Electric power is the rate of energy consumption in an electrical circuit.
The electric power is measured in units of watts.
The electrical power P is equal to the energy consumption E divided by the consumption time t:
P is the electrical power in watts (W).
E is the energy consumption in joules (J).
t is the time in seconds (s) .
Find the electrical power of a circuit that consumes 120 joules for 20 seconds.
Solution:
E = 120J
t = 20s
P = E / t = 120J / 20s = 6W
P = V ⋅ I
or
P = I 2 ⋅ R
or
P = V 2 / R
P is the electrical power in watts (W).
V is the voltage in volts (V).
I is the current in amperes (A) . .
R is resistance in ohms (Ω).
Formulas apply to single-phase AC power.
For 3-phase AC:
If you use the phase-to-phase voltage (VL-L) in the formula, multiply the single-phase voltage - Phase power divided by the square root of 3 (√3=1.73).
When the line is at zero voltage (VL- 0 ) is used in the formula, multiply the single-phase power by 3.
Real power or true power is the power used to do work on of the load .
P = Vrms Irms cos φ
P is the real power in watts [W]
Vrms is the rms voltage = Vpeak/√2 in Volts [V]
Irms is the rms current = Ipeak/√2 in Amperes [A]
φ is the impedance phase angle = phase difference between voltage and current.
Reactive power is the power that is wasted and not used to do work on the load.
Q = Vrms Irms sin φ
Q is the reactive power in volt-ampere-reactive [VAR]
Vrms is the rms voltage = Vpeak/√2 in Volts [V]
Irms is the rms current = Ipeak/√2 in Amperes [A]
φ is the impedance phase angle = phase difference between voltage and current.
The apparent power is the power that is supplied to the circuit.
S = Vrms Irms
S is the apparent power in Volt-amper [VA]
Vrms is the rms voltage = Vpeak/√2 in Volts [V]
Irms is the rms current = Ipeak/√2 in Amperes [A]
The real power P and reactive power Q give together the apparent power S:
P2 + Q2 = S2
P is the real power in watts [W]
Q is the reactive power in volt-ampere-reactive [VAR]
S is the apparent power in Volt-amper [VA]
Advertising