Power is the rate at which energy is transferred or converted. It is measured in watts (W), where one watt is equivalent to one joule per second. Power can be classified into different types depending on the nature of the electrical system.
In DC circuits, power (P) is simply the product of voltage (V) and current (I).
Formula:P = V × I
Formula Breakdown:
P: Power (watts, W)
V: Voltage (volts, V)
I: Current (amperes, A)
Power in AC Circuits
In AC circuits, power is more complex due to the phase difference between voltage and current. Power can be divided into active, reactive, and apparent power.
AC Active Power (P)
Formula:P = V × I × cos(φ)
Formula Breakdown:
P: Active power (watts, W)
V: Voltage (volts, V)
I: Current (amperes, A)
cos(φ): Power factor (dimensionless)
AC Reactive Power (Q)
Formula:Q = V × I × sin(φ)
Formula Breakdown:
Q: Reactive power (volt-amperes reactive, VAR)
V: Voltage (volts, V)
I: Current (amperes, A)
sin(φ): Power factor (dimensionless)
AC Apparent Power (S)
Formula:S = V × I
Formula Breakdown:
S: Apparent power (volt-amperes, VA)
V: Voltage (volts, V)
I: Current (amperes, A)
AC Power Factor (PF)
Formula:PF = P / S
Formula Breakdown:
PF: Power factor (dimensionless)
P: Active power (watts, W)
S: Apparent power (volt-amperes, VA)
Power in Three-Phase Systems
Three-phase systems are widely used in industrial applications for their efficiency and ability to deliver constant power. Power calculations in three-phase systems are slightly different from single-phase systems.