Basic Electrical - Power

Power:

Power is the rate at which electrical energy is transferred, used or transformed.   For example, the rate at which a light bulb transforms electrical energy into heat and light energy is called power.
The unit of power is watts (W).
There are two different types of power.
1. DC power, 2. AC power.

1)DC Power:
Direct current (DC) is the unidirectional flow of electric charge. DC power is produced by sources such as batteries, thermocouples, solar cells, etc., Direct Current (DC) always flows in the same direction, but it may increase and decrease.  Cells, batteries and regulated power supplies provide steady DC which is ideal for electronic circuits.
For a resistor in a DC Circuit the power is given by the product of applied voltage and the electric current. P = VI

2)AC Power:
Alternating Current (AC) flows one way, then the other way, it continually reversing the direction.  An AC voltage is continually changing between positive (+) and negative (-).  AC can be easily converted from one voltage to another using a transformer.
1Φ Power = VI cosθ 
3Φ Power = = √3 VL IL cosθ
Where
cosθ is the power factor                                                    
θ is the phase angle difference between AC voltage and AC current.
VL is the line voltage and IL is the line current.