, and power factor; pre-select transformer capacity.
Key points
Demand-Factor Load Calculation: Compute active / reactive / apparent load and design current from installed capacity, demand factor, simultaneity factor, and power factor; pre-select transformer capacity. Formula: P_js = K_x·K_Σ·P_e ｜ Q_js = P_js·tanφ ｜ S_js = √(P²+Q²) ｜ I_js = S_js/(√3·U). Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. The demand-factor method suits preliminary design / estimates; obtain K_x and K_Σ from design manuals or local supply guides for each load type. Design current is used for the incoming breaker, busbars, and cables; transformer rating also considers loading, future expansion, starting current, and reactive compensation.
Inputs
P_js = K_x·K_Σ·P_e ｜ Q_js = P_js·tanφ ｜ S_js = √(P²+Q²) ｜ I_js = S_js/(√3·U)Calculation model (updates with parameters)
| Total installed capacity P_e | 100 kW | 铭牌Power之和 |
| Calculated active power P_js | 70 kW | P_e·K_x·K_Σ = 100 kW×0.70×1.00 |
| Calculated reactive power Q_js | 43.38 kvar | P_js·tanφ，tanφ=0.620 |
| Calculated apparent power S_js | 82.35 kVA | √(P²+Q²) |
| Calculated current I_js | 125.1 A | S/(√3·U) |
| Power factor cosφ | 0.85 | 低于 0.9，建议补偿 |
| Transformer for 0.8 loading | 102.9 kVA | S_js/0.8 |
| Recommended transformer rating | 125 kVA | 按常用配变容量档向上取整 |
Engineering notes
- The demand-factor method suits preliminary design / estimates; obtain K_x and K_Σ from design manuals or local supply guides for each load type.
- Design current is used for the incoming breaker, busbars, and cables; transformer rating also considers loading, future expansion, starting current, and reactive compensation.
- Calculate P and Q for each load group and sum them; do not add apparent powers directly. Low power factor means large reactive share, occupying transformer and line capacity.
FAQ
- What is Demand-Factor Load Calculation for?
- Compute active / reactive / apparent load and design current from installed capacity, demand factor, simultaneity factor, and power factor; pre-select transformer capacity.
- What is the formula for Demand-Factor Load Calculation?
- Core formula: P_js = K_x·K_Σ·P_e ｜ Q_js = P_js·tanφ ｜ S_js = √(P²+Q²) ｜ I_js = S_js/(√3·U). The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Demand-Factor Load Calculation?
- The demand-factor method suits preliminary design / estimates; obtain K_x and K_Σ from design manuals or local supply guides for each load type. Design current is used for the incoming breaker, busbars, and cables; transformer rating also considers loading, future expansion, starting current, and reactive compensation. Calculate P and Q for each load group and sum them; do not add apparent powers directly. Low power factor means large reactive share, occupying transformer an…