Electrical Load Calculation Guide for Industrial Plants
A step-by-step guide for electrical load calculation in industrial plants. Covers demand factor, diversity factor, load factor, and transformer sizing.
本文为中文技术阅读版本，工程参数、标准和项目边界仍应以正式图纸、技术协议和书面报价为准。
Load Calculation Basics
Electrical load calculation determines the total power demand of a facility, used for transformer sizing, cable sizing, and tariff calculation.
Key concepts: Connected load (all equipment), demand load (actual maximum), diversity factor, load factor.
Goal: Size equipment correctly (not oversized = wasted cost, not undersized = overload).
Demand Factor and Diversity Factor
Demand factor = Maximum demand / Connected load. Typically 0.6-0.8 for industrial plants.
Diversity factor = Sum of individual maximum demands / Simultaneous maximum demand. Typically 1.2-1.5.
Example: 10 machines, each 100kW, but only 6 run at same time. Demand factor = 0.6, Diversity factor = 1.67.
Use diversity factor when adding loads from different departments/facilities.
Load Calculation Steps
Step 1: List all equipment with power ratings (kW or HP).
Step 2: Apply demand factor for each equipment type (motors, lighting, HVAC, etc.).
Step 3: Add loads by department, apply diversity factor.
Step 4: Calculate total demand, add 20-30% spare capacity for future expansion.
Step 5: Select transformer (typically 80-90% loading for optimal efficiency).
Motor Load Calculation
Motors have starting current 5-7 times running current (induction motors).
Consider: Starting method (DOL, star-delta, soft starter, VFD) affects starting current.
For generator sizing: Motor starting kVA = Locked rotor kVA (from motor nameplate).
For transformer sizing: Consider motor starting, may need larger transformer or soft starter.
Example Calculation
Assume: Factory with 10 machines (100kW each), lighting (50kW), HVAC (150kW).
Demand factors: Machines 0.7, lighting 0.9, HVAC 0.8.
Demand load: 10×100×0.7 + 50×0.9 + 150×0.8 = 700 + 45 + 120 = 865kW.
Diversity factor: 1.3 (different departments don't peak at same time).
Final demand: 865 / 1.3 = 665kW.
Transformer sizing: 665kW / 0.8 (power factor) = 831kVA. Select 1000kVA transformer.
Common Calculation Mistakes
1. No demand factor (oversized equipment, wasted cost)
2. Ignoring motor starting (transformer trips on motor start)
3. No spare capacity (cannot expand in future)
4. Wrong power factor assumption (leads to wrong kVA calculation)
5. Ignoring harmonic loads (causes overheating, failures)