Static loads are electrical devices or equipment that consume a constant amount of power over time. Correct sizing and selection of static loads are crucial for designing efficient electrical systems that ensure safe and reliable operation. This involves determining key electrical parameters such as active power, reactive power, and apparent power to size components like transformers, generators, and cables accurately.
Key Parameters for Static Load Calculation
1.Active Power (P): The real power consumed by the load to perform useful work. It is measured in Watts (W) or kilowatts (kW).
2.Reactive Power (Q): The power that does not perform any useful work but oscillates
between the source and the load due to
inductive or capacitive elements. It is
measured in reactive volt-amperes (VAR) or
kilovolt-amperes reactive (kVAR).
3.Apparent Power (S): The total power supplied to the load, combining both active and reactive power. It is measured in volt-amperes (VA) or kilovolt-amperes (kVA).
4.Power Factor (PF): The ratio of active power to apparent power, indicating the efficiency of
power usage. It is a dimensionless number
ranging from 0 to 1. A higher power factor
indicates more efficient use of electrical power.
Formulas for Static Load Calculation
1. Active Power (P): P = V x I x cos(φ)
2. Reactive Power (Q): Q = V x I x sin(φ)
3. Apparent Power (S): S = V x I or S = P / cos(φ)
Example Calculation for Static Load Sizing
Step 1: Calculate Active Power (P)
Formula: P = V x I x cos(φ)
Given values:
Voltage (V) = 400 V
Current (I) = 10 A
Power Factor (cos(φ)) = 0.85
Calculation:
P = 400 V x 10 A x 0.85= 3400 W (3.4 kW)
Step 2: Calculate Apparent Power (S)
Formula 1: S = P / cos(φ)
Formula 2: S = V x I
Given values:
Active Power (P) = 3400 W (from Step 1)
Power Factor (cos(φ)) = 0.85
Voltage (V) = 400 V
Current (I) = 10 A
Calculation using Formula 1:
S = 3400 W / 0.85
= 4000 VA (4 kVA)
Calculation using Formula 2:
S = 400 V x 10 A
= 4000 VA (4 kVA)
Step 3: Calculate Reactive Power (Q)
Formula: Q = V x I x sin(φ)
Given values:
Voltage (V) = 400 V
Current (I) = 10 A
Power Factor (cos(φ)) = 0.85
Calculation:
Find sin(φ) = √(1 - cos^2(φ))
= √(1 - 0.85^2)
= √0.2775
≈ 0.53
Q = 400 V x 10 A x 0.53
= 2120 VAR (2.12 kVAR)
These steps calculate the active power, apparent power, and reactive power for the given static load, ensuring accurate sizing and selection of electrical components.