Lumped Load Sizing and Selection
Lumped loads are multiple individual loads treated as a single entity for ease of analysis. These are typically used when a cluster of loads is geographically close and can be approximated by a single equivalent load.
Total Power (P total) = P1 + P2 + … + Pn
P total = Total Power of Lumped Loads in Watts (W)
P1, P2, …, Pn = Individual Power Consumption of Each Load in Watts (W)
If the loads operate at different power factors, the apparent power (S) can be calculated using:
S = P total / cos(φ)
Where:
S = Apparent Power in Volt-Amperes (VA)
cos(φ) = Overall Power Factor of Lumped Loads
Example Calculation for Lumped Load Sizing
Load 1: 1.5 kW with a power factor of 0.9
Load 2: 2 kW with a power factor of 0.8
Load 3: 3 kW with a power factor of 0.85
Step 1: Calculate the total active power
Calculate the total load:
P total = 1.5 kW + 2 kW + 3 kW = 6.5 kW
Step 2: Calculate the overall power factor
1. Calculate the weighted average of the
individual power factors:
Load 1: 1.5 kW x 0.9 = 1.35
Load 2: 2 kW x 0.8 = 1.6
Load 3: 3 kW x 0.85 = 2.55
2. Add up the weighted values:
1.35 + 1.6 + 2.55 = 5.5
3. Calculate the total load:
1.5 kW + 2 kW + 3 kW = 6.5 kW
4. Calculate the overall power factor:
Overall Power Factor = 5.5 / 6.5 ≈ 0.88
Step 3: Calculate the apparent power
1. Calculate the apparent power using the
formula:
S = P_total / cos(φ)
S = 6.5 kW / 0.88 ≈ 7.39 kVA